Fix health check: use DEPLOY_PORT variable for host port

The frontend port varies per deployment (80 on dev, 8088 on
dedicated host). Use a Gitea variable so it works across environments.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.env.example

@@ -21,6 +21,15 @@ ENVIRONMENT=development
 # Timezone (applied to backend + db containers via env_file)
 TZ=Australia/Perth
 
+# ──────────────────────────────────────
+# WebAuthn / Passkeys
+# ──────────────────────────────────────
+# REQUIRED for passkeys to work. Must match the domain users access UMBRA on.
+# RP_ID = eTLD+1 (no scheme, no port). ORIGIN = full origin with scheme.
+WEBAUTHN_RP_ID=umbra.example.com
+WEBAUTHN_RP_NAME=UMBRA
+WEBAUTHN_ORIGIN=https://umbra.example.com
+
 # ──────────────────────────────────────
 # Integrations
 # ──────────────────────────────────────

.gitea/workflows/deploy.yml

@@ -0,0 +1,86 @@
+name: Build and Deploy UMBRA
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+jobs:
+  build-and-deploy:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: https://github.com/actions/checkout@v4
+        with:
+          token: ${{ secrets.REGISTRY_TOKEN }}
+
+      - name: Login to Gitea Container Registry
+        run: echo "${{ secrets.REGISTRY_TOKEN }}" | docker login ${{ vars.REGISTRY_HOST }} -u ${{ secrets.REGISTRY_USER }} --password-stdin
+
+      - name: Build and push backend
+        run: |
+          docker build --pull \
+                       -t ${{ vars.REGISTRY_HOST }}/rohskiddo/umbra-backend:main-latest \
+                       -t ${{ vars.REGISTRY_HOST }}/rohskiddo/umbra-backend:${{ github.sha }} \
+                       ./backend
+          docker push ${{ vars.REGISTRY_HOST }}/rohskiddo/umbra-backend:main-latest
+          docker push ${{ vars.REGISTRY_HOST }}/rohskiddo/umbra-backend:${{ github.sha }}
+
+      - name: Build and push frontend
+        run: |
+          docker build --pull \
+                       -t ${{ vars.REGISTRY_HOST }}/rohskiddo/umbra-frontend:main-latest \
+                       -t ${{ vars.REGISTRY_HOST }}/rohskiddo/umbra-frontend:${{ github.sha }} \
+                       ./frontend
+          docker push ${{ vars.REGISTRY_HOST }}/rohskiddo/umbra-frontend:main-latest
+          docker push ${{ vars.REGISTRY_HOST }}/rohskiddo/umbra-frontend:${{ github.sha }}
+
+      - name: Deploy
+        run: |
+          # Spawn a short-lived container that mounts the host deploy path
+          # and runs compose commands against the host Docker daemon.
+          # DEPLOY_PATH is a Gitea variable — update it when moving hosts.
+          docker run --rm \
+            --network host \
+            --security-opt label:disable \
+            -v /var/run/docker.sock:/var/run/docker.sock \
+            -v ${{ vars.DEPLOY_PATH }}:/deploy \
+            -w /deploy \
+            docker:27-cli sh -c "
+              docker compose -p umbra --env-file stack.env pull backend frontend &&
+              docker compose -p umbra --env-file stack.env up -d db backend frontend
+            "
+
+      - name: Health check
+        run: |
+          echo "Waiting for services to start..."
+          sleep 30
+          curl -f http://localhost:${{ vars.DEPLOY_PORT }}/health || exit 1
+
+      - name: Prune old images
+        if: success()
+        run: docker image prune -f
+
+      - name: Notify success
+        if: success()
+        run: |
+          curl -s \
+            -H "Title: UMBRA Deploy Success" \
+            -H "Tags: white_check_mark" \
+            --data-binary @- https://ntfy.ghost6.xyz/claude <<'NTFY_EOF'
+          Build ${{ github.sha }} deployed successfully to umbra.ghost6.xyz.
+          Triggered by push to main.
+          NTFY_EOF
+
+      - name: Notify failure
+        if: failure()
+        run: |
+          curl -s \
+            -H "Title: UMBRA Deploy FAILED" \
+            -H "Tags: fire" \
+            -H "Priority: high" \
+            --data-binary @- https://ntfy.ghost6.xyz/claude <<'NTFY_EOF'
+          Deploy failed for commit ${{ github.sha }}.
+          Check Gitea Actions logs at git.sentinelforest.xyz.
+          NTFY_EOF

README.md

@@ -4,18 +4,20 @@ A self-hosted, multi-user life administration app with a dark-themed UI and role
 
 ## Features
 
-- **Multi-user RBAC** - Admin and standard user roles, per-user data isolation, admin portal with IAM, system config, and audit logs
-- **Dashboard** - Contextual greeting, week timeline, stat cards, upcoming events, weather widget, day briefing
-- **Todos** - Task management with priorities, due dates, recurrence, and grouped sections (overdue/today/upcoming)
-- **Calendar** - Multi-calendar system with month/week/day views, recurring events, drag-and-drop, event templates
-- **Projects** - Project boards with kanban view, nested tasks/subtasks, comments, progress tracking
-- **Reminders** - Time-based reminders with snooze, dismiss, recurrence, and real-time alert notifications (dashboard banner + toasts)
-- **People** - Contact directory with avatar initials, favourites, birthday tracking, category filtering
-- **Locations** - Location management with OSM search integration, category filtering, frequent locations
-- **Weather** - Dashboard weather widget with temperature, conditions, and contextual rain warnings
-- **Settings** - Accent color picker (8 presets), first day of week, weather city, ntfy push notifications, TOTP two-factor auth, auto-lock, password management
-- **Notifications** - ntfy push notifications for reminders (configurable per-user)
-- **Admin Portal** - User management (create, delete, activate/deactivate, role assignment, password reset), system configuration (open registration, MFA enforcement), audit log viewer
+- **Multi-user RBAC** — Admin and standard user roles, per-user data isolation, admin portal with IAM, system config, and audit logs
+- **Dashboard** — Contextual greeting, week timeline, stat cards, upcoming events, weather widget, day briefing
+- **Todos** — Task management with priorities, due dates, recurrence, and grouped sections (overdue/today/upcoming)
+- **Calendar** — Multi-calendar system with month/week/day views, recurring events, drag-and-drop, event templates, shared calendars with permission-based access
+- **Shared Calendars** — Invite connections to calendars with granular permissions (read-only, create/modify, full access). Event locking prevents concurrent edits. Near-real-time sync via 5s polling
+- **Event Invitations** — Invite connections to individual events with RSVP (accept/tentative/decline), per-occurrence status overrides for recurring events, display calendar assignment, and optional edit access via can_modify toggle
+- **Projects** — Project boards with kanban view, nested tasks/subtasks, comments, progress tracking
+- **Reminders** — Time-based reminders with snooze, dismiss, recurrence, and real-time alert notifications (dashboard banner + toasts)
+- **People & Connections** — Contact directory with avatar initials, favourites, birthday tracking. Social connections via umbral name search with bidirectional Person records on accept
+- **Locations** — Location management with OSM search integration, category filtering, frequent locations
+- **Weather** — Dashboard weather widget with temperature, conditions, and contextual rain warnings
+- **Settings** — Accent color picker (8 presets), first day of week, weather city, ntfy push notifications, TOTP two-factor auth, auto-lock, password management
+- **Notifications** — In-app notification centre with toast popups, plus ntfy push notifications for reminders (configurable per-user)
+- **Admin Portal** — User management (create, delete, activate/deactivate, role assignment, password reset), system configuration (open registration, MFA enforcement), audit log viewer
 
 ## Tech Stack
 
@@ -26,7 +28,7 @@ A self-hosted, multi-user life administration app with a dark-themed UI and role
 | Fonts        | Sora (headings), DM Sans (body) via Google Fonts |
 | State        | TanStack Query v5, React Router v6 |
 | Backend      | FastAPI, Python 3.12, Pydantic v2 |
-| Database     | PostgreSQL 16, SQLAlchemy 2.0 (async), Alembic (37 migrations) |
+| Database     | PostgreSQL 16, SQLAlchemy 2.0 (async), Alembic (56 migrations) |
 | Auth         | Argon2id hashing, DB-backed sessions (signed httpOnly cookies), TOTP MFA, CSRF middleware, role-based access control |
 | Scheduler    | APScheduler (async) for ntfy notification dispatch |
 | Deployment   | Docker Compose (3 services), Nginx reverse proxy |
@@ -108,27 +110,7 @@ A self-hosted, multi-user life administration app with a dark-themed UI and role
 
 ## Security
 
-### Hardened by default
-
-- **Multi-user data isolation** — all resources scoped by `user_id` with per-query filtering; pentest-verified (51+ test cases, 0 exploitable IDOR findings)
-- **Role-based access control** — `admin` and `standard` roles with `require_admin` dependency on all admin endpoints
-- **CSRF protection** — global `CSRFHeaderMiddleware` requires `X-Requested-With: XMLHttpRequest` on all mutating requests
-- **Input validation** — `extra="forbid"` on all Pydantic schemas prevents mass-assignment; `max_length` on all string fields; `ge=1, le=2147483647` on path IDs
-- **Non-root containers** — both backend (`appuser:1000`) and frontend (`nginx-unprivileged`) run as non-root
-- **No external backend port** — port 8000 is internal-only; all traffic flows through nginx
-- **Server version suppression** — `server_tokens off` (nginx) and `--no-server-header` (uvicorn)
-- **Rate limiting** — nginx `limit_req_zone` (10 req/min) on `/api/auth/login` (burst=5), `/verify-password` (burst=5), `/change-password` (burst=5), `/totp-verify` (burst=5), `/setup` (burst=3)
-- **DB-backed account lockout** — 10 failed attempts triggers 30-minute lock per account
-- **Inactive user blocking** — disabled accounts rejected at login (HTTP 403) without session creation, lockout reset, or last_login_at update
-- **Timing-safe login** — dummy Argon2id hash for non-existent users prevents username enumeration
-- **Password reuse prevention** — change-password endpoint rejects same password as old
-- **Dotfile blocking** — `/.env`, `/.git/config`, etc. return 404 (`.well-known` preserved for ACME)
-- **CSP headers** — Content-Security-Policy on all responses, scoped for Google Fonts
-- **CORS** — configurable origins with explicit method/header allowlists
-- **API docs disabled in production** — Swagger/ReDoc/OpenAPI only available when `ENVIRONMENT=development`
-- **Argon2id password hashing** with transparent bcrypt migration on first login
-- **DB-backed sessions** — revocable, with signed itsdangerous httpOnly cookies, 7-day sliding window with 30-day hard ceiling
-- **Optional TOTP MFA** — authenticator app support with backup codes, admin-enforced MFA for new users
+UMBRA is hardened by default with multi-user data isolation, role-based access control, CSRF protection, non-root containers, rate limiting, account lockout, optional TOTP MFA, and secure session management. Multiple penetration tests have been conducted with no exploitable findings.
 
 ### Production Hardening
 
@@ -137,21 +119,15 @@ Before deploying to production, generate secure values for your `.env`:
 ```bash
 # Generate a secure SECRET_KEY (64-char hex string)
 python3 -c "import secrets; print(secrets.token_hex(32))"
-# or: openssl rand -hex 32
 
 # Generate a secure database password
 python3 -c "import secrets; print(secrets.token_urlsafe(24))"
-# or: openssl rand -base64 24
-
-# Set ENVIRONMENT to disable Swagger/ReDoc and auto-enable secure cookies
-ENVIRONMENT=production
 ```
 
 Additionally for production:
+- Set `ENVIRONMENT=production` — disables API docs and auto-enables HTTPS-only session cookies
 - Place behind a reverse proxy with TLS termination (e.g., Caddy, Traefik, or nginx with Let's Encrypt)
-- Set `ENVIRONMENT=production` — this disables API docs and auto-enables HTTPS-only session cookies (`COOKIE_SECURE` derives from `ENVIRONMENT`; override with `COOKIE_SECURE=false` if running non-TLS prod behind a proxy)
 - Set `CORS_ORIGINS` to your actual domain (e.g., `https://umbra.example.com`)
-- Consider adding HSTS headers at the TLS-terminating proxy layer
 
 ## API Overview
 
@@ -163,9 +139,11 @@ All endpoints require authentication (signed session cookie) except auth routes
 | `/api/auth/*`         | Login, logout, setup, register, status, password change, TOTP MFA |
 | `/api/admin/*`        | User management, system config, audit logs (admin only) |
 | `/api/todos/*`        | Todos CRUD + toggle completion |
-| `/api/events/*`       | Calendar events CRUD (incl. recurring) |
+| `/api/events/*`       | Calendar events CRUD (incl. recurring) + event invitations |
+| `/api/event-invitations/*` | Invitation responses, per-occurrence overrides, can_modify toggle, leave |
 | `/api/event-templates/*` | Event templates CRUD |
 | `/api/calendars/*`    | User calendars CRUD + visibility |
+| `/api/shared-calendars/*` | Shared calendar management, invitations, permissions, event locking |
 | `/api/reminders/*`    | Reminders CRUD + dismiss + snooze + due alerts |
 | `/api/projects/*`     | Projects + nested tasks + comments CRUD |
 | `/api/people/*`       | People CRUD |
@@ -174,6 +152,8 @@ All endpoints require authentication (signed session cookie) except auth routes
 | `/api/dashboard`      | Dashboard aggregation |
 | `/api/upcoming`       | Unified upcoming items feed |
 | `/api/weather/*`      | Weather data proxy |
+| `/api/connections/*`  | Social connections (search, request, respond, manage) |
+| `/api/notifications/*` | In-app notifications (list, read, delete) |
 
 API documentation is available at `/api/docs` (Swagger UI) when `ENVIRONMENT=development`.
 
@@ -215,15 +195,15 @@ umbra/
 │   ├── Dockerfile
 │   ├── requirements.txt
 │   ├── alembic.ini
-│   ├── alembic/versions/        # 37 migrations (001–037)
+│   ├── alembic/versions/        # 56 migrations (001–056)
 │   └── app/
 │       ├── main.py              # FastAPI app, CSRF middleware, router registration, health endpoint
 │       ├── config.py            # Pydantic BaseSettings (DATABASE_URL, SECRET_KEY, CORS, etc.)
 │       ├── database.py          # Async SQLAlchemy engine + session factory
-│       ├── models/              # 18 SQLAlchemy ORM models (incl. User, UserSession, SystemConfig, AuditLog)
-│       ├── schemas/             # 13 Pydantic v2 request/response schema modules (incl. admin)
-│       ├── routers/             # 14 API route handlers (incl. auth, admin, totp)
-│       ├── services/            # Auth (Argon2id), recurrence, TOTP, ntfy, audit
+│       ├── models/              # 20 SQLAlchemy ORM models (incl. User, UserSession, EventInvitation, CalendarMember)
+│       ├── schemas/             # 14 Pydantic v2 request/response schema modules
+│       ├── routers/             # 16 API route handlers (incl. auth, admin, event_invitations, shared_calendars)
+│       ├── services/            # Auth (Argon2id), recurrence, TOTP, ntfy, audit, calendar_sharing, event_invitation, notification
 │       └── jobs/                # APScheduler notification dispatch
 └── frontend/
     ├── Dockerfile
@@ -233,20 +213,22 @@ umbra/
     └── src/
         ├── App.tsx              # Routes, ProtectedRoute, AdminRoute auth guards
         ├── lib/                 # api.ts (axios + 401 interceptor), date-utils.ts, utils.ts
-        ├── hooks/               # useAuth, useAdmin, useSettings, useTheme, useCalendars, useConfirmAction, useCategoryOrder, useTableVisibility
+        ├── hooks/               # useAuth, useAdmin, useSettings, useTheme, useCalendars, useConfirmAction, useConnections, useNotifications, useEventInvitations
         ├── types/               # TypeScript interfaces
         └── components/
-            ├── ui/              # 17 base components (Button, Dialog, Sheet, Card, Input, Select, Switch, etc.)
+            ├── ui/              # 18 base components (Button, Dialog, Sheet, Card, Input, Select, Switch, DatePicker, ...)
             ├── shared/          # EntityTable, EntityDetailPanel, CategoryFilterBar, CategoryAutocomplete, CopyableField
             ├── layout/          # AppLayout, Sidebar, LockOverlay
             ├── auth/            # LockScreen, AmbientBackground
-            ├── admin/           # AdminPortal, IAMPage, ConfigPage, AdminDashboardPage, CreateUserDialog, UserActionsMenu, UserDetailSection
+            ├── admin/           # AdminPortal, IAMPage, ConfigPage, AdminDashboardPage, CreateUserDialog, UserActionsMenu
             ├── dashboard/       # DashboardPage + 8 widgets
-            ├── calendar/        # CalendarPage, CalendarSidebar, CalendarForm, EventForm, TemplateForm
-            ├── todos/           # TodosPage, TodoList, TodoItem, TodoForm
+            ├── calendar/        # CalendarPage, CalendarSidebar, EventDetailPanel, InviteeSection, LeaveEventDialog, CalendarForm, EventForm, TemplateForm
+            ├── todos/           # TodosPage, TodoList, TodoItem, TodoForm, TodoDetailPanel
             ├── reminders/       # RemindersPage, ReminderList, ReminderItem, ReminderForm, SnoozeDropdown, AlertBanner
             ├── projects/        # ProjectsPage, ProjectCard, ProjectDetail, ProjectForm, KanbanBoard, TaskRow, TaskForm, TaskDetailPanel
             ├── people/          # PeoplePage, PersonForm
+            ├── connections/     # ConnectionSearch, ConnectionRequestCard, ConnectionsTab
+            ├── notifications/   # NotificationsPage, NotificationToaster
             ├── locations/       # LocationsPage, LocationForm
             └── settings/        # SettingsPage, NtfySettingsSection, TotpSetupSection
 ```

act_runner_config.yaml

@@ -0,0 +1,20 @@
+log:
+  level: info
+
+runner:
+  capacity: 1
+  timeout: 3h
+  insecure: false
+
+cache:
+  enabled: false
+
+container:
+  network: host
+  privileged: false
+  options: "--security-opt label:disable"
+  valid_volumes:
+    - "**"
+
+host:
+  workdir_parent: /tmp/act_runner

backend/.dockerignore

@@ -0,0 +1,44 @@
+# Version control
+.git
+.gitignore
+
+# Python artifacts
+__pycache__
+*.pyc
+*.pyo
+*.egg-info
+dist
+build
+.eggs
+
+# Virtual environments
+.venv
+venv
+env
+
+# IDE
+.vscode
+.idea
+
+# Environment files — never bake secrets into the image
+.env
+.env.*
+
+# Tests
+tests
+pytest.ini
+.pytest_cache
+.coverage
+htmlcov
+
+# Documentation
+README.md
+CHANGELOG.md
+LICENSE
+
+# Dev scripts
+start.sh
+
+# Docker files (no need to copy into the image)
+Dockerfile
+docker-compose*.yaml

backend/.env.example

@@ -1,2 +1,14 @@
 DATABASE_URL=postgresql+asyncpg://postgres:postgres@localhost:5432/umbra
 SECRET_KEY=your-secret-key-change-in-production
+ENVIRONMENT=development
+
+# Public-facing URL (used for ntfy click links, CORS derivation)
+UMBRA_URL=http://localhost
+
+# WebAuthn / Passkey authentication
+# RP_ID must be the eTLD+1 domain of the live site (e.g. umbra.ghost6.xyz)
+# ORIGIN must include the scheme (https://)
+# These defaults work for local development; override in production .env
+WEBAUTHN_RP_ID=localhost
+WEBAUTHN_RP_NAME=UMBRA
+WEBAUTHN_ORIGIN=http://localhost

backend/Dockerfile

@@ -1,5 +1,5 @@
 # ── Build stage: compile C extensions ──────────────────────────────────
-FROM python:3.12-slim AS builder
+FROM python:3.12.9-slim-bookworm AS builder
 
 WORKDIR /build
 
@@ -11,24 +11,25 @@ COPY requirements.txt .
 RUN pip install --no-cache-dir --prefix=/install -r requirements.txt
 
 # ── Runtime stage: lean production image ───────────────────────────────
-FROM python:3.12-slim
+FROM python:3.12.9-slim-bookworm
+
+# Create non-root user first, then copy with correct ownership (DW-2)
+RUN useradd -m -u 1000 appuser
 
 WORKDIR /app
 
 # Copy pre-built Python packages from builder
 COPY --from=builder /install /usr/local
 
-# Copy application code
-COPY . .
+# Copy application code with correct ownership — avoids redundant chown layer
+COPY --chown=appuser:appuser . .
+
+# Make entrypoint executable
+RUN chmod +x entrypoint.sh
 
-# Create non-root user
-RUN useradd -m -u 1000 appuser && chown -R appuser:appuser /app
 USER appuser
 
 EXPOSE 8000
 
-# Run migrations and start server
-# --no-server-header: suppresses uvicorn version disclosure
-# --proxy-headers: reads X-Forwarded-Proto/For from reverse proxy so redirects use correct scheme
-# --forwarded-allow-ips '*': trusts proxy headers from any IP (nginx is on Docker bridge network)
-CMD ["sh", "-c", "alembic upgrade head && uvicorn app.main:app --host 0.0.0.0 --port 8000 --no-server-header --proxy-headers --forwarded-allow-ips '*'"]
+# Use entrypoint with exec so uvicorn runs as PID 1 and receives signals (DW-5)
+ENTRYPOINT ["./entrypoint.sh"]

backend/README.md

@@ -1,39 +1,37 @@
 # UMBRA Backend
 
-A complete FastAPI backend for the UMBRA application with async SQLAlchemy, PostgreSQL, authentication, and comprehensive CRUD operations.
+FastAPI backend for the UMBRA life management application with async SQLAlchemy, PostgreSQL, multi-user RBAC, and comprehensive security.
 
 ## Features
 
-- **FastAPI** with async/await support
-- **SQLAlchemy 2.0** with async engine
-- **PostgreSQL** with asyncpg driver
-- **Alembic** for database migrations
-- **bcrypt** for password hashing
-- **itsdangerous** for session management
-- **PIN-based authentication** with secure session cookies
-- **Full CRUD operations** for all entities
-- **Dashboard** with aggregated data
-- **CORS enabled** for frontend integration
+- **FastAPI** with async/await and Pydantic v2
+- **SQLAlchemy 2.0** async engine with `Mapped[]` types
+- **PostgreSQL 16** via asyncpg
+- **Alembic** database migrations (001-061)
+- **Authentication**: Argon2id passwords + signed httpOnly cookies + optional TOTP MFA + passkey (WebAuthn/FIDO2)
+- **Multi-user RBAC**: admin/standard roles, per-user resource scoping
+- **Session management**: DB-backed sessions, sliding window expiry, concurrent session cap
+- **Account security**: Account lockout (10 failures = 30-min lock), CSRF protection, rate limiting
+- **APScheduler** for background notification dispatch
 
 ## Project Structure
 
 ```
 backend/
-├── alembic/                 # Database migrations
-│   ├── versions/           # Migration files
-│   ├── env.py             # Alembic environment
-│   └── script.py.mako     # Migration template
+├── alembic/versions/      # 61 database migrations
 ├── app/
-│   ├── models/            # SQLAlchemy models
-│   ├── schemas/           # Pydantic schemas
-│   ├── routers/           # API route handlers
-│   ├── config.py          # Configuration
-│   ├── database.py        # Database setup
-│   └── main.py            # FastAPI application
-├── requirements.txt       # Python dependencies
-├── Dockerfile            # Docker configuration
-├── alembic.ini          # Alembic configuration
-└── start.sh             # Startup script
+│   ├── models/            # 21 SQLAlchemy 2.0 models
+│   ├── schemas/           # 14 Pydantic v2 schema modules
+│   ├── routers/           # 17 API routers
+│   ├── services/          # Auth, session, passkey, TOTP, audit, recurrence, etc.
+│   ├── jobs/              # APScheduler notification dispatch
+│   ├── config.py          # Pydantic Settings (env vars)
+│   ├── database.py        # Async engine + session factory
+│   └── main.py            # FastAPI app + CSRF middleware
+├── requirements.txt
+├── Dockerfile
+├── alembic.ini
+└── start.sh
 ```
 
 ## Setup
@@ -41,160 +39,87 @@ backend/
 ### 1. Install Dependencies
 
 ```bash
-cd backend
 pip install -r requirements.txt
 ```
 
 ### 2. Configure Environment
 
-Create a `.env` file:
+Copy `.env.example` to `.env` and configure:
 
 ```bash
-DATABASE_URL=postgresql+asyncpg://postgres:postgres@localhost:5432/umbra
-SECRET_KEY=your-secret-key-change-in-production
+DATABASE_URL=postgresql+asyncpg://postgres:postgres@db:5432/umbra
+SECRET_KEY=generate-a-strong-random-key
+ENVIRONMENT=production
+
+# WebAuthn / Passkeys (required for passkey auth)
+WEBAUTHN_RP_ID=your-domain.com
+WEBAUTHN_RP_NAME=UMBRA
+WEBAUTHN_ORIGIN=https://your-domain.com
 ```
 
-### 3. Create Database
-
-```bash
-createdb umbra
-```
-
-### 4. Run Migrations
+### 3. Run Migrations
 
 ```bash
 alembic upgrade head
 ```
 
-### 5. Start Server
+### 4. Start Server
 
 ```bash
-# Using the start script
-chmod +x start.sh
-./start.sh
-
-# Or directly with uvicorn
-uvicorn app.main:app --reload
+uvicorn app.main:app --host 0.0.0.0 --port 8000
 ```
 
-The API will be available at `http://localhost:8000`
+## API Routes
 
-## API Documentation
+All routes require authentication (signed session cookie) except `/api/auth/*` and `/health`.
 
-Interactive API documentation is available at:
-- **Swagger UI**: http://localhost:8000/docs
-- **ReDoc**: http://localhost:8000/redoc
+| Prefix | Description |
+|--------|-------------|
+| `/api/auth` | Login, logout, register, setup, status, password, TOTP, passkeys |
+| `/api/admin` | User management, system config, audit logs (admin only) |
+| `/api/todos` | Task management with categories and priorities |
+| `/api/events` | Calendar events with recurrence support |
+| `/api/event-invitations` | Event invitation RSVP and management |
+| `/api/event-templates` | Reusable event templates |
+| `/api/calendars` | Calendar CRUD |
+| `/api/shared-calendars` | Calendar sharing with permission levels |
+| `/api/reminders` | Reminder management with snooze |
+| `/api/projects` | Projects with tasks, comments, and collaboration |
+| `/api/people` | Contact management |
+| `/api/locations` | Location management |
+| `/api/connections` | User connections (friend requests) |
+| `/api/notifications` | In-app notification centre |
+| `/api/settings` | User preferences and ntfy configuration |
+| `/api/dashboard` | Aggregated dashboard data |
+| `/api/weather` | Weather widget data |
 
-## API Endpoints
+## Authentication
 
-### Authentication
-- `POST /api/auth/setup` - Initial PIN setup
-- `POST /api/auth/login` - Login with PIN
-- `POST /api/auth/logout` - Logout
-- `GET /api/auth/status` - Check auth status
+UMBRA supports three authentication methods:
 
-### Todos
-- `GET /api/todos` - List todos (with filters)
-- `POST /api/todos` - Create todo
-- `GET /api/todos/{id}` - Get todo
-- `PUT /api/todos/{id}` - Update todo
-- `DELETE /api/todos/{id}` - Delete todo
-- `PATCH /api/todos/{id}/toggle` - Toggle completion
+1. **Password** (Argon2id) - Primary login method
+2. **TOTP MFA** - Optional second factor via authenticator apps
+3. **Passkeys** (WebAuthn/FIDO2) - Optional passwordless login via biometrics, security keys, or password managers
 
-### Calendar Events
-- `GET /api/events` - List events (with date range)
-- `POST /api/events` - Create event
-- `GET /api/events/{id}` - Get event
-- `PUT /api/events/{id}` - Update event
-- `DELETE /api/events/{id}` - Delete event
+Passkey login bypasses TOTP (a passkey is inherently two-factor: possession + biometric/PIN).
 
-### Reminders
-- `GET /api/reminders` - List reminders (with filters)
-- `POST /api/reminders` - Create reminder
-- `GET /api/reminders/{id}` - Get reminder
-- `PUT /api/reminders/{id}` - Update reminder
-- `DELETE /api/reminders/{id}` - Delete reminder
-- `PATCH /api/reminders/{id}/dismiss` - Dismiss reminder
+## Security
 
-### Projects
-- `GET /api/projects` - List projects
-- `POST /api/projects` - Create project
-- `GET /api/projects/{id}` - Get project
-- `PUT /api/projects/{id}` - Update project
-- `DELETE /api/projects/{id}` - Delete project
-- `GET /api/projects/{id}/tasks` - List project tasks
-- `POST /api/projects/{id}/tasks` - Create project task
-- `PUT /api/projects/{id}/tasks/{task_id}` - Update task
-- `DELETE /api/projects/{id}/tasks/{task_id}` - Delete task
-
-### People
-- `GET /api/people` - List people (with search)
-- `POST /api/people` - Create person
-- `GET /api/people/{id}` - Get person
-- `PUT /api/people/{id}` - Update person
-- `DELETE /api/people/{id}` - Delete person
-
-### Locations
-- `GET /api/locations` - List locations (with category filter)
-- `POST /api/locations` - Create location
-- `GET /api/locations/{id}` - Get location
-- `PUT /api/locations/{id}` - Update location
-- `DELETE /api/locations/{id}` - Delete location
-
-### Settings
-- `GET /api/settings` - Get settings
-- `PUT /api/settings` - Update settings
-- `PUT /api/settings/pin` - Change PIN
-
-### Dashboard
-- `GET /api/dashboard` - Get dashboard data
-- `GET /api/upcoming?days=7` - Get upcoming items
-
-## Database Schema
-
-The application uses the following tables:
-- `settings` - Application settings and PIN
-- `todos` - Task items
-- `calendar_events` - Calendar events
-- `reminders` - Reminders
-- `projects` - Projects
-- `project_tasks` - Tasks within projects
-- `people` - Contacts/people
-- `locations` - Physical locations
+- CSRF protection via `X-Requested-With` header middleware
+- All Pydantic schemas use `extra="forbid"` (mass-assignment prevention)
+- Nginx rate limiting on auth, registration, and admin endpoints
+- DB-backed account lockout after 10 failed attempts
+- Timing-safe dummy hash for non-existent users (prevents enumeration)
+- SSRF validation on ntfy webhook URLs
+- Naive datetimes throughout (Docker runs UTC)
 
 ## Docker
 
-Build and run with Docker:
+The backend runs as non-root `appuser` in `python:3.12-slim`:
 
 ```bash
 docker build -t umbra-backend .
-docker run -p 8000:8000 -e DATABASE_URL=... -e SECRET_KEY=... umbra-backend
+docker run -p 8000:8000 --env-file .env umbra-backend
 ```
 
-## Development
-
-### Create New Migration
-
-```bash
-alembic revision --autogenerate -m "Description of changes"
-```
-
-### Apply Migrations
-
-```bash
-alembic upgrade head
-```
-
-### Rollback Migration
-
-```bash
-alembic downgrade -1
-```
-
-## Security Notes
-
-- Change `SECRET_KEY` in production
-- Use strong PINs (minimum 4 digits recommended)
-- Session cookies are httpOnly and last 30 days
-- All API endpoints (except auth) require authentication
-- PINs are hashed with bcrypt before storage
+In production, use Docker Compose (see root `docker-compose.yaml`).

backend/alembic/versions/047_add_is_shared_to_calendars.py

@@ -0,0 +1,23 @@
+"""Add is_shared to calendars
+
+Revision ID: 047
+Revises: 046
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "047"
+down_revision = "046"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "calendars",
+        sa.Column("is_shared", sa.Boolean(), nullable=False, server_default="false"),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("calendars", "is_shared")

backend/alembic/versions/048_create_calendar_members.py

@@ -0,0 +1,47 @@
+"""Create calendar_members table
+
+Revision ID: 048
+Revises: 047
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "048"
+down_revision = "047"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "calendar_members",
+        sa.Column("id", sa.Integer(), primary_key=True, autoincrement=True),
+        sa.Column("calendar_id", sa.Integer(), sa.ForeignKey("calendars.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("user_id", sa.Integer(), sa.ForeignKey("users.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("invited_by", sa.Integer(), sa.ForeignKey("users.id", ondelete="SET NULL"), nullable=True),
+        sa.Column("permission", sa.String(20), nullable=False),
+        sa.Column("can_add_others", sa.Boolean(), nullable=False, server_default="false"),
+        sa.Column("local_color", sa.String(20), nullable=True),
+        sa.Column("status", sa.String(20), nullable=False, server_default="pending"),
+        sa.Column("invited_at", sa.DateTime(), nullable=False, server_default=sa.func.now()),
+        sa.Column("accepted_at", sa.DateTime(), nullable=True),
+        sa.UniqueConstraint("calendar_id", "user_id", name="uq_calendar_members_cal_user"),
+        sa.CheckConstraint(
+            "permission IN ('read_only', 'create_modify', 'full_access')",
+            name="ck_calendar_members_permission",
+        ),
+        sa.CheckConstraint(
+            "status IN ('pending', 'accepted', 'rejected')",
+            name="ck_calendar_members_status",
+        ),
+    )
+    op.create_index("ix_calendar_members_user_id", "calendar_members", ["user_id"])
+    op.create_index("ix_calendar_members_calendar_id", "calendar_members", ["calendar_id"])
+    op.create_index("ix_calendar_members_status", "calendar_members", ["status"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_calendar_members_status", table_name="calendar_members")
+    op.drop_index("ix_calendar_members_calendar_id", table_name="calendar_members")
+    op.drop_index("ix_calendar_members_user_id", table_name="calendar_members")
+    op.drop_table("calendar_members")

backend/alembic/versions/049_create_event_locks.py

@@ -0,0 +1,30 @@
+"""Create event_locks table
+
+Revision ID: 049
+Revises: 048
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "049"
+down_revision = "048"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "event_locks",
+        sa.Column("id", sa.Integer(), primary_key=True, autoincrement=True),
+        sa.Column("event_id", sa.Integer(), sa.ForeignKey("calendar_events.id", ondelete="CASCADE"), nullable=False, unique=True),
+        sa.Column("locked_by", sa.Integer(), sa.ForeignKey("users.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("locked_at", sa.DateTime(), nullable=False, server_default=sa.func.now()),
+        sa.Column("expires_at", sa.DateTime(), nullable=True),
+        sa.Column("is_permanent", sa.Boolean(), nullable=False, server_default="false"),
+    )
+    op.create_index("ix_event_locks_expires_at", "event_locks", ["expires_at"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_event_locks_expires_at", table_name="event_locks")
+    op.drop_table("event_locks")

backend/alembic/versions/050_expand_notification_types_calendar.py

@@ -0,0 +1,33 @@
+"""Expand notification type CHECK for calendar invite types
+
+Revision ID: 050
+Revises: 049
+"""
+from alembic import op
+
+revision = "050"
+down_revision = "049"
+branch_labels = None
+depends_on = None
+
+_OLD_TYPES = (
+    "connection_request", "connection_accepted", "connection_rejected",
+    "info", "warning", "reminder", "system",
+)
+_NEW_TYPES = _OLD_TYPES + (
+    "calendar_invite", "calendar_invite_accepted", "calendar_invite_rejected",
+)
+
+
+def _check_sql(types: tuple) -> str:
+    return f"type IN ({', '.join(repr(t) for t in types)})"
+
+
+def upgrade() -> None:
+    op.drop_constraint("ck_notifications_type", "notifications", type_="check")
+    op.create_check_constraint("ck_notifications_type", "notifications", _check_sql(_NEW_TYPES))
+
+
+def downgrade() -> None:
+    op.drop_constraint("ck_notifications_type", "notifications", type_="check")
+    op.create_check_constraint("ck_notifications_type", "notifications", _check_sql(_OLD_TYPES))

backend/alembic/versions/051_add_updated_by_to_calendar_events.py

@@ -0,0 +1,34 @@
+"""Add updated_by to calendar_events and ensure updated_at index
+
+Revision ID: 051
+Revises: 050
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "051"
+down_revision = "050"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "calendar_events",
+        sa.Column(
+            "updated_by",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="SET NULL"),
+            nullable=True,
+        ),
+    )
+    op.create_index(
+        "ix_calendar_events_updated_at",
+        "calendar_events",
+        ["updated_at"],
+    )
+
+
+def downgrade() -> None:
+    op.drop_index("ix_calendar_events_updated_at", table_name="calendar_events")
+    op.drop_column("calendar_events", "updated_by")

backend/alembic/versions/052_add_session_lock_columns.py

@@ -0,0 +1,18 @@
+"""add is_locked and locked_at to user_sessions
+
+Revision ID: 052
+Revises: 051
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "052"
+down_revision = "051"
+
+def upgrade():
+    op.add_column("user_sessions", sa.Column("is_locked", sa.Boolean(), server_default="false", nullable=False))
+    op.add_column("user_sessions", sa.Column("locked_at", sa.DateTime(), nullable=True))
+
+def downgrade():
+    op.drop_column("user_sessions", "locked_at")
+    op.drop_column("user_sessions", "is_locked")

backend/alembic/versions/053_add_composite_indexes.py

@@ -0,0 +1,29 @@
+"""Add composite indexes for calendar_members and ntfy_sent
+
+Revision ID: 053
+Revises: 052
+"""
+from alembic import op
+
+revision = "053"
+down_revision = "052"
+
+
+def upgrade():
+    # AW-1: Hot query polled every 5s uses (user_id, status) together
+    op.create_index(
+        "ix_calendar_members_user_id_status",
+        "calendar_members",
+        ["user_id", "status"],
+    )
+    # AS-6: Dedup lookup in notification dispatch uses (user_id, sent_at)
+    op.create_index(
+        "ix_ntfy_sent_user_id_sent_at",
+        "ntfy_sent",
+        ["user_id", "sent_at"],
+    )
+
+
+def downgrade():
+    op.drop_index("ix_ntfy_sent_user_id_sent_at", table_name="ntfy_sent")
+    op.drop_index("ix_calendar_members_user_id_status", table_name="calendar_members")

backend/alembic/versions/054_event_invitations.py

@@ -0,0 +1,116 @@
+"""Event invitations tables and notification types.
+
+Revision ID: 054
+Revises: 053
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+revision = "054"
+down_revision = "053"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # ── event_invitations table ──
+    op.create_table(
+        "event_invitations",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column(
+            "event_id",
+            sa.Integer(),
+            sa.ForeignKey("calendar_events.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column(
+            "user_id",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column(
+            "invited_by",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="SET NULL"),
+            nullable=True,
+        ),
+        sa.Column("status", sa.String(20), nullable=False, server_default="pending"),
+        sa.Column("invited_at", sa.DateTime(), nullable=False, server_default=sa.func.now()),
+        sa.Column("responded_at", sa.DateTime(), nullable=True),
+        sa.UniqueConstraint("event_id", "user_id", name="uq_event_invitations_event_user"),
+        sa.CheckConstraint(
+            "status IN ('pending', 'accepted', 'tentative', 'declined')",
+            name="ck_event_invitations_status",
+        ),
+    )
+    op.create_index(
+        "ix_event_invitations_user_status",
+        "event_invitations",
+        ["user_id", "status"],
+    )
+    op.create_index(
+        "ix_event_invitations_event_id",
+        "event_invitations",
+        ["event_id"],
+    )
+
+    # ── event_invitation_overrides table ──
+    op.create_table(
+        "event_invitation_overrides",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column(
+            "invitation_id",
+            sa.Integer(),
+            sa.ForeignKey("event_invitations.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column(
+            "occurrence_id",
+            sa.Integer(),
+            sa.ForeignKey("calendar_events.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column("status", sa.String(20), nullable=False),
+        sa.Column("responded_at", sa.DateTime(), nullable=False, server_default=sa.func.now()),
+        sa.UniqueConstraint("invitation_id", "occurrence_id", name="uq_invitation_override"),
+        sa.CheckConstraint(
+            "status IN ('accepted', 'tentative', 'declined')",
+            name="ck_invitation_override_status",
+        ),
+    )
+    op.create_index(
+        "ix_invitation_overrides_lookup",
+        "event_invitation_overrides",
+        ["invitation_id", "occurrence_id"],
+    )
+
+    # ── Expand notification type check constraint ──
+    op.drop_constraint("ck_notifications_type", "notifications", type_="check")
+    op.create_check_constraint(
+        "ck_notifications_type",
+        "notifications",
+        "type IN ('connection_request', 'connection_accepted', 'connection_rejected', "
+        "'calendar_invite', 'calendar_invite_accepted', 'calendar_invite_rejected', "
+        "'event_invite', 'event_invite_response', "
+        "'info', 'warning', 'reminder', 'system')",
+    )
+
+
+def downgrade():
+    op.drop_index("ix_invitation_overrides_lookup", table_name="event_invitation_overrides")
+    op.drop_table("event_invitation_overrides")
+    op.drop_index("ix_event_invitations_event_id", table_name="event_invitations")
+    op.drop_index("ix_event_invitations_user_status", table_name="event_invitations")
+    op.drop_table("event_invitations")
+
+    # Restore original notification type constraint
+    op.drop_constraint("ck_notifications_type", "notifications", type_="check")
+    op.create_check_constraint(
+        "ck_notifications_type",
+        "notifications",
+        "type IN ('connection_request', 'connection_accepted', 'connection_rejected', "
+        "'calendar_invite', 'calendar_invite_accepted', 'calendar_invite_rejected', "
+        "'info', 'warning', 'reminder', 'system')",
+    )

backend/alembic/versions/055_add_display_calendar_to_event_invitations.py

@@ -0,0 +1,51 @@
+"""Add display_calendar_id to event_invitations.
+
+Allows invitees to assign invited events to their own calendars
+for personal organization, color, and visibility control.
+
+Revision ID: 055
+Revises: 054
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+revision = "055"
+down_revision = "054"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "event_invitations",
+        sa.Column(
+            "display_calendar_id",
+            sa.Integer(),
+            sa.ForeignKey("calendars.id", ondelete="SET NULL", name="fk_event_invitations_display_calendar_id"),
+            nullable=True,
+        ),
+    )
+    op.create_index(
+        "ix_event_invitations_display_calendar",
+        "event_invitations",
+        ["display_calendar_id"],
+    )
+
+    # Backfill accepted/tentative invitations with each user's default calendar
+    op.execute("""
+        UPDATE event_invitations
+        SET display_calendar_id = (
+            SELECT c.id FROM calendars c
+            WHERE c.user_id = event_invitations.user_id
+              AND c.is_default = true
+            LIMIT 1
+        )
+        WHERE status IN ('accepted', 'tentative')
+          AND display_calendar_id IS NULL
+    """)
+
+
+def downgrade() -> None:
+    op.drop_index("ix_event_invitations_display_calendar", table_name="event_invitations")
+    op.drop_column("event_invitations", "display_calendar_id")

backend/alembic/versions/056_add_can_modify_to_event_invitations.py

@@ -0,0 +1,26 @@
+"""add can_modify to event_invitations
+
+Revision ID: 056
+Revises: 055
+Create Date: 2025-01-01 00:00:00.000000
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision = "056"
+down_revision = "055"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "event_invitations",
+        sa.Column("can_modify", sa.Boolean(), server_default=sa.false(), nullable=False),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("event_invitations", "can_modify")

backend/alembic/versions/057_project_collab_prep.py

@@ -0,0 +1,49 @@
+"""project collab prep: indexes, task version, comment user_id
+
+Revision ID: 057
+Revises: 056
+Create Date: 2025-01-01 00:00:00.000000
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision = "057"
+down_revision = "056"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # 1a. Performance indexes for project_tasks
+    # Use IF NOT EXISTS to handle indexes that may already exist on the DB
+    op.execute("CREATE INDEX IF NOT EXISTS ix_project_tasks_project_id ON project_tasks (project_id)")
+    op.execute("CREATE INDEX IF NOT EXISTS ix_project_tasks_parent_task_id ON project_tasks (parent_task_id) WHERE parent_task_id IS NOT NULL")
+    op.execute("CREATE INDEX IF NOT EXISTS ix_project_tasks_project_updated ON project_tasks (project_id, updated_at DESC)")
+    op.execute("CREATE INDEX IF NOT EXISTS ix_projects_user_updated ON projects (user_id, updated_at DESC)")
+
+    # 1b. Add user_id to task_comments for multi-user attribution
+    op.add_column(
+        "task_comments",
+        sa.Column("user_id", sa.Integer(), sa.ForeignKey("users.id", ondelete="SET NULL"), nullable=True),
+    )
+
+    # 1c. Add version column to project_tasks for optimistic locking
+    op.add_column(
+        "project_tasks",
+        sa.Column("version", sa.Integer(), server_default="1", nullable=False),
+    )
+
+    # Calendar delta polling index (Phase 4 prep)
+    op.execute("CREATE INDEX IF NOT EXISTS ix_events_calendar_updated ON calendar_events (calendar_id, updated_at DESC)")
+
+
+def downgrade() -> None:
+    op.drop_index("ix_events_calendar_updated", table_name="calendar_events")
+    op.drop_column("project_tasks", "version")
+    op.drop_column("task_comments", "user_id")
+    op.drop_index("ix_projects_user_updated", table_name="projects")
+    op.drop_index("ix_project_tasks_project_updated", table_name="project_tasks")
+    op.drop_index("ix_project_tasks_parent_task_id", table_name="project_tasks")
+    op.drop_index("ix_project_tasks_project_id", table_name="project_tasks")

backend/alembic/versions/058_project_members.py

@@ -0,0 +1,45 @@
+"""add project_members table
+
+Revision ID: 058
+Revises: 057
+Create Date: 2025-01-01 00:00:00.000000
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision = "058"
+down_revision = "057"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "project_members",
+        sa.Column("id", sa.Integer(), primary_key=True, autoincrement=True),
+        sa.Column("project_id", sa.Integer(), sa.ForeignKey("projects.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("user_id", sa.Integer(), sa.ForeignKey("users.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("invited_by", sa.Integer(), sa.ForeignKey("users.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("permission", sa.String(20), nullable=False),
+        sa.Column("status", sa.String(20), nullable=False, server_default="pending"),
+        sa.Column("source", sa.String(20), nullable=False, server_default="invited"),
+        sa.Column("created_at", sa.DateTime(), server_default=sa.func.now()),
+        sa.Column("updated_at", sa.DateTime(), server_default=sa.func.now()),
+        sa.Column("accepted_at", sa.DateTime(), nullable=True),
+        sa.UniqueConstraint("project_id", "user_id", name="uq_project_members_proj_user"),
+        sa.CheckConstraint("permission IN ('read_only', 'create_modify')", name="ck_project_members_permission"),
+        sa.CheckConstraint("status IN ('pending', 'accepted', 'rejected')", name="ck_project_members_status"),
+        sa.CheckConstraint("source IN ('invited', 'auto_assigned')", name="ck_project_members_source"),
+    )
+    op.create_index("ix_project_members_user_id", "project_members", ["user_id"])
+    op.create_index("ix_project_members_project_id", "project_members", ["project_id"])
+    op.create_index("ix_project_members_status", "project_members", ["status"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_project_members_status", table_name="project_members")
+    op.drop_index("ix_project_members_project_id", table_name="project_members")
+    op.drop_index("ix_project_members_user_id", table_name="project_members")
+    op.drop_table("project_members")

backend/alembic/versions/059_project_task_assignments.py

@@ -0,0 +1,35 @@
+"""add project_task_assignments table
+
+Revision ID: 059
+Revises: 058
+Create Date: 2025-01-01 00:00:00.000000
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision = "059"
+down_revision = "058"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "project_task_assignments",
+        sa.Column("id", sa.Integer(), primary_key=True, autoincrement=True),
+        sa.Column("task_id", sa.Integer(), sa.ForeignKey("project_tasks.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("user_id", sa.Integer(), sa.ForeignKey("users.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("assigned_by", sa.Integer(), sa.ForeignKey("users.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("created_at", sa.DateTime(), server_default=sa.func.now()),
+        sa.UniqueConstraint("task_id", "user_id", name="uq_task_assignments_task_user"),
+    )
+    op.create_index("ix_task_assignments_task_id", "project_task_assignments", ["task_id"])
+    op.create_index("ix_task_assignments_user_id", "project_task_assignments", ["user_id"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_task_assignments_user_id", table_name="project_task_assignments")
+    op.drop_index("ix_task_assignments_task_id", table_name="project_task_assignments")
+    op.drop_table("project_task_assignments")

backend/alembic/versions/060_expand_notification_types_project.py

@@ -0,0 +1,36 @@
+"""Expand notification type CHECK for project invite types
+
+Revision ID: 060
+Revises: 059
+"""
+from alembic import op
+
+revision = "060"
+down_revision = "059"
+branch_labels = None
+depends_on = None
+
+_OLD_TYPES = (
+    "connection_request", "connection_accepted", "connection_rejected",
+    "calendar_invite", "calendar_invite_accepted", "calendar_invite_rejected",
+    "event_invite", "event_invite_response",
+    "info", "warning", "reminder", "system",
+)
+_NEW_TYPES = _OLD_TYPES + (
+    "project_invite", "project_invite_accepted", "project_invite_rejected",
+    "task_assigned",
+)
+
+
+def _check_sql(types: tuple) -> str:
+    return f"type IN ({', '.join(repr(t) for t in types)})"
+
+
+def upgrade() -> None:
+    op.drop_constraint("ck_notifications_type", "notifications", type_="check")
+    op.create_check_constraint("ck_notifications_type", "notifications", _check_sql(_NEW_TYPES))
+
+
+def downgrade() -> None:
+    op.drop_constraint("ck_notifications_type", "notifications", type_="check")
+    op.create_check_constraint("ck_notifications_type", "notifications", _check_sql(_OLD_TYPES))

backend/alembic/versions/061_add_passkey_credentials.py

@@ -0,0 +1,40 @@
+"""Add passkey_credentials table for WebAuthn/FIDO2 authentication
+
+Revision ID: 061
+Revises: 060
+"""
+import sqlalchemy as sa
+from alembic import op
+
+revision = "061"
+down_revision = "060"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.create_table(
+        "passkey_credentials",
+        sa.Column("id", sa.Integer, primary_key=True),
+        sa.Column(
+            "user_id",
+            sa.Integer,
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column("credential_id", sa.Text, unique=True, nullable=False),
+        sa.Column("public_key", sa.Text, nullable=False),
+        sa.Column("sign_count", sa.Integer, nullable=False, server_default="0"),
+        sa.Column("name", sa.String(100), nullable=False),
+        sa.Column("transports", sa.Text, nullable=True),
+        sa.Column("backed_up", sa.Boolean, nullable=False, server_default="false"),
+        sa.Column("created_at", sa.DateTime, server_default=sa.text("now()")),
+        sa.Column("last_used_at", sa.DateTime, nullable=True),
+    )
+    op.create_index(
+        "ix_passkey_credentials_user_id", "passkey_credentials", ["user_id"]
+    )
+
+
+def downgrade():
+    op.drop_table("passkey_credentials")

backend/alembic/versions/062_passwordless_login.py

@@ -0,0 +1,40 @@
+"""Passwordless login — add passwordless_enabled to users and allow_passwordless to system_config.
+
+Revision ID: 062
+Revises: 061
+Create Date: 2026-03-18
+"""
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision = "062"
+down_revision = "061"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "users",
+        sa.Column(
+            "passwordless_enabled",
+            sa.Boolean(),
+            nullable=False,
+            server_default="false",
+        ),
+    )
+    op.add_column(
+        "system_config",
+        sa.Column(
+            "allow_passwordless",
+            sa.Boolean(),
+            nullable=False,
+            server_default="false",
+        ),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("users", "passwordless_enabled")
+    op.drop_column("system_config", "allow_passwordless")

backend/app/config.py

@@ -30,6 +30,12 @@ class Settings(BaseSettings):
     # Concurrent session limit per user (oldest evicted when exceeded)
     MAX_SESSIONS_PER_USER: int = 10
 
+    # WebAuthn / Passkey configuration
+    WEBAUTHN_RP_ID: str = "localhost"                # eTLD+1 domain, e.g. "umbra.ghost6.xyz"
+    WEBAUTHN_RP_NAME: str = "UMBRA"
+    WEBAUTHN_ORIGIN: str = "http://localhost"        # Full origin with scheme, e.g. "https://umbra.ghost6.xyz"
+    WEBAUTHN_CHALLENGE_TTL: int = 60                 # Challenge token lifetime in seconds
+
     model_config = SettingsConfigDict(
         env_file=".env",
         env_file_encoding="utf-8",
@@ -47,6 +53,9 @@ class Settings(BaseSettings):
                 self.CORS_ORIGINS = "http://localhost:5173"
         assert self.COOKIE_SECURE is not None  # type narrowing
         assert self.CORS_ORIGINS is not None
+        # Validate WebAuthn origin includes scheme (S-04)
+        if not self.WEBAUTHN_ORIGIN.startswith(("http://", "https://")):
+            raise ValueError("WEBAUTHN_ORIGIN must include scheme (http:// or https://)")
         return self
 
 

backend/app/database.py

@@ -2,11 +2,15 @@ from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession, async_sess
 from sqlalchemy.orm import declarative_base
 from app.config import settings
 
-# Create async engine
+# Create async engine with tuned pool (AW-7)
 engine = create_async_engine(
     settings.DATABASE_URL,
     echo=False,
-    future=True
+    future=True,
+    pool_size=10,
+    max_overflow=5,
+    pool_pre_ping=True,
+    pool_recycle=1800,
 )
 
 # Create async session factory

backend/app/jobs/notifications.py

@@ -21,6 +21,7 @@ from app.models.notification import Notification as AppNotification
 from app.models.reminder import Reminder
 from app.models.calendar_event import CalendarEvent
 from app.models.calendar import Calendar
+from app.models.event_lock import EventLock
 from app.models.todo import Todo
 from app.models.project import Project
 from app.models.ntfy_sent import NtfySent
@@ -55,8 +56,8 @@ async def _get_sent_keys(db: AsyncSession, user_id: int) -> set[str]:
 
 
 async def _mark_sent(db: AsyncSession, key: str, user_id: int) -> None:
+    """Stage a sent record — caller must commit (AW-4: bulk commit per user)."""
     db.add(NtfySent(notification_key=key, user_id=user_id))
-    await db.commit()
 
 
 # ── Dispatch functions ────────────────────────────────────────────────────────
@@ -238,14 +239,20 @@ async def _dispatch_for_user(db: AsyncSession, settings: Settings, now: datetime
     # Batch-fetch all sent keys once per user instead of one query per entity
     sent_keys = await _get_sent_keys(db, settings.user_id)
 
+    # AW-4: Commit after each category to preserve dedup records if a later
+    # category fails (prevents re-sending already-sent notifications)
     if settings.ntfy_reminders_enabled:
         await _dispatch_reminders(db, settings, now, sent_keys)
+        await db.commit()
     if settings.ntfy_events_enabled:
         await _dispatch_events(db, settings, now, sent_keys)
+        await db.commit()
     if settings.ntfy_todos_enabled:
         await _dispatch_todos(db, settings, now.date(), sent_keys)
+        await db.commit()
     if settings.ntfy_projects_enabled:
         await _dispatch_projects(db, settings, now.date(), sent_keys)
+        await db.commit()
 
 
 async def _purge_old_sent_records(db: AsyncSession) -> None:
@@ -300,6 +307,18 @@ async def _purge_resolved_requests(db: AsyncSession) -> None:
     await db.commit()
 
 
+
+async def _purge_expired_locks(db: AsyncSession) -> None:
+    """Remove non-permanent event locks that have expired."""
+    await db.execute(
+        delete(EventLock).where(
+            EventLock.is_permanent == False,  # noqa: E712
+            EventLock.expires_at < datetime.now(),
+        )
+    )
+    await db.commit()
+
+
 # ── Entry point ───────────────────────────────────────────────────────────────
 
 async def run_notification_dispatch() -> None:
@@ -343,6 +362,7 @@ async def run_notification_dispatch() -> None:
             await _purge_expired_sessions(db)
             await _purge_old_notifications(db)
             await _purge_resolved_requests(db)
+            await _purge_expired_locks(db)
 
     except Exception:
         # Broad catch: job failure must never crash the scheduler or the app

backend/app/main.py

@@ -7,7 +7,7 @@ from apscheduler.schedulers.asyncio import AsyncIOScheduler
 from app.config import settings
 from app.database import engine
 from app.routers import auth, todos, events, calendars, reminders, projects, people, locations, settings as settings_router, dashboard, weather, event_templates
-from app.routers import totp, admin, notifications as notifications_router, connections as connections_router
+from app.routers import totp, admin, notifications as notifications_router, connections as connections_router, shared_calendars as shared_calendars_router, event_invitations as event_invitations_router, passkeys as passkeys_router
 from app.jobs.notifications import run_notification_dispatch
 
 # Import models so Alembic's autogenerate can discover them
@@ -20,6 +20,10 @@ from app.models import audit_log as _audit_log_model  # noqa: F401
 from app.models import notification as _notification_model  # noqa: F401
 from app.models import connection_request as _connection_request_model  # noqa: F401
 from app.models import user_connection as _user_connection_model  # noqa: F401
+from app.models import calendar_member as _calendar_member_model  # noqa: F401
+from app.models import event_lock as _event_lock_model  # noqa: F401
+from app.models import event_invitation as _event_invitation_model  # noqa: F401
+from app.models import passkey_credential as _passkey_credential_model  # noqa: F401
 
 
 # ---------------------------------------------------------------------------
@@ -46,6 +50,8 @@ class CSRFHeaderMiddleware:
         "/api/auth/totp-verify",
         "/api/auth/totp/enforce-setup",
         "/api/auth/totp/enforce-confirm",
+        "/api/auth/passkeys/login/begin",
+        "/api/auth/passkeys/login/complete",
     })
     _MUTATING_METHODS = frozenset({"POST", "PUT", "PATCH", "DELETE"})
 
@@ -131,9 +137,13 @@ app.include_router(dashboard.router, prefix="/api", tags=["Dashboard"])
 app.include_router(weather.router, prefix="/api/weather", tags=["Weather"])
 app.include_router(event_templates.router, prefix="/api/event-templates", tags=["Event Templates"])
 app.include_router(totp.router, prefix="/api/auth", tags=["TOTP MFA"])
+app.include_router(passkeys_router.router, prefix="/api/auth/passkeys", tags=["Passkeys"])
 app.include_router(admin.router, prefix="/api/admin", tags=["Admin"])
 app.include_router(notifications_router.router, prefix="/api/notifications", tags=["Notifications"])
 app.include_router(connections_router.router, prefix="/api/connections", tags=["Connections"])
+app.include_router(shared_calendars_router.router, prefix="/api/shared-calendars", tags=["Shared Calendars"])
+app.include_router(event_invitations_router.events_router, prefix="/api/events", tags=["Event Invitations"])
+app.include_router(event_invitations_router.router, prefix="/api/event-invitations", tags=["Event Invitations"])
 
 
 @app.get("/")

backend/app/models/__init__.py

@@ -18,6 +18,12 @@ from app.models.audit_log import AuditLog
 from app.models.notification import Notification
 from app.models.connection_request import ConnectionRequest
 from app.models.user_connection import UserConnection
+from app.models.calendar_member import CalendarMember
+from app.models.event_lock import EventLock
+from app.models.event_invitation import EventInvitation, EventInvitationOverride
+from app.models.project_member import ProjectMember
+from app.models.project_task_assignment import ProjectTaskAssignment
+from app.models.passkey_credential import PasskeyCredential
 
 __all__ = [
     "Settings",
@@ -40,4 +46,11 @@ __all__ = [
     "Notification",
     "ConnectionRequest",
     "UserConnection",
+    "CalendarMember",
+    "EventLock",
+    "EventInvitation",
+    "EventInvitationOverride",
+    "ProjectMember",
+    "ProjectTaskAssignment",
+    "PasskeyCredential",
 ]

backend/app/models/calendar.py

@@ -1,7 +1,10 @@
 from sqlalchemy import String, Boolean, Integer, ForeignKey, func
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 from datetime import datetime
-from typing import List
+from typing import List, TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from app.models.calendar_member import CalendarMember
 from app.database import Base
 
 
@@ -17,7 +20,9 @@ class Calendar(Base):
     is_default: Mapped[bool] = mapped_column(Boolean, default=False, server_default="false")
     is_system: Mapped[bool] = mapped_column(Boolean, default=False, server_default="false")
     is_visible: Mapped[bool] = mapped_column(Boolean, default=True, server_default="true")
+    is_shared: Mapped[bool] = mapped_column(Boolean, default=False, server_default="false")
     created_at: Mapped[datetime] = mapped_column(default=func.now())
     updated_at: Mapped[datetime] = mapped_column(default=func.now(), onupdate=func.now())
 
     events: Mapped[List["CalendarEvent"]] = relationship(back_populates="calendar")
+    members: Mapped[List["CalendarMember"]] = relationship(back_populates="calendar", cascade="all, delete-orphan")

backend/app/models/calendar_event.py

@@ -32,6 +32,11 @@ class CalendarEvent(Base):
     # original_start: the originally computed occurrence datetime (children only)
     original_start: Mapped[Optional[datetime]] = mapped_column(nullable=True)
 
+    updated_by: Mapped[Optional[int]] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="SET NULL"), nullable=True
+    )
+
+
     created_at: Mapped[datetime] = mapped_column(default=func.now())
     updated_at: Mapped[datetime] = mapped_column(default=func.now(), onupdate=func.now())
 

backend/app/models/calendar_member.py

@@ -0,0 +1,53 @@
+from sqlalchemy import (
+    Boolean, CheckConstraint, DateTime, Integer, ForeignKey, Index,
+    String, UniqueConstraint, func,
+)
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+from datetime import datetime
+from typing import Optional
+from app.database import Base
+
+
+class CalendarMember(Base):
+    __tablename__ = "calendar_members"
+    __table_args__ = (
+        UniqueConstraint("calendar_id", "user_id", name="uq_calendar_members_cal_user"),
+        CheckConstraint(
+            "permission IN ('read_only', 'create_modify', 'full_access')",
+            name="ck_calendar_members_permission",
+        ),
+        CheckConstraint(
+            "status IN ('pending', 'accepted', 'rejected')",
+            name="ck_calendar_members_status",
+        ),
+        Index("ix_calendar_members_user_id", "user_id"),
+        Index("ix_calendar_members_calendar_id", "calendar_id"),
+        Index("ix_calendar_members_status", "status"),
+    )
+
+    id: Mapped[int] = mapped_column(primary_key=True, index=True)
+    calendar_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("calendars.id", ondelete="CASCADE"), nullable=False
+    )
+    user_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False
+    )
+    invited_by: Mapped[Optional[int]] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="SET NULL"), nullable=True
+    )
+    permission: Mapped[str] = mapped_column(String(20), nullable=False)
+    can_add_others: Mapped[bool] = mapped_column(
+        Boolean, default=False, server_default="false"
+    )
+    local_color: Mapped[Optional[str]] = mapped_column(String(20), nullable=True)
+    status: Mapped[str] = mapped_column(String(20), nullable=False, default="pending")
+    invited_at: Mapped[datetime] = mapped_column(
+        DateTime, default=func.now(), server_default=func.now()
+    )
+    accepted_at: Mapped[Optional[datetime]] = mapped_column(DateTime, nullable=True)
+
+    calendar: Mapped["Calendar"] = relationship(back_populates="members", lazy="raise")
+    user: Mapped["User"] = relationship(foreign_keys=[user_id], lazy="raise")
+    inviter: Mapped[Optional["User"]] = relationship(
+        foreign_keys=[invited_by], lazy="raise"
+    )

backend/app/models/event_invitation.py

@@ -0,0 +1,77 @@
+from sqlalchemy import (
+    Boolean, CheckConstraint, DateTime, Integer, ForeignKey, Index,
+    String, UniqueConstraint, false as sa_false, func,
+)
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+from datetime import datetime
+from typing import Optional
+from app.database import Base
+
+
+class EventInvitation(Base):
+    __tablename__ = "event_invitations"
+    __table_args__ = (
+        UniqueConstraint("event_id", "user_id", name="uq_event_invitations_event_user"),
+        CheckConstraint(
+            "status IN ('pending', 'accepted', 'tentative', 'declined')",
+            name="ck_event_invitations_status",
+        ),
+        Index("ix_event_invitations_user_status", "user_id", "status"),
+        Index("ix_event_invitations_event_id", "event_id"),
+    )
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    event_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("calendar_events.id", ondelete="CASCADE"), nullable=False
+    )
+    user_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False
+    )
+    invited_by: Mapped[Optional[int]] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="SET NULL"), nullable=True
+    )
+    status: Mapped[str] = mapped_column(String(20), default="pending")
+    invited_at: Mapped[datetime] = mapped_column(
+        DateTime, default=func.now(), server_default=func.now()
+    )
+    responded_at: Mapped[Optional[datetime]] = mapped_column(DateTime, nullable=True)
+    display_calendar_id: Mapped[Optional[int]] = mapped_column(
+        Integer, ForeignKey("calendars.id", ondelete="SET NULL"), nullable=True
+    )
+    can_modify: Mapped[bool] = mapped_column(
+        Boolean, default=False, server_default=sa_false()
+    )
+
+    event: Mapped["CalendarEvent"] = relationship(lazy="raise")
+    user: Mapped["User"] = relationship(foreign_keys=[user_id], lazy="raise")
+    inviter: Mapped[Optional["User"]] = relationship(
+        foreign_keys=[invited_by], lazy="raise"
+    )
+    display_calendar: Mapped[Optional["Calendar"]] = relationship(lazy="raise")
+    overrides: Mapped[list["EventInvitationOverride"]] = relationship(
+        lazy="raise", cascade="all, delete-orphan"
+    )
+
+
+class EventInvitationOverride(Base):
+    __tablename__ = "event_invitation_overrides"
+    __table_args__ = (
+        UniqueConstraint("invitation_id", "occurrence_id", name="uq_invitation_override"),
+        CheckConstraint(
+            "status IN ('accepted', 'tentative', 'declined')",
+            name="ck_invitation_override_status",
+        ),
+        Index("ix_invitation_overrides_lookup", "invitation_id", "occurrence_id"),
+    )
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    invitation_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("event_invitations.id", ondelete="CASCADE"), nullable=False
+    )
+    occurrence_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("calendar_events.id", ondelete="CASCADE"), nullable=False
+    )
+    status: Mapped[str] = mapped_column(String(20), nullable=False)
+    responded_at: Mapped[datetime] = mapped_column(
+        DateTime, default=func.now(), server_default=func.now()
+    )

backend/app/models/event_lock.py

@@ -0,0 +1,31 @@
+from sqlalchemy import Boolean, DateTime, Integer, ForeignKey, Index, func
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+from datetime import datetime
+from typing import Optional
+from app.database import Base
+
+
+class EventLock(Base):
+    __tablename__ = "event_locks"
+    __table_args__ = (Index("ix_event_locks_expires_at", "expires_at"),)
+
+    id: Mapped[int] = mapped_column(primary_key=True, index=True)
+    event_id: Mapped[int] = mapped_column(
+        Integer,
+        ForeignKey("calendar_events.id", ondelete="CASCADE"),
+        nullable=False,
+        unique=True,
+    )
+    locked_by: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False
+    )
+    locked_at: Mapped[datetime] = mapped_column(
+        DateTime, default=func.now(), server_default=func.now()
+    )
+    expires_at: Mapped[Optional[datetime]] = mapped_column(DateTime, nullable=True)
+    is_permanent: Mapped[bool] = mapped_column(
+        Boolean, default=False, server_default="false"
+    )
+
+    event: Mapped["CalendarEvent"] = relationship(lazy="selectin")
+    holder: Mapped["User"] = relationship(foreign_keys=[locked_by], lazy="selectin")

backend/app/models/notification.py

@@ -5,10 +5,12 @@ from datetime import datetime
 from typing import Optional
 from app.database import Base
 
-# Active: connection_request, connection_accepted
-# Reserved: connection_rejected, info, warning, reminder, system
 _NOTIFICATION_TYPES = (
     "connection_request", "connection_accepted", "connection_rejected",
+    "calendar_invite", "calendar_invite_accepted", "calendar_invite_rejected",
+    "event_invite", "event_invite_response",
+    "project_invite", "project_invite_accepted", "project_invite_rejected",
+    "task_assigned",
     "info", "warning", "reminder", "system",
 )
 

backend/app/models/passkey_credential.py

@@ -0,0 +1,30 @@
+from datetime import datetime
+
+from sqlalchemy import Boolean, ForeignKey, Integer, String, Text, func
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.database import Base
+
+
+class PasskeyCredential(Base):
+    __tablename__ = "passkey_credentials"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    user_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    # base64url-encoded credential ID (spec allows up to 1023 bytes → ~1363 chars)
+    credential_id: Mapped[str] = mapped_column(Text, unique=True, nullable=False)
+    # base64url-encoded COSE public key
+    public_key: Mapped[str] = mapped_column(Text, nullable=False)
+    # Authenticator sign count for clone detection
+    sign_count: Mapped[int] = mapped_column(Integer, default=0)
+    # User-assigned label (e.g. "MacBook Pro — Chrome")
+    name: Mapped[str] = mapped_column(String(100), nullable=False)
+    # JSON array of transport hints (e.g. '["usb","hybrid"]')
+    transports: Mapped[str | None] = mapped_column(Text, nullable=True)
+    # Whether the credential is backed up / synced across devices
+    backed_up: Mapped[bool] = mapped_column(Boolean, default=False)
+
+    created_at: Mapped[datetime] = mapped_column(default=func.now())
+    last_used_at: Mapped[datetime | None] = mapped_column(nullable=True)

backend/app/models/project.py

@@ -22,6 +22,7 @@ class Project(Base):
     created_at: Mapped[datetime] = mapped_column(default=func.now())
     updated_at: Mapped[datetime] = mapped_column(default=func.now(), onupdate=func.now())
 
-    # Relationships
-    tasks: Mapped[List["ProjectTask"]] = relationship(back_populates="project", cascade="all, delete-orphan")
-    todos: Mapped[List["Todo"]] = relationship(back_populates="project")
+    # Relationships — lazy="raise" to prevent N+1 (mirrors CalendarMember pattern)
+    tasks: Mapped[List["ProjectTask"]] = relationship(back_populates="project", cascade="all, delete-orphan", passive_deletes=True, lazy="raise")
+    todos: Mapped[List["Todo"]] = relationship(back_populates="project", lazy="raise")
+    members: Mapped[List["ProjectMember"]] = relationship(back_populates="project", cascade="all, delete-orphan", passive_deletes=True, lazy="raise")

backend/app/models/project_member.py

@@ -0,0 +1,58 @@
+from sqlalchemy import (
+    CheckConstraint, DateTime, Integer, ForeignKey, Index,
+    String, UniqueConstraint, func,
+)
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+from datetime import datetime
+from typing import Optional
+from app.database import Base
+
+
+class ProjectMember(Base):
+    __tablename__ = "project_members"
+    __table_args__ = (
+        UniqueConstraint("project_id", "user_id", name="uq_project_members_proj_user"),
+        CheckConstraint(
+            "permission IN ('read_only', 'create_modify')",
+            name="ck_project_members_permission",
+        ),
+        CheckConstraint(
+            "status IN ('pending', 'accepted', 'rejected')",
+            name="ck_project_members_status",
+        ),
+        CheckConstraint(
+            "source IN ('invited', 'auto_assigned')",
+            name="ck_project_members_source",
+        ),
+        Index("ix_project_members_user_id", "user_id"),
+        Index("ix_project_members_project_id", "project_id"),
+        Index("ix_project_members_status", "status"),
+    )
+
+    id: Mapped[int] = mapped_column(primary_key=True, index=True)
+    project_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("projects.id", ondelete="CASCADE"), nullable=False
+    )
+    user_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False
+    )
+    invited_by: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False
+    )
+    permission: Mapped[str] = mapped_column(String(20), nullable=False)
+    status: Mapped[str] = mapped_column(String(20), nullable=False, default="pending")
+    source: Mapped[str] = mapped_column(String(20), nullable=False, default="invited")
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime, default=func.now(), server_default=func.now()
+    )
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime, default=func.now(), server_default=func.now(), onupdate=func.now()
+    )
+    accepted_at: Mapped[Optional[datetime]] = mapped_column(DateTime, nullable=True)
+
+    # Relationships — lazy="raise" to prevent N+1 (mirrors CalendarMember)
+    project: Mapped["Project"] = relationship(back_populates="members", lazy="raise")
+    user: Mapped["User"] = relationship(foreign_keys=[user_id], lazy="raise")
+    inviter: Mapped[Optional["User"]] = relationship(
+        foreign_keys=[invited_by], lazy="raise"
+    )

backend/app/models/project_task.py

@@ -1,3 +1,4 @@
+import sqlalchemy as sa
 from sqlalchemy import String, Text, Integer, Date, ForeignKey, func
 from sqlalchemy.orm import Mapped, mapped_column, relationship as sa_relationship
 from datetime import datetime, date
@@ -20,21 +21,33 @@ class ProjectTask(Base):
     due_date: Mapped[Optional[date]] = mapped_column(Date, nullable=True)
     person_id: Mapped[Optional[int]] = mapped_column(Integer, ForeignKey("people.id", ondelete="SET NULL"), nullable=True)
     sort_order: Mapped[int] = mapped_column(Integer, default=0)
+    version: Mapped[int] = mapped_column(Integer, default=1, server_default=sa.text("1"))
     created_at: Mapped[datetime] = mapped_column(default=func.now())
     updated_at: Mapped[datetime] = mapped_column(default=func.now(), onupdate=func.now())
 
-    # Relationships
-    project: Mapped["Project"] = sa_relationship(back_populates="tasks")
-    person: Mapped[Optional["Person"]] = sa_relationship(back_populates="assigned_tasks")
+    # Relationships — lazy="raise" to prevent N+1 (mirrors CalendarMember pattern)
+    project: Mapped["Project"] = sa_relationship(back_populates="tasks", lazy="raise")
+    person: Mapped[Optional["Person"]] = sa_relationship(back_populates="assigned_tasks", lazy="raise")
     parent_task: Mapped[Optional["ProjectTask"]] = sa_relationship(
         back_populates="subtasks",
         remote_side=[id],
+        lazy="raise",
     )
     subtasks: Mapped[List["ProjectTask"]] = sa_relationship(
         back_populates="parent_task",
         cascade="all, delete-orphan",
+        passive_deletes=True,
+        lazy="raise",
     )
     comments: Mapped[List["TaskComment"]] = sa_relationship(
         back_populates="task",
         cascade="all, delete-orphan",
+        passive_deletes=True,
+        lazy="raise",
+    )
+    assignments: Mapped[List["ProjectTaskAssignment"]] = sa_relationship(
+        back_populates="task",
+        cascade="all, delete-orphan",
+        passive_deletes=True,
+        lazy="raise",
     )

backend/app/models/project_task_assignment.py

@@ -0,0 +1,30 @@
+from sqlalchemy import DateTime, Integer, ForeignKey, UniqueConstraint, func
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+from datetime import datetime
+from app.database import Base
+
+
+class ProjectTaskAssignment(Base):
+    __tablename__ = "project_task_assignments"
+    __table_args__ = (
+        UniqueConstraint("task_id", "user_id", name="uq_task_assignments_task_user"),
+    )
+
+    id: Mapped[int] = mapped_column(primary_key=True, index=True)
+    task_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("project_tasks.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    user_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    assigned_by: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False
+    )
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime, default=func.now(), server_default=func.now()
+    )
+
+    # Relationships — lazy="raise" to prevent N+1
+    task: Mapped["ProjectTask"] = relationship(back_populates="assignments", lazy="raise")
+    user: Mapped["User"] = relationship(foreign_keys=[user_id], lazy="raise")
+    assigner: Mapped["User"] = relationship(foreign_keys=[assigned_by], lazy="raise")

backend/app/models/session.py

@@ -18,6 +18,10 @@ class UserSession(Base):
     expires_at: Mapped[datetime] = mapped_column(nullable=False)
     revoked: Mapped[bool] = mapped_column(Boolean, default=False)
 
+    # Session lock — persists across page refresh
+    is_locked: Mapped[bool] = mapped_column(Boolean, default=False, server_default="false")
+    locked_at: Mapped[datetime | None] = mapped_column(nullable=True)
+
     # Audit fields for security logging
     ip_address: Mapped[str | None] = mapped_column(String(45), nullable=True)
     user_agent: Mapped[str | None] = mapped_column(String(255), nullable=True)

backend/app/models/system_config.py

@@ -21,6 +21,9 @@ class SystemConfig(Base):
     enforce_mfa_new_users: Mapped[bool] = mapped_column(
         Boolean, default=False, server_default="false"
     )
+    allow_passwordless: Mapped[bool] = mapped_column(
+        Boolean, default=False, server_default="false"
+    )
     created_at: Mapped[datetime] = mapped_column(default=func.now(), server_default=func.now())
     updated_at: Mapped[datetime] = mapped_column(
         default=func.now(), onupdate=func.now(), server_default=func.now()

backend/app/models/task_comment.py

@@ -1,6 +1,7 @@
 from sqlalchemy import Text, Integer, ForeignKey
 from sqlalchemy.orm import Mapped, mapped_column, relationship as sa_relationship
 from datetime import datetime
+from typing import Optional
 from app.database import Base
 
 
@@ -11,8 +12,12 @@ class TaskComment(Base):
     task_id: Mapped[int] = mapped_column(
         Integer, ForeignKey("project_tasks.id", ondelete="CASCADE"), nullable=False, index=True
     )
+    user_id: Mapped[Optional[int]] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="SET NULL"), nullable=True
+    )
     content: Mapped[str] = mapped_column(Text, nullable=False)
     created_at: Mapped[datetime] = mapped_column(default=datetime.now)
 
-    # Relationships
-    task: Mapped["ProjectTask"] = sa_relationship(back_populates="comments")
+    # Relationships — lazy="raise" to prevent N+1 (mirrors CalendarMember pattern)
+    task: Mapped["ProjectTask"] = sa_relationship(back_populates="comments", lazy="raise")
+    user: Mapped[Optional["User"]] = sa_relationship(lazy="raise")

backend/app/models/user.py

@@ -43,6 +43,11 @@ class User(Base):
         Boolean, default=False, server_default="false"
     )
 
+    # Passwordless login — requires >= 2 passkeys registered
+    passwordless_enabled: Mapped[bool] = mapped_column(
+        Boolean, default=False, server_default="false"
+    )
+
     # Audit
     created_at: Mapped[datetime] = mapped_column(default=func.now())
     updated_at: Mapped[datetime] = mapped_column(default=func.now(), onupdate=func.now())

backend/app/routers/admin.py

@@ -22,6 +22,8 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.database import get_db
 from app.models.audit_log import AuditLog
+from app.models.calendar import Calendar
+from app.models.calendar_member import CalendarMember
 from app.models.backup_code import BackupCode
 from app.models.session import UserSession
 from app.models.settings import Settings
@@ -43,13 +45,14 @@ from app.schemas.admin import (
     SystemConfigUpdate,
     ToggleActiveRequest,
     ToggleMfaEnforceRequest,
+    TogglePasswordlessRequest,
     UpdateUserRoleRequest,
     UserDetailResponse,
     UserListItem,
     UserListResponse,
 )
 from app.services.audit import get_client_ip, log_audit_event
-from app.services.auth import hash_password
+from app.services.auth import ahash_password
 
 # ---------------------------------------------------------------------------
 # Router — all endpoints inherit require_admin
@@ -223,7 +226,7 @@ async def create_user(
     new_user = User(
         username=data.username,
         umbral_name=data.username,
-        password_hash=hash_password(data.password),
+        password_hash=await ahash_password(data.password),
         role=data.role,
         email=email,
         first_name=data.first_name,
@@ -339,7 +342,7 @@ async def reset_user_password(
         raise HTTPException(status_code=404, detail="User not found")
 
     temp_password = secrets.token_urlsafe(16)
-    user.password_hash = hash_password(temp_password)
+    user.password_hash = await ahash_password(temp_password)
     user.must_change_password = True
     user.last_password_change_at = datetime.now()
 
@@ -618,6 +621,106 @@ async def list_user_sessions(
     }
 
 
+# ---------------------------------------------------------------------------
+# GET /users/{user_id}/sharing-stats
+# ---------------------------------------------------------------------------
+
+@router.get("/users/{user_id}/sharing-stats")
+async def get_user_sharing_stats(
+    user_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    _actor: User = Depends(get_current_user),
+):
+    """Return sharing statistics for a user."""
+    result = await db.execute(sa.select(User).where(User.id == user_id))
+    if not result.scalar_one_or_none():
+        raise HTTPException(status_code=404, detail="User not found")
+
+    # Calendars owned that are shared
+    shared_owned = await db.scalar(
+        sa.select(sa.func.count())
+        .select_from(Calendar)
+        .where(Calendar.user_id == user_id, Calendar.is_shared == True)
+    ) or 0
+
+    # Calendars the user is a member of (accepted)
+    member_of = await db.scalar(
+        sa.select(sa.func.count())
+        .select_from(CalendarMember)
+        .where(CalendarMember.user_id == user_id, CalendarMember.status == "accepted")
+    ) or 0
+
+    # Pending invites sent by this user
+    pending_sent = await db.scalar(
+        sa.select(sa.func.count())
+        .select_from(CalendarMember)
+        .where(CalendarMember.invited_by == user_id, CalendarMember.status == "pending")
+    ) or 0
+
+    # Pending invites received by this user
+    pending_received = await db.scalar(
+        sa.select(sa.func.count())
+        .select_from(CalendarMember)
+        .where(CalendarMember.user_id == user_id, CalendarMember.status == "pending")
+    ) or 0
+
+    return {
+        "shared_calendars_owned": shared_owned,
+        "calendars_member_of": member_of,
+        "pending_invites_sent": pending_sent,
+        "pending_invites_received": pending_received,
+    }
+
+# ---------------------------------------------------------------------------
+# PUT /users/{user_id}/passwordless
+# ---------------------------------------------------------------------------
+
+@router.put("/users/{user_id}/passwordless")
+async def admin_toggle_passwordless(
+    request: Request,
+    data: TogglePasswordlessRequest,
+    user_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    actor: User = Depends(get_current_user),
+):
+    """
+    Admin-only: disable passwordless login for a user.
+    Only enabled=False is allowed — admin cannot remotely enable passwordless.
+    Revokes all sessions so the user must re-authenticate.
+    """
+    if data.enabled:
+        raise HTTPException(
+            status_code=400,
+            detail="Admin can only disable passwordless login, not enable it",
+        )
+
+    _guard_self_action(actor, user_id, "toggle passwordless for")
+
+    result = await db.execute(sa.select(User).where(User.id == user_id))
+    user = result.scalar_one_or_none()
+    if not user:
+        raise HTTPException(status_code=404, detail="User not found")
+
+    if not user.passwordless_enabled:
+        raise HTTPException(status_code=409, detail="Passwordless login is not enabled for this user")
+
+    user.passwordless_enabled = False
+
+    revoked = await _revoke_all_sessions(db, user_id)
+
+    await log_audit_event(
+        db,
+        action="admin.passwordless_disabled",
+        actor_id=actor.id,
+        target_id=user_id,
+        detail={"sessions_revoked": revoked, "username": user.username},
+        ip=get_client_ip(request),
+    )
+    await db.commit()
+
+    return {"passwordless_enabled": False, "sessions_revoked": revoked}
+
+
 # ---------------------------------------------------------------------------
 # GET /config
 # ---------------------------------------------------------------------------
@@ -664,6 +767,9 @@ async def update_system_config(
     if data.enforce_mfa_new_users is not None:
         changes["enforce_mfa_new_users"] = data.enforce_mfa_new_users
         config.enforce_mfa_new_users = data.enforce_mfa_new_users
+    if data.allow_passwordless is not None:
+        changes["allow_passwordless"] = data.allow_passwordless
+        config.allow_passwordless = data.allow_passwordless
 
     if changes:
         await log_audit_event(
@@ -688,18 +794,18 @@ async def admin_dashboard(
     _actor: User = Depends(get_current_user),
 ):
     """Aggregate stats for the admin portal dashboard."""
-    total_users = await db.scalar(
-        sa.select(sa.func.count()).select_from(User)
-    )
-    active_users = await db.scalar(
-        sa.select(sa.func.count()).select_from(User).where(User.is_active == True)
-    )
-    admin_count = await db.scalar(
-        sa.select(sa.func.count()).select_from(User).where(User.role == "admin")
-    )
-    totp_count = await db.scalar(
-        sa.select(sa.func.count()).select_from(User).where(User.totp_enabled == True)
+    # AW-6: Single conditional aggregation instead of 5 separate COUNT queries
+    user_stats = await db.execute(
+        sa.select(
+            sa.func.count().label("total"),
+            sa.func.count().filter(User.is_active == True).label("active"),
+            sa.func.count().filter(User.role == "admin").label("admins"),
+            sa.func.count().filter(User.totp_enabled == True).label("totp"),
+        ).select_from(User)
     )
+    row = user_stats.one()
+    total_users, active_users, admin_count, totp_count = row.tuple()
+
     active_sessions = await db.scalar(
         sa.select(sa.func.count()).select_from(UserSession).where(
             UserSession.revoked == False,

backend/app/routers/auth.py

@@ -16,7 +16,6 @@ Security layers:
   4. bcrypt→Argon2id transparent upgrade on first login
   5. Role-based authorization via require_role() dependency factory
 """
-import uuid
 from datetime import datetime, timedelta
 from typing import Optional
 
@@ -25,10 +24,12 @@ from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy import select, func
 
 from app.database import get_db
+from app.services.connection import sync_birthday_to_contacts
 from app.models.user import User
 from app.models.session import UserSession
 from app.models.settings import Settings
 from app.models.system_config import SystemConfig
+from app.models.passkey_credential import PasskeyCredential
 from app.models.calendar import Calendar
 from app.schemas.auth import (
     SetupRequest, LoginRequest, RegisterRequest,
@@ -36,6 +37,9 @@ from app.schemas.auth import (
     ProfileUpdate, ProfileResponse,
 )
 from app.services.auth import (
+    ahash_password,
+    averify_password,
+    averify_password_with_upgrade,
     hash_password,
     verify_password,
     verify_password_with_upgrade,
@@ -45,6 +49,13 @@ from app.services.auth import (
     create_mfa_enforce_token,
 )
 from app.services.audit import get_client_ip, log_audit_event
+from app.services.session import (
+    set_session_cookie,
+    check_account_lockout,
+    record_failed_login,
+    record_successful_login,
+    create_db_session,
+)
 from app.config import settings as app_settings
 
 router = APIRouter()
@@ -55,22 +66,6 @@ router = APIRouter()
 # is indistinguishable from a wrong-password attempt.
 _DUMMY_HASH = hash_password("timing-equalization-dummy")
 
-# ---------------------------------------------------------------------------
-# Cookie helper
-# ---------------------------------------------------------------------------
-
-def _set_session_cookie(response: Response, token: str) -> None:
-    response.set_cookie(
-        key="session",
-        value=token,
-        httponly=True,
-        secure=app_settings.COOKIE_SECURE,
-        max_age=app_settings.SESSION_MAX_AGE_DAYS * 86400,
-        samesite="lax",
-        path="/",
-    )
-
-
 # ---------------------------------------------------------------------------
 # Auth dependencies — export get_current_user and get_current_settings
 # ---------------------------------------------------------------------------
@@ -100,25 +95,22 @@ async def get_current_user(
     if user_id is None or session_id is None:
         raise HTTPException(status_code=401, detail="Malformed session token")
 
-    # Verify session is active in DB (covers revocation + expiry)
-    session_result = await db.execute(
-        select(UserSession).where(
+    # AC-1: Single JOIN query for session + user (was 2 sequential queries)
+    result = await db.execute(
+        select(UserSession, User)
+        .join(User, UserSession.user_id == User.id)
+        .where(
             UserSession.id == session_id,
             UserSession.user_id == user_id,
             UserSession.revoked == False,
             UserSession.expires_at > datetime.now(),
+            User.is_active == True,
         )
     )
-    db_session = session_result.scalar_one_or_none()
-    if not db_session:
-        raise HTTPException(status_code=401, detail="Session has been revoked or expired")
-
-    user_result = await db.execute(
-        select(User).where(User.id == user_id, User.is_active == True)
-    )
-    user = user_result.scalar_one_or_none()
-    if not user:
-        raise HTTPException(status_code=401, detail="User not found or inactive")
+    row = result.one_or_none()
+    if not row:
+        raise HTTPException(status_code=401, detail="Session expired or user inactive")
+    db_session, user = row.tuple()
 
     # L-03: Sliding window renewal — extend session if >1 day has elapsed since
     # last renewal (i.e. remaining time < SESSION_MAX_AGE_DAYS - 1 day).
@@ -129,25 +121,46 @@ async def get_current_user(
         await db.flush()
         # Re-issue cookie with fresh signed token to reset browser max_age timer
         fresh_token = create_session_token(user_id, session_id)
-        _set_session_cookie(response, fresh_token)
+        set_session_cookie(response, fresh_token)
+
+    # Stash session on request so lock/unlock endpoints can access it
+    request.state.db_session = db_session
+
+    # Defense-in-depth: block API access while session is locked.
+    # Exempt endpoints needed for unlocking, locking, checking status, and logout.
+    if db_session.is_locked:
+        lock_exempt = {
+            "/api/auth/lock", "/api/auth/verify-password",
+            "/api/auth/status", "/api/auth/logout",
+            "/api/auth/passkeys/login/begin", "/api/auth/passkeys/login/complete",
+        }
+        if request.url.path not in lock_exempt:
+            raise HTTPException(status_code=423, detail="Session is locked")
 
     return user
 
 
 async def get_current_settings(
+    request: Request,
     current_user: User = Depends(get_current_user),
     db: AsyncSession = Depends(get_db),
 ) -> Settings:
     """
     Convenience dependency for routers that need Settings access.
     Always chain after get_current_user — never use standalone.
+
+    AC-3: Cache in request.state so multiple dependencies don't re-query.
     """
+    cached = getattr(request.state, "settings", None)
+    if cached is not None:
+        return cached
     result = await db.execute(
         select(Settings).where(Settings.user_id == current_user.id)
     )
     settings_obj = result.scalar_one_or_none()
     if not settings_obj:
         raise HTTPException(status_code=500, detail="Settings not found for user")
+    request.state.settings = settings_obj
     return settings_obj
 
 
@@ -169,82 +182,6 @@ def require_role(*allowed_roles: str):
 require_admin = require_role("admin")
 
 
-# ---------------------------------------------------------------------------
-# Account lockout helpers
-# ---------------------------------------------------------------------------
-
-async def _check_account_lockout(user: User) -> None:
-    """Raise HTTP 423 if the account is currently locked."""
-    if user.locked_until and datetime.now() < user.locked_until:
-        remaining = int((user.locked_until - datetime.now()).total_seconds() / 60) + 1
-        raise HTTPException(
-            status_code=423,
-            detail=f"Account locked. Try again in {remaining} minutes.",
-        )
-
-
-async def _record_failed_login(db: AsyncSession, user: User) -> None:
-    """Increment failure counter; lock account after 10 failures."""
-    user.failed_login_count += 1
-    if user.failed_login_count >= 10:
-        user.locked_until = datetime.now() + timedelta(minutes=30)
-    await db.commit()
-
-
-async def _record_successful_login(db: AsyncSession, user: User) -> None:
-    """Reset failure counter and update last_login_at."""
-    user.failed_login_count = 0
-    user.locked_until = None
-    user.last_login_at = datetime.now()
-    await db.commit()
-
-
-# ---------------------------------------------------------------------------
-# Session creation helper
-# ---------------------------------------------------------------------------
-
-async def _create_db_session(
-    db: AsyncSession,
-    user: User,
-    ip: str,
-    user_agent: str | None,
-) -> tuple[str, str]:
-    """Insert a UserSession row and return (session_id, signed_cookie_token)."""
-    session_id = uuid.uuid4().hex
-    expires_at = datetime.now() + timedelta(days=app_settings.SESSION_MAX_AGE_DAYS)
-    db_session = UserSession(
-        id=session_id,
-        user_id=user.id,
-        expires_at=expires_at,
-        ip_address=ip[:45] if ip else None,
-        user_agent=(user_agent or "")[:255] if user_agent else None,
-    )
-    db.add(db_session)
-    await db.flush()
-
-    # Enforce concurrent session limit: revoke oldest sessions beyond the cap
-    active_sessions = (
-        await db.execute(
-            select(UserSession)
-            .where(
-                UserSession.user_id == user.id,
-                UserSession.revoked == False,  # noqa: E712
-                UserSession.expires_at > datetime.now(),
-            )
-            .order_by(UserSession.created_at.asc())
-        )
-    ).scalars().all()
-
-    max_sessions = app_settings.MAX_SESSIONS_PER_USER
-    if len(active_sessions) > max_sessions:
-        for old_session in active_sessions[: len(active_sessions) - max_sessions]:
-            old_session.revoked = True
-        await db.flush()
-
-    token = create_session_token(user.id, session_id)
-    return session_id, token
-
-
 # ---------------------------------------------------------------------------
 # User bootstrapping helper (Settings + default calendars)
 # ---------------------------------------------------------------------------
@@ -285,7 +222,7 @@ async def setup(
     if user_count.scalar_one() > 0:
         raise HTTPException(status_code=400, detail="Setup already completed")
 
-    password_hash = hash_password(data.password)
+    password_hash = await ahash_password(data.password)
     new_user = User(
         username=data.username,
         umbral_name=data.username,
@@ -300,8 +237,8 @@ async def setup(
 
     ip = get_client_ip(request)
     user_agent = request.headers.get("user-agent")
-    _, token = await _create_db_session(db, new_user, ip, user_agent)
-    _set_session_cookie(response, token)
+    _, token = await create_db_session(db, new_user, ip, user_agent)
+    set_session_cookie(response, token)
 
     await log_audit_event(
         db, action="auth.setup_complete", actor_id=new_user.id, ip=ip,
@@ -338,26 +275,45 @@ async def login(
     if not user:
         # M-02: Run Argon2id against a dummy hash so the response time is
         # indistinguishable from a wrong-password attempt (prevents username enumeration).
-        verify_password("x", _DUMMY_HASH)
+        await averify_password("x", _DUMMY_HASH)
         raise HTTPException(status_code=401, detail="Invalid username or password")
 
     # M-02: Run password verification BEFORE lockout check so Argon2id always
     # executes — prevents distinguishing "locked" from "wrong password" via timing.
-    valid, new_hash = verify_password_with_upgrade(data.password, user.password_hash)
+    valid, new_hash = await averify_password_with_upgrade(data.password, user.password_hash)
 
-    await _check_account_lockout(user)
+    await check_account_lockout(user)
 
     if not valid:
-        await _record_failed_login(db, user)
+        remaining = await record_failed_login(db, user)
         await log_audit_event(
             db, action="auth.login_failed", actor_id=user.id,
-            detail={"reason": "invalid_password"}, ip=client_ip,
+            detail={"reason": "invalid_password", "attempts_remaining": remaining}, ip=client_ip,
         )
         await db.commit()
-        raise HTTPException(status_code=401, detail="Invalid username or password")
+        if remaining == 0:
+            detail = "Account temporarily locked. Try again in 30 minutes."
+        elif remaining <= 3:
+            detail = f"Invalid username or password. {remaining} attempt(s) remaining before account locks."
+        else:
+            detail = "Invalid username or password"
+        raise HTTPException(status_code=401, detail=detail)
+
+    # Block passwordless-only accounts from using the password login path.
+    # Checked after password verification to avoid leaking account existence via timing.
+    if user.passwordless_enabled:
+        await log_audit_event(
+            db, action="auth.login_blocked_passwordless", actor_id=user.id,
+            detail={"reason": "passwordless_enabled"}, ip=client_ip,
+        )
+        await db.commit()
+        raise HTTPException(
+            status_code=403,
+            detail="This account uses passwordless login. Sign in with a passkey.",
+        )
 
     # Block disabled accounts — checked AFTER password verification to avoid
-    # leaking account-state info, and BEFORE _record_successful_login so
+    # leaking account-state info, and BEFORE record_successful_login so
     # last_login_at and lockout counters are not reset for inactive users.
     if not user.is_active:
         await log_audit_event(
@@ -370,7 +326,7 @@ async def login(
     if new_hash:
         user.password_hash = new_hash
 
-    await _record_successful_login(db, user)
+    await record_successful_login(db, user)
 
     # SEC-03: MFA enforcement — block login entirely until MFA setup completes
     if user.mfa_enforce_pending and not user.totp_enabled:
@@ -388,6 +344,7 @@ async def login(
     # If TOTP is enabled, issue a short-lived MFA challenge token
     if user.totp_enabled:
         mfa_token = create_mfa_token(user.id)
+        await db.commit()
         return {
             "authenticated": False,
             "totp_required": True,
@@ -398,8 +355,8 @@ async def login(
     if user.must_change_password:
         # Issue a session but flag the frontend to show password change
         user_agent = request.headers.get("user-agent")
-        _, token = await _create_db_session(db, user, client_ip, user_agent)
-        _set_session_cookie(response, token)
+        _, token = await create_db_session(db, user, client_ip, user_agent)
+        set_session_cookie(response, token)
         await db.commit()
         return {
             "authenticated": True,
@@ -407,8 +364,8 @@ async def login(
         }
 
     user_agent = request.headers.get("user-agent")
-    _, token = await _create_db_session(db, user, client_ip, user_agent)
-    _set_session_cookie(response, token)
+    _, token = await create_db_session(db, user, client_ip, user_agent)
+    set_session_cookie(response, token)
 
     await log_audit_event(
         db, action="auth.login_success", actor_id=user.id, ip=client_ip,
@@ -451,7 +408,7 @@ async def register(
         if existing_email.scalar_one_or_none():
             raise HTTPException(status_code=400, detail="Registration could not be completed. Please check your details and try again.")
 
-    password_hash = hash_password(data.password)
+    password_hash = await ahash_password(data.password)
     # SEC-01: Explicit field assignment — never **data.model_dump()
     new_user = User(
         username=data.username,
@@ -490,8 +447,8 @@ async def register(
             "mfa_token": enforce_token,
         }
 
-    _, token = await _create_db_session(db, new_user, ip, user_agent)
-    _set_session_cookie(response, token)
+    _, token = await create_db_session(db, new_user, ip, user_agent)
+    set_session_cookie(response, token)
     await db.commit()
 
     return {"message": "Registration successful", "authenticated": True}
@@ -541,32 +498,36 @@ async def auth_status(
     authenticated = False
     role = None
 
+    is_locked = False
+
+    u = None
     if not setup_required and session_cookie:
         payload = verify_session_token(session_cookie)
         if payload:
             user_id = payload.get("uid")
             session_id = payload.get("sid")
             if user_id and session_id:
-                session_result = await db.execute(
-                    select(UserSession).where(
+                # Single JOIN query (was 2 sequential queries — P-01 fix)
+                result = await db.execute(
+                    select(UserSession, User)
+                    .join(User, UserSession.user_id == User.id)
+                    .where(
                         UserSession.id == session_id,
                         UserSession.user_id == user_id,
                         UserSession.revoked == False,
                         UserSession.expires_at > datetime.now(),
+                        User.is_active == True,
                     )
                 )
-                if session_result.scalar_one_or_none() is not None:
+                row = result.one_or_none()
+                if row is not None:
+                    db_sess, u = row.tuple()
                     authenticated = True
-                    user_obj_result = await db.execute(
-                        select(User).where(User.id == user_id, User.is_active == True)
-                    )
-                    u = user_obj_result.scalar_one_or_none()
-                    if u:
+                    is_locked = db_sess.is_locked
                     role = u.role
-                    else:
-                        authenticated = False
 
     # Check registration availability
+    config = None
     registration_open = False
     if not setup_required:
         config_result = await db.execute(
@@ -575,18 +536,50 @@ async def auth_status(
         config = config_result.scalar_one_or_none()
         registration_open = config.allow_registration if config else False
 
+    # Perf-3: Check passkey existence with EXISTS (not COUNT) — this endpoint
+    # is polled every 15s. Count is derived from GET /auth/passkeys list instead.
+    has_passkeys = False
+    passwordless_enabled = False
+    if authenticated and u:
+        pk_result = await db.execute(
+            select(PasskeyCredential.id).where(
+                PasskeyCredential.user_id == u.id
+            ).limit(1)
+        )
+        has_passkeys = pk_result.scalar_one_or_none() is not None
+        passwordless_enabled = u.passwordless_enabled
+
     return {
         "authenticated": authenticated,
         "setup_required": setup_required,
         "role": role,
         "username": u.username if authenticated and u else None,
         "registration_open": registration_open,
+        "is_locked": is_locked,
+        "has_passkeys": has_passkeys,
+        "passwordless_enabled": passwordless_enabled,
+        "allow_passwordless": config.allow_passwordless if config else False,
     }
 
 
+@router.post("/lock")
+async def lock_session(
+    request: Request,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Mark the current session as locked. Frontend must verify password to unlock."""
+    db_session: UserSession = request.state.db_session
+    db_session.is_locked = True
+    db_session.locked_at = datetime.now()
+    await db.commit()
+    return {"locked": True}
+
+
 @router.post("/verify-password")
-async def verify_password(
+async def verify_password_endpoint(
     data: VerifyPasswordRequest,
+    request: Request,
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user),
 ):
@@ -594,15 +587,21 @@ async def verify_password(
     Verify the current user's password without changing anything.
     Used by the frontend lock screen to re-authenticate without a full login.
     """
-    await _check_account_lockout(current_user)
+    await check_account_lockout(current_user)
 
-    valid, new_hash = verify_password_with_upgrade(data.password, current_user.password_hash)
+    valid, new_hash = await averify_password_with_upgrade(data.password, current_user.password_hash)
     if not valid:
-        await _record_failed_login(db, current_user)
+        await record_failed_login(db, current_user)
+        await db.commit()
         raise HTTPException(status_code=401, detail="Invalid password")
 
     if new_hash:
         current_user.password_hash = new_hash
+
+    # Clear session lock on successful password verification
+    db_session: UserSession = request.state.db_session
+    db_session.is_locked = False
+    db_session.locked_at = None
     await db.commit()
 
     return {"verified": True}
@@ -615,17 +614,18 @@ async def change_password(
     current_user: User = Depends(get_current_user),
 ):
     """Change the current user's password. Requires old password verification."""
-    await _check_account_lockout(current_user)
+    await check_account_lockout(current_user)
 
-    valid, _ = verify_password_with_upgrade(data.old_password, current_user.password_hash)
+    valid, _ = await averify_password_with_upgrade(data.old_password, current_user.password_hash)
     if not valid:
-        await _record_failed_login(db, current_user)
+        await record_failed_login(db, current_user)
+        await db.commit()
         raise HTTPException(status_code=401, detail="Invalid current password")
 
     if data.new_password == data.old_password:
         raise HTTPException(status_code=400, detail="New password must be different from your current password")
 
-    current_user.password_hash = hash_password(data.new_password)
+    current_user.password_hash = await ahash_password(data.new_password)
     current_user.last_password_change_at = datetime.now()
 
     # Clear forced password change flag if set (SEC-12)
@@ -686,6 +686,12 @@ async def update_profile(
         current_user.email = update_data["email"]
     if "date_of_birth" in update_data:
         current_user.date_of_birth = update_data["date_of_birth"]
+        settings_result = await db.execute(
+            select(Settings).where(Settings.user_id == current_user.id)
+        )
+        user_settings = settings_result.scalar_one_or_none()
+        share = user_settings.share_birthday if user_settings else False
+        await sync_birthday_to_contacts(db, current_user.id, share_birthday=share, date_of_birth=update_data["date_of_birth"])
     if "umbral_name" in update_data:
         current_user.umbral_name = update_data["umbral_name"]
 

backend/app/routers/calendars.py

@@ -1,12 +1,17 @@
-from fastapi import APIRouter, Depends, HTTPException, Path
+from datetime import datetime
+
+from fastapi import APIRouter, Depends, HTTPException, Path, Query
+from pydantic import BaseModel
 from sqlalchemy.ext.asyncio import AsyncSession
-from sqlalchemy import select, update
+from sqlalchemy import func, select, update
 from typing import List
 
 from app.database import get_db
 from app.models.calendar import Calendar
 from app.models.calendar_event import CalendarEvent
+from app.models.calendar_member import CalendarMember
 from app.schemas.calendar import CalendarCreate, CalendarUpdate, CalendarResponse
+from app.services.calendar_sharing import require_permission
 from app.routers.auth import get_current_user
 from app.models.user import User
 
@@ -23,7 +28,28 @@ async def get_calendars(
         .where(Calendar.user_id == current_user.id)
         .order_by(Calendar.is_default.desc(), Calendar.name.asc())
     )
-    return result.scalars().all()
+    calendars = result.scalars().all()
+
+    # Populate member_count for shared calendars
+    cal_ids = [c.id for c in calendars if c.is_shared]
+    count_map: dict[int, int] = {}
+    if cal_ids:
+        counts = await db.execute(
+            select(CalendarMember.calendar_id, func.count())
+            .where(
+                CalendarMember.calendar_id.in_(cal_ids),
+                CalendarMember.status == "accepted",
+            )
+            .group_by(CalendarMember.calendar_id)
+        )
+        count_map = dict(counts.all())
+
+    return [
+        CalendarResponse.model_validate(c, from_attributes=True).model_copy(
+            update={"member_count": count_map.get(c.id, 0)}
+        )
+        for c in calendars
+    ]
 
 
 @router.post("/", response_model=CalendarResponse, status_code=201)
@@ -114,3 +140,62 @@ async def delete_calendar(
     await db.delete(calendar)
     await db.commit()
     return None
+
+
+# ──────────────────────────────────────────────
+# DELTA POLLING
+# ──────────────────────────────────────────────
+
+class CalendarPollResponse(BaseModel):
+    has_changes: bool
+    calendar_updated_at: str | None = None
+    changed_event_ids: list[int] = []
+
+
+@router.get("/{calendar_id}/poll", response_model=CalendarPollResponse)
+async def poll_calendar(
+    calendar_id: int = Path(ge=1, le=2147483647),
+    since: str = Query(..., description="ISO timestamp to check for changes since"),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user)
+):
+    """Lightweight poll endpoint — returns changed event IDs since timestamp."""
+    await require_permission(db, calendar_id, current_user.id, "read_only")
+
+    try:
+        since_dt = datetime.fromisoformat(since)
+    except ValueError:
+        raise HTTPException(status_code=400, detail="Invalid ISO timestamp")
+
+    # Clamp to max 24h in the past to prevent expensive full-table scans
+    from datetime import timedelta
+    min_since = datetime.now() - timedelta(hours=24)
+    if since_dt < min_since:
+        since_dt = min_since
+
+    # Check calendar-level update
+    cal_result = await db.execute(
+        select(Calendar.updated_at).where(Calendar.id == calendar_id)
+    )
+    calendar_updated = cal_result.scalar_one_or_none()
+    if not calendar_updated:
+        raise HTTPException(status_code=404, detail="Calendar not found")
+
+    calendar_changed = calendar_updated > since_dt
+
+    # Check event-level changes using the ix_events_calendar_updated index
+    event_result = await db.execute(
+        select(CalendarEvent.id).where(
+            CalendarEvent.calendar_id == calendar_id,
+            CalendarEvent.updated_at > since_dt,
+        )
+    )
+    changed_event_ids = [r[0] for r in event_result.all()]
+
+    has_changes = calendar_changed or len(changed_event_ids) > 0
+
+    return CalendarPollResponse(
+        has_changes=has_changes,
+        calendar_updated_at=calendar_updated.isoformat() if calendar_updated else None,
+        changed_event_ids=changed_event_ids,
+    )

backend/app/routers/connections.py

@@ -49,7 +49,9 @@ from app.services.connection import (
     resolve_shared_profile,
     send_connection_ntfy,
 )
+from app.services.calendar_sharing import cascade_on_disconnect
 from app.services.notification import create_notification
+from app.services.project_sharing import cascade_projects_on_disconnect
 
 router = APIRouter()
 logger = logging.getLogger(__name__)
@@ -823,6 +825,12 @@ async def remove_connection(
     if reverse_conn:
         await db.delete(reverse_conn)
 
+    # Cascade: remove calendar memberships and event locks between these users
+    await cascade_on_disconnect(db, current_user.id, counterpart_id)
+
+    # Cascade: remove project memberships and task assignments between these users
+    await cascade_projects_on_disconnect(db, current_user.id, counterpart_id)
+
     await log_audit_event(
         db,
         action="connection.removed",

backend/app/routers/dashboard.py

@@ -1,6 +1,6 @@
 from fastapi import APIRouter, Depends, Query
 from sqlalchemy.ext.asyncio import AsyncSession
-from sqlalchemy import select, func, or_
+from sqlalchemy import false as sa_false, select, func, or_, case
 from datetime import datetime, date, timedelta
 from typing import Optional, List, Dict, Any
 
@@ -8,11 +8,12 @@ from app.database import get_db
 from app.models.settings import Settings
 from app.models.todo import Todo
 from app.models.calendar_event import CalendarEvent
-from app.models.calendar import Calendar
 from app.models.reminder import Reminder
 from app.models.project import Project
 from app.models.user import User
 from app.routers.auth import get_current_user, get_current_settings
+from app.models.event_invitation import EventInvitation
+from app.services.calendar_sharing import get_accessible_event_scope
 
 router = APIRouter()
 
@@ -35,14 +36,18 @@ async def get_dashboard(
     today = client_date or date.today()
     upcoming_cutoff = today + timedelta(days=current_settings.upcoming_days)
 
-    # Subquery: calendar IDs belonging to this user (for event scoping)
-    user_calendar_ids = select(Calendar.id).where(Calendar.user_id == current_user.id)
+    # Fetch all accessible calendar IDs + invited event IDs
+    user_calendar_ids, invited_event_ids = await get_accessible_event_scope(current_user.id, db)
 
     # Today's events (exclude parent templates — they are hidden, children are shown)
     today_start = datetime.combine(today, datetime.min.time())
     today_end = datetime.combine(today, datetime.max.time())
     events_query = select(CalendarEvent).where(
+        or_(
             CalendarEvent.calendar_id.in_(user_calendar_ids),
+            CalendarEvent.id.in_(invited_event_ids) if invited_event_ids else sa_false(),
+            CalendarEvent.parent_event_id.in_(invited_event_ids) if invited_event_ids else sa_false(),
+        ),
         CalendarEvent.start_datetime >= today_start,
         CalendarEvent.start_datetime <= today_end,
         _not_parent_template,
@@ -50,6 +55,22 @@ async def get_dashboard(
     events_result = await db.execute(events_query)
     todays_events = events_result.scalars().all()
 
+    # Build invitation lookup for today's events
+    invited_event_id_set = set(invited_event_ids)
+    today_inv_map: dict[int, tuple[str, int | None]] = {}
+    today_event_ids = [e.id for e in todays_events]
+    parent_ids_in_today = [e.parent_event_id for e in todays_events if e.parent_event_id and e.parent_event_id in invited_event_id_set]
+    inv_lookup_ids = list(set(today_event_ids + parent_ids_in_today) & invited_event_id_set)
+    if inv_lookup_ids:
+        inv_result = await db.execute(
+            select(EventInvitation.event_id, EventInvitation.status, EventInvitation.display_calendar_id).where(
+                EventInvitation.user_id == current_user.id,
+                EventInvitation.event_id.in_(inv_lookup_ids),
+            )
+        )
+        for eid, status, disp_cal_id in inv_result.all():
+            today_inv_map[eid] = (status, disp_cal_id)
+
     # Upcoming todos (not completed, with due date from today through upcoming_days)
     todos_query = select(Todo).where(
         Todo.user_id == current_user.id,
@@ -71,31 +92,35 @@ async def get_dashboard(
     reminders_result = await db.execute(reminders_query)
     active_reminders = reminders_result.scalars().all()
 
-    # Project stats (scoped to user)
-    total_projects_result = await db.execute(
-        select(func.count(Project.id)).where(Project.user_id == current_user.id)
-    )
-    total_projects = total_projects_result.scalar()
-
-    projects_by_status_query = select(
+    # Project stats — single GROUP BY query, derive total in Python
+    projects_by_status_result = await db.execute(
+        select(
             Project.status,
-        func.count(Project.id).label("count")
+            func.count(Project.id).label("count"),
         ).where(Project.user_id == current_user.id).group_by(Project.status)
-    projects_by_status_result = await db.execute(projects_by_status_query)
+    )
     projects_by_status = {row[0]: row[1] for row in projects_by_status_result}
+    total_projects = sum(projects_by_status.values())
 
-    # Total incomplete todos count (scoped to user)
-    total_incomplete_result = await db.execute(
-        select(func.count(Todo.id)).where(
-            Todo.user_id == current_user.id,
-            Todo.completed == False,
+    # Todo counts: total and incomplete in a single query
+    todo_counts_result = await db.execute(
+        select(
+            func.count(Todo.id).label("total"),
+            func.count(case((Todo.completed == False, Todo.id))).label("incomplete"),
+        ).where(Todo.user_id == current_user.id)
     )
-    )
-    total_incomplete_todos = total_incomplete_result.scalar()
+    todo_row = todo_counts_result.one()
+    total_todos = todo_row.total
+    total_incomplete_todos = todo_row.incomplete
 
-    # Starred events (upcoming, ordered by date, scoped to user's calendars)
+    # Starred events — no upper date bound so future events always appear in countdown.
+    # _not_parent_template excludes recurring parent templates (children still show).
     starred_query = select(CalendarEvent).where(
+        or_(
             CalendarEvent.calendar_id.in_(user_calendar_ids),
+            CalendarEvent.id.in_(invited_event_ids) if invited_event_ids else sa_false(),
+            CalendarEvent.parent_event_id.in_(invited_event_ids) if invited_event_ids else sa_false(),
+        ),
         CalendarEvent.is_starred == True,
         CalendarEvent.start_datetime > today_start,
         _not_parent_template,
@@ -121,7 +146,10 @@ async def get_dashboard(
                 "end_datetime": event.end_datetime,
                 "all_day": event.all_day,
                 "color": event.color,
-                "is_starred": event.is_starred
+                "is_starred": event.is_starred,
+                "is_invited": (event.parent_event_id or event.id) in invited_event_id_set,
+                "invitation_status": today_inv_map.get(event.parent_event_id or event.id, (None,))[0],
+                "display_calendar_id": today_inv_map.get(event.parent_event_id or event.id, (None, None))[1],
             }
             for event in todays_events
         ],
@@ -148,6 +176,7 @@ async def get_dashboard(
             "by_status": projects_by_status
         },
         "total_incomplete_todos": total_incomplete_todos,
+        "total_todos": total_todos,
         "starred_events": starred_events_data
     }
 
@@ -165,42 +194,64 @@ async def get_upcoming(
     cutoff_date = today + timedelta(days=days)
     cutoff_datetime = datetime.combine(cutoff_date, datetime.max.time())
     today_start = datetime.combine(today, datetime.min.time())
+    overdue_floor = today - timedelta(days=30)
+    overdue_floor_dt = datetime.combine(overdue_floor, datetime.min.time())
 
-    # Subquery: calendar IDs belonging to this user
-    user_calendar_ids = select(Calendar.id).where(Calendar.user_id == current_user.id)
+    # Fetch all accessible calendar IDs + invited event IDs
+    user_calendar_ids, invited_event_ids = await get_accessible_event_scope(current_user.id, db)
 
-    # Get upcoming todos with due dates (today onward only, scoped to user)
+    # Build queries — include overdue todos (up to 30 days back) and snoozed reminders
     todos_query = select(Todo).where(
         Todo.user_id == current_user.id,
         Todo.completed == False,
         Todo.due_date.isnot(None),
-        Todo.due_date >= today,
+        Todo.due_date >= overdue_floor,
         Todo.due_date <= cutoff_date
     )
-    todos_result = await db.execute(todos_query)
-    todos = todos_result.scalars().all()
 
-    # Get upcoming events (from today onward, exclude parent templates, scoped to user's calendars)
     events_query = select(CalendarEvent).where(
+        or_(
             CalendarEvent.calendar_id.in_(user_calendar_ids),
+            CalendarEvent.id.in_(invited_event_ids) if invited_event_ids else sa_false(),
+            CalendarEvent.parent_event_id.in_(invited_event_ids) if invited_event_ids else sa_false(),
+        ),
         CalendarEvent.start_datetime >= today_start,
         CalendarEvent.start_datetime <= cutoff_datetime,
         _not_parent_template,
     )
-    events_result = await db.execute(events_query)
-    events = events_result.scalars().all()
 
-    # Get upcoming reminders (today onward only, scoped to user)
     reminders_query = select(Reminder).where(
         Reminder.user_id == current_user.id,
         Reminder.is_active == True,
         Reminder.is_dismissed == False,
-        Reminder.remind_at >= today_start,
+        Reminder.remind_at >= overdue_floor_dt,
         Reminder.remind_at <= cutoff_datetime
     )
+
+    # Execute queries sequentially (single session cannot run concurrent queries)
+    todos_result = await db.execute(todos_query)
+    todos = todos_result.scalars().all()
+
+    events_result = await db.execute(events_query)
+    events = events_result.scalars().all()
+
     reminders_result = await db.execute(reminders_query)
     reminders = reminders_result.scalars().all()
 
+    # Build invitation lookup for upcoming events
+    invited_event_id_set_up = set(invited_event_ids)
+    upcoming_inv_map: dict[int, tuple[str, int | None]] = {}
+    up_parent_ids = list({e.parent_event_id or e.id for e in events} & invited_event_id_set_up)
+    if up_parent_ids:
+        up_inv_result = await db.execute(
+            select(EventInvitation.event_id, EventInvitation.status, EventInvitation.display_calendar_id).where(
+                EventInvitation.user_id == current_user.id,
+                EventInvitation.event_id.in_(up_parent_ids),
+            )
+        )
+        for eid, status, disp_cal_id in up_inv_result.all():
+            upcoming_inv_map[eid] = (status, disp_cal_id)
+
     # Combine into unified list
     upcoming_items: List[Dict[str, Any]] = []
 
@@ -212,28 +263,39 @@ async def get_upcoming(
             "date": todo.due_date.isoformat() if todo.due_date else None,
             "datetime": None,
             "priority": todo.priority,
-            "category": todo.category
+            "category": todo.category,
+            "is_overdue": todo.due_date < today if todo.due_date else False,
         })
 
     for event in events:
+        end_dt = event.end_datetime
+        parent_id = event.parent_event_id or event.id
+        is_inv = parent_id in invited_event_id_set_up
         upcoming_items.append({
             "type": "event",
             "id": event.id,
             "title": event.title,
             "date": event.start_datetime.date().isoformat(),
             "datetime": event.start_datetime.isoformat(),
+            "end_datetime": end_dt.isoformat() if end_dt else None,
             "all_day": event.all_day,
             "color": event.color,
-            "is_starred": event.is_starred
+            "is_starred": event.is_starred,
+            "is_invited": is_inv,
+            "invitation_status": upcoming_inv_map.get(parent_id, (None,))[0] if is_inv else None,
+            "display_calendar_id": upcoming_inv_map.get(parent_id, (None, None))[1] if is_inv else None,
         })
 
     for reminder in reminders:
+        remind_at_date = reminder.remind_at.date() if reminder.remind_at else None
         upcoming_items.append({
             "type": "reminder",
             "id": reminder.id,
             "title": reminder.title,
-            "date": reminder.remind_at.date().isoformat(),
-            "datetime": reminder.remind_at.isoformat()
+            "date": remind_at_date.isoformat() if remind_at_date else None,
+            "datetime": reminder.remind_at.isoformat() if reminder.remind_at else None,
+            "snoozed_until": reminder.snoozed_until.isoformat() if reminder.snoozed_until else None,
+            "is_overdue": remind_at_date < today if remind_at_date else False,
         })
 
     # Sort by date/datetime

backend/app/routers/event_invitations.py

@@ -0,0 +1,307 @@
+"""
+Event invitation endpoints — invite users to events, respond, override per-occurrence, leave.
+
+Two routers:
+- events_router: mounted at /api/events for POST/GET /{event_id}/invitations
+- router: mounted at /api/event-invitations for respond/override/delete/pending
+"""
+from fastapi import APIRouter, Depends, HTTPException, Path
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy import select
+
+from app.database import get_db
+from app.models.calendar_event import CalendarEvent
+from app.models.event_invitation import EventInvitation
+from app.models.user import User
+from app.routers.auth import get_current_user
+from sqlalchemy.orm import selectinload
+from app.schemas.event_invitation import (
+    EventInvitationCreate,
+    EventInvitationRespond,
+    EventInvitationOverrideCreate,
+    UpdateCanModify,
+    UpdateDisplayCalendar,
+)
+from app.services.calendar_sharing import get_accessible_calendar_ids, get_user_permission
+from app.services.event_invitation import (
+    send_event_invitations,
+    respond_to_invitation,
+    override_occurrence_status,
+    dismiss_invitation,
+    dismiss_invitation_by_owner,
+    get_event_invitations,
+    get_pending_invitations,
+)
+
+# Mounted at /api/events — event-scoped invitation endpoints
+events_router = APIRouter()
+
+# Mounted at /api/event-invitations — invitation-scoped endpoints
+router = APIRouter()
+
+
+async def _get_event_with_access_check(
+    db: AsyncSession, event_id: int, user_id: int
+) -> CalendarEvent:
+    """Fetch event and verify the user has access (owner, shared member, or invitee)."""
+    result = await db.execute(
+        select(CalendarEvent).where(CalendarEvent.id == event_id)
+    )
+    event = result.scalar_one_or_none()
+    if not event:
+        raise HTTPException(status_code=404, detail="Event not found")
+
+    # Check calendar access
+    perm = await get_user_permission(db, event.calendar_id, user_id)
+    if perm is not None:
+        return event
+
+    # Check if invitee (also check parent for recurring children)
+    event_ids_to_check = [event_id]
+    if event.parent_event_id:
+        event_ids_to_check.append(event.parent_event_id)
+
+    inv_result = await db.execute(
+        select(EventInvitation.id).where(
+            EventInvitation.event_id.in_(event_ids_to_check),
+            EventInvitation.user_id == user_id,
+        )
+    )
+    if inv_result.first() is not None:
+        return event
+
+    raise HTTPException(status_code=404, detail="Event not found")
+
+
+# ── Event-scoped endpoints (mounted at /api/events) ──
+
+
+@events_router.post("/{event_id}/invitations", status_code=201)
+async def invite_to_event(
+    body: EventInvitationCreate,
+    event_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Invite connected users to an event. Requires event ownership or create_modify+ permission."""
+    result = await db.execute(
+        select(CalendarEvent).where(CalendarEvent.id == event_id)
+    )
+    event = result.scalar_one_or_none()
+    if not event:
+        raise HTTPException(status_code=404, detail="Event not found")
+
+    # Permission check: owner or create_modify+
+    perm = await get_user_permission(db, event.calendar_id, current_user.id)
+    if perm is None:
+        raise HTTPException(status_code=404, detail="Event not found")
+    if perm not in ("owner", "create_modify", "full_access"):
+        raise HTTPException(status_code=403, detail="Insufficient permission")
+
+    # For recurring child events, invite to the parent (series)
+    target_event_id = event.parent_event_id if event.parent_event_id else event_id
+
+    invitations = await send_event_invitations(
+        db=db,
+        event_id=target_event_id,
+        user_ids=body.user_ids,
+        invited_by=current_user.id,
+    )
+
+    await db.commit()
+
+    return {"invited": len(invitations), "event_id": target_event_id}
+
+
+@events_router.get("/{event_id}/invitations")
+async def list_event_invitations(
+    event_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """List all invitees and their statuses for an event."""
+    event = await _get_event_with_access_check(db, event_id, current_user.id)
+
+    # For recurring children, also fetch parent's invitations
+    target_id = event.parent_event_id if event.parent_event_id else event_id
+    invitations = await get_event_invitations(db, target_id)
+    return invitations
+
+
+# ── Invitation-scoped endpoints (mounted at /api/event-invitations) ──
+
+
+@router.get("/pending")
+async def my_pending_invitations(
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Get all pending event invitations for the current user."""
+    return await get_pending_invitations(db, current_user.id)
+
+
+@router.put("/{invitation_id}/respond")
+async def respond_invitation(
+    body: EventInvitationRespond,
+    invitation_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Accept, tentative, or decline an event invitation."""
+    invitation = await respond_to_invitation(
+        db=db,
+        invitation_id=invitation_id,
+        user_id=current_user.id,
+        status=body.status,
+    )
+
+    # Build response before commit (ORM objects expire after commit)
+    response_data = {
+        "id": invitation.id,
+        "event_id": invitation.event_id,
+        "status": invitation.status,
+        "responded_at": invitation.responded_at,
+    }
+
+    await db.commit()
+    return response_data
+
+
+@router.put("/{invitation_id}/respond/{occurrence_id}")
+async def override_occurrence(
+    body: EventInvitationOverrideCreate,
+    invitation_id: int = Path(ge=1, le=2147483647),
+    occurrence_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Override invitation status for a specific occurrence of a recurring event."""
+    override = await override_occurrence_status(
+        db=db,
+        invitation_id=invitation_id,
+        occurrence_id=occurrence_id,
+        user_id=current_user.id,
+        status=body.status,
+    )
+
+    response_data = {
+        "invitation_id": override.invitation_id,
+        "occurrence_id": override.occurrence_id,
+        "status": override.status,
+    }
+
+    await db.commit()
+    return response_data
+
+
+@router.put("/{invitation_id}/display-calendar")
+async def update_display_calendar(
+    body: UpdateDisplayCalendar,
+    invitation_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Change the display calendar for an accepted/tentative invitation."""
+    inv_result = await db.execute(
+        select(EventInvitation).where(
+            EventInvitation.id == invitation_id,
+            EventInvitation.user_id == current_user.id,
+        )
+    )
+    invitation = inv_result.scalar_one_or_none()
+    if not invitation:
+        raise HTTPException(status_code=404, detail="Invitation not found")
+
+    if invitation.status not in ("accepted", "tentative"):
+        raise HTTPException(status_code=400, detail="Can only set display calendar for accepted or tentative invitations")
+
+    # Verify calendar is accessible to this user
+    accessible_ids = await get_accessible_calendar_ids(current_user.id, db)
+    if body.calendar_id not in accessible_ids:
+        raise HTTPException(status_code=404, detail="Calendar not found")
+
+    invitation.display_calendar_id = body.calendar_id
+
+    # Extract response before commit (ORM expiry rule)
+    response_data = {
+        "id": invitation.id,
+        "event_id": invitation.event_id,
+        "display_calendar_id": invitation.display_calendar_id,
+    }
+
+    await db.commit()
+    return response_data
+
+
+@router.put("/{invitation_id}/can-modify")
+async def update_can_modify(
+    body: UpdateCanModify,
+    invitation_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Toggle can_modify on an invitation. Owner-only."""
+    inv_result = await db.execute(
+        select(EventInvitation)
+        .options(selectinload(EventInvitation.event))
+        .where(EventInvitation.id == invitation_id)
+    )
+    invitation = inv_result.scalar_one_or_none()
+    if not invitation:
+        raise HTTPException(status_code=404, detail="Invitation not found")
+
+    # Only the calendar owner can toggle can_modify (W-03)
+    perm = await get_user_permission(db, invitation.event.calendar_id, current_user.id)
+    if perm != "owner":
+        raise HTTPException(status_code=403, detail="Only the calendar owner can grant edit access")
+
+    invitation.can_modify = body.can_modify
+
+    response_data = {
+        "id": invitation.id,
+        "event_id": invitation.event_id,
+        "can_modify": invitation.can_modify,
+    }
+
+    await db.commit()
+    return response_data
+
+
+@router.delete("/{invitation_id}", status_code=204)
+async def leave_or_revoke_invitation(
+    invitation_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """
+    Leave an event (invitee) or revoke an invitation (event owner).
+    Invitees can only delete their own invitations.
+    Event owners can delete any invitation for their events.
+    """
+    inv_result = await db.execute(
+        select(EventInvitation).where(EventInvitation.id == invitation_id)
+    )
+    invitation = inv_result.scalar_one_or_none()
+    if not invitation:
+        raise HTTPException(status_code=404, detail="Invitation not found")
+
+    if invitation.user_id == current_user.id:
+        # Invitee leaving
+        await dismiss_invitation(db, invitation_id, current_user.id)
+    else:
+        # Check if current user is the event owner
+        event_result = await db.execute(
+            select(CalendarEvent).where(CalendarEvent.id == invitation.event_id)
+        )
+        event = event_result.scalar_one_or_none()
+        if not event:
+            raise HTTPException(status_code=404, detail="Event not found")
+
+        perm = await get_user_permission(db, event.calendar_id, current_user.id)
+        if perm != "owner":
+            raise HTTPException(status_code=403, detail="Only the event owner can revoke invitations")
+
+        await dismiss_invitation_by_owner(db, invitation_id)
+
+    await db.commit()
+    return None

backend/app/routers/events.py

@@ -1,7 +1,7 @@
 import json
 from fastapi import APIRouter, Depends, HTTPException, Path, Query
 from sqlalchemy.ext.asyncio import AsyncSession
-from sqlalchemy import select, delete
+from sqlalchemy import false as sa_false, select, delete, or_
 from sqlalchemy.orm import selectinload
 from typing import Optional, List, Any, Literal
 
@@ -19,13 +19,38 @@ from app.schemas.calendar_event import (
 from app.routers.auth import get_current_user
 from app.models.user import User
 from app.services.recurrence import generate_occurrences
+from app.services.calendar_sharing import check_lock_for_edit, get_accessible_calendar_ids, get_accessible_event_scope, require_permission
+from app.services.event_invitation import get_invited_event_ids, get_invitation_overrides_for_user
+from app.models.event_invitation import EventInvitation
 
 router = APIRouter()
 
 
-def _event_to_dict(event: CalendarEvent) -> dict:
+def _event_to_dict(
+    event: CalendarEvent,
+    is_invited: bool = False,
+    invitation_status: str | None = None,
+    invitation_id: int | None = None,
+    display_calendar_id: int | None = None,
+    display_calendar_name: str | None = None,
+    display_calendar_color: str | None = None,
+    can_modify: bool = False,
+    has_active_invitees: bool = False,
+) -> dict:
     """Serialize a CalendarEvent ORM object to a response dict including calendar info."""
-    return {
+    # For invited events: use display calendar if set, otherwise fallback to "Invited"/gray
+    if is_invited:
+        if display_calendar_name:
+            cal_name = display_calendar_name
+            cal_color = display_calendar_color or "#6B7280"
+        else:
+            cal_name = "Invited"
+            cal_color = "#6B7280"
+    else:
+        cal_name = event.calendar.name if event.calendar else ""
+        cal_color = event.calendar.color if event.calendar else ""
+
+    d = {
         "id": event.id,
         "title": event.title,
         "description": event.description,
@@ -37,15 +62,22 @@ def _event_to_dict(event: CalendarEvent) -> dict:
         "recurrence_rule": event.recurrence_rule,
         "is_starred": event.is_starred,
         "calendar_id": event.calendar_id,
-        "calendar_name": event.calendar.name if event.calendar else "",
-        "calendar_color": event.calendar.color if event.calendar else "",
+        "calendar_name": cal_name,
+        "calendar_color": cal_color,
         "is_virtual": False,
         "parent_event_id": event.parent_event_id,
         "is_recurring": event.is_recurring,
         "original_start": event.original_start,
         "created_at": event.created_at,
         "updated_at": event.updated_at,
+        "is_invited": is_invited,
+        "invitation_status": invitation_status,
+        "invitation_id": invitation_id,
+        "display_calendar_id": display_calendar_id,
+        "can_modify": can_modify,
+        "has_active_invitees": has_active_invitees,
     }
+    return d
 
 
 def _birthday_events_for_range(
@@ -142,13 +174,20 @@ async def get_events(
     recurrence_rule IS NOT NULL) are excluded — their materialised children
     are what get displayed on the calendar.
     """
-    # Scope events through calendar ownership
-    user_calendar_ids = select(Calendar.id).where(Calendar.user_id == current_user.id)
+    # Scope events through calendar ownership + shared memberships + invitations
+    all_calendar_ids, invited_event_ids = await get_accessible_event_scope(current_user.id, db)
+
 
     query = (
         select(CalendarEvent)
         .options(selectinload(CalendarEvent.calendar))
-        .where(CalendarEvent.calendar_id.in_(user_calendar_ids))
+        .where(
+            or_(
+                CalendarEvent.calendar_id.in_(all_calendar_ids),
+                CalendarEvent.id.in_(invited_event_ids) if invited_event_ids else sa_false(),
+                CalendarEvent.parent_event_id.in_(invited_event_ids) if invited_event_ids else sa_false(),
+            )
+        )
     )
 
     # Exclude parent template rows — they are not directly rendered
@@ -165,12 +204,93 @@ async def get_events(
     if end:
         query = query.where(CalendarEvent.start_datetime <= end)
 
-    query = query.order_by(CalendarEvent.start_datetime.asc())
+    query = query.order_by(CalendarEvent.start_datetime.asc()).limit(2000)
 
     result = await db.execute(query)
     events = result.scalars().all()
 
-    response: List[dict] = [_event_to_dict(e) for e in events]
+    # Build invitation lookup for the current user
+    invited_event_id_set = set(invited_event_ids)
+    invitation_map: dict[int, tuple[str, int, int | None, bool]] = {}  # event_id -> (status, invitation_id, display_calendar_id, can_modify)
+    if invited_event_ids:
+        inv_result = await db.execute(
+            select(
+                EventInvitation.event_id,
+                EventInvitation.status,
+                EventInvitation.id,
+                EventInvitation.display_calendar_id,
+                EventInvitation.can_modify,
+            ).where(
+                EventInvitation.user_id == current_user.id,
+                EventInvitation.event_id.in_(invited_event_ids),
+            )
+        )
+        for eid, status, inv_id, disp_cal_id, cm in inv_result.all():
+            invitation_map[eid] = (status, inv_id, disp_cal_id, cm)
+
+    # Batch-fetch display calendars for invited events
+    display_cal_ids = {t[2] for t in invitation_map.values() if t[2] is not None}
+    display_cal_map: dict[int, dict] = {}  # cal_id -> {name, color}
+    if display_cal_ids:
+        cal_result = await db.execute(
+            select(Calendar.id, Calendar.name, Calendar.color).where(
+                Calendar.id.in_(display_cal_ids),
+                Calendar.id.in_(all_calendar_ids),
+            )
+        )
+        for cal_id, cal_name, cal_color in cal_result.all():
+            display_cal_map[cal_id] = {"name": cal_name, "color": cal_color}
+
+    # Get per-occurrence overrides for invited events
+    all_event_ids = [e.id for e in events]
+    override_map = await get_invitation_overrides_for_user(db, current_user.id, all_event_ids)
+
+    # Batch-fetch event IDs that have accepted/tentative invitees (for owner's shared icon)
+    active_invitee_set: set[int] = set()
+    if all_event_ids:
+        active_inv_result = await db.execute(
+            select(EventInvitation.event_id).where(
+                EventInvitation.event_id.in_(all_event_ids),
+                EventInvitation.status.in_(["accepted", "tentative"]),
+            ).distinct()
+        )
+        active_invitee_set = {r[0] for r in active_inv_result.all()}
+        # Also mark parent events: if a parent has active invitees, all its children should show the icon
+        parent_ids = {e.parent_event_id for e in events if e.parent_event_id and e.parent_event_id in active_invitee_set}
+        if parent_ids:
+            active_invitee_set.update(e.id for e in events if e.parent_event_id in active_invitee_set)
+
+    response: List[dict] = []
+    for e in events:
+        # Determine if this event is from an invitation
+        parent_id = e.parent_event_id or e.id
+        is_invited = parent_id in invited_event_id_set
+        inv_status = None
+        inv_id = None
+        disp_cal_id = None
+        disp_cal_name = None
+        disp_cal_color = None
+        inv_can_modify = False
+        if is_invited and parent_id in invitation_map:
+            inv_status, inv_id, disp_cal_id, inv_can_modify = invitation_map[parent_id]
+            # Check for per-occurrence override
+            if e.id in override_map:
+                inv_status = override_map[e.id]
+            # Resolve display calendar info
+            if disp_cal_id and disp_cal_id in display_cal_map:
+                disp_cal_name = display_cal_map[disp_cal_id]["name"]
+                disp_cal_color = display_cal_map[disp_cal_id]["color"]
+        response.append(_event_to_dict(
+            e,
+            is_invited=is_invited,
+            invitation_status=inv_status,
+            invitation_id=inv_id,
+            display_calendar_id=disp_cal_id,
+            display_calendar_name=disp_cal_name,
+            display_calendar_color=disp_cal_color,
+            can_modify=inv_can_modify,
+            has_active_invitees=(parent_id in active_invitee_set or e.id in active_invitee_set),
+        ))
 
     # Fetch the user's Birthdays system calendar; only generate virtual events if visible
     bday_result = await db.execute(
@@ -219,8 +339,13 @@ async def create_event(
     if not data.get("calendar_id"):
         data["calendar_id"] = await _get_default_calendar_id(db, current_user.id)
     else:
-        # SEC-04: verify the target calendar belongs to the requesting user
-        await _verify_calendar_ownership(db, data["calendar_id"], current_user.id)
+        # SEC-04: verify ownership OR shared calendar permission
+        cal_ownership_result = await db.execute(
+            select(Calendar).where(Calendar.id == data["calendar_id"], Calendar.user_id == current_user.id)
+        )
+        if not cal_ownership_result.scalar_one_or_none():
+            # Not owned — check shared calendar permission
+            await require_permission(db, data["calendar_id"], current_user.id, "create_modify")
 
     # Serialize RecurrenceRule object to JSON string for DB storage
     # Exclude None values so defaults in recurrence service work correctly
@@ -229,13 +354,12 @@ async def create_event(
 
     if rule_json:
         # Parent template: is_recurring=True, no parent_event_id
-        parent = CalendarEvent(**data, recurrence_rule=rule_json, is_recurring=True)
+        parent = CalendarEvent(**data, recurrence_rule=rule_json, is_recurring=True, updated_by=current_user.id)
         db.add(parent)
         await db.flush()  # assign parent.id before generating children
 
         children = generate_occurrences(parent)
-        for child in children:
-            db.add(child)
+        db.add_all(children)
 
         await db.commit()
 
@@ -258,7 +382,7 @@ async def create_event(
         return result.scalar_one()
 
     else:
-        new_event = CalendarEvent(**data, recurrence_rule=None)
+        new_event = CalendarEvent(**data, recurrence_rule=None, updated_by=current_user.id)
         db.add(new_event)
         await db.commit()
 
@@ -276,14 +400,20 @@ async def get_event(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user),
 ):
-    user_calendar_ids = select(Calendar.id).where(Calendar.user_id == current_user.id)
+    all_calendar_ids, invited_event_ids = await get_accessible_event_scope(current_user.id, db)
+    invited_set = set(invited_event_ids)
+
 
     result = await db.execute(
         select(CalendarEvent)
         .options(selectinload(CalendarEvent.calendar))
         .where(
             CalendarEvent.id == event_id,
-            CalendarEvent.calendar_id.in_(user_calendar_ids),
+            or_(
+                CalendarEvent.calendar_id.in_(all_calendar_ids),
+                CalendarEvent.id.in_(invited_event_ids) if invited_event_ids else sa_false(),
+                CalendarEvent.parent_event_id.in_(invited_event_ids) if invited_event_ids else sa_false(),
+            ),
         )
     )
     event = result.scalar_one_or_none()
@@ -301,23 +431,79 @@ async def update_event(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user),
 ):
-    user_calendar_ids = select(Calendar.id).where(Calendar.user_id == current_user.id)
+    # IMPORTANT: Uses get_accessible_calendar_ids (NOT get_accessible_event_scope).
+    # Event invitees can VIEW events but must NOT be able to edit them
+    # UNLESS they have can_modify=True (checked in fallback path below).
+    all_calendar_ids = await get_accessible_calendar_ids(current_user.id, db)
+    is_invited_editor = False
 
     result = await db.execute(
         select(CalendarEvent)
         .options(selectinload(CalendarEvent.calendar))
         .where(
             CalendarEvent.id == event_id,
-            CalendarEvent.calendar_id.in_(user_calendar_ids),
+            CalendarEvent.calendar_id.in_(all_calendar_ids),
         )
     )
     event = result.scalar_one_or_none()
 
     if not event:
+        # Fallback: check if user has can_modify invitation for this event
+        # Must check both event_id (direct) and parent_event_id (recurring child)
+        # because invitations are stored against the parent event
+        target_event_result = await db.execute(
+            select(CalendarEvent.parent_event_id).where(CalendarEvent.id == event_id)
+        )
+        target_row = target_event_result.one_or_none()
+        if not target_row:
+            raise HTTPException(status_code=404, detail="Calendar event not found")
+        candidate_ids = [event_id]
+        if target_row[0] is not None:
+            candidate_ids.append(target_row[0])
+
+        inv_result = await db.execute(
+            select(EventInvitation).where(
+                EventInvitation.event_id.in_(candidate_ids),
+                EventInvitation.user_id == current_user.id,
+                EventInvitation.can_modify == True,
+                EventInvitation.status.in_(["accepted", "tentative"]),
+            )
+        )
+        inv = inv_result.scalar_one_or_none()
+        if not inv:
             raise HTTPException(status_code=404, detail="Calendar event not found")
 
+        # Load the event directly (bypassing calendar filter)
+        event_result = await db.execute(
+            select(CalendarEvent)
+            .options(selectinload(CalendarEvent.calendar))
+            .where(CalendarEvent.id == event_id)
+        )
+        event = event_result.scalar_one_or_none()
+        if not event:
+            raise HTTPException(status_code=404, detail="Calendar event not found")
+        is_invited_editor = True
+
     update_data = event_update.model_dump(exclude_unset=True)
 
+    if is_invited_editor:
+        # Invited editor restrictions — enforce BEFORE any data mutation
+        # Field allowlist: invited editors can only modify event content, not structure
+        INVITED_EDITOR_ALLOWED = {"title", "description", "start_datetime", "end_datetime", "all_day", "color", "edit_scope", "location_id"}
+        disallowed = set(update_data.keys()) - INVITED_EDITOR_ALLOWED
+        if disallowed:
+            raise HTTPException(status_code=403, detail="Invited editors cannot modify: " + ", ".join(sorted(disallowed)))
+        scope_peek = update_data.get("edit_scope")
+        # Block all bulk-scope edits on recurring events (C-01/F-01)
+        if event.is_recurring and scope_peek != "this":
+            raise HTTPException(status_code=403, detail="Invited editors can only edit individual occurrences")
+    else:
+        # Standard calendar-access path: require create_modify+ permission
+        await require_permission(db, event.calendar_id, current_user.id, "create_modify")
+
+    # Lock check applies to both paths (uses owner's calendar_id)
+    await check_lock_for_edit(db, event_id, current_user.id, event.calendar_id)
+
     # Extract scope before applying fields to the model
     scope: Optional[str] = update_data.pop("edit_scope", None)
 
@@ -326,10 +512,25 @@ async def update_event(
     if rule_obj is not None:
         update_data["recurrence_rule"] = json.dumps({k: v for k, v in rule_obj.items() if v is not None}) if rule_obj else None
 
+    if not is_invited_editor:
         # SEC-04: if calendar_id is being changed, verify the target belongs to the user
-    if "calendar_id" in update_data and update_data["calendar_id"] is not None:
+        # Only verify ownership when the calendar is actually changing — members submitting
+        # an unchanged calendar_id must not be rejected just because they aren't the owner.
+        if "calendar_id" in update_data and update_data["calendar_id"] is not None and update_data["calendar_id"] != event.calendar_id:
             await _verify_calendar_ownership(db, update_data["calendar_id"], current_user.id)
 
+        # M-01: Block non-owners from moving events off shared calendars
+        if "calendar_id" in update_data and update_data["calendar_id"] != event.calendar_id:
+            source_cal_result = await db.execute(
+                select(Calendar).where(Calendar.id == event.calendar_id)
+            )
+            source_cal = source_cal_result.scalar_one_or_none()
+            if source_cal and source_cal.is_shared and source_cal.user_id != current_user.id:
+                raise HTTPException(
+                    status_code=403,
+                    detail="Only the calendar owner can move events between calendars",
+                )
+
     start = update_data.get("start_datetime", event.start_datetime)
     end_dt = update_data.get("end_datetime", event.end_datetime)
     if end_dt is not None and end_dt < start:
@@ -342,6 +543,7 @@ async def update_event(
         # Detach from parent so it's an independent event going forward
         event.parent_event_id = None
         event.is_recurring = False
+        event.updated_by = current_user.id
         await db.commit()
 
     elif scope == "this_and_future":
@@ -371,6 +573,7 @@ async def update_event(
             event.parent_event_id = None
             event.is_recurring = True
             event.original_start = None
+            event.updated_by = current_user.id
 
             # Inherit parent's recurrence_rule if none was provided in update
             if not event.recurrence_rule and parent_rule:
@@ -380,12 +583,12 @@ async def update_event(
             if event.recurrence_rule:
                 await db.flush()
                 children = generate_occurrences(event)
-                for child in children:
-                    db.add(child)
+                db.add_all(children)
         else:
             # This IS a parent — update it and regenerate all children
             for key, value in update_data.items():
                 setattr(event, key, value)
+            event.updated_by = current_user.id
 
             # Delete all existing children and regenerate
             if event.recurrence_rule:
@@ -396,8 +599,7 @@ async def update_event(
                 )
                 await db.flush()
                 children = generate_occurrences(event)
-                for child in children:
-                    db.add(child)
+                db.add_all(children)
 
         await db.commit()
 
@@ -405,6 +607,7 @@ async def update_event(
         # No scope — plain update (non-recurring events or full-series metadata)
         for key, value in update_data.items():
             setattr(event, key, value)
+        event.updated_by = current_user.id
         await db.commit()
 
     result = await db.execute(
@@ -426,12 +629,15 @@ async def delete_event(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user),
 ):
-    user_calendar_ids = select(Calendar.id).where(Calendar.user_id == current_user.id)
+    # IMPORTANT: Uses get_accessible_calendar_ids (NOT get_accessible_event_scope).
+    # Event invitees can VIEW events but must NOT be able to delete them.
+    # Invitees use DELETE /api/event-invitations/{id} to leave instead.
+    all_calendar_ids = await get_accessible_calendar_ids(current_user.id, db)
 
     result = await db.execute(
         select(CalendarEvent).where(
             CalendarEvent.id == event_id,
-            CalendarEvent.calendar_id.in_(user_calendar_ids),
+            CalendarEvent.calendar_id.in_(all_calendar_ids),
         )
     )
     event = result.scalar_one_or_none()
@@ -439,6 +645,10 @@ async def delete_event(
     if not event:
         raise HTTPException(status_code=404, detail="Calendar event not found")
 
+    # Shared calendar: require full_access+ and check lock
+    await require_permission(db, event.calendar_id, current_user.id, "full_access")
+    await check_lock_for_edit(db, event_id, current_user.id, event.calendar_id)
+
     if scope == "this":
         # Delete just this one occurrence
         await db.delete(event)
@@ -448,20 +658,13 @@ async def delete_event(
         this_original_start = event.original_start or event.start_datetime
 
         if parent_id is not None:
-            # Delete this + all future siblings
+            # Delete this + all future siblings (original_start is always set on children)
             await db.execute(
                 delete(CalendarEvent).where(
                     CalendarEvent.parent_event_id == parent_id,
                     CalendarEvent.original_start >= this_original_start,
                 )
             )
-            # Ensure the target event itself is deleted (edge case: original_start fallback mismatch)
-            existing = await db.execute(
-                select(CalendarEvent).where(CalendarEvent.id == event_id)
-            )
-            target = existing.scalar_one_or_none()
-            if target:
-                await db.delete(target)
         else:
             # This event IS the parent — delete it and all children (CASCADE handles children)
             await db.delete(event)

backend/app/routers/locations.py

@@ -8,6 +8,7 @@ import json
 import urllib.request
 import urllib.parse
 import logging
+import re
 
 from app.database import get_db
 from app.models.location import Location
@@ -57,7 +58,7 @@ async def search_locations(
     # Nominatim proxy search (run in thread executor to avoid blocking event loop)
     def _fetch_nominatim() -> list:
         encoded_q = urllib.parse.quote(q)
-        url = f"https://nominatim.openstreetmap.org/search?q={encoded_q}&format=json&limit=5"
+        url = f"https://nominatim.openstreetmap.org/search?q={encoded_q}&format=json&addressdetails=1&limit=5"
         req = urllib.request.Request(url, headers={"User-Agent": "UMBRA-LifeManager/1.0"})
         with urllib.request.urlopen(req, timeout=5) as resp:
             return json.loads(resp.read().decode())
@@ -67,9 +68,37 @@ async def search_locations(
         osm_data = await loop.run_in_executor(None, _fetch_nominatim)
         for item in osm_data:
             display_name = item.get("display_name", "")
-            name_parts = display_name.split(",", 1)
-            name = name_parts[0].strip()
-            address = name_parts[1].strip() if len(name_parts) > 1 else display_name
+            addr = item.get("address", {})
+            house_number = addr.get("house_number", "")
+            road = addr.get("road", "")
+
+            # If Nominatim didn't return a house_number but the user's
+            # query starts with one, preserve it from the original query.
+            if not house_number and road:
+                m = re.match(r"^(\d+[\w/-]*)\s+", q.strip())
+                if m:
+                    house_number = m.group(1)
+
+            # Name = place/building label from Nominatim (e.g. "The Quadrant").
+            # Falls back to street address if no distinct place name exists.
+            osm_name = item.get("name", "")
+            street = f"{house_number} {road}" if house_number and road else road
+            if osm_name and osm_name != road:
+                name = osm_name
+            elif street:
+                name = street
+            else:
+                name = display_name.split(",", 1)[0].strip()
+
+            # Address = full street address with suburb/state/postcode.
+            addr_parts = []
+            if street:
+                addr_parts.append(street)
+            for key in ("suburb", "city", "state", "postcode", "country"):
+                val = addr.get(key, "")
+                if val:
+                    addr_parts.append(val)
+            address = ", ".join(addr_parts) if addr_parts else display_name
             results.append(
                 LocationSearchResult(
                     source="nominatim",

backend/app/routers/passkeys.py

@@ -0,0 +1,675 @@
+"""
+Passkey (WebAuthn/FIDO2) router.
+
+Endpoints (all under /api/auth/passkeys — registered in main.py):
+
+  POST /register/begin      — Start passkey registration (auth + password required)
+  POST /register/complete    — Complete registration ceremony (auth required)
+  POST /login/begin          — Start passkey authentication (public, CSRF-exempt)
+  POST /login/complete       — Complete authentication ceremony (public, CSRF-exempt)
+  GET  /                     — List registered passkeys (auth required)
+  DELETE /{id}               — Remove a passkey (auth + password required)
+
+Security:
+  - Challenge tokens signed with itsdangerous (60s TTL, single-use nonce)
+  - Registration binds challenge to user_id, validated on complete (S-01)
+  - Registration requires password re-entry (V-02)
+  - Generic 401 on all auth failures (no credential enumeration)
+  - Constant-time response on login/begin (V-03)
+  - Failed passkey logins increment shared lockout counter
+  - Passkey login bypasses TOTP (passkey IS 2FA)
+"""
+import asyncio
+import json
+import logging
+from datetime import datetime
+
+from fastapi import APIRouter, Depends, HTTPException, Path, Request, Response
+from pydantic import BaseModel, ConfigDict, Field
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy import select, func
+
+from app.database import get_db
+from app.models.passkey_credential import PasskeyCredential
+from app.models.system_config import SystemConfig
+from app.models.user import User
+from app.routers.auth import get_current_user
+from app.services.audit import get_client_ip, log_audit_event
+from app.services.auth import averify_password_with_upgrade, verify_session_token
+from app.services.session import (
+    create_db_session,
+    set_session_cookie,
+    check_account_lockout,
+    record_failed_login,
+    record_successful_login,
+)
+from app.services.passkey import (
+    create_challenge_token,
+    verify_challenge_token,
+    build_registration_options,
+    verify_registration as verify_registration_response_svc,
+    build_authentication_options,
+    verify_authentication as verify_authentication_response_svc,
+    extract_credential_raw_id,
+)
+from app.models.session import UserSession
+from webauthn.helpers import bytes_to_base64url, base64url_to_bytes
+
+logger = logging.getLogger(__name__)
+
+router = APIRouter()
+
+
+# ---------------------------------------------------------------------------
+# Request/Response schemas
+# ---------------------------------------------------------------------------
+
+class PasskeyRegisterBeginRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    password: str = Field(max_length=128)
+
+
+class PasskeyRegisterCompleteRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    credential: str = Field(max_length=8192)
+    challenge_token: str = Field(max_length=2048)
+    name: str = Field(min_length=1, max_length=100)
+
+
+class PasskeyLoginBeginRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    username: str | None = Field(None, max_length=50)
+
+
+class PasskeyLoginCompleteRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    credential: str = Field(max_length=8192)
+    challenge_token: str = Field(max_length=2048)
+    unlock: bool = False
+
+
+class PasskeyDeleteRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    password: str = Field(max_length=128)
+
+
+class PasswordlessEnableRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    password: str = Field(max_length=128)
+
+
+class PasswordlessDisableRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    credential: str = Field(max_length=8192)
+    challenge_token: str = Field(max_length=2048)
+
+
+# ---------------------------------------------------------------------------
+# Registration endpoints (authenticated)
+# ---------------------------------------------------------------------------
+
+@router.post("/register/begin")
+async def passkey_register_begin(
+    data: PasskeyRegisterBeginRequest,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Start passkey registration. Requires password re-entry (V-02)."""
+    # V-02: Verify password before allowing registration
+    valid, new_hash = await averify_password_with_upgrade(
+        data.password, current_user.password_hash
+    )
+    if not valid:
+        raise HTTPException(status_code=401, detail="Invalid password")
+    if new_hash:
+        current_user.password_hash = new_hash
+        await db.commit()
+
+    # Load existing credential IDs for exclusion
+    result = await db.execute(
+        select(PasskeyCredential.credential_id).where(
+            PasskeyCredential.user_id == current_user.id
+        )
+    )
+    existing_ids = [
+        base64url_to_bytes(row[0]) for row in result.all()
+    ]
+
+    options_json, challenge = build_registration_options(
+        user_id=current_user.id,
+        username=current_user.username,
+        existing_credential_ids=existing_ids,
+    )
+    token = create_challenge_token(challenge, user_id=current_user.id)
+
+    return {
+        "options": json.loads(options_json),
+        "challenge_token": token,
+    }
+
+
+@router.post("/register/complete")
+async def passkey_register_complete(
+    data: PasskeyRegisterCompleteRequest,
+    request: Request,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Complete passkey registration ceremony."""
+    # Verify challenge token — cross-check user binding (S-01) + single-use nonce (V-01)
+    challenge = verify_challenge_token(
+        data.challenge_token, expected_user_id=current_user.id
+    )
+    if challenge is None:
+        raise HTTPException(status_code=401, detail="Invalid or expired challenge")
+
+    try:
+        verified = verify_registration_response_svc(
+            credential_json=data.credential,
+            challenge=challenge,
+        )
+    except Exception as e:
+        logger.warning("Passkey registration verification failed: %s", e)
+        raise HTTPException(status_code=400, detail="Registration verification failed")
+
+    # Store credential
+    credential_id_b64 = bytes_to_base64url(verified.credential_id)
+
+    # Check for duplicate (race condition safety)
+    existing = await db.execute(
+        select(PasskeyCredential).where(
+            PasskeyCredential.credential_id == credential_id_b64
+        )
+    )
+    if existing.scalar_one_or_none():
+        raise HTTPException(status_code=409, detail="Credential already registered")
+
+    # Extract transport hints if available
+    transports_json = None
+    if hasattr(verified, 'credential_device_type'):
+        pass  # py_webauthn doesn't expose transports on VerifiedRegistration
+    # Transports come from the browser response — parse from credential JSON
+    try:
+        cred_data = json.loads(data.credential)
+        if "response" in cred_data and "transports" in cred_data["response"]:
+            transports_json = json.dumps(cred_data["response"]["transports"])
+    except (json.JSONDecodeError, KeyError):
+        pass
+
+    # Determine backup state from py_webauthn flags
+    backed_up = getattr(verified, 'credential_backed_up', False)
+
+    new_credential = PasskeyCredential(
+        user_id=current_user.id,
+        credential_id=credential_id_b64,
+        public_key=bytes_to_base64url(verified.credential_public_key),
+        sign_count=verified.sign_count,
+        name=data.name,
+        transports=transports_json,
+        backed_up=backed_up,
+    )
+    db.add(new_credential)
+
+    # B-02: If user has mfa_enforce_pending, clear it (passkey = MFA)
+    if current_user.mfa_enforce_pending:
+        current_user.mfa_enforce_pending = False
+
+    # Extract response data BEFORE commit (ORM expiry rule)
+    response_data = {
+        "id": None,  # will be set after flush
+        "name": new_credential.name,
+        "created_at": None,
+        "backed_up": backed_up,
+    }
+
+    await db.flush()
+    response_data["id"] = new_credential.id
+    response_data["created_at"] = str(new_credential.created_at) if new_credential.created_at else None
+
+    await log_audit_event(
+        db, action="passkey.registered", actor_id=current_user.id,
+        detail={"credential_name": data.name},
+        ip=get_client_ip(request),
+    )
+    await db.commit()
+
+    return response_data
+
+
+# ---------------------------------------------------------------------------
+# Authentication endpoints (unauthenticated — CSRF-exempt)
+# ---------------------------------------------------------------------------
+
+@router.post("/login/begin")
+async def passkey_login_begin(
+    data: PasskeyLoginBeginRequest,
+    db: AsyncSession = Depends(get_db),
+):
+    """Start passkey authentication. CSRF-exempt, public endpoint."""
+    credential_data = None
+
+    if data.username:
+        # Look up user's credentials for allowCredentials
+        result = await db.execute(
+            select(User).where(User.username == data.username.lower().strip())
+        )
+        user = result.scalar_one_or_none()
+        if user:
+            cred_result = await db.execute(
+                select(
+                    PasskeyCredential.credential_id,
+                    PasskeyCredential.transports,
+                ).where(PasskeyCredential.user_id == user.id)
+            )
+            rows = cred_result.all()
+            if rows:
+                credential_data = []
+                for row in rows:
+                    cid_bytes = base64url_to_bytes(row[0])
+                    transports = json.loads(row[1]) if row[1] else None
+                    credential_data.append((cid_bytes, transports))
+        else:
+            # F-01: User not found — run a no-op DB query to equalize timing with
+            # the credential fetch that executes for existing users.  Without this,
+            # the absence of the second query makes the "no user" path measurably
+            # faster, leaking whether the username exists.
+            await db.execute(
+                select(PasskeyCredential.credential_id).where(
+                    PasskeyCredential.user_id == 0
+                ).limit(1)
+            )
+
+    # V-03: Generate options regardless of whether user exists or has passkeys.
+    # Identical response shape prevents timing enumeration.
+    options_json, challenge = build_authentication_options(
+        credential_ids_and_transports=credential_data,
+    )
+    token = create_challenge_token(challenge)
+
+    return {
+        "options": json.loads(options_json),
+        "challenge_token": token,
+    }
+
+
+@router.post("/login/complete")
+async def passkey_login_complete(
+    data: PasskeyLoginCompleteRequest,
+    request: Request,
+    response: Response,
+    db: AsyncSession = Depends(get_db),
+):
+    """Complete passkey authentication. CSRF-exempt, public endpoint."""
+    # Verify challenge token (60s TTL, single-use nonce V-01)
+    challenge = verify_challenge_token(data.challenge_token)
+    if challenge is None:
+        raise HTTPException(status_code=401, detail="Authentication failed")
+
+    # Parse credential_id from browser response (S-02: shared helper)
+    raw_id_b64 = extract_credential_raw_id(data.credential)
+    if not raw_id_b64:
+        raise HTTPException(status_code=401, detail="Authentication failed")
+
+    # Look up credential + user in a single JOIN query (W-1 perf fix)
+    result = await db.execute(
+        select(PasskeyCredential, User)
+        .join(User, User.id == PasskeyCredential.user_id)
+        .where(PasskeyCredential.credential_id == raw_id_b64)
+    )
+    row = result.one_or_none()
+    if not row:
+        raise HTTPException(status_code=401, detail="Authentication failed")
+    credential, user = row.tuple()
+
+    # Check account lockout (C-03)
+    await check_account_lockout(user)
+
+    # Check active status (C-03)
+    if not user.is_active:
+        raise HTTPException(status_code=401, detail="Authentication failed")
+
+    # Verify the authentication response
+    try:
+        verified = verify_authentication_response_svc(
+            credential_json=data.credential,
+            challenge=challenge,
+            credential_public_key=base64url_to_bytes(credential.public_key),
+            credential_current_sign_count=credential.sign_count,
+        )
+    except Exception as e:
+        logger.warning("Passkey authentication verification failed for user %s: %s", user.id, e)
+        # Increment failed login counter (shared with password auth)
+        remaining = await record_failed_login(db, user)
+        await log_audit_event(
+            db, action="passkey.login_failed", actor_id=user.id,
+            detail={"reason": "verification_failed", "attempts_remaining": remaining},
+            ip=get_client_ip(request),
+        )
+        await db.commit()
+        # Generic message for all failures — don't leak lockout state (C-02/F-02)
+        raise HTTPException(status_code=401, detail="Authentication failed")
+
+    # Update sign count (log anomaly but don't fail — S-05)
+    new_sign_count = verified.new_sign_count
+    if new_sign_count < credential.sign_count and credential.sign_count > 0:
+        logger.warning(
+            "Sign count anomaly for user %s credential %s: expected >= %d, got %d",
+            user.id, credential.id, credential.sign_count, new_sign_count,
+        )
+        await log_audit_event(
+            db, action="passkey.sign_count_anomaly", actor_id=user.id,
+            detail={
+                "credential_id": credential.id,
+                "expected": credential.sign_count,
+                "received": new_sign_count,
+            },
+            ip=get_client_ip(request),
+        )
+
+    credential.sign_count = new_sign_count
+    credential.last_used_at = datetime.now()
+
+    # Passkey unlock — re-authenticate into a locked session instead of creating a new one
+    if data.unlock:
+        session_cookie = request.cookies.get("session")
+        payload = verify_session_token(session_cookie) if session_cookie else None
+        if not payload or payload.get("uid") != user.id:
+            raise HTTPException(status_code=401, detail="Authentication failed")
+        sess_result = await db.execute(
+            select(UserSession).where(
+                UserSession.id == payload["sid"],
+                UserSession.user_id == user.id,
+                UserSession.revoked == False,
+            )
+        )
+        db_sess = sess_result.scalar_one_or_none()
+        if not db_sess:
+            raise HTTPException(status_code=401, detail="Authentication failed")
+        db_sess.is_locked = False
+        db_sess.locked_at = None
+        # Reset failed login counter on successful passkey unlock (W-02)
+        await record_successful_login(db, user)
+        await log_audit_event(
+            db, action="passkey.unlock_success", actor_id=user.id,
+            ip=get_client_ip(request),
+        )
+        await db.commit()
+        return {"unlocked": True}
+
+    # Record successful login
+    await record_successful_login(db, user)
+
+    # Create session (shared service — enforces session cap)
+    client_ip = get_client_ip(request)
+    user_agent = request.headers.get("user-agent")
+    _, token = await create_db_session(db, user, client_ip, user_agent)
+    set_session_cookie(response, token)
+
+    # Handle special flags for passkey login
+    result_data: dict = {"authenticated": True}
+    # W-05: Passkey login auto-clears must_change_password — user can't provide
+    # old password in the forced-change form since they authenticated via passkey.
+    if user.must_change_password:
+        user.must_change_password = False
+    # Passkey satisfies MFA — if mfa_enforce_pending, clear it (before commit)
+    if user.mfa_enforce_pending:
+        user.mfa_enforce_pending = False
+
+    await log_audit_event(
+        db, action="passkey.login_success", actor_id=user.id,
+        detail={"credential_name": credential.name},
+        ip=client_ip,
+    )
+    await db.commit()
+
+    return result_data
+
+
+# ---------------------------------------------------------------------------
+# Passwordless toggle endpoints (authenticated)
+# ---------------------------------------------------------------------------
+
+@router.put("/passwordless/enable")
+async def passwordless_enable(
+    data: PasswordlessEnableRequest,
+    request: Request,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """
+    Enable passwordless login for the current user.
+
+    Requirements:
+    - System config must have allow_passwordless = True
+    - User must have >= 2 registered passkeys
+    - Password confirmation required
+    """
+    # Verify password first
+    valid, new_hash = await averify_password_with_upgrade(
+        data.password, current_user.password_hash
+    )
+    if not valid:
+        raise HTTPException(status_code=401, detail="Invalid password")
+    if new_hash:
+        current_user.password_hash = new_hash
+
+    # Check system config
+    config_result = await db.execute(
+        select(SystemConfig).where(SystemConfig.id == 1)
+    )
+    config = config_result.scalar_one_or_none()
+    if not config or not config.allow_passwordless:
+        raise HTTPException(
+            status_code=403,
+            detail="Passwordless login is not enabled on this system",
+        )
+
+    # Require >= 2 passkeys as safety net (can't get locked out)
+    pk_count_result = await db.execute(
+        select(func.count()).select_from(PasskeyCredential).where(
+            PasskeyCredential.user_id == current_user.id
+        )
+    )
+    pk_count = pk_count_result.scalar_one()
+    if pk_count < 2:
+        raise HTTPException(
+            status_code=400,
+            detail="At least 2 passkeys must be registered before enabling passwordless login",
+        )
+
+    current_user.passwordless_enabled = True
+
+    await log_audit_event(
+        db, action="passkey.passwordless_enabled", actor_id=current_user.id,
+        ip=get_client_ip(request),
+    )
+    await db.commit()
+
+    return {"passwordless_enabled": True}
+
+
+@router.post("/passwordless/disable/begin")
+async def passwordless_disable_begin(
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """
+    Begin the passkey authentication ceremony to disable passwordless login.
+    Returns challenge options for the browser to present to the authenticator.
+    """
+    # Load user's credentials for allowCredentials
+    cred_result = await db.execute(
+        select(
+            PasskeyCredential.credential_id,
+            PasskeyCredential.transports,
+        ).where(PasskeyCredential.user_id == current_user.id)
+    )
+    rows = cred_result.all()
+
+    credential_data = None
+    if rows:
+        credential_data = []
+        for row in rows:
+            cid_bytes = base64url_to_bytes(row[0])
+            transports = json.loads(row[1]) if row[1] else None
+            credential_data.append((cid_bytes, transports))
+
+    options_json, challenge = build_authentication_options(
+        credential_ids_and_transports=credential_data,
+    )
+    # Bind challenge to this user so complete endpoint can cross-check
+    token = create_challenge_token(challenge, user_id=current_user.id)
+
+    return {
+        "options": json.loads(options_json),
+        "challenge_token": token,
+    }
+
+
+@router.put("/passwordless/disable")
+async def passwordless_disable(
+    data: PasswordlessDisableRequest,
+    request: Request,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """
+    Complete passkey authentication to disable passwordless login.
+    Verifies the credential belongs to the current user.
+    """
+    # Verify challenge token — user-bound (single-use nonce V-01, cross-user binding S-01)
+    challenge = verify_challenge_token(
+        data.challenge_token, expected_user_id=current_user.id
+    )
+    if challenge is None:
+        raise HTTPException(status_code=401, detail="Invalid or expired challenge")
+
+    # Parse rawId from credential (S-02: shared helper)
+    raw_id_b64 = extract_credential_raw_id(data.credential)
+    if not raw_id_b64:
+        raise HTTPException(status_code=401, detail="Authentication failed")
+
+    # Look up credential — verify ownership (IDOR prevention)
+    cred_result = await db.execute(
+        select(PasskeyCredential).where(
+            PasskeyCredential.credential_id == raw_id_b64,
+            PasskeyCredential.user_id == current_user.id,
+        )
+    )
+    credential = cred_result.scalar_one_or_none()
+    if not credential:
+        raise HTTPException(status_code=401, detail="Authentication failed")
+
+    # Verify the authentication response
+    try:
+        verified = verify_authentication_response_svc(
+            credential_json=data.credential,
+            challenge=challenge,
+            credential_public_key=base64url_to_bytes(credential.public_key),
+            credential_current_sign_count=credential.sign_count,
+        )
+    except Exception as e:
+        logger.warning(
+            "Passwordless disable: auth verification failed for user %s: %s",
+            current_user.id, e,
+        )
+        raise HTTPException(status_code=401, detail="Authentication failed")
+
+    # Update sign count
+    credential.sign_count = verified.new_sign_count
+    credential.last_used_at = datetime.now()
+
+    current_user.passwordless_enabled = False
+
+    await log_audit_event(
+        db, action="passkey.passwordless_disabled", actor_id=current_user.id,
+        ip=get_client_ip(request),
+    )
+    await db.commit()
+
+    return {"passwordless_enabled": False}
+
+
+# ---------------------------------------------------------------------------
+# Management endpoints (authenticated)
+# ---------------------------------------------------------------------------
+
+@router.get("/")
+async def list_passkeys(
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """List all passkeys for the current user."""
+    result = await db.execute(
+        select(PasskeyCredential)
+        .where(PasskeyCredential.user_id == current_user.id)
+        .order_by(PasskeyCredential.created_at.desc())
+    )
+    credentials = result.scalars().all()
+
+    return [
+        {
+            "id": c.id,
+            "name": c.name,
+            "created_at": str(c.created_at) if c.created_at else None,
+            "last_used_at": str(c.last_used_at) if c.last_used_at else None,
+            "backed_up": c.backed_up,
+        }
+        for c in credentials
+    ]
+
+
+@router.delete("/{credential_id}")
+async def delete_passkey(
+    request: Request,
+    credential_id: int = Path(ge=1, le=2147483647),
+    data: PasskeyDeleteRequest = ...,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Delete a passkey. Requires password confirmation (S-06)."""
+    # Verify password
+    valid, new_hash = await averify_password_with_upgrade(
+        data.password, current_user.password_hash
+    )
+    if not valid:
+        raise HTTPException(status_code=401, detail="Invalid password")
+    if new_hash:
+        current_user.password_hash = new_hash
+
+    # Look up credential — verify ownership (IDOR prevention)
+    result = await db.execute(
+        select(PasskeyCredential).where(
+            PasskeyCredential.id == credential_id,
+            PasskeyCredential.user_id == current_user.id,
+        )
+    )
+    credential = result.scalar_one_or_none()
+    if not credential:
+        raise HTTPException(status_code=404, detail="Passkey not found")
+
+    # Guard: passwordless users must retain at least 2 passkeys
+    if current_user.passwordless_enabled:
+        pk_count_result = await db.execute(
+            select(func.count()).select_from(PasskeyCredential).where(
+                PasskeyCredential.user_id == current_user.id
+            )
+        )
+        pk_count = pk_count_result.scalar_one()
+        if pk_count <= 2:
+            raise HTTPException(
+                status_code=409,
+                detail="Cannot delete: passwordless requires at least 2 passkeys",
+            )
+
+    cred_name = credential.name
+    await db.delete(credential)
+
+    await log_audit_event(
+        db, action="passkey.deleted", actor_id=current_user.id,
+        detail={"credential_name": cred_name, "credential_db_id": credential_id},
+        ip=get_client_ip(request),
+    )
+    await db.commit()
+
+    return {"message": "Passkey removed"}

backend/app/routers/projects.py

@@ -1,18 +1,31 @@
 from fastapi import APIRouter, Depends, HTTPException, Path, Query
 from sqlalchemy.ext.asyncio import AsyncSession
-from sqlalchemy import select
+from sqlalchemy import delete as sa_delete, select, update
 from sqlalchemy.orm import selectinload
 from typing import List, Optional
-from datetime import date, timedelta
-from pydantic import BaseModel
+from datetime import date, datetime, timedelta
+from pydantic import BaseModel, ConfigDict
 
 from app.database import get_db
 from app.models.project import Project
 from app.models.project_task import ProjectTask
 from app.models.task_comment import TaskComment
+from app.models.project_member import ProjectMember
+from app.models.project_task_assignment import ProjectTaskAssignment
+from app.models.settings import Settings
 from app.schemas.project import ProjectCreate, ProjectUpdate, ProjectResponse, TrackedTaskResponse
 from app.schemas.project_task import ProjectTaskCreate, ProjectTaskUpdate, ProjectTaskResponse
 from app.schemas.task_comment import TaskCommentCreate, TaskCommentResponse
+from app.schemas.project_member import (
+    ProjectMemberInvite, ProjectMemberUpdate, ProjectMemberRespond, ProjectMemberResponse,
+)
+from app.schemas.project_task_assignment import TaskAssignmentCreate, TaskAssignmentResponse
+from app.services.project_sharing import (
+    get_project_permission, require_project_permission, get_accessible_project_ids,
+    validate_project_connections, get_effective_task_permission, ensure_auto_membership,
+    cleanup_auto_membership, ASSIGNEE_ALLOWED_FIELDS,
+)
+from app.services.notification import create_notification
 from app.routers.auth import get_current_user
 from app.models.user import User
 
@@ -20,39 +33,67 @@ router = APIRouter()
 
 
 class ReorderItem(BaseModel):
+    model_config = ConfigDict(extra="forbid")
     id: int
     sort_order: int
 
 
 def _project_load_options():
-    """All load options needed for project responses (tasks + subtasks + comments at each level)."""
+    """All load options needed for project responses (tasks + subtasks + comments + assignments)."""
     return [
-        selectinload(Project.tasks).selectinload(ProjectTask.comments),
-        selectinload(Project.tasks).selectinload(ProjectTask.subtasks).selectinload(ProjectTask.comments),
+        selectinload(Project.tasks).selectinload(ProjectTask.comments).selectinload(TaskComment.user),
+        selectinload(Project.tasks).selectinload(ProjectTask.subtasks).selectinload(ProjectTask.comments).selectinload(TaskComment.user),
         selectinload(Project.tasks).selectinload(ProjectTask.subtasks).selectinload(ProjectTask.subtasks),
+        selectinload(Project.tasks).selectinload(ProjectTask.assignments).selectinload(ProjectTaskAssignment.user),
+        selectinload(Project.tasks).selectinload(ProjectTask.subtasks).selectinload(ProjectTask.assignments).selectinload(ProjectTaskAssignment.user),
+        selectinload(Project.members),
     ]
 
 
 def _task_load_options():
     """All load options needed for task responses."""
     return [
-        selectinload(ProjectTask.comments),
-        selectinload(ProjectTask.subtasks).selectinload(ProjectTask.comments),
+        selectinload(ProjectTask.comments).selectinload(TaskComment.user),
+        selectinload(ProjectTask.subtasks).selectinload(ProjectTask.comments).selectinload(TaskComment.user),
         selectinload(ProjectTask.subtasks).selectinload(ProjectTask.subtasks),
+        selectinload(ProjectTask.assignments).selectinload(ProjectTaskAssignment.user),
+        selectinload(ProjectTask.subtasks).selectinload(ProjectTask.assignments).selectinload(ProjectTaskAssignment.user),
     ]
 
 
+async def _get_user_name(db: AsyncSession, user_id: int) -> str | None:
+    """Get display name for a user from settings.preferred_name or user.username."""
+    result = await db.execute(
+        select(Settings.preferred_name, User.username)
+        .outerjoin(Settings, Settings.user_id == User.id)
+        .where(User.id == user_id)
+    )
+    row = result.one_or_none()
+    if not row:
+        return None
+    preferred, username = row.tuple()
+    return preferred or username
+
+
+# ──────────────────────────────────────────────
+# PROJECT CRUD
+# ──────────────────────────────────────────────
+
 @router.get("/", response_model=List[ProjectResponse])
 async def get_projects(
     tracked: Optional[bool] = Query(None),
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user)
 ):
-    """Get all projects with their tasks. Optionally filter by tracked status."""
+    """Get all projects the user owns or has accepted membership in."""
+    accessible_ids = await get_accessible_project_ids(db, current_user.id)
+    if not accessible_ids:
+        return []
+
     query = (
         select(Project)
         .options(*_project_load_options())
-        .where(Project.user_id == current_user.id)
+        .where(Project.id.in_(accessible_ids))
         .order_by(Project.created_at.desc())
     )
     if tracked is not None:
@@ -71,6 +112,10 @@ async def get_tracked_tasks(
     current_user: User = Depends(get_current_user)
 ):
     """Get tasks and subtasks from tracked projects with due dates within the next N days."""
+    accessible_ids = await get_accessible_project_ids(db, current_user.id)
+    if not accessible_ids:
+        return []
+
     today = date.today()
     cutoff = today + timedelta(days=days)
 
@@ -82,7 +127,7 @@ async def get_tracked_tasks(
             selectinload(ProjectTask.parent_task),
         )
         .where(
-            Project.user_id == current_user.id,
+            Project.id.in_(accessible_ids),
             Project.is_tracked == True,
             ProjectTask.due_date.isnot(None),
             ProjectTask.due_date >= today,
@@ -109,6 +154,31 @@ async def get_tracked_tasks(
     ]
 
 
+@router.get("/shared", response_model=List[ProjectResponse])
+async def get_shared_projects(
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user)
+):
+    """List projects where user is an accepted member (not owner)."""
+    member_result = await db.execute(
+        select(ProjectMember.project_id).where(
+            ProjectMember.user_id == current_user.id,
+            ProjectMember.status == "accepted",
+        )
+    )
+    project_ids = [r[0] for r in member_result.all()]
+    if not project_ids:
+        return []
+
+    result = await db.execute(
+        select(Project)
+        .options(*_project_load_options())
+        .where(Project.id.in_(project_ids))
+        .order_by(Project.created_at.desc())
+    )
+    return result.scalars().unique().all()
+
+
 @router.post("/", response_model=ProjectResponse, status_code=201)
 async def create_project(
     project: ProjectCreate,
@@ -120,7 +190,6 @@ async def create_project(
     db.add(new_project)
     await db.commit()
 
-    # Re-fetch with eagerly loaded tasks for response serialization
     query = select(Project).options(*_project_load_options()).where(Project.id == new_project.id)
     result = await db.execute(query)
     return result.scalar_one()
@@ -133,10 +202,12 @@ async def get_project(
     current_user: User = Depends(get_current_user)
 ):
     """Get a specific project by ID with its tasks."""
+    await require_project_permission(db, project_id, current_user.id, "read_only")
+
     query = (
         select(Project)
         .options(*_project_load_options())
-        .where(Project.id == project_id, Project.user_id == current_user.id)
+        .where(Project.id == project_id)
     )
     result = await db.execute(query)
     project = result.scalar_one_or_none()
@@ -154,10 +225,10 @@ async def update_project(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user)
 ):
-    """Update a project."""
-    result = await db.execute(
-        select(Project).where(Project.id == project_id, Project.user_id == current_user.id)
-    )
+    """Update a project. Owner only."""
+    await require_project_permission(db, project_id, current_user.id, "owner")
+
+    result = await db.execute(select(Project).where(Project.id == project_id))
     project = result.scalar_one_or_none()
 
     if not project:
@@ -170,7 +241,6 @@ async def update_project(
 
     await db.commit()
 
-    # Re-fetch with eagerly loaded tasks for response serialization
     query = select(Project).options(*_project_load_options()).where(Project.id == project_id)
     result = await db.execute(query)
     return result.scalar_one()
@@ -182,10 +252,10 @@ async def delete_project(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user)
 ):
-    """Delete a project and all its tasks."""
-    result = await db.execute(
-        select(Project).where(Project.id == project_id, Project.user_id == current_user.id)
-    )
+    """Delete a project and all its tasks. Owner only."""
+    await require_project_permission(db, project_id, current_user.id, "owner")
+
+    result = await db.execute(select(Project).where(Project.id == project_id))
     project = result.scalar_one_or_none()
 
     if not project:
@@ -197,6 +267,10 @@ async def delete_project(
     return None
 
 
+# ──────────────────────────────────────────────
+# TASK CRUD (permission-aware)
+# ──────────────────────────────────────────────
+
 @router.get("/{project_id}/tasks", response_model=List[ProjectTaskResponse])
 async def get_project_tasks(
     project_id: int = Path(ge=1, le=2147483647),
@@ -204,14 +278,7 @@ async def get_project_tasks(
     current_user: User = Depends(get_current_user)
 ):
     """Get top-level tasks for a specific project (subtasks are nested)."""
-    # Verify project ownership first
-    result = await db.execute(
-        select(Project).where(Project.id == project_id, Project.user_id == current_user.id)
-    )
-    project = result.scalar_one_or_none()
-
-    if not project:
-        raise HTTPException(status_code=404, detail="Project not found")
+    await require_project_permission(db, project_id, current_user.id, "read_only")
 
     query = (
         select(ProjectTask)
@@ -235,15 +302,8 @@ async def create_project_task(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user)
 ):
-    """Create a new task or subtask for a project."""
-    # Verify project ownership first
-    result = await db.execute(
-        select(Project).where(Project.id == project_id, Project.user_id == current_user.id)
-    )
-    project = result.scalar_one_or_none()
-
-    if not project:
-        raise HTTPException(status_code=404, detail="Project not found")
+    """Create a new task or subtask for a project. Requires create_modify permission."""
+    await require_project_permission(db, project_id, current_user.id, "create_modify")
 
     # Validate parent_task_id if creating a subtask
     if task.parent_task_id is not None:
@@ -267,7 +327,6 @@ async def create_project_task(
     db.add(new_task)
     await db.commit()
 
-    # Re-fetch with subtasks loaded
     query = (
         select(ProjectTask)
         .options(*_task_load_options())
@@ -284,26 +343,23 @@ async def reorder_tasks(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user)
 ):
-    """Bulk update sort_order for tasks."""
-    # Verify project ownership first
-    result = await db.execute(
-        select(Project).where(Project.id == project_id, Project.user_id == current_user.id)
-    )
-    project = result.scalar_one_or_none()
+    """Bulk update sort_order for tasks. Requires create_modify permission."""
+    await require_project_permission(db, project_id, current_user.id, "create_modify")
 
-    if not project:
-        raise HTTPException(status_code=404, detail="Project not found")
-
-    for item in items:
+    # AC-4: Batch-fetch all tasks in one query instead of N sequential queries
+    task_ids = [item.id for item in items]
     task_result = await db.execute(
         select(ProjectTask).where(
-                ProjectTask.id == item.id,
-                ProjectTask.project_id == project_id
+            ProjectTask.id.in_(task_ids),
+            ProjectTask.project_id == project_id,
         )
     )
-        task = task_result.scalar_one_or_none()
-        if task:
-            task.sort_order = item.sort_order
+    tasks_by_id = {t.id: t for t in task_result.scalars().all()}
+
+    order_map = {item.id: item.sort_order for item in items}
+    for task_id, task in tasks_by_id.items():
+        if task_id in order_map:
+            task.sort_order = order_map[task_id]
 
     await db.commit()
 
@@ -318,13 +374,12 @@ async def update_project_task(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user)
 ):
-    """Update a project task."""
-    # Verify project ownership first, then fetch task scoped to that project
-    project_result = await db.execute(
-        select(Project).where(Project.id == project_id, Project.user_id == current_user.id)
-    )
-    if not project_result.scalar_one_or_none():
+    """Update a project task. Permission checked at project and task level."""
+    perm, project_perm = await get_effective_task_permission(db, current_user.id, task_id, project_id)
+    if perm is None:
         raise HTTPException(status_code=404, detail="Project not found")
+    if perm == "read_only":
+        raise HTTPException(status_code=403, detail="Insufficient permission")
 
     result = await db.execute(
         select(ProjectTask).where(
@@ -339,12 +394,28 @@ async def update_project_task(
 
     update_data = task_update.model_dump(exclude_unset=True)
 
+    # SEC-P02: Assignees (non-owner, non-project-member with create_modify) restricted to content fields
+    if project_perm not in ("owner", "create_modify"):
+        # This user's create_modify comes from task assignment — enforce allowlist
+        disallowed = set(update_data.keys()) - ASSIGNEE_ALLOWED_FIELDS
+        if disallowed:
+            raise HTTPException(
+                status_code=403,
+                detail=f"Task assignees cannot modify: {', '.join(sorted(disallowed))}",
+            )
+
+    # Optimistic locking: if version provided, check it matches
+    client_version = update_data.pop("version", None)
+    if client_version is not None and task.version != client_version:
+        raise HTTPException(status_code=409, detail="Task was modified by another user")
+
     for key, value in update_data.items():
         setattr(task, key, value)
 
+    task.version += 1
+
     await db.commit()
 
-    # Re-fetch with subtasks loaded
     query = (
         select(ProjectTask)
         .options(*_task_load_options())
@@ -361,13 +432,8 @@ async def delete_project_task(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user)
 ):
-    """Delete a project task (cascades to subtasks)."""
-    # Verify project ownership first, then fetch task scoped to that project
-    project_result = await db.execute(
-        select(Project).where(Project.id == project_id, Project.user_id == current_user.id)
-    )
-    if not project_result.scalar_one_or_none():
-        raise HTTPException(status_code=404, detail="Project not found")
+    """Delete a project task (cascades to subtasks). Requires create_modify permission."""
+    await require_project_permission(db, project_id, current_user.id, "create_modify")
 
     result = await db.execute(
         select(ProjectTask).where(
@@ -386,6 +452,10 @@ async def delete_project_task(
     return None
 
 
+# ──────────────────────────────────────────────
+# COMMENTS (permission-aware)
+# ──────────────────────────────────────────────
+
 @router.post("/{project_id}/tasks/{task_id}/comments", response_model=TaskCommentResponse, status_code=201)
 async def create_task_comment(
     project_id: int = Path(ge=1, le=2147483647),
@@ -394,13 +464,8 @@ async def create_task_comment(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user)
 ):
-    """Add a comment to a task."""
-    # Verify project ownership first, then fetch task scoped to that project
-    project_result = await db.execute(
-        select(Project).where(Project.id == project_id, Project.user_id == current_user.id)
-    )
-    if not project_result.scalar_one_or_none():
-        raise HTTPException(status_code=404, detail="Project not found")
+    """Add a comment to a task. All members can comment (read_only minimum)."""
+    await require_project_permission(db, project_id, current_user.id, "read_only")
 
     result = await db.execute(
         select(ProjectTask).where(
@@ -413,12 +478,23 @@ async def create_task_comment(
     if not task:
         raise HTTPException(status_code=404, detail="Task not found")
 
-    new_comment = TaskComment(task_id=task_id, content=comment.content)
+    new_comment = TaskComment(task_id=task_id, user_id=current_user.id, content=comment.content)
     db.add(new_comment)
+
+    # Get author name before commit
+    author_name = await _get_user_name(db, current_user.id)
+
     await db.commit()
     await db.refresh(new_comment)
 
-    return new_comment
+    return TaskCommentResponse(
+        id=new_comment.id,
+        task_id=new_comment.task_id,
+        user_id=new_comment.user_id,
+        author_name=author_name,
+        content=new_comment.content,
+        created_at=new_comment.created_at,
+    )
 
 
 @router.delete("/{project_id}/tasks/{task_id}/comments/{comment_id}", status_code=204)
@@ -429,12 +505,9 @@ async def delete_task_comment(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user)
 ):
-    """Delete a task comment."""
-    # Verify project ownership first, then fetch comment scoped through task
-    project_result = await db.execute(
-        select(Project).where(Project.id == project_id, Project.user_id == current_user.id)
-    )
-    if not project_result.scalar_one_or_none():
+    """Delete a task comment. Comment author or project owner only."""
+    perm = await get_project_permission(db, project_id, current_user.id)
+    if perm is None:
         raise HTTPException(status_code=404, detail="Project not found")
 
     result = await db.execute(
@@ -448,7 +521,484 @@ async def delete_task_comment(
     if not comment:
         raise HTTPException(status_code=404, detail="Comment not found")
 
+    # Only comment author or project owner can delete
+    if comment.user_id != current_user.id and perm != "owner":
+        raise HTTPException(status_code=403, detail="Only the comment author or project owner can delete this comment")
+
     await db.delete(comment)
     await db.commit()
 
     return None
+
+
+# ──────────────────────────────────────────────
+# MEMBERSHIP ROUTES
+# ──────────────────────────────────────────────
+
+@router.post("/{project_id}/members", response_model=List[ProjectMemberResponse], status_code=201)
+async def invite_members(
+    project_id: int = Path(ge=1, le=2147483647),
+    invite: ProjectMemberInvite = ...,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user)
+):
+    """Invite connection(s) to a project. Owner only."""
+    await require_project_permission(db, project_id, current_user.id, "owner")
+
+    # Validate connections
+    await validate_project_connections(db, current_user.id, invite.user_ids)
+
+    # Check pending invite cap (max 10 pending per project)
+    pending_count_result = await db.execute(
+        select(ProjectMember.id).where(
+            ProjectMember.project_id == project_id,
+            ProjectMember.status == "pending",
+        )
+    )
+    pending_count = len(pending_count_result.all())
+    if pending_count + len(invite.user_ids) > 10:
+        raise HTTPException(status_code=400, detail="Maximum 10 pending invites per project")
+
+    # Filter out self and existing members
+    existing_result = await db.execute(
+        select(ProjectMember.user_id).where(
+            ProjectMember.project_id == project_id,
+            ProjectMember.user_id.in_(invite.user_ids),
+        )
+    )
+    existing_user_ids = {r[0] for r in existing_result.all()}
+
+    # Get project for notifications
+    project_result = await db.execute(select(Project.name).where(Project.id == project_id))
+    project_name = project_result.scalar_one()
+
+    inviter_name = await _get_user_name(db, current_user.id)
+    created_members = []
+
+    for uid in invite.user_ids:
+        if uid == current_user.id or uid in existing_user_ids:
+            continue
+
+        member = ProjectMember(
+            project_id=project_id,
+            user_id=uid,
+            invited_by=current_user.id,
+            permission=invite.permission,
+            status="pending",
+            source="invited",
+        )
+        db.add(member)
+        created_members.append(member)
+
+        # In-app notification
+        await create_notification(
+            db, uid, "project_invite",
+            f"Project invitation from {inviter_name}",
+            f"You've been invited to collaborate on \"{project_name}\"",
+            data={"project_id": project_id},
+            source_type="project_member",
+        )
+
+    await db.flush()  # Assign IDs before commit (ORM objects expire after commit)
+    member_ids = [m.id for m in created_members]
+    await db.commit()
+
+    # Re-fetch with relationships
+    if not created_members:
+        return []
+    result = await db.execute(
+        select(ProjectMember)
+        .options(
+            selectinload(ProjectMember.user),
+            selectinload(ProjectMember.inviter),
+        )
+        .where(ProjectMember.id.in_(member_ids))
+    )
+    members = result.scalars().all()
+
+    # Build response with names
+    responses = []
+    for m in members:
+        resp = ProjectMemberResponse.model_validate(m)
+        resp.user_name = m.user.username
+        resp.inviter_name = m.inviter.username if m.inviter else None
+        responses.append(resp)
+
+    return responses
+
+
+@router.get("/{project_id}/members", response_model=List[ProjectMemberResponse])
+async def get_members(
+    project_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user)
+):
+    """List members + statuses. Any member can view."""
+    await require_project_permission(db, project_id, current_user.id, "read_only")
+
+    result = await db.execute(
+        select(ProjectMember)
+        .options(
+            selectinload(ProjectMember.user),
+            selectinload(ProjectMember.inviter),
+        )
+        .where(ProjectMember.project_id == project_id)
+        .order_by(ProjectMember.created_at.asc())
+    )
+    members = result.scalars().all()
+
+    # Batch-fetch settings for preferred_name
+    user_ids = [m.user_id for m in members] + [m.invited_by for m in members]
+    settings_result = await db.execute(
+        select(Settings.user_id, Settings.preferred_name).where(Settings.user_id.in_(user_ids))
+    )
+    name_map = {r[0]: r[1] for r in settings_result.all()}
+
+    responses = []
+    for m in members:
+        resp = ProjectMemberResponse.model_validate(m)
+        resp.user_name = name_map.get(m.user_id) or m.user.username
+        resp.inviter_name = name_map.get(m.invited_by) or (m.inviter.username if m.inviter else None)
+        responses.append(resp)
+
+    return responses
+
+
+@router.patch("/{project_id}/members/{user_id}", response_model=ProjectMemberResponse)
+async def update_member_permission(
+    project_id: int = Path(ge=1, le=2147483647),
+    user_id: int = Path(ge=1, le=2147483647),
+    update: ProjectMemberUpdate = ...,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user)
+):
+    """Update a member's permission level. Owner only."""
+    await require_project_permission(db, project_id, current_user.id, "owner")
+
+    result = await db.execute(
+        select(ProjectMember)
+        .options(selectinload(ProjectMember.user), selectinload(ProjectMember.inviter))
+        .where(
+            ProjectMember.project_id == project_id,
+            ProjectMember.user_id == user_id,
+        )
+    )
+    member = result.scalar_one_or_none()
+    if not member:
+        raise HTTPException(status_code=404, detail="Member not found")
+
+    member.permission = update.permission
+
+    # Extract response data BEFORE commit (ORM objects expire after commit)
+    resp = ProjectMemberResponse.model_validate(member)
+    resp.user_name = member.user.username
+    resp.inviter_name = member.inviter.username if member.inviter else None
+
+    await db.commit()
+
+    return resp
+
+
+@router.delete("/{project_id}/members/{user_id}", status_code=204)
+async def remove_member(
+    project_id: int = Path(ge=1, le=2147483647),
+    user_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user)
+):
+    """Remove a member. Owner or self (leave project)."""
+    perm = await get_project_permission(db, project_id, current_user.id)
+    if perm is None:
+        raise HTTPException(status_code=404, detail="Project not found")
+
+    # Only owner can remove others; anyone can remove themselves
+    if user_id != current_user.id and perm != "owner":
+        raise HTTPException(status_code=403, detail="Only the project owner can remove members")
+
+    result = await db.execute(
+        select(ProjectMember).where(
+            ProjectMember.project_id == project_id,
+            ProjectMember.user_id == user_id,
+        )
+    )
+    member = result.scalar_one_or_none()
+    if not member:
+        raise HTTPException(status_code=404, detail="Member not found")
+
+    # Remove task assignments for this user in this project
+    await db.execute(
+        sa_delete(ProjectTaskAssignment).where(
+            ProjectTaskAssignment.user_id == user_id,
+            ProjectTaskAssignment.task_id.in_(
+                select(ProjectTask.id).where(ProjectTask.project_id == project_id)
+            ),
+        )
+    )
+
+    await db.delete(member)
+    await db.commit()
+
+    return None
+
+
+@router.post("/memberships/{project_id}/respond", response_model=ProjectMemberResponse)
+async def respond_to_invite(
+    project_id: int = Path(ge=1, le=2147483647),
+    respond: ProjectMemberRespond = ...,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user)
+):
+    """Accept or reject a project invite."""
+    result = await db.execute(
+        select(ProjectMember)
+        .options(selectinload(ProjectMember.user), selectinload(ProjectMember.inviter))
+        .where(
+            ProjectMember.project_id == project_id,
+            ProjectMember.user_id == current_user.id,
+            ProjectMember.status == "pending",
+        )
+    )
+    member = result.scalar_one_or_none()
+    if not member:
+        raise HTTPException(status_code=404, detail="No pending invitation found")
+
+    # Extract response data before any mutations (ORM objects expire after commit)
+    resp = ProjectMemberResponse.model_validate(member)
+    resp.user_name = member.user.username
+    resp.inviter_name = member.inviter.username if member.inviter else None
+
+    if respond.response == "accepted":
+        member.status = "accepted"
+        member.accepted_at = datetime.now()
+
+        # Get project owner for notification
+        project_result = await db.execute(
+            select(Project.user_id, Project.name).where(Project.id == project_id)
+        )
+        project_row = project_result.one()
+        owner_id, project_name = project_row.tuple()
+
+        responder_name = await _get_user_name(db, current_user.id)
+
+        await create_notification(
+            db, owner_id, "project_invite_accepted",
+            f"{responder_name} joined your project",
+            f"{responder_name} accepted the invitation to \"{project_name}\"",
+            data={"project_id": project_id},
+            source_type="project_member",
+        )
+
+        resp.status = "accepted"
+    else:
+        # Rejected — delete the row to prevent accumulation (W-06)
+        await db.delete(member)
+        resp.status = "rejected"
+
+    await db.commit()
+
+    return resp
+
+
+# ──────────────────────────────────────────────
+# TASK ASSIGNMENT ROUTES
+# ──────────────────────────────────────────────
+
+@router.post("/{project_id}/tasks/{task_id}/assignments", response_model=List[TaskAssignmentResponse], status_code=201)
+async def assign_users_to_task(
+    project_id: int = Path(ge=1, le=2147483647),
+    task_id: int = Path(ge=1, le=2147483647),
+    assignment: TaskAssignmentCreate = ...,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user)
+):
+    """Assign user(s) to a task. Requires create_modify on project or be owner."""
+    await require_project_permission(db, project_id, current_user.id, "create_modify")
+
+    # Verify task exists in project
+    task_result = await db.execute(
+        select(ProjectTask).where(
+            ProjectTask.id == task_id,
+            ProjectTask.project_id == project_id,
+        )
+    )
+    task = task_result.scalar_one_or_none()
+    if not task:
+        raise HTTPException(status_code=404, detail="Task not found")
+
+    # Get project owner for connection validation
+    project_result = await db.execute(
+        select(Project.user_id, Project.name).where(Project.id == project_id)
+    )
+    project_row = project_result.one()
+    owner_id, project_name = project_row.tuple()
+
+    # Validate connections (all assignees must be connections of the project owner)
+    non_owner_ids = [uid for uid in assignment.user_ids if uid != owner_id]
+    if non_owner_ids:
+        await validate_project_connections(db, owner_id, non_owner_ids)
+
+    # Filter out existing assignments
+    existing_result = await db.execute(
+        select(ProjectTaskAssignment.user_id).where(
+            ProjectTaskAssignment.task_id == task_id,
+            ProjectTaskAssignment.user_id.in_(assignment.user_ids),
+        )
+    )
+    existing_user_ids = {r[0] for r in existing_result.all()}
+
+    assigner_name = await _get_user_name(db, current_user.id)
+    created = []
+
+    for uid in assignment.user_ids:
+        if uid in existing_user_ids:
+            continue
+
+        # Auto-membership: ensure user has ProjectMember row
+        if uid != owner_id:
+            await ensure_auto_membership(db, project_id, uid, current_user.id)
+
+        new_assignment = ProjectTaskAssignment(
+            task_id=task_id,
+            user_id=uid,
+            assigned_by=current_user.id,
+        )
+        db.add(new_assignment)
+        created.append(new_assignment)
+
+        # Notify assignee (don't notify self)
+        if uid != current_user.id:
+            await create_notification(
+                db, uid, "task_assigned",
+                f"Task assigned by {assigner_name}",
+                f"You've been assigned to \"{task.title}\" in \"{project_name}\"",
+                data={"project_id": project_id, "task_id": task_id},
+                source_type="task_assignment",
+            )
+
+    await db.flush()  # Assign IDs before commit (ORM objects expire after commit)
+    assignment_ids = [a.id for a in created]
+    await db.commit()
+
+    if not created:
+        return []
+
+    # Re-fetch with user info
+    result = await db.execute(
+        select(ProjectTaskAssignment)
+        .options(selectinload(ProjectTaskAssignment.user))
+        .where(ProjectTaskAssignment.id.in_(assignment_ids))
+    )
+    assignments = result.scalars().all()
+
+    # Get names
+    user_ids = [a.user_id for a in assignments]
+    settings_result = await db.execute(
+        select(Settings.user_id, Settings.preferred_name).where(Settings.user_id.in_(user_ids))
+    )
+    name_map = {r[0]: r[1] for r in settings_result.all()}
+
+    return [
+        TaskAssignmentResponse(
+            id=a.id,
+            task_id=a.task_id,
+            user_id=a.user_id,
+            assigned_by=a.assigned_by,
+            user_name=name_map.get(a.user_id) or a.user.username,
+            created_at=a.created_at,
+        )
+        for a in assignments
+    ]
+
+
+@router.delete("/{project_id}/tasks/{task_id}/assignments/{user_id}", status_code=204)
+async def remove_task_assignment(
+    project_id: int = Path(ge=1, le=2147483647),
+    task_id: int = Path(ge=1, le=2147483647),
+    user_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user)
+):
+    """Remove a task assignment. Owner, create_modify member, or the assignee themselves."""
+    perm = await get_project_permission(db, project_id, current_user.id)
+    if perm is None:
+        raise HTTPException(status_code=404, detail="Project not found")
+
+    # Self-unassign is always allowed; otherwise need create_modify or owner
+    if user_id != current_user.id and perm not in ("owner", "create_modify"):
+        raise HTTPException(status_code=403, detail="Insufficient permission")
+
+    result = await db.execute(
+        sa_delete(ProjectTaskAssignment)
+        .where(
+            ProjectTaskAssignment.task_id == task_id,
+            ProjectTaskAssignment.user_id == user_id,
+        )
+        .returning(ProjectTaskAssignment.id)
+    )
+    if not result.scalar_one_or_none():
+        raise HTTPException(status_code=404, detail="Assignment not found")
+
+    # Cleanup auto-membership if no more assignments
+    await cleanup_auto_membership(db, project_id, user_id)
+
+    await db.commit()
+
+    return None
+
+
+# ──────────────────────────────────────────────
+# DELTA POLLING
+# ──────────────────────────────────────────────
+
+class PollResponse(BaseModel):
+    has_changes: bool
+    project_updated_at: str | None = None
+    changed_task_ids: list[int] = []
+
+
+@router.get("/{project_id}/poll", response_model=PollResponse)
+async def poll_project(
+    project_id: int = Path(ge=1, le=2147483647),
+    since: str = Query(..., description="ISO timestamp to check for changes since"),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user)
+):
+    """Lightweight poll endpoint — returns changed task IDs since timestamp."""
+    await require_project_permission(db, project_id, current_user.id, "read_only")
+
+    try:
+        since_dt = datetime.fromisoformat(since)
+    except ValueError:
+        raise HTTPException(status_code=400, detail="Invalid ISO timestamp")
+
+    # Clamp to max 24h in the past to prevent expensive full-table scans
+    min_since = datetime.now() - timedelta(hours=24)
+    if since_dt < min_since:
+        since_dt = min_since
+
+    # Check project-level update
+    proj_result = await db.execute(
+        select(Project.updated_at).where(Project.id == project_id)
+    )
+    project_updated = proj_result.scalar_one_or_none()
+    if not project_updated:
+        raise HTTPException(status_code=404, detail="Project not found")
+
+    project_changed = project_updated > since_dt
+
+    # Check task-level changes using the index
+    task_result = await db.execute(
+        select(ProjectTask.id).where(
+            ProjectTask.project_id == project_id,
+            ProjectTask.updated_at > since_dt,
+        )
+    )
+    changed_task_ids = [r[0] for r in task_result.all()]
+
+    has_changes = project_changed or len(changed_task_ids) > 0
+
+    return PollResponse(
+        has_changes=has_changes,
+        project_updated_at=project_updated.isoformat() if project_updated else None,
+        changed_task_ids=changed_task_ids,
+    )

backend/app/routers/settings.py

@@ -7,6 +7,7 @@ from app.models.settings import Settings
 from app.models.user import User
 from app.schemas.settings import SettingsUpdate, SettingsResponse
 from app.routers.auth import get_current_user, get_current_settings
+from app.services.connection import sync_birthday_to_contacts
 
 router = APIRouter()
 
@@ -78,6 +79,7 @@ async def get_settings(
 async def update_settings(
     settings_update: SettingsUpdate,
     db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
     current_settings: Settings = Depends(get_current_settings)
 ):
     """Update settings."""
@@ -91,9 +93,18 @@ async def update_settings(
         except ValueError as e:
             raise HTTPException(status_code=400, detail=str(e))
 
+    old_share_birthday = current_settings.share_birthday
+
     for key, value in update_data.items():
         setattr(current_settings, key, value)
 
+    if "share_birthday" in update_data and update_data["share_birthday"] != old_share_birthday:
+        await sync_birthday_to_contacts(
+            db, current_user.id,
+            share_birthday=update_data["share_birthday"],
+            date_of_birth=current_user.date_of_birth,
+        )
+
     await db.commit()
     await db.refresh(current_settings)
 

backend/app/routers/shared_calendars.py

@@ -0,0 +1,871 @@
+"""
+Shared calendars router — invites, membership, locks, sync.
+
+All endpoints live under /api/shared-calendars.
+"""
+import logging
+from datetime import datetime, timedelta
+from typing import Optional
+
+from fastapi import APIRouter, Depends, HTTPException, Path, Query, Request
+from sqlalchemy import delete, func, select, text
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy.orm import selectinload
+
+from app.database import get_db
+from app.models.calendar import Calendar
+from app.models.calendar_event import CalendarEvent
+from app.models.calendar_member import CalendarMember
+from app.models.event_lock import EventLock
+from app.models.settings import Settings
+from app.models.user import User
+from app.models.user_connection import UserConnection
+from app.routers.auth import get_current_user
+from app.schemas.shared_calendar import (
+    CalendarInviteResponse,
+    CalendarMemberResponse,
+    InviteMemberRequest,
+    LockStatusResponse,
+    RespondInviteRequest,
+    SyncResponse,
+    UpdateLocalColorRequest,
+    UpdateMemberRequest,
+)
+from app.services.audit import get_client_ip, log_audit_event
+from app.services.calendar_sharing import (
+    PERMISSION_RANK,
+    acquire_lock,
+    get_user_permission,
+    release_lock,
+    require_permission,
+)
+from app.services.notification import create_notification
+
+router = APIRouter()
+logger = logging.getLogger(__name__)
+
+PENDING_INVITE_CAP = 10
+
+
+# -- Helpers ---------------------------------------------------------------
+
+async def _get_settings_for_user(db: AsyncSession, user_id: int) -> Settings | None:
+    result = await db.execute(select(Settings).where(Settings.user_id == user_id))
+    return result.scalar_one_or_none()
+
+
+def _build_member_response(member: CalendarMember) -> dict:
+    return {
+        "id": member.id,
+        "calendar_id": member.calendar_id,
+        "user_id": member.user_id,
+        "umbral_name": member.user.umbral_name if member.user else "",
+        "preferred_name": None,
+        "permission": member.permission,
+        "can_add_others": member.can_add_others,
+        "local_color": member.local_color,
+        "status": member.status,
+        "invited_at": member.invited_at,
+        "accepted_at": member.accepted_at,
+    }
+
+
+# -- GET / — List accepted memberships ------------------------------------
+
+@router.get("/")
+async def list_shared_calendars(
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """List calendars the current user has accepted membership in."""
+    result = await db.execute(
+        select(CalendarMember)
+        .where(
+            CalendarMember.user_id == current_user.id,
+            CalendarMember.status == "accepted",
+        )
+        .options(selectinload(CalendarMember.calendar))
+        .order_by(CalendarMember.accepted_at.desc())
+    )
+    members = result.scalars().all()
+
+    return [
+        {
+            "id": m.id,
+            "calendar_id": m.calendar_id,
+            "calendar_name": m.calendar.name if m.calendar else "",
+            "calendar_color": m.calendar.color if m.calendar else "",
+            "local_color": m.local_color,
+            "permission": m.permission,
+            "can_add_others": m.can_add_others,
+            "is_owner": False,
+        }
+        for m in members
+    ]
+
+
+# -- POST /{cal_id}/invite — Invite via connection_id ---------------------
+
+@router.post("/{cal_id}/invite", status_code=201)
+async def invite_member(
+    body: InviteMemberRequest,
+    request: Request,
+    cal_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Invite a connected user to a shared calendar."""
+    cal_result = await db.execute(
+        select(Calendar).where(Calendar.id == cal_id)
+    )
+    calendar = cal_result.scalar_one_or_none()
+    if not calendar:
+        raise HTTPException(status_code=404, detail="Calendar not found")
+
+    is_owner = calendar.user_id == current_user.id
+    inviter_perm = "owner" if is_owner else None
+
+    if not is_owner:
+        member_result = await db.execute(
+            select(CalendarMember).where(
+                CalendarMember.calendar_id == cal_id,
+                CalendarMember.user_id == current_user.id,
+                CalendarMember.status == "accepted",
+            )
+        )
+        member = member_result.scalar_one_or_none()
+        if not member:
+            raise HTTPException(status_code=404, detail="Calendar not found")
+        if not member.can_add_others:
+            raise HTTPException(status_code=403, detail="You do not have permission to invite others")
+        if PERMISSION_RANK.get(member.permission, 0) < PERMISSION_RANK.get("create_modify", 0):
+            raise HTTPException(status_code=403, detail="Read-only members cannot invite others")
+        inviter_perm = member.permission
+
+    # Permission ceiling
+    if inviter_perm != "owner":
+        if PERMISSION_RANK.get(body.permission, 0) > PERMISSION_RANK.get(inviter_perm, 0):
+            raise HTTPException(
+                status_code=403,
+                detail="Cannot grant a permission level higher than your own",
+            )
+
+    # Resolve connection_id -> connected user
+    conn_result = await db.execute(
+        select(UserConnection).where(
+            UserConnection.id == body.connection_id,
+            UserConnection.user_id == current_user.id,
+        )
+    )
+    connection = conn_result.scalar_one_or_none()
+    if not connection:
+        raise HTTPException(status_code=404, detail="Connection not found")
+
+    target_user_id = connection.connected_user_id
+
+    # W-03: Verify bidirectional connection still active
+    reverse_conn = await db.execute(
+        select(UserConnection.id).where(
+            UserConnection.user_id == target_user_id,
+            UserConnection.connected_user_id == current_user.id,
+        )
+    )
+    if not reverse_conn.scalar_one_or_none():
+        raise HTTPException(status_code=400, detail="Connection is no longer active")
+
+    if target_user_id == calendar.user_id:
+        raise HTTPException(status_code=400, detail="Cannot invite the calendar owner")
+
+    target_result = await db.execute(
+        select(User).where(User.id == target_user_id)
+    )
+    target = target_result.scalar_one_or_none()
+    if not target or not target.is_active:
+        raise HTTPException(status_code=404, detail="Target user not found or inactive")
+
+    existing = await db.execute(
+        select(CalendarMember).where(
+            CalendarMember.calendar_id == cal_id,
+            CalendarMember.user_id == target_user_id,
+        )
+    )
+    if existing.scalar_one_or_none():
+        raise HTTPException(status_code=409, detail="User already invited or is a member")
+
+    pending_count = await db.scalar(
+        select(func.count())
+        .select_from(CalendarMember)
+        .where(
+            CalendarMember.calendar_id == cal_id,
+            CalendarMember.status == "pending",
+        )
+    ) or 0
+    if pending_count >= PENDING_INVITE_CAP:
+        raise HTTPException(status_code=429, detail="Too many pending invites for this calendar")
+
+    if not calendar.is_shared:
+        calendar.is_shared = True
+
+    new_member = CalendarMember(
+        calendar_id=cal_id,
+        user_id=target_user_id,
+        invited_by=current_user.id,
+        permission=body.permission,
+        can_add_others=body.can_add_others,
+        status="pending",
+    )
+    db.add(new_member)
+    await db.flush()
+
+    inviter_settings = await _get_settings_for_user(db, current_user.id)
+    inviter_display = (inviter_settings.preferred_name if inviter_settings else None) or current_user.umbral_name
+
+    cal_name = calendar.name
+    await create_notification(
+        db,
+        user_id=target_user_id,
+        type="calendar_invite",
+        title="Calendar Invite",
+        message=f"{inviter_display} invited you to '{cal_name}'",
+        data={"calendar_id": cal_id, "calendar_name": cal_name},
+        source_type="calendar_invite",
+        source_id=new_member.id,
+    )
+
+    await log_audit_event(
+        db,
+        action="calendar.invite_sent",
+        actor_id=current_user.id,
+        target_id=target_user_id,
+        detail={
+            "calendar_id": cal_id,
+            "calendar_name": cal_name,
+            "permission": body.permission,
+        },
+        ip=get_client_ip(request),
+    )
+
+    response = {
+        "message": "Invite sent",
+        "member_id": new_member.id,
+        "calendar_id": cal_id,
+    }
+
+    await db.commit()
+    return response
+
+
+# -- PUT /invites/{id}/respond — Accept or reject -------------------------
+
+@router.put("/invites/{invite_id}/respond")
+async def respond_to_invite(
+    body: RespondInviteRequest,
+    request: Request,
+    invite_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Accept or reject a calendar invite."""
+    result = await db.execute(
+        select(CalendarMember)
+        .where(
+            CalendarMember.id == invite_id,
+            CalendarMember.user_id == current_user.id,
+            CalendarMember.status == "pending",
+        )
+        .options(selectinload(CalendarMember.calendar))
+    )
+    invite = result.scalar_one_or_none()
+    if not invite:
+        raise HTTPException(status_code=404, detail="Invite not found or already resolved")
+
+    calendar_name = invite.calendar.name if invite.calendar else "Unknown"
+    calendar_owner_id = invite.calendar.user_id if invite.calendar else None
+    inviter_id = invite.invited_by
+
+    if body.action == "accept":
+        invite.status = "accepted"
+        invite.accepted_at = datetime.now()
+
+        notify_user_id = inviter_id or calendar_owner_id
+        if notify_user_id:
+            user_settings = await _get_settings_for_user(db, current_user.id)
+            display = (user_settings.preferred_name if user_settings else None) or current_user.umbral_name
+            await create_notification(
+                db,
+                user_id=notify_user_id,
+                type="calendar_invite_accepted",
+                title="Invite Accepted",
+                message=f"{display} accepted your invite to '{calendar_name}'",
+                data={"calendar_id": invite.calendar_id},
+                source_type="calendar_invite",
+                source_id=invite.id,
+            )
+
+        await log_audit_event(
+            db,
+            action="calendar.invite_accepted",
+            actor_id=current_user.id,
+            detail={"calendar_id": invite.calendar_id, "calendar_name": calendar_name},
+            ip=get_client_ip(request),
+        )
+
+        await db.commit()
+        return {"message": "Invite accepted"}
+
+    else:
+        member_id = invite.id
+        calendar_id = invite.calendar_id
+
+        notify_user_id = inviter_id or calendar_owner_id
+        if notify_user_id:
+            user_settings = await _get_settings_for_user(db, current_user.id)
+            display = (user_settings.preferred_name if user_settings else None) or current_user.umbral_name
+            await create_notification(
+                db,
+                user_id=notify_user_id,
+                type="calendar_invite_rejected",
+                title="Invite Rejected",
+                message=f"{display} declined your invite to '{calendar_name}'",
+                data={"calendar_id": calendar_id},
+                source_type="calendar_invite",
+                source_id=member_id,
+            )
+
+        await log_audit_event(
+            db,
+            action="calendar.invite_rejected",
+            actor_id=current_user.id,
+            detail={"calendar_id": calendar_id, "calendar_name": calendar_name},
+            ip=get_client_ip(request),
+        )
+
+        await db.delete(invite)
+        await db.commit()
+        return {"message": "Invite rejected"}
+
+
+# -- GET /invites/incoming — Pending invites -------------------------------
+
+@router.get("/invites/incoming", response_model=list[CalendarInviteResponse])
+async def get_incoming_invites(
+    page: int = Query(1, ge=1),
+    per_page: int = Query(20, ge=1, le=100),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """List pending calendar invites for the current user."""
+    offset = (page - 1) * per_page
+    result = await db.execute(
+        select(CalendarMember)
+        .where(
+            CalendarMember.user_id == current_user.id,
+            CalendarMember.status == "pending",
+        )
+        .options(
+            selectinload(CalendarMember.calendar),
+            selectinload(CalendarMember.inviter),
+        )
+        .order_by(CalendarMember.invited_at.desc())
+        .offset(offset)
+        .limit(per_page)
+    )
+    invites = result.scalars().all()
+
+    # Batch-fetch owner names to avoid N+1
+    owner_ids = list({inv.calendar.user_id for inv in invites if inv.calendar})
+    if owner_ids:
+        owner_result = await db.execute(
+            select(User.id, User.umbral_name).where(User.id.in_(owner_ids))
+        )
+        owner_names = {row.id: row.umbral_name for row in owner_result.all()}
+    else:
+        owner_names = {}
+
+    responses = []
+    for inv in invites:
+        owner_name = owner_names.get(inv.calendar.user_id, "") if inv.calendar else ""
+
+        responses.append(CalendarInviteResponse(
+            id=inv.id,
+            calendar_id=inv.calendar_id,
+            calendar_name=inv.calendar.name if inv.calendar else "",
+            calendar_color=inv.calendar.color if inv.calendar else "",
+            owner_umbral_name=owner_name,
+            inviter_umbral_name=inv.inviter.umbral_name if inv.inviter else "",
+            permission=inv.permission,
+            invited_at=inv.invited_at,
+        ))
+
+    return responses
+
+
+# -- GET /{cal_id}/members — Member list -----------------------------------
+
+@router.get("/{cal_id}/members", response_model=list[CalendarMemberResponse])
+async def list_members(
+    cal_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """List all members of a shared calendar. Requires membership or ownership."""
+    perm = await get_user_permission(db, cal_id, current_user.id)
+    if perm is None:
+        raise HTTPException(status_code=404, detail="Calendar not found")
+
+    result = await db.execute(
+        select(CalendarMember)
+        .where(CalendarMember.calendar_id == cal_id)
+        .options(selectinload(CalendarMember.user))
+        .order_by(CalendarMember.invited_at.asc())
+    )
+    members = result.scalars().all()
+
+    user_ids = [m.user_id for m in members]
+    if user_ids:
+        settings_result = await db.execute(
+            select(Settings.user_id, Settings.preferred_name)
+            .where(Settings.user_id.in_(user_ids))
+        )
+        pref_names = {row.user_id: row.preferred_name for row in settings_result.all()}
+    else:
+        pref_names = {}
+
+    responses = []
+    for m in members:
+        resp = _build_member_response(m)
+        resp["preferred_name"] = pref_names.get(m.user_id)
+        responses.append(resp)
+
+    return responses
+
+
+# -- PUT /{cal_id}/members/{mid} — Update permission (owner only) ----------
+
+@router.put("/{cal_id}/members/{member_id}")
+async def update_member(
+    body: UpdateMemberRequest,
+    request: Request,
+    cal_id: int = Path(ge=1, le=2147483647),
+    member_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Update a member permission or can_add_others. Owner only."""
+    cal_result = await db.execute(
+        select(Calendar).where(Calendar.id == cal_id, Calendar.user_id == current_user.id)
+    )
+    if not cal_result.scalar_one_or_none():
+        raise HTTPException(status_code=403, detail="Only the calendar owner can update members")
+
+    member_result = await db.execute(
+        select(CalendarMember).where(
+            CalendarMember.id == member_id,
+            CalendarMember.calendar_id == cal_id,
+        )
+    )
+    member = member_result.scalar_one_or_none()
+    if not member:
+        raise HTTPException(status_code=404, detail="Member not found")
+
+    update_data = body.model_dump(exclude_unset=True)
+    if not update_data:
+        raise HTTPException(status_code=400, detail="No fields to update")
+
+    if "permission" in update_data:
+        member.permission = update_data["permission"]
+    if "can_add_others" in update_data:
+        member.can_add_others = update_data["can_add_others"]
+
+    await log_audit_event(
+        db,
+        action="calendar.member_updated",
+        actor_id=current_user.id,
+        target_id=member.user_id,
+        detail={"calendar_id": cal_id, "member_id": member_id, "changes": update_data},
+        ip=get_client_ip(request),
+    )
+
+    await db.commit()
+    return {"message": "Member updated"}
+
+
+# -- DELETE /{cal_id}/members/{mid} — Remove member or leave ---------------
+
+@router.delete("/{cal_id}/members/{member_id}", status_code=204)
+async def remove_member(
+    request: Request,
+    cal_id: int = Path(ge=1, le=2147483647),
+    member_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Remove a member or leave a shared calendar."""
+    member_result = await db.execute(
+        select(CalendarMember).where(
+            CalendarMember.id == member_id,
+            CalendarMember.calendar_id == cal_id,
+        )
+    )
+    member = member_result.scalar_one_or_none()
+    if not member:
+        raise HTTPException(status_code=404, detail="Member not found")
+
+    cal_result = await db.execute(
+        select(Calendar).where(Calendar.id == cal_id)
+    )
+    calendar = cal_result.scalar_one_or_none()
+
+    is_self = member.user_id == current_user.id
+    is_owner = calendar and calendar.user_id == current_user.id
+
+    if not is_self and not is_owner:
+        raise HTTPException(status_code=403, detail="Only the calendar owner can remove other members")
+
+    target_user_id = member.user_id
+
+    await db.execute(
+        delete(EventLock).where(
+            EventLock.locked_by == target_user_id,
+            EventLock.event_id.in_(
+                select(CalendarEvent.id).where(CalendarEvent.calendar_id == cal_id)
+            ),
+        )
+    )
+
+    await db.delete(member)
+
+    remaining = await db.execute(
+        select(CalendarMember.id).where(CalendarMember.calendar_id == cal_id).limit(1)
+    )
+    if not remaining.scalar_one_or_none() and calendar:
+        calendar.is_shared = False
+
+    action = "calendar.member_left" if is_self else "calendar.member_removed"
+    await log_audit_event(
+        db,
+        action=action,
+        actor_id=current_user.id,
+        target_id=target_user_id,
+        detail={"calendar_id": cal_id, "member_id": member_id},
+        ip=get_client_ip(request),
+    )
+
+    await db.commit()
+    return None
+
+
+# -- PUT /{cal_id}/members/me/color — Update local color -------------------
+
+@router.put("/{cal_id}/members/me/color")
+async def update_local_color(
+    body: UpdateLocalColorRequest,
+    cal_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Update the current user local color for a shared calendar."""
+    member_result = await db.execute(
+        select(CalendarMember).where(
+            CalendarMember.calendar_id == cal_id,
+            CalendarMember.user_id == current_user.id,
+            CalendarMember.status == "accepted",
+        )
+    )
+    member = member_result.scalar_one_or_none()
+    if not member:
+        raise HTTPException(status_code=404, detail="Membership not found")
+
+    member.local_color = body.local_color
+    await db.commit()
+    return {"message": "Color updated"}
+
+
+# -- GET /sync — Sync endpoint ---------------------------------------------
+
+@router.get("/sync", response_model=SyncResponse)
+async def sync_shared_calendars(
+    since: datetime = Query(...),
+    calendar_ids: Optional[str] = Query(None, description="Comma-separated calendar IDs"),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Sync events and member changes since a given timestamp. Cap 500 events."""
+    MAX_EVENTS = 500
+
+    # Cap since to 7 days ago to prevent unbounded scans
+    floor = datetime.now() - timedelta(days=7)
+    if since < floor:
+        since = floor
+
+    cal_id_list: list[int] = []
+    if calendar_ids:
+        for part in calendar_ids.split(","):
+            part = part.strip()
+            if part.isdigit():
+                cal_id_list.append(int(part))
+    cal_id_list = cal_id_list[:50]  # Cap to prevent unbounded IN clause
+
+    owned_ids_result = await db.execute(
+        select(Calendar.id).where(Calendar.user_id == current_user.id)
+    )
+    owned_ids = {row[0] for row in owned_ids_result.all()}
+
+    member_ids_result = await db.execute(
+        select(CalendarMember.calendar_id).where(
+            CalendarMember.user_id == current_user.id,
+            CalendarMember.status == "accepted",
+        )
+    )
+    member_ids = {row[0] for row in member_ids_result.all()}
+
+    accessible = owned_ids | member_ids
+    if cal_id_list:
+        accessible = accessible & set(cal_id_list)
+
+    if not accessible:
+        return SyncResponse(events=[], member_changes=[], server_time=datetime.now())
+
+    accessible_list = list(accessible)
+
+    events_result = await db.execute(
+        select(CalendarEvent)
+        .where(
+            CalendarEvent.calendar_id.in_(accessible_list),
+            CalendarEvent.updated_at >= since,
+        )
+        .options(selectinload(CalendarEvent.calendar))
+        .order_by(CalendarEvent.updated_at.desc())
+        .limit(MAX_EVENTS + 1)
+    )
+    events = events_result.scalars().all()
+    truncated = len(events) > MAX_EVENTS
+    events = events[:MAX_EVENTS]
+
+    event_dicts = []
+    for e in events:
+        event_dicts.append({
+            "id": e.id,
+            "title": e.title,
+            "start_datetime": e.start_datetime.isoformat() if e.start_datetime else None,
+            "end_datetime": e.end_datetime.isoformat() if e.end_datetime else None,
+            "all_day": e.all_day,
+            "calendar_id": e.calendar_id,
+            "calendar_name": e.calendar.name if e.calendar else "",
+            "updated_at": e.updated_at.isoformat() if e.updated_at else None,
+            "updated_by": e.updated_by,
+        })
+
+    members_result = await db.execute(
+        select(CalendarMember)
+        .where(
+            CalendarMember.calendar_id.in_(accessible_list),
+            (CalendarMember.invited_at >= since) | (CalendarMember.accepted_at >= since),
+        )
+        .options(selectinload(CalendarMember.user))
+    )
+    member_changes = members_result.scalars().all()
+
+    member_dicts = []
+    for m in member_changes:
+        member_dicts.append({
+            "id": m.id,
+            "calendar_id": m.calendar_id,
+            "user_id": m.user_id,
+            "umbral_name": m.user.umbral_name if m.user else "",
+            "permission": m.permission,
+            "status": m.status,
+            "invited_at": m.invited_at.isoformat() if m.invited_at else None,
+            "accepted_at": m.accepted_at.isoformat() if m.accepted_at else None,
+        })
+
+    return SyncResponse(
+        events=event_dicts,
+        member_changes=member_dicts,
+        server_time=datetime.now(),
+        truncated=truncated,
+    )
+
+
+# -- Event Lock Endpoints --------------------------------------------------
+
+@router.post("/events/{event_id}/lock")
+async def lock_event(
+    event_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Acquire a 5-minute editing lock on an event."""
+    event_result = await db.execute(
+        select(CalendarEvent).where(CalendarEvent.id == event_id)
+    )
+    event = event_result.scalar_one_or_none()
+    if not event:
+        raise HTTPException(status_code=404, detail="Event not found")
+
+    await require_permission(db, event.calendar_id, current_user.id, "create_modify")
+
+    lock = await acquire_lock(db, event_id, current_user.id)
+
+    # Build response BEFORE commit — ORM objects expire after commit
+    response = {
+        "locked": True,
+        "locked_by_name": current_user.umbral_name,
+        "expires_at": lock.expires_at,
+        "is_permanent": lock.is_permanent,
+    }
+
+    await db.commit()
+    return response
+
+
+@router.delete("/events/{event_id}/lock", status_code=204)
+async def unlock_event(
+    event_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Release a lock. Only the holder or calendar owner can release."""
+    event_result = await db.execute(
+        select(CalendarEvent).where(CalendarEvent.id == event_id)
+    )
+    event = event_result.scalar_one_or_none()
+    if not event:
+        raise HTTPException(status_code=404, detail="Event not found")
+
+    # SC-01: Verify caller has access to this calendar before revealing lock state
+    perm = await get_user_permission(db, event.calendar_id, current_user.id)
+    if perm is None:
+        raise HTTPException(status_code=404, detail="Event not found")
+
+    lock_result = await db.execute(
+        select(EventLock).where(EventLock.event_id == event_id)
+    )
+    lock = lock_result.scalar_one_or_none()
+    if not lock:
+        return None
+
+    cal_result = await db.execute(
+        select(Calendar).where(Calendar.id == event.calendar_id)
+    )
+    calendar = cal_result.scalar_one_or_none()
+    is_owner = calendar and calendar.user_id == current_user.id
+
+    if lock.locked_by != current_user.id and not is_owner:
+        raise HTTPException(status_code=403, detail="Only the lock holder or calendar owner can release")
+
+    await db.delete(lock)
+    await db.commit()
+    return None
+
+
+@router.get("/events/{event_id}/lock", response_model=LockStatusResponse)
+async def get_lock_status(
+    event_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Get the lock status of an event."""
+    event_result = await db.execute(
+        select(CalendarEvent).where(CalendarEvent.id == event_id)
+    )
+    event = event_result.scalar_one_or_none()
+    if not event:
+        raise HTTPException(status_code=404, detail="Event not found")
+
+    perm = await get_user_permission(db, event.calendar_id, current_user.id)
+    if perm is None:
+        raise HTTPException(status_code=404, detail="Event not found")
+
+    lock_result = await db.execute(
+        select(EventLock)
+        .where(EventLock.event_id == event_id)
+        .options(selectinload(EventLock.holder))
+    )
+    lock = lock_result.scalar_one_or_none()
+
+    if not lock:
+        return LockStatusResponse(locked=False)
+
+    now = datetime.now()
+    if not lock.is_permanent and lock.expires_at and lock.expires_at < now:
+        await db.delete(lock)
+        await db.commit()
+        return LockStatusResponse(locked=False)
+
+    return LockStatusResponse(
+        locked=True,
+        locked_by_name=lock.holder.umbral_name if lock.holder else None,
+        expires_at=lock.expires_at,
+        is_permanent=lock.is_permanent,
+    )
+
+
+@router.post("/events/{event_id}/owner-lock")
+async def set_permanent_lock(
+    event_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Set a permanent lock on an event. Calendar owner only."""
+    event_result = await db.execute(
+        select(CalendarEvent).where(CalendarEvent.id == event_id)
+    )
+    event = event_result.scalar_one_or_none()
+    if not event:
+        raise HTTPException(status_code=404, detail="Event not found")
+
+    cal_result = await db.execute(
+        select(Calendar).where(Calendar.id == event.calendar_id, Calendar.user_id == current_user.id)
+    )
+    if not cal_result.scalar_one_or_none():
+        raise HTTPException(status_code=403, detail="Only the calendar owner can set permanent locks")
+
+    now = datetime.now()
+    await db.execute(
+        text("""
+            INSERT INTO event_locks (event_id, locked_by, locked_at, expires_at, is_permanent)
+            VALUES (:event_id, :user_id, :now, NULL, true)
+            ON CONFLICT (event_id)
+            DO UPDATE SET
+                locked_by = :user_id,
+                locked_at = :now,
+                expires_at = NULL,
+                is_permanent = true
+        """),
+        {"event_id": event_id, "user_id": current_user.id, "now": now},
+    )
+
+    await db.commit()
+    return {"message": "Permanent lock set", "is_permanent": True}
+
+
+@router.delete("/events/{event_id}/owner-lock", status_code=204)
+async def remove_permanent_lock(
+    event_id: int = Path(ge=1, le=2147483647),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Remove a permanent lock. Calendar owner only."""
+    event_result = await db.execute(
+        select(CalendarEvent).where(CalendarEvent.id == event_id)
+    )
+    event = event_result.scalar_one_or_none()
+    if not event:
+        raise HTTPException(status_code=404, detail="Event not found")
+
+    cal_result = await db.execute(
+        select(Calendar).where(Calendar.id == event.calendar_id, Calendar.user_id == current_user.id)
+    )
+    if not cal_result.scalar_one_or_none():
+        raise HTTPException(status_code=403, detail="Only the calendar owner can remove permanent locks")
+
+    await db.execute(
+        delete(EventLock).where(
+            EventLock.event_id == event_id,
+            EventLock.is_permanent == True,
+        )
+    )
+
+    await db.commit()
+    return None

backend/app/routers/totp.py

@@ -17,10 +17,10 @@ Security:
   - Failed TOTP attempts increment user.failed_login_count (shared lockout counter)
   - totp-verify uses mfa_token (not session cookie) — user is not yet authenticated
 """
-import uuid
+import asyncio
 import secrets
 import logging
-from datetime import datetime, timedelta
+from datetime import datetime
 from typing import Optional
 
 from fastapi import APIRouter, Depends, HTTPException, Request, Response
@@ -31,17 +31,21 @@ from sqlalchemy.exc import IntegrityError
 
 from app.database import get_db
 from app.models.user import User
-from app.models.session import UserSession
 from app.models.totp_usage import TOTPUsage
 from app.models.backup_code import BackupCode
-from app.routers.auth import get_current_user, _set_session_cookie
+from app.routers.auth import get_current_user
 from app.services.audit import get_client_ip
 from app.services.auth import (
-    verify_password_with_upgrade,
-    hash_password,
+    averify_password_with_upgrade,
     verify_mfa_token,
     verify_mfa_enforce_token,
-    create_session_token,
+)
+from app.services.session import (
+    create_db_session,
+    set_session_cookie,
+    check_account_lockout,
+    record_failed_login,
+    record_successful_login,
 )
 from app.services.totp import (
     generate_totp_secret,
@@ -52,7 +56,7 @@ from app.services.totp import (
     generate_qr_base64,
     generate_backup_codes,
 )
-from app.config import settings as app_settings
+
 
 # Argon2id for backup code hashing — treat each code like a password
 from argon2 import PasswordHasher
@@ -117,8 +121,10 @@ class EnforceConfirmRequest(BaseModel):
 
 async def _store_backup_codes(db: AsyncSession, user_id: int, plaintext_codes: list[str]) -> None:
     """Hash and insert backup codes for the given user."""
+    # AC-2: Run Argon2id hashing in executor to avoid blocking event loop
+    loop = asyncio.get_running_loop()
     for code in plaintext_codes:
-        code_hash = _ph.hash(code)
+        code_hash = await loop.run_in_executor(None, _ph.hash, code)
         db.add(BackupCode(user_id=user_id, code_hash=code_hash))
     await db.commit()
 
@@ -145,9 +151,12 @@ async def _verify_backup_code(
     )
     unused_codes = result.scalars().all()
 
+    # AC-2: Run Argon2id verification in executor to avoid blocking event loop
+    loop = asyncio.get_running_loop()
     for record in unused_codes:
         try:
-            if _ph.verify(record.code_hash, submitted_code):
+            matched = await loop.run_in_executor(None, _ph.verify, record.code_hash, submitted_code)
+            if matched:
                 record.used_at = datetime.now()
                 await db.commit()
                 return True
@@ -157,29 +166,6 @@ async def _verify_backup_code(
     return False
 
 
-async def _create_full_session(
-    db: AsyncSession,
-    user: User,
-    request: Request,
-) -> str:
-    """Create a UserSession row and return the signed cookie token."""
-    session_id = uuid.uuid4().hex
-    expires_at = datetime.now() + timedelta(days=app_settings.SESSION_MAX_AGE_DAYS)
-    ip = get_client_ip(request)
-    user_agent = request.headers.get("user-agent")
-
-    db_session = UserSession(
-        id=session_id,
-        user_id=user.id,
-        expires_at=expires_at,
-        ip_address=ip[:45] if ip else None,
-        user_agent=(user_agent or "")[:255] if user_agent else None,
-    )
-    db.add(db_session)
-    await db.commit()
-    return create_session_token(user.id, session_id)
-
-
 # ---------------------------------------------------------------------------
 # Routes
 # ---------------------------------------------------------------------------
@@ -283,60 +269,55 @@ async def totp_verify(
         raise HTTPException(status_code=400, detail="TOTP not configured for this account")
 
     # Check account lockout (shared counter with password failures)
-    if user.locked_until and datetime.now() < user.locked_until:
-        remaining = int((user.locked_until - datetime.now()).total_seconds() / 60) + 1
-        raise HTTPException(
-            status_code=423,
-            detail=f"Account locked. Try again in {remaining} minutes.",
-        )
+    await check_account_lockout(user)
 
     # --- Backup code path ---
     if data.backup_code:
         normalized = data.backup_code.strip().upper()
         valid = await _verify_backup_code(db, user.id, normalized)
         if not valid:
-            user.failed_login_count += 1
-            if user.failed_login_count >= 10:
-                user.locked_until = datetime.now() + timedelta(minutes=30)
+            remaining = await record_failed_login(db, user)
             await db.commit()
+            if remaining == 0:
+                raise HTTPException(status_code=401, detail="Account temporarily locked. Try again in 30 minutes.")
             raise HTTPException(status_code=401, detail="Invalid backup code")
 
         # Backup code accepted — reset lockout counter and issue session
-        user.failed_login_count = 0
-        user.locked_until = None
-        user.last_login_at = datetime.now()
-        await db.commit()
+        await record_successful_login(db, user)
 
-        token = await _create_full_session(db, user, request)
-        _set_session_cookie(response, token)
+        ip = get_client_ip(request)
+        user_agent = request.headers.get("user-agent")
+        _, token = await create_db_session(db, user, ip, user_agent)
+        set_session_cookie(response, token)
+        await db.commit()
         return {"authenticated": True}
 
     # --- TOTP code path ---
     matched_window = verify_totp_code(user.totp_secret, data.code)
     if matched_window is None:
-        user.failed_login_count += 1
-        if user.failed_login_count >= 10:
-            user.locked_until = datetime.now() + timedelta(minutes=30)
+        remaining = await record_failed_login(db, user)
         await db.commit()
+        if remaining == 0:
+            raise HTTPException(status_code=401, detail="Account temporarily locked. Try again in 30 minutes.")
         raise HTTPException(status_code=401, detail="Invalid code")
 
     # Replay prevention — record (user_id, code, actual_matching_window)
     totp_record = TOTPUsage(user_id=user.id, code=data.code, window=matched_window)
     db.add(totp_record)
     try:
-        await db.commit()
+        await db.flush()
     except IntegrityError:
         await db.rollback()
         raise HTTPException(status_code=401, detail="Code already used — wait for the next code")
 
     # Success — reset lockout counter, update last_login_at, issue full session
-    user.failed_login_count = 0
-    user.locked_until = None
-    user.last_login_at = datetime.now()
-    await db.commit()
+    await record_successful_login(db, user)
 
-    token = await _create_full_session(db, user, request)
-    _set_session_cookie(response, token)
+    ip = get_client_ip(request)
+    user_agent = request.headers.get("user-agent")
+    _, token = await create_db_session(db, user, ip, user_agent)
+    set_session_cookie(response, token)
+    await db.commit()
     return {"authenticated": True}
 
 
@@ -355,7 +336,8 @@ async def totp_disable(
         raise HTTPException(status_code=400, detail="TOTP is not enabled")
 
     # Verify password (handles bcrypt→Argon2id upgrade transparently)
-    valid, new_hash = verify_password_with_upgrade(data.password, current_user.password_hash)
+    # AC-2: async wrapper to avoid blocking event loop
+    valid, new_hash = await averify_password_with_upgrade(data.password, current_user.password_hash)
     if not valid:
         raise HTTPException(status_code=401, detail="Invalid password")
 
@@ -391,7 +373,8 @@ async def regenerate_backup_codes(
     if not current_user.totp_enabled:
         raise HTTPException(status_code=400, detail="TOTP is not enabled")
 
-    valid, new_hash = verify_password_with_upgrade(data.password, current_user.password_hash)
+    # AC-2: async wrapper to avoid blocking event loop
+    valid, new_hash = await averify_password_with_upgrade(data.password, current_user.password_hash)
     if not valid:
         raise HTTPException(status_code=401, detail="Invalid password")
 
@@ -506,9 +489,11 @@ async def enforce_confirm_totp(
     user.last_login_at = datetime.now()
     await db.commit()
 
-    # Issue a full session
-    token = await _create_full_session(db, user, request)
-    _set_session_cookie(response, token)
+    # Issue a full session (now uses shared session service with cap enforcement)
+    ip = get_client_ip(request)
+    user_agent = request.headers.get("user-agent")
+    _, token = await create_db_session(db, user, ip, user_agent)
+    set_session_cookie(response, token)
 
     return {"authenticated": True}
 

backend/app/schemas/admin.py

@@ -30,6 +30,7 @@ class UserListItem(BaseModel):
     last_password_change_at: Optional[datetime] = None
     totp_enabled: bool
     mfa_enforce_pending: bool
+    passwordless_enabled: bool = False
     created_at: datetime
     active_sessions: int = 0
 
@@ -107,6 +108,7 @@ class ToggleMfaEnforceRequest(BaseModel):
 class SystemConfigResponse(BaseModel):
     allow_registration: bool
     enforce_mfa_new_users: bool
+    allow_passwordless: bool = False
 
     model_config = ConfigDict(from_attributes=True)
 
@@ -115,6 +117,12 @@ class SystemConfigUpdate(BaseModel):
     model_config = ConfigDict(extra="forbid")
     allow_registration: Optional[bool] = None
     enforce_mfa_new_users: Optional[bool] = None
+    allow_passwordless: Optional[bool] = None
+
+
+class TogglePasswordlessRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    enabled: bool
 
 
 # ---------------------------------------------------------------------------

backend/app/schemas/calendar.py

@@ -25,7 +25,13 @@ class CalendarResponse(BaseModel):
     is_default: bool
     is_system: bool
     is_visible: bool
+    is_shared: bool = False
     created_at: datetime
     updated_at: datetime
+    owner_umbral_name: Optional[str] = None
+    my_permission: Optional[str] = None
+    my_can_add_others: bool = False
+    my_local_color: Optional[str] = None
+    member_count: int = 0
 
     model_config = ConfigDict(from_attributes=True)

backend/app/schemas/calendar_event.py

@@ -1,6 +1,6 @@
 import json as _json
 
-from pydantic import BaseModel, ConfigDict, Field, field_validator
+from pydantic import BaseModel, ConfigDict, Field, field_validator, model_validator
 from datetime import datetime
 from typing import Literal, Optional
 
@@ -17,6 +17,20 @@ class RecurrenceRule(BaseModel):
     # monthly_date
     day: Optional[int] = Field(None, ge=1, le=31)
 
+    @model_validator(mode="after")
+    def validate_required_fields(self):
+        """Enforce required fields per rule type."""
+        if self.type == "every_n_days" and self.interval is None:
+            raise ValueError("every_n_days rule requires 'interval'")
+        if self.type == "weekly" and self.weekday is None:
+            raise ValueError("weekly rule requires 'weekday'")
+        if self.type == "monthly_nth_weekday":
+            if self.week is None or self.weekday is None:
+                raise ValueError("monthly_nth_weekday rule requires both 'week' and 'weekday'")
+        if self.type == "monthly_date" and self.day is None:
+            raise ValueError("monthly_date rule requires 'day'")
+        return self
+
 
 def _coerce_recurrence_rule(v):
     """Accept None, dict, RecurrenceRule, or JSON/legacy strings gracefully."""
@@ -47,10 +61,10 @@ class CalendarEventCreate(BaseModel):
     end_datetime: datetime
     all_day: bool = False
     color: Optional[str] = Field(None, max_length=20)
-    location_id: Optional[int] = None
+    location_id: Optional[int] = Field(None, ge=1, le=2147483647)
     recurrence_rule: Optional[RecurrenceRule] = None
     is_starred: bool = False
-    calendar_id: Optional[int] = None  # If None, server assigns default calendar
+    calendar_id: Optional[int] = Field(None, ge=1, le=2147483647)
 
     @field_validator("recurrence_rule", mode="before")
     @classmethod
@@ -67,10 +81,10 @@ class CalendarEventUpdate(BaseModel):
     end_datetime: Optional[datetime] = None
     all_day: Optional[bool] = None
     color: Optional[str] = Field(None, max_length=20)
-    location_id: Optional[int] = None
+    location_id: Optional[int] = Field(None, ge=1, le=2147483647)
     recurrence_rule: Optional[RecurrenceRule] = None
     is_starred: Optional[bool] = None
-    calendar_id: Optional[int] = None
+    calendar_id: Optional[int] = Field(None, ge=1, le=2147483647)
     # Controls which occurrences an edit applies to; absent = non-recurring or whole-series
     edit_scope: Optional[Literal["this", "this_and_future"]] = None
 

backend/app/schemas/event_invitation.py

@@ -0,0 +1,43 @@
+from typing import Annotated, Literal, Optional
+from datetime import datetime
+
+from pydantic import BaseModel, ConfigDict, Field
+
+
+class EventInvitationCreate(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    user_ids: list[Annotated[int, Field(ge=1, le=2147483647)]] = Field(..., min_length=1, max_length=20)
+
+
+class EventInvitationRespond(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    status: Literal["accepted", "tentative", "declined"]
+
+
+class EventInvitationOverrideCreate(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    status: Literal["accepted", "tentative", "declined"]
+
+
+class UpdateDisplayCalendar(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    calendar_id: Annotated[int, Field(ge=1, le=2147483647)]
+
+
+class UpdateCanModify(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    can_modify: bool
+
+
+class EventInvitationResponse(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+    id: int
+    event_id: int
+    user_id: int
+    invited_by: Optional[int]
+    status: str
+    invited_at: datetime
+    responded_at: Optional[datetime]
+    invitee_name: Optional[str] = None
+    invitee_umbral_name: Optional[str] = None
+    can_modify: bool = False

backend/app/schemas/project.py

@@ -1,8 +1,11 @@
-from pydantic import BaseModel, ConfigDict, Field
+import logging
+from pydantic import BaseModel, ConfigDict, Field, model_validator
 from datetime import datetime, date
 from typing import Optional, List, Literal
 from app.schemas.project_task import ProjectTaskResponse
 
+logger = logging.getLogger(__name__)
+
 ProjectStatus = Literal["not_started", "in_progress", "completed", "blocked", "review", "on_hold"]
 
 
@@ -30,18 +33,44 @@ class ProjectUpdate(BaseModel):
 
 class ProjectResponse(BaseModel):
     id: int
+    user_id: int = 0
     name: str
     description: Optional[str]
     status: str
     color: Optional[str]
     due_date: Optional[date]
     is_tracked: bool
+    member_count: int = 0
     created_at: datetime
     updated_at: datetime
     tasks: List[ProjectTaskResponse] = []
 
     model_config = ConfigDict(from_attributes=True)
 
+    @model_validator(mode="before")
+    @classmethod
+    def compute_member_count(cls, data):  # type: ignore[override]
+        """Compute member_count from eagerly loaded members relationship."""
+        if hasattr(data, "members"):
+            try:
+                data = dict(
+                    id=data.id,
+                    user_id=data.user_id,
+                    name=data.name,
+                    description=data.description,
+                    status=data.status,
+                    color=data.color,
+                    due_date=data.due_date,
+                    is_tracked=data.is_tracked,
+                    member_count=len([m for m in data.members if m.status == "accepted"]),
+                    created_at=data.created_at,
+                    updated_at=data.updated_at,
+                    tasks=data.tasks,
+                )
+            except Exception as exc:
+                logger.debug("member_count compute skipped: %s", exc)
+        return data
+
 
 class TrackedTaskResponse(BaseModel):
     id: int

backend/app/schemas/project_member.py

@@ -0,0 +1,43 @@
+from typing import Annotated, Optional, Literal
+from pydantic import BaseModel, ConfigDict, Field
+from datetime import datetime
+
+MemberPermission = Literal["read_only", "create_modify"]
+MemberStatus = Literal["pending", "accepted", "rejected"]
+InviteResponse = Literal["accepted", "rejected"]
+
+
+class ProjectMemberInvite(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+
+    user_ids: list[Annotated[int, Field(ge=1, le=2147483647)]] = Field(min_length=1, max_length=10)
+    permission: MemberPermission = "create_modify"
+
+
+class ProjectMemberUpdate(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+
+    permission: MemberPermission
+
+
+class ProjectMemberRespond(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+
+    response: InviteResponse
+
+
+class ProjectMemberResponse(BaseModel):
+    id: int
+    project_id: int
+    user_id: int
+    invited_by: int
+    permission: str
+    status: str
+    source: str
+    user_name: str | None = None
+    inviter_name: str | None = None
+    created_at: datetime
+    updated_at: datetime
+    accepted_at: datetime | None = None
+
+    model_config = ConfigDict(from_attributes=True)

backend/app/schemas/project_task.py

@@ -2,6 +2,7 @@ from pydantic import BaseModel, ConfigDict, Field
 from datetime import datetime, date
 from typing import Optional, List, Literal
 from app.schemas.task_comment import TaskCommentResponse
+from app.schemas.project_task_assignment import TaskAssignmentResponse
 
 TaskStatus = Literal["pending", "in_progress", "completed", "blocked", "review", "on_hold"]
 TaskPriority = Literal["none", "low", "medium", "high"]
@@ -30,6 +31,7 @@ class ProjectTaskUpdate(BaseModel):
     due_date: Optional[date] = None
     person_id: Optional[int] = None
     sort_order: Optional[int] = None
+    version: Optional[int] = None  # For optimistic locking
 
 
 class ProjectTaskResponse(BaseModel):
@@ -43,10 +45,12 @@ class ProjectTaskResponse(BaseModel):
     due_date: Optional[date]
     person_id: Optional[int]
     sort_order: int
+    version: int = 1
     created_at: datetime
     updated_at: datetime
     subtasks: List["ProjectTaskResponse"] = []
     comments: List[TaskCommentResponse] = []
+    assignments: List[TaskAssignmentResponse] = []
 
     model_config = ConfigDict(from_attributes=True)
 

backend/app/schemas/project_task_assignment.py

@@ -0,0 +1,31 @@
+from typing import Annotated
+from pydantic import BaseModel, ConfigDict, Field, model_validator
+from datetime import datetime
+
+
+class TaskAssignmentCreate(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+
+    user_ids: list[Annotated[int, Field(ge=1, le=2147483647)]] = Field(min_length=1, max_length=20)
+
+
+class TaskAssignmentResponse(BaseModel):
+    id: int
+    task_id: int
+    user_id: int
+    assigned_by: int
+    user_name: str | None = None
+    created_at: datetime
+
+    model_config = ConfigDict(from_attributes=True)
+
+    @model_validator(mode="before")
+    @classmethod
+    def resolve_user_name(cls, data):  # type: ignore[override]
+        """Populate user_name from eagerly loaded user relationship."""
+        if hasattr(data, "user") and data.user is not None and not getattr(data, "user_name", None):
+            # Build dict from ORM columns so new fields are auto-included
+            cols = {c.key: getattr(data, c.key) for c in data.__table__.columns}
+            cols["user_name"] = data.user.username
+            return cols
+        return data

backend/app/schemas/reminder.py

@@ -27,7 +27,7 @@ class ReminderUpdate(BaseModel):
 class ReminderSnooze(BaseModel):
     model_config = ConfigDict(extra="forbid")
 
-    minutes: Literal[5, 10, 15]
+    minutes: int = Field(ge=1, le=1440)
     client_now: Optional[datetime] = None
 
 

backend/app/schemas/shared_calendar.py

@@ -0,0 +1,76 @@
+import re
+from pydantic import BaseModel, ConfigDict, Field, field_validator
+from typing import Optional, Literal
+from datetime import datetime
+
+
+class InviteMemberRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    connection_id: int = Field(ge=1, le=2147483647)
+    permission: Literal["read_only", "create_modify", "full_access"]
+    can_add_others: bool = False
+
+
+class RespondInviteRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    action: Literal["accept", "reject"]
+
+
+class UpdateMemberRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    permission: Optional[Literal["read_only", "create_modify", "full_access"]] = None
+    can_add_others: Optional[bool] = None
+
+
+class UpdateLocalColorRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    local_color: Optional[str] = Field(None, max_length=20)
+
+    @field_validator("local_color")
+    @classmethod
+    def validate_color(cls, v: Optional[str]) -> Optional[str]:
+        if v is not None and not re.match(r"^#[0-9a-fA-F]{6}$", v):
+            raise ValueError("Color must be a hex color code (#RRGGBB)")
+        return v
+
+
+
+class CalendarMemberResponse(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+    id: int
+    calendar_id: int
+    user_id: int
+    umbral_name: str
+    preferred_name: Optional[str] = None
+    permission: str
+    can_add_others: bool
+    local_color: Optional[str] = None
+    status: str
+    invited_at: datetime
+    accepted_at: Optional[datetime] = None
+
+
+class CalendarInviteResponse(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+    id: int
+    calendar_id: int
+    calendar_name: str
+    calendar_color: str
+    owner_umbral_name: str
+    inviter_umbral_name: str
+    permission: str
+    invited_at: datetime
+
+
+class LockStatusResponse(BaseModel):
+    locked: bool
+    locked_by_name: Optional[str] = None
+    expires_at: Optional[datetime] = None
+    is_permanent: bool = False
+
+
+class SyncResponse(BaseModel):
+    events: list[dict]
+    member_changes: list[dict]
+    server_time: datetime
+    truncated: bool = False

backend/app/schemas/task_comment.py

@@ -1,4 +1,4 @@
-from pydantic import BaseModel, ConfigDict, Field
+from pydantic import BaseModel, ConfigDict, Field, model_validator
 from datetime import datetime
 
 
@@ -11,7 +11,19 @@ class TaskCommentCreate(BaseModel):
 class TaskCommentResponse(BaseModel):
     id: int
     task_id: int
+    user_id: int | None = None
+    author_name: str | None = None
     content: str
     created_at: datetime
 
     model_config = ConfigDict(from_attributes=True)
+
+    @model_validator(mode="before")
+    @classmethod
+    def resolve_author_name(cls, data):  # type: ignore[override]
+        """Populate author_name from eagerly loaded user relationship."""
+        if hasattr(data, "user") and data.user is not None and not getattr(data, "author_name", None):
+            cols = {c.key: getattr(data, c.key) for c in data.__table__.columns}
+            cols["author_name"] = data.user.username
+            return cols
+        return data

backend/app/services/auth.py

@@ -6,6 +6,8 @@ Password strategy:
 - Legacy bcrypt hashes (migrated from PIN auth): accepted on login, immediately
   rehashed to Argon2id on first successful use.
 """
+import asyncio
+
 from argon2 import PasswordHasher
 from argon2.exceptions import VerifyMismatchError, VerificationError, InvalidHashError
 from itsdangerous import URLSafeTimedSerializer, BadSignature, SignatureExpired
@@ -76,6 +78,28 @@ def verify_password_with_upgrade(password: str, hashed: str) -> tuple[bool, str
     return valid, new_hash
 
 
+# ---------------------------------------------------------------------------
+# Async wrappers — run CPU-bound Argon2id ops in a thread pool (AC-2/S-01)
+# ---------------------------------------------------------------------------
+
+async def ahash_password(password: str) -> str:
+    """Async wrapper for hash_password — runs Argon2id in executor."""
+    loop = asyncio.get_running_loop()
+    return await loop.run_in_executor(None, hash_password, password)
+
+
+async def averify_password(password: str, hashed: str) -> bool:
+    """Async wrapper for verify_password — runs Argon2id in executor."""
+    loop = asyncio.get_running_loop()
+    return await loop.run_in_executor(None, verify_password, password, hashed)
+
+
+async def averify_password_with_upgrade(password: str, hashed: str) -> tuple[bool, str | None]:
+    """Async wrapper for verify_password_with_upgrade — runs Argon2id in executor."""
+    loop = asyncio.get_running_loop()
+    return await loop.run_in_executor(None, verify_password_with_upgrade, password, hashed)
+
+
 # ---------------------------------------------------------------------------
 # Session tokens
 # ---------------------------------------------------------------------------

backend/app/services/calendar_sharing.py

@@ -0,0 +1,281 @@
+"""
+Calendar sharing service — permission checks, lock management, disconnect cascade.
+
+All functions accept an AsyncSession and do NOT commit — callers manage transactions.
+"""
+import logging
+from datetime import datetime, timedelta
+
+from fastapi import HTTPException
+from sqlalchemy import delete, literal_column, select, text, union_all, update
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.models.calendar import Calendar
+from app.models.calendar_member import CalendarMember
+from app.models.event_lock import EventLock
+
+logger = logging.getLogger(__name__)
+
+PERMISSION_RANK = {"read_only": 1, "create_modify": 2, "full_access": 3}
+LOCK_DURATION_MINUTES = 5
+
+
+async def get_accessible_calendar_ids(user_id: int, db: AsyncSession) -> list[int]:
+    """Return all calendar IDs the user can access (owned + accepted shared memberships)."""
+    result = await db.execute(
+        select(Calendar.id).where(Calendar.user_id == user_id)
+        .union(
+            select(CalendarMember.calendar_id).where(
+                CalendarMember.user_id == user_id,
+                CalendarMember.status == "accepted",
+            )
+        )
+    )
+    return [r[0] for r in result.all()]
+
+
+async def get_accessible_event_scope(
+    user_id: int, db: AsyncSession
+) -> tuple[list[int], list[int]]:
+    """
+    Returns (calendar_ids, invited_parent_event_ids) in a single DB round-trip.
+    calendar_ids: all calendars the user can access (owned + accepted shared).
+    invited_parent_event_ids: event IDs where the user has a non-declined invitation.
+    """
+    from app.models.event_invitation import EventInvitation
+
+    result = await db.execute(
+        union_all(
+            select(literal_column("'c'").label("kind"), Calendar.id.label("val"))
+            .where(Calendar.user_id == user_id),
+            select(literal_column("'c'"), CalendarMember.calendar_id)
+            .where(
+                CalendarMember.user_id == user_id,
+                CalendarMember.status == "accepted",
+            ),
+            select(literal_column("'i'"), EventInvitation.event_id)
+            .where(
+                EventInvitation.user_id == user_id,
+                EventInvitation.status != "declined",
+            ),
+        )
+    )
+    cal_ids: list[int] = []
+    inv_ids: list[int] = []
+    for kind, val in result.all():
+        if kind == "c":
+            cal_ids.append(val)
+        else:
+            inv_ids.append(val)
+    return cal_ids, inv_ids
+
+
+async def get_user_permission(db: AsyncSession, calendar_id: int, user_id: int) -> str | None:
+    """
+    Returns "owner" if the user owns the calendar, the permission string
+    if they are an accepted member, or None if they have no access.
+
+    AW-5: Single query with LEFT JOIN instead of 2 sequential queries.
+    """
+    result = await db.execute(
+        select(
+            Calendar.user_id,
+            CalendarMember.permission,
+        )
+        .outerjoin(
+            CalendarMember,
+            (CalendarMember.calendar_id == Calendar.id)
+            & (CalendarMember.user_id == user_id)
+            & (CalendarMember.status == "accepted"),
+        )
+        .where(Calendar.id == calendar_id)
+    )
+    row = result.one_or_none()
+    if not row:
+        return None
+    owner_id, member_permission = row.tuple()
+    if owner_id == user_id:
+        return "owner"
+    return member_permission
+
+
+async def require_permission(
+    db: AsyncSession, calendar_id: int, user_id: int, min_level: str
+) -> str:
+    """
+    Raises 403 if the user lacks at least min_level permission.
+    Returns the actual permission string (or "owner").
+    """
+    perm = await get_user_permission(db, calendar_id, user_id)
+    if perm is None:
+        raise HTTPException(status_code=404, detail="Calendar not found")
+    if perm == "owner":
+        return "owner"
+    if PERMISSION_RANK.get(perm, 0) < PERMISSION_RANK.get(min_level, 0):
+        raise HTTPException(status_code=403, detail="Insufficient permission on this calendar")
+    return perm
+
+
+async def acquire_lock(db: AsyncSession, event_id: int, user_id: int) -> EventLock:
+    """
+    Atomic INSERT ON CONFLICT — acquires a 5-minute lock on the event.
+    Only succeeds if no unexpired lock exists or the existing lock is held by the same user.
+    Permanent locks are never overwritten — if the same user holds one, it is returned as-is.
+    Returns the lock or raises 423 Locked.
+    """
+    # Check for existing permanent lock first
+    existing = await db.execute(
+        select(EventLock).where(EventLock.event_id == event_id)
+    )
+    existing_lock = existing.scalar_one_or_none()
+    if existing_lock and existing_lock.is_permanent:
+        if existing_lock.locked_by == user_id:
+            # Owner holds permanent lock — return it without downgrading
+            return existing_lock
+        raise HTTPException(status_code=423, detail="Event is permanently locked by the calendar owner")
+
+    now = datetime.now()
+    expires = now + timedelta(minutes=LOCK_DURATION_MINUTES)
+
+    result = await db.execute(
+        text("""
+            INSERT INTO event_locks (event_id, locked_by, locked_at, expires_at, is_permanent)
+            VALUES (:event_id, :user_id, :now, :expires, false)
+            ON CONFLICT (event_id)
+            DO UPDATE SET
+                locked_by = :user_id,
+                locked_at = :now,
+                expires_at = :expires,
+                is_permanent = false
+            WHERE event_locks.expires_at < :now
+               OR event_locks.locked_by = :user_id
+            RETURNING id, event_id, locked_by, locked_at, expires_at, is_permanent
+        """),
+        {"event_id": event_id, "user_id": user_id, "now": now, "expires": expires},
+    )
+    row = result.first()
+    if not row:
+        raise HTTPException(status_code=423, detail="Event is locked by another user")
+
+    lock_result = await db.execute(
+        select(EventLock).where(EventLock.id == row.id)
+    )
+    return lock_result.scalar_one()
+
+
+async def release_lock(db: AsyncSession, event_id: int, user_id: int) -> None:
+    """Delete the lock only if held by this user."""
+    await db.execute(
+        delete(EventLock).where(
+            EventLock.event_id == event_id,
+            EventLock.locked_by == user_id,
+        )
+    )
+
+
+async def check_lock_for_edit(
+    db: AsyncSession, event_id: int, user_id: int, calendar_id: int
+) -> None:
+    """
+    For shared calendars: verify no active lock by another user blocks this edit.
+    For personal (non-shared) calendars: no-op.
+    """
+    cal_result = await db.execute(
+        select(Calendar.is_shared).where(Calendar.id == calendar_id)
+    )
+    is_shared = cal_result.scalar_one_or_none()
+    if not is_shared:
+        return
+
+    lock_result = await db.execute(
+        select(EventLock).where(EventLock.event_id == event_id)
+    )
+    lock = lock_result.scalar_one_or_none()
+    if not lock:
+        return
+    now = datetime.now()
+    if lock.is_permanent and lock.locked_by != user_id:
+        raise HTTPException(status_code=423, detail="Event is permanently locked by the calendar owner")
+    if lock.locked_by != user_id and (lock.expires_at is None or lock.expires_at > now):
+        raise HTTPException(status_code=423, detail="Event is locked by another user")
+
+
+async def cascade_on_disconnect(db: AsyncSession, user_a_id: int, user_b_id: int) -> None:
+    """
+    When a connection is severed:
+    1. Delete CalendarMember rows where one user is a member of the other's calendars
+    2. Delete EventLock rows held by the disconnected user on affected calendars
+    3. Reset is_shared=False on calendars with no remaining members
+    """
+    # Find calendars owned by each user
+    a_cal_ids_result = await db.execute(
+        select(Calendar.id).where(Calendar.user_id == user_a_id)
+    )
+    a_cal_ids = [row[0] for row in a_cal_ids_result.all()]
+
+    b_cal_ids_result = await db.execute(
+        select(Calendar.id).where(Calendar.user_id == user_b_id)
+    )
+    b_cal_ids = [row[0] for row in b_cal_ids_result.all()]
+
+    # Delete user_b's memberships on user_a's calendars + locks
+    if a_cal_ids:
+        await db.execute(
+            delete(CalendarMember).where(
+                CalendarMember.calendar_id.in_(a_cal_ids),
+                CalendarMember.user_id == user_b_id,
+            )
+        )
+        await db.execute(
+            text("""
+                DELETE FROM event_locks
+                WHERE locked_by = :user_id
+                AND event_id IN (
+                    SELECT id FROM calendar_events WHERE calendar_id = ANY(:cal_ids)
+                )
+            """),
+            {"user_id": user_b_id, "cal_ids": a_cal_ids},
+        )
+
+    # Delete user_a's memberships on user_b's calendars + locks
+    if b_cal_ids:
+        await db.execute(
+            delete(CalendarMember).where(
+                CalendarMember.calendar_id.in_(b_cal_ids),
+                CalendarMember.user_id == user_a_id,
+            )
+        )
+        await db.execute(
+            text("""
+                DELETE FROM event_locks
+                WHERE locked_by = :user_id
+                AND event_id IN (
+                    SELECT id FROM calendar_events WHERE calendar_id = ANY(:cal_ids)
+                )
+            """),
+            {"user_id": user_a_id, "cal_ids": b_cal_ids},
+        )
+
+    # Clean up event invitations between the two users
+    from app.services.event_invitation import cascade_event_invitations_on_disconnect
+    await cascade_event_invitations_on_disconnect(db, user_a_id, user_b_id)
+
+    # AC-5: Single aggregation query instead of N per-calendar checks
+    all_cal_ids = a_cal_ids + b_cal_ids
+    if all_cal_ids:
+        # Find which calendars still have members
+        has_members_result = await db.execute(
+            select(CalendarMember.calendar_id)
+            .where(CalendarMember.calendar_id.in_(all_cal_ids))
+            .group_by(CalendarMember.calendar_id)
+        )
+        cals_with_members = {row[0] for row in has_members_result.all()}
+
+        # Reset is_shared on calendars with no remaining members
+        empty_cal_ids = [cid for cid in all_cal_ids if cid not in cals_with_members]
+        if empty_cal_ids:
+            await db.execute(
+                update(Calendar)
+                .where(Calendar.id.in_(empty_cal_ids))
+                .values(is_shared=False)
+            )

backend/app/services/connection.py

@@ -9,6 +9,7 @@ from datetime import date as date_type
 from types import SimpleNamespace
 from typing import Optional
 
+from sqlalchemy import update
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.models.person import Person
@@ -134,6 +135,25 @@ def create_person_from_connection(
     )
 
 
+
+async def sync_birthday_to_contacts(
+    db: AsyncSession,
+    user_id: int,
+    share_birthday: bool,
+    date_of_birth: Optional[date_type],
+) -> None:
+    """Sync user's DOB to all Person records where linked_user_id == user_id.
+    Caller passes resolved values — no internal re-query."""
+    new_birthday = date_of_birth if share_birthday else None
+
+    result = await db.execute(
+        update(Person)
+        .where(Person.linked_user_id == user_id)
+        .values(birthday=new_birthday)
+    )
+    logger.info("sync_birthday_to_contacts user_id=%s updated %s person(s)", user_id, result.rowcount)
+
+
 async def detach_umbral_contact(person: Person) -> None:
     """Convert an umbral contact back to a standard contact. Does NOT commit.
 

backend/app/services/event_invitation.py

@@ -0,0 +1,421 @@
+"""
+Event invitation service — send, respond, override, dismiss invitations.
+
+All functions accept an AsyncSession and do NOT commit — callers manage transactions.
+"""
+import logging
+from datetime import datetime
+
+from fastapi import HTTPException
+from sqlalchemy import delete, func, select, update
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy.orm import selectinload
+
+from app.models.calendar import Calendar
+from app.models.calendar_event import CalendarEvent
+from app.models.event_invitation import EventInvitation, EventInvitationOverride
+from app.models.user_connection import UserConnection
+from app.models.settings import Settings
+from app.models.user import User
+from app.services.notification import create_notification
+
+logger = logging.getLogger(__name__)
+
+
+async def validate_connections(
+    db: AsyncSession, inviter_id: int, user_ids: list[int]
+) -> None:
+    """Verify bidirectional connections exist for all invitees. Raises 404 on failure."""
+    if not user_ids:
+        return
+    result = await db.execute(
+        select(UserConnection.connected_user_id).where(
+            UserConnection.user_id == inviter_id,
+            UserConnection.connected_user_id.in_(user_ids),
+        )
+    )
+    connected_ids = {r[0] for r in result.all()}
+    missing = set(user_ids) - connected_ids
+    if missing:
+        raise HTTPException(status_code=404, detail="One or more users not found in your connections")
+
+
+async def send_event_invitations(
+    db: AsyncSession,
+    event_id: int,
+    user_ids: list[int],
+    invited_by: int,
+) -> list[EventInvitation]:
+    """
+    Bulk-insert invitations for an event. Skips self-invites and existing invitations.
+    Creates in-app notifications for each invitee.
+    """
+    # Remove self from list
+    user_ids = [uid for uid in user_ids if uid != invited_by]
+    if not user_ids:
+        raise HTTPException(status_code=400, detail="Cannot invite yourself")
+
+    # Validate connections
+    await validate_connections(db, invited_by, user_ids)
+
+    # Check existing invitations to skip duplicates
+    existing_result = await db.execute(
+        select(EventInvitation.user_id).where(
+            EventInvitation.event_id == event_id,
+            EventInvitation.user_id.in_(user_ids),
+        )
+    )
+    existing_ids = {r[0] for r in existing_result.all()}
+
+    # Cap: max 20 invitations per event
+    count_result = await db.execute(
+        select(func.count(EventInvitation.id)).where(EventInvitation.event_id == event_id)
+    )
+    current_count = count_result.scalar_one()
+    new_ids = [uid for uid in user_ids if uid not in existing_ids]
+    if current_count + len(new_ids) > 20:
+        raise HTTPException(status_code=400, detail="Maximum 20 invitations per event")
+
+    if not new_ids:
+        return []
+
+    # Fetch event title for notifications
+    event_result = await db.execute(
+        select(CalendarEvent.title, CalendarEvent.start_datetime).where(
+            CalendarEvent.id == event_id
+        )
+    )
+    event_row = event_result.one_or_none()
+    event_title = event_row[0] if event_row else "an event"
+    event_start = event_row[1] if event_row else None
+
+    # Fetch inviter's name
+    inviter_settings = await db.execute(
+        select(Settings.preferred_name).where(Settings.user_id == invited_by)
+    )
+    inviter_name_row = inviter_settings.one_or_none()
+    inviter_name = inviter_name_row[0] if inviter_name_row and inviter_name_row[0] else "Someone"
+
+    invitations = []
+    for uid in new_ids:
+        inv = EventInvitation(
+            event_id=event_id,
+            user_id=uid,
+            invited_by=invited_by,
+            status="pending",
+        )
+        db.add(inv)
+        invitations.append(inv)
+
+    # Flush to populate invitation IDs before creating notifications
+    await db.flush()
+
+    for inv in invitations:
+        start_str = event_start.strftime("%b %d, %I:%M %p") if event_start else ""
+        await create_notification(
+            db=db,
+            user_id=inv.user_id,
+            type="event_invite",
+            title="Event Invitation",
+            message=f"{inviter_name} invited you to {event_title}" + (f" · {start_str}" if start_str else ""),
+            data={"event_id": event_id, "event_title": event_title, "invitation_id": inv.id},
+            source_type="event_invitation",
+            source_id=event_id,
+        )
+
+    return invitations
+
+
+async def respond_to_invitation(
+    db: AsyncSession,
+    invitation_id: int,
+    user_id: int,
+    status: str,
+) -> EventInvitation:
+    """Update invitation status. Returns the updated invitation."""
+    result = await db.execute(
+        select(EventInvitation)
+        .options(selectinload(EventInvitation.event))
+        .where(
+            EventInvitation.id == invitation_id,
+            EventInvitation.user_id == user_id,
+        )
+    )
+    invitation = result.scalar_one_or_none()
+    if not invitation:
+        raise HTTPException(status_code=404, detail="Invitation not found")
+
+    # Build response data before modifying
+    event_title = invitation.event.title
+    old_status = invitation.status
+
+    invitation.status = status
+    invitation.responded_at = datetime.now()
+
+    # Clear can_modify on decline (F-02: prevent silent re-grant)
+    if status == "declined":
+        invitation.can_modify = False
+
+    # Auto-assign display calendar on accept/tentative (atomic: only if not already set)
+    if status in ("accepted", "tentative"):
+        default_cal = await db.execute(
+            select(Calendar.id).where(
+                Calendar.user_id == user_id,
+                Calendar.is_default == True,
+            ).limit(1)
+        )
+        default_cal_id = default_cal.scalar_one_or_none()
+        if default_cal_id and invitation.display_calendar_id is None:
+            # Atomic: only set if still NULL (race-safe)
+            await db.execute(
+                update(EventInvitation)
+                .where(
+                    EventInvitation.id == invitation_id,
+                    EventInvitation.display_calendar_id == None,
+                )
+                .values(display_calendar_id=default_cal_id)
+            )
+            invitation.display_calendar_id = default_cal_id
+
+    # Notify the inviter only if status actually changed (prevents duplicate notifications)
+    if invitation.invited_by and old_status != status:
+        status_label = {"accepted": "Going", "tentative": "Tentative", "declined": "Declined"}
+        # Fetch responder name
+        responder_settings = await db.execute(
+            select(Settings.preferred_name).where(Settings.user_id == user_id)
+        )
+        responder_row = responder_settings.one_or_none()
+        responder_name = responder_row[0] if responder_row and responder_row[0] else "Someone"
+
+        await create_notification(
+            db=db,
+            user_id=invitation.invited_by,
+            type="event_invite_response",
+            title="Event RSVP",
+            message=f"{responder_name} is {status_label.get(status, status)} for {event_title}",
+            data={"event_id": invitation.event_id, "status": status},
+            source_type="event_invitation",
+            source_id=invitation.event_id,
+        )
+
+    return invitation
+
+
+async def override_occurrence_status(
+    db: AsyncSession,
+    invitation_id: int,
+    occurrence_id: int,
+    user_id: int,
+    status: str,
+) -> EventInvitationOverride:
+    """Create or update a per-occurrence status override."""
+    # Verify invitation belongs to user
+    inv_result = await db.execute(
+        select(EventInvitation).where(
+            EventInvitation.id == invitation_id,
+            EventInvitation.user_id == user_id,
+        )
+    )
+    invitation = inv_result.scalar_one_or_none()
+    if not invitation:
+        raise HTTPException(status_code=404, detail="Invitation not found")
+    if invitation.status not in ("accepted", "tentative"):
+        raise HTTPException(status_code=400, detail="Must accept or tentatively accept the invitation first")
+
+    # Verify occurrence belongs to the invited event's series
+    occ_result = await db.execute(
+        select(CalendarEvent).where(CalendarEvent.id == occurrence_id)
+    )
+    occurrence = occ_result.scalar_one_or_none()
+    if not occurrence:
+        raise HTTPException(status_code=404, detail="Occurrence not found")
+
+    # Occurrence must be the event itself OR a child of the invited event
+    if occurrence.id != invitation.event_id and occurrence.parent_event_id != invitation.event_id:
+        raise HTTPException(status_code=400, detail="Occurrence does not belong to this event series")
+
+    # Upsert override
+    existing = await db.execute(
+        select(EventInvitationOverride).where(
+            EventInvitationOverride.invitation_id == invitation_id,
+            EventInvitationOverride.occurrence_id == occurrence_id,
+        )
+    )
+    override = existing.scalar_one_or_none()
+    if override:
+        override.status = status
+        override.responded_at = datetime.now()
+    else:
+        override = EventInvitationOverride(
+            invitation_id=invitation_id,
+            occurrence_id=occurrence_id,
+            status=status,
+            responded_at=datetime.now(),
+        )
+        db.add(override)
+
+    return override
+
+
+async def dismiss_invitation(
+    db: AsyncSession,
+    invitation_id: int,
+    user_id: int,
+) -> None:
+    """Delete an invitation (invitee leaving or owner revoking)."""
+    result = await db.execute(
+        delete(EventInvitation).where(
+            EventInvitation.id == invitation_id,
+            EventInvitation.user_id == user_id,
+        )
+    )
+    if result.rowcount == 0:
+        raise HTTPException(status_code=404, detail="Invitation not found")
+
+
+async def dismiss_invitation_by_owner(
+    db: AsyncSession,
+    invitation_id: int,
+) -> None:
+    """Delete an invitation by the event owner (revoking)."""
+    result = await db.execute(
+        delete(EventInvitation).where(EventInvitation.id == invitation_id)
+    )
+    if result.rowcount == 0:
+        raise HTTPException(status_code=404, detail="Invitation not found")
+
+
+async def get_event_invitations(
+    db: AsyncSession,
+    event_id: int,
+) -> list[dict]:
+    """Get all invitations for an event with invitee names."""
+    result = await db.execute(
+        select(
+            EventInvitation,
+            Settings.preferred_name,
+            User.umbral_name,
+        )
+        .join(User, EventInvitation.user_id == User.id)
+        .outerjoin(Settings, Settings.user_id == User.id)
+        .where(EventInvitation.event_id == event_id)
+        .order_by(EventInvitation.invited_at.asc())
+    )
+    rows = result.all()
+    return [
+        {
+            "id": inv.id,
+            "event_id": inv.event_id,
+            "user_id": inv.user_id,
+            "invited_by": inv.invited_by,
+            "status": inv.status,
+            "invited_at": inv.invited_at,
+            "responded_at": inv.responded_at,
+            "invitee_name": preferred_name or umbral_name or "Unknown",
+            "invitee_umbral_name": umbral_name or "Unknown",
+            "can_modify": inv.can_modify,
+        }
+        for inv, preferred_name, umbral_name in rows
+    ]
+
+
+async def get_invited_event_ids(
+    db: AsyncSession,
+    user_id: int,
+) -> list[int]:
+    """Return event IDs where user has a non-declined invitation."""
+    result = await db.execute(
+        select(EventInvitation.event_id).where(
+            EventInvitation.user_id == user_id,
+            EventInvitation.status != "declined",
+        )
+    )
+    return [r[0] for r in result.all()]
+
+
+async def get_pending_invitations(
+    db: AsyncSession,
+    user_id: int,
+) -> list[dict]:
+    """Return pending invitations for the current user."""
+    result = await db.execute(
+        select(
+            EventInvitation,
+            CalendarEvent.title,
+            CalendarEvent.start_datetime,
+            Settings.preferred_name,
+        )
+        .join(CalendarEvent, EventInvitation.event_id == CalendarEvent.id)
+        .outerjoin(
+            User, EventInvitation.invited_by == User.id
+        )
+        .outerjoin(
+            Settings, Settings.user_id == User.id
+        )
+        .where(
+            EventInvitation.user_id == user_id,
+            EventInvitation.status == "pending",
+        )
+        .order_by(EventInvitation.invited_at.desc())
+    )
+    rows = result.all()
+    return [
+        {
+            "id": inv.id,
+            "event_id": inv.event_id,
+            "event_title": title,
+            "event_start": start_dt,
+            "invited_by_name": inviter_name or "Someone",
+            "invited_at": inv.invited_at,
+            "status": inv.status,
+        }
+        for inv, title, start_dt, inviter_name in rows
+    ]
+
+
+async def get_invitation_overrides_for_user(
+    db: AsyncSession,
+    user_id: int,
+    event_ids: list[int],
+) -> dict[int, str]:
+    """
+    For a list of occurrence event IDs, return a map of occurrence_id -> override status.
+    Used to annotate event listings with per-occurrence invitation status.
+    """
+    if not event_ids:
+        return {}
+
+    result = await db.execute(
+        select(
+            EventInvitationOverride.occurrence_id,
+            EventInvitationOverride.status,
+        )
+        .join(EventInvitation, EventInvitationOverride.invitation_id == EventInvitation.id)
+        .where(
+            EventInvitation.user_id == user_id,
+            EventInvitationOverride.occurrence_id.in_(event_ids),
+        )
+    )
+    return {r[0]: r[1] for r in result.all()}
+
+
+async def cascade_event_invitations_on_disconnect(
+    db: AsyncSession,
+    user_a_id: int,
+    user_b_id: int,
+) -> None:
+    """Delete event invitations between two users when connection is severed."""
+    # Delete invitations where A invited B
+    await db.execute(
+        delete(EventInvitation).where(
+            EventInvitation.invited_by == user_a_id,
+            EventInvitation.user_id == user_b_id,
+        )
+    )
+    # Delete invitations where B invited A
+    await db.execute(
+        delete(EventInvitation).where(
+            EventInvitation.invited_by == user_b_id,
+            EventInvitation.user_id == user_a_id,
+        )
+    )

backend/app/services/passkey.py

@@ -0,0 +1,240 @@
+"""
+Passkey (WebAuthn/FIDO2) service.
+
+Handles challenge token creation/verification (itsdangerous + nonce replay protection)
+and wraps py_webauthn library calls for registration and authentication ceremonies.
+"""
+import base64
+import json
+import logging
+import secrets
+import time
+import threading
+
+from itsdangerous import URLSafeTimedSerializer, BadSignature, SignatureExpired
+
+from webauthn import (
+    generate_registration_options,
+    verify_registration_response,
+    generate_authentication_options,
+    verify_authentication_response,
+    options_to_json,
+)
+from webauthn.helpers.structs import (
+    PublicKeyCredentialDescriptor,
+    AuthenticatorSelectionCriteria,
+    AuthenticatorTransport,
+    ResidentKeyRequirement,
+    UserVerificationRequirement,
+    AttestationConveyancePreference,
+)
+from webauthn.helpers import (
+    bytes_to_base64url,
+    base64url_to_bytes,
+    parse_registration_credential_json,
+    parse_authentication_credential_json,
+)
+
+from app.config import settings as app_settings
+
+# ---------------------------------------------------------------------------
+# Credential JSON helpers
+# ---------------------------------------------------------------------------
+
+
+def extract_credential_raw_id(credential_json: str) -> str | None:
+    """Extract the base64url-encoded rawId from a WebAuthn credential JSON string.
+
+    Returns None if parsing fails.
+    """
+    try:
+        cred_data = json.loads(credential_json)
+        return cred_data.get("rawId") or cred_data.get("id") or None
+    except (json.JSONDecodeError, KeyError, TypeError):
+        return None
+
+logger = logging.getLogger(__name__)
+
+# ---------------------------------------------------------------------------
+# Challenge token management (itsdangerous + nonce replay protection V-01)
+# ---------------------------------------------------------------------------
+
+_challenge_serializer = URLSafeTimedSerializer(
+    secret_key=app_settings.SECRET_KEY,
+    salt="webauthn-challenge-v1",
+)
+
+# Thread-safe nonce cache for single-use enforcement.
+# Keys: nonce string, Values: expiry timestamp.
+# NOTE: This is process-local. If scaling to multiple uvicorn workers,
+# move nonce tracking to Redis or a DB table with unique constraint.
+# Current deployment: single worker (Dockerfile --workers 1).
+_used_nonces: dict[str, float] = {}
+_nonce_lock = threading.Lock()
+
+
+def create_challenge_token(challenge: bytes, user_id: int | None = None) -> str:
+    """Sign challenge + nonce + optional user_id. Returns opaque token string."""
+    nonce = secrets.token_urlsafe(16)
+    payload = {
+        "ch": base64.b64encode(challenge).decode(),
+        "n": nonce,
+    }
+    if user_id is not None:
+        payload["uid"] = user_id
+    return _challenge_serializer.dumps(payload)
+
+
+def verify_challenge_token(token: str, expected_user_id: int | None = None) -> bytes | None:
+    """Verify token (TTL from config), enforce single-use via nonce.
+
+    If expected_user_id provided, cross-check user binding (for registration).
+    Returns challenge bytes or None on failure.
+    """
+    try:
+        data = _challenge_serializer.loads(
+            token, max_age=app_settings.WEBAUTHN_CHALLENGE_TTL
+        )
+    except (BadSignature, SignatureExpired):
+        return None
+
+    nonce = data.get("n")
+    if not nonce:
+        return None
+
+    now = time.time()
+    with _nonce_lock:
+        # Lazy cleanup of expired nonces
+        expired = [k for k, v in _used_nonces.items() if v <= now]
+        for k in expired:
+            del _used_nonces[k]
+
+        # Check for replay
+        if nonce in _used_nonces:
+            return None
+
+        # Mark nonce as used
+        _used_nonces[nonce] = now + app_settings.WEBAUTHN_CHALLENGE_TTL
+
+    # Cross-check user binding for registration tokens
+    if expected_user_id is not None:
+        if data.get("uid") != expected_user_id:
+            return None
+
+    return base64.b64decode(data["ch"])
+
+
+# ---------------------------------------------------------------------------
+# py_webauthn wrappers
+# All synchronous — ECDSA P-256 verification is ~0.1ms, faster than executor overhead.
+# ---------------------------------------------------------------------------
+
+def build_registration_options(
+    user_id: int,
+    username: str,
+    existing_credential_ids: list[bytes],
+) -> tuple[str, bytes]:
+    """Generate WebAuthn registration options.
+
+    Returns (options_json_str, challenge_bytes).
+    """
+    exclude_credentials = [
+        PublicKeyCredentialDescriptor(id=cid)
+        for cid in existing_credential_ids
+    ]
+
+    options = generate_registration_options(
+        rp_id=app_settings.WEBAUTHN_RP_ID,
+        rp_name=app_settings.WEBAUTHN_RP_NAME,
+        user_id=str(user_id).encode(),
+        user_name=username,
+        attestation=AttestationConveyancePreference.NONE,
+        authenticator_selection=AuthenticatorSelectionCriteria(
+            resident_key=ResidentKeyRequirement.PREFERRED,
+            user_verification=UserVerificationRequirement.PREFERRED,
+        ),
+        exclude_credentials=exclude_credentials,
+        timeout=60000,
+    )
+
+    options_json = options_to_json(options)
+    return options_json, options.challenge
+
+
+def verify_registration(
+    credential_json: str,
+    challenge: bytes,
+) -> "VerifiedRegistration":
+    """Verify a registration response from the browser.
+
+    Returns VerifiedRegistration on success, raises on failure.
+    """
+    credential = parse_registration_credential_json(credential_json)
+    return verify_registration_response(
+        credential=credential,
+        expected_challenge=challenge,
+        expected_rp_id=app_settings.WEBAUTHN_RP_ID,
+        expected_origin=app_settings.WEBAUTHN_ORIGIN,
+        require_user_verification=False,
+    )
+
+
+def build_authentication_options(
+    credential_ids_and_transports: list[tuple[bytes, list[str] | None]] | None = None,
+) -> tuple[str, bytes]:
+    """Generate WebAuthn authentication options.
+
+    If credential_ids_and_transports provided, includes allowCredentials.
+    Otherwise, allows discoverable credential flow.
+    Returns (options_json_str, challenge_bytes).
+    """
+    allow_credentials = None
+    if credential_ids_and_transports:
+        allow_credentials = []
+        for cid, transports in credential_ids_and_transports:
+            transport_list = None
+            if transports:
+                transport_list = [
+                    AuthenticatorTransport(t)
+                    for t in transports
+                    if t in [e.value for e in AuthenticatorTransport]
+                ]
+            allow_credentials.append(
+                PublicKeyCredentialDescriptor(
+                    id=cid,
+                    transports=transport_list or None,
+                )
+            )
+
+    options = generate_authentication_options(
+        rp_id=app_settings.WEBAUTHN_RP_ID,
+        allow_credentials=allow_credentials,
+        user_verification=UserVerificationRequirement.PREFERRED,
+        timeout=60000,
+    )
+
+    options_json = options_to_json(options)
+    return options_json, options.challenge
+
+
+def verify_authentication(
+    credential_json: str,
+    challenge: bytes,
+    credential_public_key: bytes,
+    credential_current_sign_count: int,
+) -> "VerifiedAuthentication":
+    """Verify an authentication response from the browser.
+
+    Returns VerifiedAuthentication on success, raises on failure.
+    Sign count anomalies are NOT hard-failed — caller should log and continue.
+    """
+    credential = parse_authentication_credential_json(credential_json)
+    return verify_authentication_response(
+        credential=credential,
+        expected_challenge=challenge,
+        expected_rp_id=app_settings.WEBAUTHN_RP_ID,
+        expected_origin=app_settings.WEBAUTHN_ORIGIN,
+        credential_public_key=credential_public_key,
+        credential_current_sign_count=credential_current_sign_count,
+        require_user_verification=False,
+    )

backend/app/services/project_sharing.py

@@ -0,0 +1,269 @@
+"""
+Project sharing service — permission checks, auto-membership, disconnect cascade.
+
+All functions accept an AsyncSession and do NOT commit — callers manage transactions.
+"""
+import logging
+from datetime import datetime
+
+from fastapi import HTTPException
+from sqlalchemy import delete, select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.models.project import Project
+from app.models.project_member import ProjectMember
+from app.models.project_task import ProjectTask
+from app.models.project_task_assignment import ProjectTaskAssignment
+from app.models.user_connection import UserConnection
+
+logger = logging.getLogger(__name__)
+
+PERMISSION_RANK = {"read_only": 1, "create_modify": 2}
+
+# Fields task assignees (from assignment, not project membership) may edit
+ASSIGNEE_ALLOWED_FIELDS = {"title", "description", "status", "priority", "due_date"}
+
+
+async def get_project_permission(
+    db: AsyncSession, project_id: int, user_id: int
+) -> str | None:
+    """
+    Returns 'owner', 'create_modify', 'read_only', or None.
+    Single query with LEFT JOIN (mirrors calendar_sharing pattern).
+    """
+    result = await db.execute(
+        select(
+            Project.user_id,
+            ProjectMember.permission,
+        )
+        .outerjoin(
+            ProjectMember,
+            (ProjectMember.project_id == Project.id)
+            & (ProjectMember.user_id == user_id)
+            & (ProjectMember.status == "accepted"),
+        )
+        .where(Project.id == project_id)
+    )
+    row = result.one_or_none()
+    if not row:
+        return None
+    owner_id, member_permission = row.tuple()
+    if owner_id == user_id:
+        return "owner"
+    return member_permission
+
+
+async def require_project_permission(
+    db: AsyncSession, project_id: int, user_id: int, min_level: str
+) -> str:
+    """
+    Raises 404 if project doesn't exist or user has no access.
+    Raises 403 if user has insufficient permission.
+    Returns the actual permission string (or 'owner').
+    """
+    perm = await get_project_permission(db, project_id, user_id)
+    if perm is None:
+        raise HTTPException(status_code=404, detail="Project not found")
+    if perm == "owner":
+        return "owner"
+    if min_level == "owner":
+        raise HTTPException(status_code=403, detail="Only the project owner can perform this action")
+    if PERMISSION_RANK.get(perm, 0) < PERMISSION_RANK.get(min_level, 0):
+        raise HTTPException(status_code=403, detail="Insufficient permission on this project")
+    return perm
+
+
+async def get_accessible_project_ids(db: AsyncSession, user_id: int) -> set[int]:
+    """Returns owned + accepted membership project IDs."""
+    result = await db.execute(
+        select(Project.id).where(Project.user_id == user_id)
+        .union(
+            select(ProjectMember.project_id).where(
+                ProjectMember.user_id == user_id,
+                ProjectMember.status == "accepted",
+            )
+        )
+    )
+    return {r[0] for r in result.all()}
+
+
+async def validate_project_connections(
+    db: AsyncSession, owner_id: int, user_ids: list[int]
+) -> None:
+    """Validates all target users are active connections of the owner. Raises 400 on failure."""
+    if not user_ids:
+        return
+    result = await db.execute(
+        select(UserConnection.connected_user_id).where(
+            UserConnection.user_id == owner_id,
+            UserConnection.connected_user_id.in_(user_ids),
+        )
+    )
+    connected = {r[0] for r in result.all()}
+    missing = set(user_ids) - connected
+    if missing:
+        raise HTTPException(
+            status_code=400,
+            detail=f"Users {sorted(missing)} are not your connections",
+        )
+
+
+async def get_effective_task_permission(
+    db: AsyncSession, user_id: int, task_id: int, project_id: int
+) -> tuple[str | None, str | None]:
+    """
+    Returns (effective_permission, project_level_permission) for a specific task.
+    1. Get project-level permission (owner/create_modify/read_only)
+    2. If user is assigned to THIS task → max(project_perm, create_modify)
+    3. If task has parent and user assigned to PARENT → same as above
+    4. Return (effective, project_level)
+    """
+    project_perm = await get_project_permission(db, project_id, user_id)
+    if project_perm is None:
+        return None, None
+    if project_perm == "owner":
+        return "owner", "owner"
+
+    # Check direct assignment on this task
+    task_result = await db.execute(
+        select(ProjectTask.parent_task_id).where(ProjectTask.id == task_id)
+    )
+    task_row = task_result.one_or_none()
+    if not task_row:
+        return project_perm, project_perm
+
+    parent_task_id = task_row[0]
+
+    # Check assignment on this task or its parent
+    check_task_ids = [task_id]
+    if parent_task_id is not None:
+        check_task_ids.append(parent_task_id)
+
+    assignment_result = await db.execute(
+        select(ProjectTaskAssignment.id).where(
+            ProjectTaskAssignment.task_id.in_(check_task_ids),
+            ProjectTaskAssignment.user_id == user_id,
+        ).limit(1)
+    )
+    if assignment_result.scalar_one_or_none() is not None:
+        # Assignment grants at least create_modify
+        if PERMISSION_RANK.get(project_perm, 0) >= PERMISSION_RANK["create_modify"]:
+            return project_perm, project_perm
+        return "create_modify", project_perm
+
+    return project_perm, project_perm
+
+
+async def ensure_auto_membership(
+    db: AsyncSession, project_id: int, user_id: int, invited_by: int
+) -> None:
+    """
+    When assigning a user to a task, ensure they have a ProjectMember row.
+    If none exists, create one with read_only + auto_assigned + accepted (no invite flow).
+    """
+    existing = await db.execute(
+        select(ProjectMember.id).where(
+            ProjectMember.project_id == project_id,
+            ProjectMember.user_id == user_id,
+        )
+    )
+    if existing.scalar_one_or_none() is not None:
+        return
+
+    member = ProjectMember(
+        project_id=project_id,
+        user_id=user_id,
+        invited_by=invited_by,
+        permission="read_only",
+        status="accepted",
+        source="auto_assigned",
+        accepted_at=datetime.now(),
+    )
+    db.add(member)
+
+
+async def cleanup_auto_membership(
+    db: AsyncSession, project_id: int, user_id: int
+) -> None:
+    """
+    After removing a task assignment, check if user has any remaining assignments
+    in this project. If not and membership is auto_assigned, remove it.
+    """
+    remaining = await db.execute(
+        select(ProjectTaskAssignment.id)
+        .join(ProjectTask, ProjectTaskAssignment.task_id == ProjectTask.id)
+        .where(
+            ProjectTask.project_id == project_id,
+            ProjectTaskAssignment.user_id == user_id,
+        )
+        .limit(1)
+    )
+    if remaining.scalar_one_or_none() is not None:
+        return  # Still has assignments
+
+    # Remove auto_assigned membership only
+    await db.execute(
+        delete(ProjectMember).where(
+            ProjectMember.project_id == project_id,
+            ProjectMember.user_id == user_id,
+            ProjectMember.source == "auto_assigned",
+        )
+    )
+
+
+async def cascade_projects_on_disconnect(
+    db: AsyncSession, user_a_id: int, user_b_id: int
+) -> None:
+    """
+    When a connection is severed:
+    1. Find all ProjectMember rows where one user is a member of the other's projects
+    2. Find all ProjectTaskAssignment rows for those memberships
+    3. Remove assignments, then remove memberships
+    """
+    # Single query: find projects owned by each user
+    result = await db.execute(
+        select(Project.id, Project.user_id).where(
+            Project.user_id.in_([user_a_id, user_b_id])
+        )
+    )
+    a_proj_ids: list[int] = []
+    b_proj_ids: list[int] = []
+    for proj_id, owner_id in result.all():
+        if owner_id == user_a_id:
+            a_proj_ids.append(proj_id)
+        else:
+            b_proj_ids.append(proj_id)
+
+    # Remove user_b's assignments + memberships on user_a's projects
+    if a_proj_ids:
+        await db.execute(
+            delete(ProjectTaskAssignment).where(
+                ProjectTaskAssignment.user_id == user_b_id,
+                ProjectTaskAssignment.task_id.in_(
+                    select(ProjectTask.id).where(ProjectTask.project_id.in_(a_proj_ids))
+                ),
+            )
+        )
+        await db.execute(
+            delete(ProjectMember).where(
+                ProjectMember.project_id.in_(a_proj_ids),
+                ProjectMember.user_id == user_b_id,
+            )
+        )
+
+    # Remove user_a's assignments + memberships on user_b's projects
+    if b_proj_ids:
+        await db.execute(
+            delete(ProjectTaskAssignment).where(
+                ProjectTaskAssignment.user_id == user_a_id,
+                ProjectTaskAssignment.task_id.in_(
+                    select(ProjectTask.id).where(ProjectTask.project_id.in_(b_proj_ids))
+                ),
+            )
+        )
+        await db.execute(
+            delete(ProjectMember).where(
+                ProjectMember.project_id.in_(b_proj_ids),
+                ProjectMember.user_id == user_a_id,
+            )
+        )

backend/app/services/recurrence.py

@@ -10,6 +10,9 @@ from typing import Optional
 
 from app.models.calendar_event import CalendarEvent
 
+# Hard cap: never generate more than 730 child events regardless of horizon_days.
+MAX_OCCURRENCES = 730
+
 
 def _nth_weekday_of_month(year: int, month: int, weekday: int, week: int) -> Optional[datetime]:
     """
@@ -99,8 +102,12 @@ def generate_occurrences(
         interval: int = _rule_int(rule, "interval", 1)
         if interval < 1:
             interval = 1
+        # Adaptive horizon: cap daily-ish events (interval < 7) to 90 days
+        effective_horizon = horizon if interval >= 7 else min(horizon, parent_start + timedelta(days=90))
         current = parent_start + timedelta(days=interval)
-        while current < horizon:
+        while current < effective_horizon:
+            if len(occurrences) >= MAX_OCCURRENCES:
+                break
             occurrences.append(_make_child(current))
             current += timedelta(days=interval)
 
@@ -112,6 +119,8 @@ def generate_occurrences(
             days_ahead = 7
         current = parent_start + timedelta(days=days_ahead)
         while current < horizon:
+            if len(occurrences) >= MAX_OCCURRENCES:
+                break
             occurrences.append(_make_child(current))
             current += timedelta(weeks=1)
 
@@ -126,6 +135,8 @@ def generate_occurrences(
             month = 1
             year += 1
         while True:
+            if len(occurrences) >= MAX_OCCURRENCES:
+                break
             target = _nth_weekday_of_month(year, month, weekday, week)
             if target is None:
                 # Skip months where Nth weekday doesn't exist
@@ -157,6 +168,8 @@ def generate_occurrences(
             month = 1
             year += 1
         while True:
+            if len(occurrences) >= MAX_OCCURRENCES:
+                break
             # Some months don't have day 29-31
             try:
                 occ_start = datetime(

backend/app/services/session.py

@@ -0,0 +1,121 @@
+"""
+Shared session management service.
+
+Consolidates session creation, cookie handling, and account lockout logic
+that was previously duplicated between auth.py and totp.py routers.
+All auth paths (password, TOTP, passkey) use these functions to ensure
+consistent session cap enforcement and lockout behavior.
+"""
+import uuid
+from datetime import datetime, timedelta
+
+from fastapi import HTTPException, Response
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy import select, update
+
+from app.models.user import User
+from app.models.session import UserSession
+from app.services.auth import create_session_token
+from app.config import settings as app_settings
+
+
+def set_session_cookie(response: Response, token: str) -> None:
+    """Set httpOnly secure signed cookie on response."""
+    response.set_cookie(
+        key="session",
+        value=token,
+        httponly=True,
+        secure=app_settings.COOKIE_SECURE,
+        max_age=app_settings.SESSION_MAX_AGE_DAYS * 86400,
+        samesite="lax",
+        path="/",
+    )
+
+
+async def check_account_lockout(user: User) -> None:
+    """Raise HTTP 401 if the account is currently locked.
+
+    Uses 401 (same status as wrong-password) so that status-code analysis
+    cannot distinguish a locked account from an invalid credential (F-02).
+    """
+    if user.locked_until and datetime.now() < user.locked_until:
+        remaining = int((user.locked_until - datetime.now()).total_seconds() / 60) + 1
+        raise HTTPException(
+            status_code=401,
+            detail=f"Account temporarily locked. Try again in {remaining} minutes.",
+        )
+
+
+async def record_failed_login(db: AsyncSession, user: User) -> int:
+    """Increment failure counter; lock account after 10 failures.
+
+    Returns the number of attempts remaining before lockout (0 = just locked).
+    Does NOT commit — caller owns the transaction boundary.
+    """
+    user.failed_login_count += 1
+    remaining = max(0, 10 - user.failed_login_count)
+    if user.failed_login_count >= 10:
+        user.locked_until = datetime.now() + timedelta(minutes=30)
+    await db.flush()
+    return remaining
+
+
+async def record_successful_login(db: AsyncSession, user: User) -> None:
+    """Reset failure counter and update last_login_at.
+
+    Does NOT commit — caller owns the transaction boundary.
+    """
+    user.failed_login_count = 0
+    user.locked_until = None
+    user.last_login_at = datetime.now()
+    await db.flush()
+
+
+async def create_db_session(
+    db: AsyncSession,
+    user: User,
+    ip: str,
+    user_agent: str | None,
+) -> tuple[str, str]:
+    """Insert a UserSession row and return (session_id, signed_cookie_token).
+
+    Enforces MAX_SESSIONS_PER_USER by revoking oldest sessions beyond the cap.
+    """
+    session_id = uuid.uuid4().hex
+    expires_at = datetime.now() + timedelta(days=app_settings.SESSION_MAX_AGE_DAYS)
+    db_session = UserSession(
+        id=session_id,
+        user_id=user.id,
+        expires_at=expires_at,
+        ip_address=ip[:45] if ip else None,
+        user_agent=(user_agent or "")[:255] if user_agent else None,
+    )
+    db.add(db_session)
+    await db.flush()
+
+    # Enforce concurrent session limit: revoke oldest sessions beyond the cap.
+    # Perf-2: Query IDs only, bulk-update instead of loading full ORM objects.
+    max_sessions = app_settings.MAX_SESSIONS_PER_USER
+    active_ids = (
+        await db.execute(
+            select(UserSession.id)
+            .where(
+                UserSession.user_id == user.id,
+                UserSession.revoked == False,  # noqa: E712
+                UserSession.expires_at > datetime.now(),
+            )
+            .order_by(UserSession.created_at.asc())
+        )
+    ).scalars().all()
+
+    if len(active_ids) > max_sessions:
+        ids_to_revoke = active_ids[: len(active_ids) - max_sessions]
+        await db.execute(
+            update(UserSession)
+            .where(UserSession.id.in_(ids_to_revoke))
+            .values(revoked=True)
+        )
+        await db.flush()
+
+    token = create_session_token(user.id, session_id)
+    return session_id, token

backend/entrypoint.sh

@@ -0,0 +1,13 @@
+#!/bin/sh
+set -e
+
+echo "Running database migrations..."
+alembic upgrade head
+
+echo "Starting uvicorn..."
+exec uvicorn app.main:app \
+    --host 0.0.0.0 \
+    --port 8000 \
+    --no-server-header \
+    --proxy-headers \
+    --forwarded-allow-ips '*'

backend/requirements.txt

@@ -15,3 +15,4 @@ python-dateutil==2.9.0
 itsdangerous==2.2.0
 httpx==0.27.2
 apscheduler==3.10.4
+webauthn>=2.1.0,<3

backend/start.sh

@@ -1,9 +0,0 @@
-#!/bin/bash
-
-# Run database migrations
-echo "Running database migrations..."
-alembic upgrade head
-
-# Start the FastAPI application
-echo "Starting FastAPI application..."
-uvicorn app.main:app --host 0.0.0.0 --port 8000 --reload

docker-compose.yaml

@@ -2,36 +2,81 @@ services:
   db:
     image: postgres:16-alpine
     restart: unless-stopped
-    env_file: .env
+    environment:
+      - POSTGRES_USER=${POSTGRES_USER}
+      - POSTGRES_PASSWORD=${POSTGRES_PASSWORD}
+      - POSTGRES_DB=${POSTGRES_DB}
     volumes:
       - postgres_data:/var/lib/postgresql/data
+    networks:
+      - backend_net
     healthcheck:
       test: ["CMD-SHELL", "pg_isready -U $POSTGRES_USER -d $POSTGRES_DB"]
       interval: 5s
       timeout: 5s
       retries: 5
+    deploy:
+      resources:
+        limits:
+          memory: 512M
+          cpus: "1.0"
 
   backend:
-    build: ./backend
+    image: git.sentinelforest.xyz/rohskiddo/umbra-backend:main-latest
     restart: unless-stopped
-    env_file: .env
+    environment:
+      - DATABASE_URL=postgresql+asyncpg://${POSTGRES_USER}:${POSTGRES_PASSWORD}@db:5432/${POSTGRES_DB}
+      - SECRET_KEY=${SECRET_KEY}
+      - ENVIRONMENT=${ENVIRONMENT:-production}
+      - UMBRA_URL=${UMBRA_URL:-https://umbra.ghost6.xyz}
+      - OPENWEATHERMAP_API_KEY=${OPENWEATHERMAP_API_KEY:-}
+      - WEBAUTHN_RP_ID=${WEBAUTHN_RP_ID:-umbra.ghost6.xyz}
+      - WEBAUTHN_RP_NAME=${WEBAUTHN_RP_NAME:-UMBRA}
+      - WEBAUTHN_ORIGIN=${WEBAUTHN_ORIGIN:-https://umbra.ghost6.xyz}
     depends_on:
       db:
         condition: service_healthy
+    networks:
+      - backend_net
+      - frontend_net
     healthcheck:
       test: ["CMD-SHELL", "python -c \"import urllib.request; urllib.request.urlopen('http://localhost:8000/health')\""]
-      interval: 10s
+      interval: 30s
       timeout: 5s
       retries: 3
+      start_period: 30s
+    deploy:
+      resources:
+        limits:
+          memory: 512M
+          cpus: "1.0"
 
   frontend:
-    build: ./frontend
+    image: git.sentinelforest.xyz/rohskiddo/umbra-frontend:main-latest
     restart: unless-stopped
     ports:
       - "80:8080"
     depends_on:
       backend:
         condition: service_healthy
+    networks:
+      - frontend_net
+    healthcheck:
+      test: ["CMD", "wget", "--spider", "--quiet", "http://127.0.0.1:8080/"]
+      interval: 15s
+      timeout: 5s
+      retries: 3
+    deploy:
+      resources:
+        limits:
+          memory: 128M
+          cpus: "0.5"
 
 volumes:
   postgres_data:
+
+networks:
+  backend_net:
+    driver: bridge
+  frontend_net:
+    driver: bridge

frontend/.dockerignore

@@ -0,0 +1,25 @@
+# Dependencies — rebuilt inside the container from lockfile
+node_modules
+
+# Build output — rebuilt inside the container
+dist
+
+# Version control
+.git
+.gitignore
+
+# Environment files
+.env
+.env.*
+
+# IDE
+.vscode
+.idea
+
+# Documentation
+*.md
+LICENSE
+
+# Docker files
+Dockerfile
+docker-compose*.yaml

frontend/Dockerfile

@@ -1,13 +1,13 @@
 # Build stage
-FROM node:20-alpine AS build
+FROM node:20.18-alpine AS build
 
 WORKDIR /app
 
 # Copy package files
 COPY package*.json ./
 
-# Install dependencies
-RUN npm install
+# Install dependencies from lockfile (DW-3)
+RUN npm ci
 
 # Copy source files
 COPY . .
@@ -16,7 +16,7 @@ COPY . .
 RUN npm run build
 
 # Production stage — unprivileged nginx (runs as non-root, listens on 8080)
-FROM nginxinc/nginx-unprivileged:alpine
+FROM nginxinc/nginx-unprivileged:1.27-alpine
 
 # Copy built files from build stage
 COPY --from=build /app/dist /usr/share/nginx/html

frontend/index.html

@@ -3,7 +3,33 @@
   <head>
     <meta charset="UTF-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <meta name="apple-mobile-web-app-capable" content="yes" />
+    <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent" />
+    <meta name="theme-color" content="#09090b" />
+    <meta name="mobile-web-app-capable" content="yes" />
+    <link rel="icon" type="image/svg+xml" href="/favicon.svg" />
     <title>UMBRA</title>
+    <!-- Static style tag — survives Vite's head cleanup (unlike dynamically created elements).
+         The inline script below populates it with accent color from localStorage cache. -->
+    <style id="umbra-accent"></style>
+    <script>
+      // Populate the static style tag with cached accent color before first paint.
+      // Uses textContent (safe from XSS) and !important (beats @layer base defaults).
+      (function() {
+        var h = '187', s = '85.7%', l = '53.3%';
+        try {
+          var c = localStorage.getItem('umbra-accent-color');
+          if (c) {
+            var p = JSON.parse(c);
+            if (p.h && /^\d+$/.test(p.h)) h = p.h;
+            if (p.s && /^\d+\.?\d*%$/.test(p.s)) s = p.s;
+            if (p.l && /^\d+\.?\d*%$/.test(p.l)) l = p.l;
+          }
+        } catch(e) {}
+        document.getElementById('umbra-accent').textContent =
+          ':root{--accent-h:' + h + ' !important;--accent-s:' + s + ' !important;--accent-l:' + l + ' !important}';
+      })();
+    </script>
     <link rel="preconnect" href="https://fonts.googleapis.com" />
     <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
     <link href="https://fonts.googleapis.com/css2?family=Sora:wght@400;500;600;700&family=DM+Sans:ital,wght@0,400;0,500;0,600;0,700;1,400&display=swap" rel="stylesheet" />

frontend/nginx.conf

@@ -4,9 +4,16 @@ limit_req_zone $binary_remote_addr zone=auth_limit:10m rate=10r/m;
 limit_req_zone $binary_remote_addr zone=register_limit:10m rate=5r/m;
 # Admin API — generous for legitimate use but still guards against scraping/brute-force
 limit_req_zone $binary_remote_addr zone=admin_limit:10m rate=30r/m;
+# Calendar sharing endpoints
+limit_req_zone $binary_remote_addr zone=cal_invite_limit:10m rate=5r/m;
+limit_req_zone $binary_remote_addr zone=cal_sync_limit:10m rate=15r/m;
 # Connection endpoints — prevent search enumeration and request spam
 limit_req_zone $binary_remote_addr zone=conn_search_limit:10m rate=10r/m;
 limit_req_zone $binary_remote_addr zone=conn_request_limit:10m rate=3r/m;
+# Event creation — recurrence amplification means 1 POST = up to 90-365 child rows
+limit_req_zone $binary_remote_addr zone=event_create_limit:10m rate=30r/m;
+# Health endpoint — lightweight but rate-limited for resilience
+limit_req_zone $binary_remote_addr zone=health_limit:1m rate=30r/m;
 
 # Use X-Forwarded-Proto from upstream proxy when present, fall back to $scheme for direct access
 map $http_x_forwarded_proto $forwarded_proto {
@@ -24,13 +31,14 @@ server {
     # Suppress nginx version in Server header
     server_tokens off;
 
-    # ── Real client IP restoration (PT-01) ────────────────────────────
+    # ── Real client IP restoration (PT-01 / F-03) ─────────────────────
     # Pangolin (TLS-terminating reverse proxy) connects via Docker bridge.
     # Restore the real client IP from X-Forwarded-For so that limit_req_zone
     # (which keys on $binary_remote_addr) throttles per-client, not per-proxy.
-    # Safe to trust all sources: nginx is only reachable via Docker networking,
-    # never directly internet-facing. Tighten if deployment model changes.
-    set_real_ip_from 0.0.0.0/0;
+    # Restricted to RFC 1918 ranges only — trusting 0.0.0.0/0 would allow an
+    # external client to spoof X-Forwarded-For and bypass rate limiting (F-03).
+    set_real_ip_from 172.16.0.0/12;
+    set_real_ip_from 10.0.0.0/8;
     real_ip_header X-Forwarded-For;
     real_ip_recursive on;
 
@@ -38,7 +46,7 @@ server {
     gzip on;
     gzip_vary on;
     gzip_min_length 1024;
-    gzip_types text/plain text/css text/xml text/javascript application/x-javascript application/xml+rss application/javascript application/json;
+    gzip_types text/plain text/css text/xml text/javascript application/x-javascript application/xml+rss application/javascript application/json image/svg+xml;
 
     # Block dotfiles (except .well-known for ACME/Let's Encrypt) (PT-04)
     location ~ /\.(?!well-known) {
@@ -78,6 +86,36 @@ server {
         include /etc/nginx/proxy-params.conf;
     }
 
+    # Passkey authentication — rate-limited (C-04)
+    location /api/auth/passkeys/login/begin {
+        limit_req zone=auth_limit burst=5 nodelay;
+        limit_req_status 429;
+        include /etc/nginx/proxy-params.conf;
+    }
+    location /api/auth/passkeys/login/complete {
+        limit_req zone=auth_limit burst=5 nodelay;
+        limit_req_status 429;
+        include /etc/nginx/proxy-params.conf;
+    }
+    # Passkey registration — authenticated, lower burst
+    location /api/auth/passkeys/register/begin {
+        limit_req zone=auth_limit burst=3 nodelay;
+        limit_req_status 429;
+        include /etc/nginx/proxy-params.conf;
+    }
+    location /api/auth/passkeys/register/complete {
+        limit_req zone=auth_limit burst=3 nodelay;
+        limit_req_status 429;
+        include /etc/nginx/proxy-params.conf;
+    }
+
+    # Passwordless toggle — enable accepts password, rate-limit against brute force
+    location /api/auth/passkeys/passwordless {
+        limit_req zone=auth_limit burst=3 nodelay;
+        limit_req_status 429;
+        include /etc/nginx/proxy-params.conf;
+    }
+
     # SEC-14: Rate-limit public registration endpoint
     location /api/auth/register {
         limit_req zone=register_limit burst=3 nodelay;
@@ -99,6 +137,19 @@ server {
         include /etc/nginx/proxy-params.conf;
     }
 
+    # Calendar invite — rate-limited to prevent invite spam
+    location ~ /api/shared-calendars/\d+/invite {
+        limit_req zone=cal_invite_limit burst=3 nodelay;
+        limit_req_status 429;
+        include /etc/nginx/proxy-params.conf;
+    }
+
+    # Calendar sync — rate-limited to prevent excessive polling
+    location /api/shared-calendars/sync {
+        limit_req zone=cal_sync_limit burst=5 nodelay;
+        limit_req_status 429;
+        include /etc/nginx/proxy-params.conf;
+    }
     # Admin API — rate-limited separately from general /api traffic
     location /api/admin/ {
         limit_req zone=admin_limit burst=10 nodelay;
@@ -106,28 +157,28 @@ server {
         include /etc/nginx/proxy-params.conf;
     }
 
-    # API proxy
+    # Event creation — rate-limited to prevent DB flooding via recurrence amplification.
+    # Note: exact match applies to GET+POST; 30r/m with burst=10 is generous enough
+    # for polling (2r/m) and won't affect reads even with multiple tabs.
+    location = /api/events {
+        limit_req zone=event_create_limit burst=10 nodelay;
+        limit_req_status 429;
+        include /etc/nginx/proxy-params.conf;
+    }
+
+    # Health endpoint — proxied to backend for external uptime monitoring
+    location = /health {
+        limit_req zone=health_limit burst=5 nodelay;
+        limit_req_status 429;
+        include /etc/nginx/proxy-params.conf;
+    }
+
+    # API proxy (catch-all for non-rate-limited endpoints)
     location /api {
-        proxy_pass http://backend:8000;
-        proxy_http_version 1.1;
         proxy_set_header Upgrade $http_upgrade;
         proxy_set_header Connection 'upgrade';
-        proxy_set_header Host $host;
-        proxy_set_header X-Real-IP $remote_addr;
-        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $forwarded_proto;
         proxy_cache_bypass $http_upgrade;
-
-        # PT-L01: Prevent browser caching of authenticated API responses
-        add_header Cache-Control "no-store, no-cache, must-revalidate" always;
-        # Security headers (must be repeated — nginx add_header in a location block
-        # overrides server-level add_header directives, so all headers must be explicit)
-        add_header X-Frame-Options "SAMEORIGIN" always;
-        add_header X-Content-Type-Options "nosniff" always;
-        add_header Referrer-Policy "strict-origin-when-cross-origin" always;
-        add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; img-src 'self' data:; font-src 'self' https://fonts.gstatic.com; connect-src 'self';" always;
-        add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;
-        add_header Permissions-Policy "camera=(), microphone=(), geolocation=(), interest-cohort=()" always;
+        include /etc/nginx/proxy-params.conf;
     }
 
     # SPA fallback - serve index.html for all routes
@@ -142,7 +193,7 @@ server {
         add_header X-Frame-Options "SAMEORIGIN" always;
         add_header X-Content-Type-Options "nosniff" always;
         add_header Referrer-Policy "strict-origin-when-cross-origin" always;
-        add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; img-src 'self' data:; font-src 'self' https://fonts.gstatic.com; connect-src 'self';" always;
+        add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; img-src 'self' data:; font-src 'self' https://fonts.gstatic.com; connect-src 'self'; frame-ancestors 'none'; upgrade-insecure-requests;" always;
         add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;
     }
 
@@ -150,8 +201,8 @@ server {
     add_header X-Frame-Options "SAMEORIGIN" always;
     add_header X-Content-Type-Options "nosniff" always;
     add_header Referrer-Policy "strict-origin-when-cross-origin" always;
-    add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; img-src 'self' data:; font-src 'self' https://fonts.gstatic.com; connect-src 'self';" always;
+    add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; img-src 'self' data:; font-src 'self' https://fonts.gstatic.com; connect-src 'self'; frame-ancestors 'none'; upgrade-insecure-requests;" always;
     add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;
     # PT-I03: Restrict unnecessary browser APIs
-    add_header Permissions-Policy "camera=(), microphone=(), geolocation=(), interest-cohort=()" always;
+    add_header Permissions-Policy "camera=(), microphone=(), geolocation=(), interest-cohort=(), publickey-credentials-get=(self), publickey-credentials-create=(self)" always;
 }

frontend/package-lock.json

@@ -16,6 +16,7 @@
         "@fullcalendar/interaction": "^6.1.15",
         "@fullcalendar/react": "^6.1.15",
         "@fullcalendar/timegrid": "^6.1.15",
+        "@simplewebauthn/browser": "^10.0.0",
         "@tanstack/react-query": "^5.62.0",
         "axios": "^1.7.9",
         "class-variance-authority": "^0.7.1",
@@ -1348,6 +1349,22 @@
         "win32"
       ]
     },
+    "node_modules/@simplewebauthn/browser": {
+      "version": "10.0.0",
+      "resolved": "https://registry.npmjs.org/@simplewebauthn/browser/-/browser-10.0.0.tgz",
+      "integrity": "sha512-hG0JMZD+LiLUbpQcAjS4d+t4gbprE/dLYop/CkE01ugU/9sKXflxV5s0DRjdz3uNMFecatRfb4ZLG3XvF8m5zg==",
+      "license": "MIT",
+      "dependencies": {
+        "@simplewebauthn/types": "^10.0.0"
+      }
+    },
+    "node_modules/@simplewebauthn/types": {
+      "version": "10.0.0",
+      "resolved": "https://registry.npmjs.org/@simplewebauthn/types/-/types-10.0.0.tgz",
+      "integrity": "sha512-SFXke7xkgPRowY2E+8djKbdEznTVnD5R6GO7GPTthpHrokLvNKw8C3lFZypTxLI7KkCfGPfhtqB3d7OVGGa9jQ==",
+      "deprecated": "Package no longer supported. Contact Support at https://www.npmjs.com/support for more info.",
+      "license": "MIT"
+    },
     "node_modules/@tanstack/query-core": {
       "version": "5.90.20",
       "resolved": "https://registry.npmjs.org/@tanstack/query-core/-/query-core-5.90.20.tgz",

frontend/package.json

@@ -17,6 +17,7 @@
     "@fullcalendar/interaction": "^6.1.15",
     "@fullcalendar/react": "^6.1.15",
     "@fullcalendar/timegrid": "^6.1.15",
+    "@simplewebauthn/browser": "^10.0.0",
     "@tanstack/react-query": "^5.62.0",
     "axios": "^1.7.9",
     "class-variance-authority": "^0.7.1",

frontend/proxy-params.conf

@@ -4,3 +4,13 @@ proxy_set_header Host $host;
 proxy_set_header X-Real-IP $remote_addr;
 proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
 proxy_set_header X-Forwarded-Proto $forwarded_proto;
+
+# Security headers (repeated per location — nginx add_header in a location block
+# overrides server-level directives, so all headers must be explicit)
+add_header Cache-Control "no-store, no-cache, must-revalidate" always;
+add_header X-Frame-Options "SAMEORIGIN" always;
+add_header X-Content-Type-Options "nosniff" always;
+add_header Referrer-Policy "strict-origin-when-cross-origin" always;
+add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; img-src 'self' data:; font-src 'self' https://fonts.gstatic.com; connect-src 'self'; frame-ancestors 'none'; upgrade-insecure-requests;" always;
+add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;
+add_header Permissions-Policy "camera=(), microphone=(), geolocation=(), interest-cohort=(), publickey-credentials-get=(self), publickey-credentials-create=(self)" always;

frontend/public/favicon.svg

@@ -0,0 +1,5 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" fill="none" stroke="#8b5cf6" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
+  <path d="M9 10h.01"/>
+  <path d="M15 10h.01"/>
+  <path d="M12 2a8 8 0 0 0-8 8v12l3-3 2.5 2.5L12 19l2.5 2.5L17 19l3 3V10a8 8 0 0 0-8-8z"/>
+</svg>

frontend/src/App.tsx

@@ -3,28 +3,29 @@ import { Routes, Route, Navigate } from 'react-router-dom';
 import { useAuth } from '@/hooks/useAuth';
 import LockScreen from '@/components/auth/LockScreen';
 import AppLayout from '@/components/layout/AppLayout';
-import DashboardPage from '@/components/dashboard/DashboardPage';
-import TodosPage from '@/components/todos/TodosPage';
-import CalendarPage from '@/components/calendar/CalendarPage';
-import RemindersPage from '@/components/reminders/RemindersPage';
-import ProjectsPage from '@/components/projects/ProjectsPage';
-import ProjectDetail from '@/components/projects/ProjectDetail';
-import PeoplePage from '@/components/people/PeoplePage';
-import LocationsPage from '@/components/locations/LocationsPage';
-import SettingsPage from '@/components/settings/SettingsPage';
-import NotificationsPage from '@/components/notifications/NotificationsPage';
 
+// AS-2: Lazy-load all route components to reduce initial bundle parse time
+const DashboardPage = lazy(() => import('@/components/dashboard/DashboardPage'));
+const TodosPage = lazy(() => import('@/components/todos/TodosPage'));
+const CalendarPage = lazy(() => import('@/components/calendar/CalendarPage'));
+const RemindersPage = lazy(() => import('@/components/reminders/RemindersPage'));
+const ProjectsPage = lazy(() => import('@/components/projects/ProjectsPage'));
+const ProjectDetail = lazy(() => import('@/components/projects/ProjectDetail'));
+const PeoplePage = lazy(() => import('@/components/people/PeoplePage'));
+const LocationsPage = lazy(() => import('@/components/locations/LocationsPage'));
+const SettingsPage = lazy(() => import('@/components/settings/SettingsPage'));
+const NotificationsPage = lazy(() => import('@/components/notifications/NotificationsPage'));
 const AdminPortal = lazy(() => import('@/components/admin/AdminPortal'));
 
+const RouteFallback = () => (
+  <div className="flex h-full items-center justify-center text-muted-foreground">Loading...</div>
+);
+
 function ProtectedRoute({ children }: { children: React.ReactNode }) {
   const { authStatus, isLoading } = useAuth();
 
   if (isLoading) {
-    return (
-      <div className="flex h-screen items-center justify-center">
-        <div className="text-muted-foreground">Loading...</div>
-      </div>
-    );
+    return <div className="h-dvh bg-background" />;
   }
 
   if (!authStatus?.authenticated) {
@@ -38,11 +39,7 @@ function AdminRoute({ children }: { children: React.ReactNode }) {
   const { authStatus, isLoading } = useAuth();
 
   if (isLoading) {
-    return (
-      <div className="flex h-screen items-center justify-center">
-        <div className="text-muted-foreground">Loading...</div>
-      </div>
-    );
+    return <div className="h-dvh bg-background" />;
   }
 
   if (!authStatus?.authenticated || authStatus?.role !== 'admin') {
@@ -65,21 +62,21 @@ function App() {
         }
       >
         <Route index element={<Navigate to="/dashboard" replace />} />
-        <Route path="dashboard" element={<DashboardPage />} />
-        <Route path="todos" element={<TodosPage />} />
-        <Route path="calendar" element={<CalendarPage />} />
-        <Route path="reminders" element={<RemindersPage />} />
-        <Route path="projects" element={<ProjectsPage />} />
-        <Route path="projects/:id" element={<ProjectDetail />} />
-        <Route path="people" element={<PeoplePage />} />
-        <Route path="locations" element={<LocationsPage />} />
-        <Route path="notifications" element={<NotificationsPage />} />
-        <Route path="settings" element={<SettingsPage />} />
+        <Route path="dashboard" element={<Suspense fallback={<RouteFallback />}><DashboardPage /></Suspense>} />
+        <Route path="todos" element={<Suspense fallback={<RouteFallback />}><TodosPage /></Suspense>} />
+        <Route path="calendar" element={<Suspense fallback={<RouteFallback />}><CalendarPage /></Suspense>} />
+        <Route path="reminders" element={<Suspense fallback={<RouteFallback />}><RemindersPage /></Suspense>} />
+        <Route path="projects" element={<Suspense fallback={<RouteFallback />}><ProjectsPage /></Suspense>} />
+        <Route path="projects/:id" element={<Suspense fallback={<RouteFallback />}><ProjectDetail /></Suspense>} />
+        <Route path="people" element={<Suspense fallback={<RouteFallback />}><PeoplePage /></Suspense>} />
+        <Route path="locations" element={<Suspense fallback={<RouteFallback />}><LocationsPage /></Suspense>} />
+        <Route path="notifications" element={<Suspense fallback={<RouteFallback />}><NotificationsPage /></Suspense>} />
+        <Route path="settings" element={<Suspense fallback={<RouteFallback />}><SettingsPage /></Suspense>} />
         <Route
           path="admin/*"
           element={
             <AdminRoute>
-              <Suspense fallback={<div className="flex h-full items-center justify-center text-muted-foreground">Loading...</div>}>
+              <Suspense fallback={<RouteFallback />}>
                 <AdminPortal />
               </Suspense>
             </AdminRoute>

frontend/src/components/admin/AdminDashboardPage.tsx

@@ -23,9 +23,9 @@ export default function AdminDashboardPage() {
     dashboard ? dashboard.total_users - dashboard.active_users : null;
 
   return (
-    <div className="px-6 py-6 space-y-6 animate-fade-in">
+    <div className="px-4 md:px-6 py-6 space-y-6 animate-fade-in">
       {/* Stats grid */}
-      <div className="grid gap-2.5 grid-cols-2 lg:grid-cols-5">
+      <div className="grid gap-2.5 grid-cols-2 md:grid-cols-3 lg:grid-cols-5">
         {isLoading ? (
           Array.from({ length: 5 }).map((_, i) => (
             <Card key={i}>
@@ -94,10 +94,10 @@ export default function AdminDashboardPage() {
                 <table className="w-full text-sm">
                   <thead>
                     <tr className="border-b border-border bg-card-elevated/50">
-                      <th className="px-5 py-2.5 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                      <th className="px-3 lg:px-5 py-2.5 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
                         Username
                       </th>
-                      <th className="px-5 py-2.5 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                      <th className="px-3 lg:px-5 py-2.5 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
                         When
                       </th>
                     </tr>
@@ -111,8 +111,8 @@ export default function AdminDashboardPage() {
                           idx % 2 === 0 ? '' : 'bg-card-elevated/25'
                         )}
                       >
-                        <td className="px-5 py-2.5 font-medium">{entry.username}</td>
-                        <td className="px-5 py-2.5 text-xs text-muted-foreground">
+                        <td className="px-3 lg:px-5 py-2.5 font-medium">{entry.username}</td>
+                        <td className="px-3 lg:px-5 py-2.5 text-xs text-muted-foreground">
                           {getRelativeTime(entry.last_login_at)}
                         </td>
                       </tr>
@@ -142,16 +142,16 @@ export default function AdminDashboardPage() {
                 <table className="w-full text-sm">
                   <thead>
                     <tr className="border-b border-border bg-card-elevated/50">
-                      <th className="px-5 py-2.5 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                      <th className="px-3 lg:px-5 py-2.5 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
                         Action
                       </th>
-                      <th className="px-5 py-2.5 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                      <th className="px-3 lg:px-5 py-2.5 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium hidden sm:table-cell">
                         Actor
                       </th>
-                      <th className="px-5 py-2.5 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                      <th className="px-3 lg:px-5 py-2.5 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium hidden sm:table-cell">
                         Target
                       </th>
-                      <th className="px-5 py-2.5 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                      <th className="px-3 lg:px-5 py-2.5 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
                         When
                       </th>
                     </tr>
@@ -165,7 +165,7 @@ export default function AdminDashboardPage() {
                           idx % 2 === 0 ? '' : 'bg-card-elevated/25'
                         )}
                       >
-                        <td className="px-5 py-2.5">
+                        <td className="px-3 lg:px-5 py-2.5">
                           <span
                             className={cn(
                               'text-[9px] px-1.5 py-0.5 rounded font-medium uppercase tracking-wide whitespace-nowrap',
@@ -175,15 +175,15 @@ export default function AdminDashboardPage() {
                             {entry.action}
                           </span>
                         </td>
-                        <td className="px-5 py-2.5 text-xs font-medium">
+                        <td className="px-3 lg:px-5 py-2.5 text-xs font-medium hidden sm:table-cell">
                           {entry.actor_username ?? (
                             <span className="text-muted-foreground italic">system</span>
                           )}
                         </td>
-                        <td className="px-5 py-2.5 text-xs text-muted-foreground">
+                        <td className="px-3 lg:px-5 py-2.5 text-xs text-muted-foreground hidden sm:table-cell">
                           {entry.target_username ?? '—'}
                         </td>
-                        <td className="px-5 py-2.5 text-xs text-muted-foreground whitespace-nowrap">
+                        <td className="px-3 lg:px-5 py-2.5 text-xs text-muted-foreground whitespace-nowrap">
                           {getRelativeTime(entry.created_at)}
                         </td>
                       </tr>

frontend/src/components/admin/AdminPortal.tsx

@@ -17,32 +17,37 @@ export default function AdminPortal() {
   return (
     <div className="flex flex-col h-full animate-fade-in">
       {/* Portal header with tab navigation */}
-      <div className="shrink-0 border-b bg-card">
-        <div className="px-6 h-16 flex items-center gap-4">
-          <div className="flex items-center gap-2 mr-6">
+      <div className="shrink-0 border-b bg-card overflow-hidden">
+        <div className="px-3 md:px-6 h-14 md:h-16 flex items-center gap-2 md:gap-4">
+          <div className="flex items-center gap-2 shrink-0 md:mr-6">
             <div className="p-1.5 rounded-md bg-red-500/10">
               <ShieldCheck className="h-5 w-5 text-red-400" />
             </div>
-            <h1 className="font-heading text-2xl font-bold tracking-tight">Admin Portal</h1>
+            <h1 className="font-heading text-base md:text-2xl font-bold tracking-tight">
+              <span className="hidden md:inline">Admin Portal</span>
+              <span className="md:hidden">Admin</span>
+            </h1>
           </div>
 
-          {/* Horizontal tab navigation */}
-          <nav className="flex items-center gap-1 h-full">
+          {/* Horizontal tab navigation — evenly spaced on mobile, left-aligned on desktop */}
+          <nav className="flex items-center justify-evenly md:justify-start flex-1 md:flex-none md:gap-1 h-full min-w-0 overflow-hidden">
             {tabs.map(({ label, path, icon: Icon }) => {
               const isActive = location.pathname.startsWith(path);
               return (
                 <NavLink
                   key={path}
                   to={path}
+                  title={label}
+                  aria-label={label}
                   className={cn(
-                    'flex items-center gap-2 px-4 h-full text-sm font-medium transition-colors duration-150 border-b-2 -mb-px',
+                    'flex items-center justify-center md:justify-start gap-1.5 px-2.5 md:px-4 h-full text-sm font-medium transition-colors duration-150 border-b-2 -mb-px whitespace-nowrap',
                     isActive
                       ? 'text-accent border-accent'
                       : 'text-muted-foreground hover:text-foreground border-transparent'
                   )}
                 >
-                  <Icon className="h-4 w-4" />
-                  {label}
+                  <Icon className="h-4 w-4 shrink-0" />
+                  <span className="hidden sm:inline">{label}</span>
                 </NavLink>
               );
             })}

frontend/src/components/admin/ConfigPage.tsx

@@ -54,7 +54,7 @@ export default function ConfigPage() {
   const totalPages = data ? Math.ceil(data.total / PER_PAGE) : 1;
 
   return (
-    <div className="px-6 py-6 space-y-6 animate-fade-in">
+    <div className="px-4 md:px-6 py-6 space-y-6 animate-fade-in">
       <Card>
         <CardHeader className="flex-row items-center justify-between flex-wrap gap-3">
           <div className="flex items-center gap-2">
@@ -75,7 +75,7 @@ export default function ConfigPage() {
               <Filter className="h-3.5 w-3.5 text-muted-foreground" />
               <span className="text-xs text-muted-foreground">Filter:</span>
             </div>
-            <div className="w-52">
+            <div className="w-36 sm:w-52">
               <Select
                 value={filterAction}
                 onChange={(e) => {
@@ -129,22 +129,22 @@ export default function ConfigPage() {
                 <table className="w-full text-sm">
                   <thead>
                     <tr className="border-b border-border bg-card-elevated/50">
-                      <th className="px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                      <th className="px-3 lg:px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
                         Time
                       </th>
-                      <th className="px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                      <th className="px-3 lg:px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium hidden sm:table-cell">
                         Actor
                       </th>
-                      <th className="px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                      <th className="px-3 lg:px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
                         Action
                       </th>
-                      <th className="px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                      <th className="px-3 lg:px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium hidden sm:table-cell">
                         Target
                       </th>
-                      <th className="px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                      <th className="px-3 lg:px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium hidden lg:table-cell">
                         IP
                       </th>
-                      <th className="px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                      <th className="px-3 lg:px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium hidden lg:table-cell">
                         Detail
                       </th>
                     </tr>
@@ -158,15 +158,15 @@ export default function ConfigPage() {
                           idx % 2 === 0 ? '' : 'bg-card-elevated/25'
                         )}
                       >
-                        <td className="px-5 py-3 text-xs text-muted-foreground whitespace-nowrap">
+                        <td className="px-3 lg:px-5 py-3 text-xs text-muted-foreground whitespace-nowrap">
                           {getRelativeTime(entry.created_at)}
                         </td>
-                        <td className="px-5 py-3 text-xs font-medium">
+                        <td className="px-3 lg:px-5 py-3 text-xs font-medium hidden sm:table-cell">
                           {entry.actor_username ?? (
                             <span className="text-muted-foreground italic">system</span>
                           )}
                         </td>
-                        <td className="px-5 py-3">
+                        <td className="px-3 lg:px-5 py-3">
                           <span
                             className={cn(
                               'text-[9px] px-1.5 py-0.5 rounded font-medium uppercase tracking-wide whitespace-nowrap',
@@ -176,13 +176,13 @@ export default function ConfigPage() {
                             {entry.action}
                           </span>
                         </td>
-                        <td className="px-5 py-3 text-xs text-muted-foreground">
+                        <td className="px-3 lg:px-5 py-3 text-xs text-muted-foreground hidden sm:table-cell">
                           {entry.target_username ?? '—'}
                         </td>
-                        <td className="px-5 py-3 text-xs text-muted-foreground font-mono">
+                        <td className="px-3 lg:px-5 py-3 text-xs text-muted-foreground font-mono hidden lg:table-cell">
                           {entry.ip_address ?? '—'}
                         </td>
-                        <td className="px-5 py-3 text-xs text-muted-foreground max-w-xs truncate">
+                        <td className="px-3 lg:px-5 py-3 text-xs text-muted-foreground max-w-xs truncate hidden lg:table-cell">
                           {entry.detail ?? '—'}
                         </td>
                       </tr>

frontend/src/components/admin/IAMPage.tsx

@@ -81,7 +81,7 @@ export default function IAMPage() {
     );
   }, [users, searchQuery]);
 
-  const handleConfigToggle = async (key: 'allow_registration' | 'enforce_mfa_new_users', value: boolean) => {
+  const handleConfigToggle = async (key: 'allow_registration' | 'enforce_mfa_new_users' | 'allow_passwordless', value: boolean) => {
     try {
       await updateConfig.mutateAsync({ [key]: value });
       toast.success('System settings updated');
@@ -95,7 +95,7 @@ export default function IAMPage() {
     : null;
 
   return (
-    <div className="px-6 py-6 space-y-6 animate-fade-in">
+    <div className="px-4 md:px-6 py-6 space-y-6 animate-fade-in">
       {/* Stats row */}
       <div className="grid gap-2.5 grid-cols-2 lg:grid-cols-4">
         <StatCard
@@ -123,9 +123,9 @@ export default function IAMPage() {
         />
       </div>
 
-      {/* User table */}
-      <Card>
-        <CardHeader className="flex-row items-center justify-between gap-3">
+      {/* User table — relative z-10 so action dropdowns render above sibling cards */}
+      <Card className="relative z-10">
+        <CardHeader className="flex-row items-center justify-between flex-wrap gap-2 md:gap-3">
           <div className="flex items-center gap-2">
             <div className="p-1.5 rounded-md bg-accent/10">
               <Users className="h-4 w-4 text-accent" />
@@ -139,12 +139,12 @@ export default function IAMPage() {
                 value={searchQuery}
                 onChange={(e) => setSearchQuery(e.target.value)}
                 placeholder="Search users..."
-                className="pl-8 h-8 w-48 text-xs"
+                className="pl-8 h-8 w-32 sm:w-48 text-xs"
               />
             </div>
             <Button size="sm" onClick={() => setCreateOpen(true)}>
               <Plus className="h-4 w-4" />
-              Create User
+              <span className="hidden sm:inline">Create User</span>
             </Button>
           </div>
         </CardHeader>
@@ -164,34 +164,34 @@ export default function IAMPage() {
               <table className="w-full text-sm">
                 <thead>
                   <tr className="border-b border-border bg-card-elevated/50">
-                    <th className="px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                    <th className="px-3 lg:px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
                       Username
                     </th>
-                    <th className="px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                    <th className="px-3 lg:px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium hidden lg:table-cell">
                       Umbral Name
                     </th>
-                    <th className="px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                    <th className="px-3 lg:px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium hidden lg:table-cell">
                       Email
                     </th>
-                    <th className="px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                    <th className="px-3 lg:px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
                       Role
                     </th>
-                    <th className="px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                    <th className="px-3 lg:px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
                       Status
                     </th>
-                    <th className="px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                    <th className="px-3 lg:px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium hidden lg:table-cell">
                       Last Login
                     </th>
-                    <th className="px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                    <th className="px-3 lg:px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium hidden lg:table-cell">
                       MFA
                     </th>
-                    <th className="px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                    <th className="px-3 lg:px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium hidden lg:table-cell">
                       Sessions
                     </th>
-                    <th className="px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                    <th className="px-3 lg:px-5 py-3 text-left text-[11px] uppercase tracking-wider text-muted-foreground font-medium hidden lg:table-cell">
                       Created
                     </th>
-                    <th className="px-5 py-3 text-right text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
+                    <th className="px-3 lg:px-5 py-3 text-right text-[11px] uppercase tracking-wider text-muted-foreground font-medium">
                       Actions
                     </th>
                   </tr>
@@ -211,17 +211,17 @@ export default function IAMPage() {
                             )
                       )}
                     >
-                      <td className="px-5 py-3 font-medium">{user.username}</td>
-                      <td className="px-5 py-3 text-muted-foreground text-xs">
+                      <td className="px-3 lg:px-5 py-3 font-medium">{user.username}</td>
+                      <td className="px-3 lg:px-5 py-3 text-muted-foreground text-xs hidden lg:table-cell">
                         {user.umbral_name || user.username}
                       </td>
-                      <td className="px-5 py-3 text-muted-foreground text-xs">
+                      <td className="px-3 lg:px-5 py-3 text-muted-foreground text-xs hidden lg:table-cell">
                         {user.email || '—'}
                       </td>
-                      <td className="px-5 py-3">
+                      <td className="px-3 lg:px-5 py-3">
                         <RoleBadge role={user.role} />
                       </td>
-                      <td className="px-5 py-3">
+                      <td className="px-3 lg:px-5 py-3">
                         <span
                           className={cn(
                             'text-[9px] px-1.5 py-0.5 rounded font-medium uppercase tracking-wide',
@@ -233,10 +233,10 @@ export default function IAMPage() {
                           {user.is_active ? 'Active' : 'Disabled'}
                         </span>
                       </td>
-                      <td className="px-5 py-3 text-muted-foreground text-xs">
+                      <td className="px-3 lg:px-5 py-3 text-muted-foreground text-xs hidden lg:table-cell">
                         {user.last_login_at ? getRelativeTime(user.last_login_at) : '—'}
                       </td>
-                      <td className="px-5 py-3">
+                      <td className="px-3 lg:px-5 py-3 hidden lg:table-cell">
                         {user.totp_enabled ? (
                           <span className="text-[9px] px-1.5 py-0.5 rounded font-medium uppercase tracking-wide bg-green-500/15 text-green-400">
                             On
@@ -249,13 +249,13 @@ export default function IAMPage() {
                           <span className="text-muted-foreground text-xs">—</span>
                         )}
                       </td>
-                      <td className="px-5 py-3 text-muted-foreground text-xs tabular-nums">
+                      <td className="px-3 lg:px-5 py-3 text-muted-foreground text-xs tabular-nums hidden lg:table-cell">
                         {user.active_sessions}
                       </td>
-                      <td className="px-5 py-3 text-muted-foreground text-xs">
+                      <td className="px-3 lg:px-5 py-3 text-muted-foreground text-xs hidden lg:table-cell">
                         {getRelativeTime(user.created_at)}
                       </td>
-                      <td className="px-5 py-3 text-right" onClick={(e) => e.stopPropagation()}>
+                      <td className="px-3 lg:px-5 py-3 text-right" onClick={(e) => e.stopPropagation()}>
                         <UserActionsMenu user={user} currentUsername={authStatus?.username ?? null} />
                       </td>
                     </tr>
@@ -320,6 +320,20 @@ export default function IAMPage() {
                   disabled={updateConfig.isPending}
                 />
               </div>
+
+              <div className="flex items-center justify-between gap-4">
+                <div className="space-y-0.5">
+                  <Label className="text-sm font-medium">Allow Passwordless Login</Label>
+                  <p className="text-xs text-muted-foreground">
+                    Allow users to enable passkey-only login, skipping the password prompt entirely.
+                  </p>
+                </div>
+                <Switch
+                  checked={config?.allow_passwordless ?? false}
+                  onCheckedChange={(v) => handleConfigToggle('allow_passwordless', v)}
+                  disabled={updateConfig.isPending}
+                />
+              </div>
             </>
           )}
         </CardContent>

frontend/src/components/admin/UserActionsMenu.tsx

@@ -11,6 +11,7 @@ import {
   ChevronRight,
   Loader2,
   Trash2,
+  ShieldOff,
 } from 'lucide-react';
 import { Button } from '@/components/ui/button';
 import { useConfirmAction } from '@/hooks/useConfirmAction';
@@ -23,6 +24,7 @@ import {
   useToggleUserActive,
   useRevokeSessions,
   useDeleteUser,
+  useDisablePasswordless,
   getErrorMessage,
 } from '@/hooks/useAdmin';
 import type { AdminUserDetail, UserRole } from '@/types';
@@ -53,6 +55,7 @@ export default function UserActionsMenu({ user, currentUsername }: UserActionsMe
   const toggleActive = useToggleUserActive();
   const revokeSessions = useRevokeSessions();
   const deleteUser = useDeleteUser();
+  const disablePasswordless = useDisablePasswordless();
 
   // Close on outside click
   useEffect(() => {
@@ -102,6 +105,10 @@ export default function UserActionsMenu({ user, currentUsername }: UserActionsMe
     }
   });
 
+  const disablePasswordlessConfirm = useConfirmAction(() => {
+    handleAction(() => disablePasswordless.mutateAsync(user.id), 'Passwordless login disabled');
+  });
+
   const isLoading =
     updateRole.isPending ||
     resetPassword.isPending ||
@@ -110,7 +117,8 @@ export default function UserActionsMenu({ user, currentUsername }: UserActionsMe
     removeMfaEnforcement.isPending ||
     toggleActive.isPending ||
     revokeSessions.isPending ||
-    deleteUser.isPending;
+    deleteUser.isPending ||
+    disablePasswordless.isPending;
 
   return (
     <div ref={menuRef} className="relative">
@@ -147,7 +155,7 @@ export default function UserActionsMenu({ user, currentUsername }: UserActionsMe
 
             {roleSubmenuOpen && (
               <div
-                className="absolute right-full top-0 z-50 min-w-[180px] rounded-lg border bg-card shadow-lg py-1"
+                className="absolute left-0 top-full sm:left-auto sm:right-full sm:top-0 z-50 min-w-[180px] rounded-lg border bg-card shadow-lg py-1"
                 onMouseEnter={() => setRoleSubmenuOpen(true)}
                 onMouseLeave={() => setRoleSubmenuOpen(false)}
               >
@@ -258,6 +266,21 @@ export default function UserActionsMenu({ user, currentUsername }: UserActionsMe
             </button>
           )}
 
+          {user.passwordless_enabled && (
+            <button
+              className={cn(
+                'flex w-full items-center gap-2 px-3 py-2 text-sm transition-colors',
+                disablePasswordlessConfirm.confirming
+                  ? 'text-orange-400 bg-orange-500/10 hover:bg-orange-500/15'
+                  : 'hover:bg-card-elevated'
+              )}
+              onClick={disablePasswordlessConfirm.handleClick}
+            >
+              <ShieldOff className="h-4 w-4" />
+              {disablePasswordlessConfirm.confirming ? 'Sure? Click to confirm' : 'Disable Passwordless'}
+            </button>
+          )}
+
           <div className="my-1 border-t border-border" />
 
           {/* Disable / Enable Account */}

frontend/src/components/admin/UserDetailSection.tsx

@@ -1,10 +1,10 @@
-import { X, User, ShieldCheck, Loader2 } from 'lucide-react';
+import { X, User, ShieldCheck, Share2, Loader2 } from 'lucide-react';
 import { toast } from 'sonner';
 import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card';
 import { Select } from '@/components/ui/select';
 import { Button } from '@/components/ui/button';
 import { Skeleton } from '@/components/ui/skeleton';
-import { useAdminUserDetail, useUpdateRole, getErrorMessage } from '@/hooks/useAdmin';
+import { useAdminUserDetail, useAdminSharingStats, useUpdateRole, getErrorMessage } from '@/hooks/useAdmin';
 import { getRelativeTime } from '@/lib/date-utils';
 import { cn } from '@/lib/utils';
 import type { UserRole } from '@/types';
@@ -57,6 +57,7 @@ function MfaBadge({ enabled, pending }: { enabled: boolean; pending: boolean })
 export default function UserDetailSection({ userId, onClose }: UserDetailSectionProps) {
   const { data: user, isLoading, error } = useAdminUserDetail(userId);
   const updateRole = useUpdateRole();
+  const { data: sharingStats } = useAdminSharingStats(userId);
 
   const handleRoleChange = async (newRole: UserRole) => {
     if (!user || newRole === user.role) return;
@@ -70,15 +71,15 @@ export default function UserDetailSection({ userId, onClose }: UserDetailSection
 
   if (isLoading) {
     return (
-      <div className="grid grid-cols-4 gap-4">
-        <Card className="col-span-1">
+      <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-3 gap-3 md:gap-4">
+        <Card>
           <CardContent className="p-5 space-y-3">
             {Array.from({ length: 5 }).map((_, i) => (
               <Skeleton key={i} className="h-5 w-full" />
             ))}
           </CardContent>
         </Card>
-        <Card className="col-span-1">
+        <Card>
           <CardContent className="p-5 space-y-3">
             {Array.from({ length: 7 }).map((_, i) => (
               <Skeleton key={i} className="h-5 w-full" />
@@ -108,9 +109,9 @@ export default function UserDetailSection({ userId, onClose }: UserDetailSection
   if (!user) return null;
 
   return (
-    <div className="grid grid-cols-4 gap-4">
+    <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-3 gap-3 md:gap-4">
       {/* User Information (read-only) */}
-      <Card className="col-span-1">
+      <Card>
         <CardHeader className="flex-row items-center justify-between pb-3">
           <div className="flex items-center gap-2">
             <div className="p-1.5 rounded-md bg-accent/10">
@@ -151,7 +152,7 @@ export default function UserDetailSection({ userId, onClose }: UserDetailSection
       </Card>
 
       {/* Security & Permissions */}
-      <Card className="col-span-1">
+      <Card>
         <CardHeader className="pb-3">
           <div className="flex items-center gap-2">
             <div className="p-1.5 rounded-md bg-accent/10">
@@ -167,7 +168,7 @@ export default function UserDetailSection({ userId, onClose }: UserDetailSection
               <Select
                 value={user.role}
                 onChange={(e) => handleRoleChange(e.target.value as UserRole)}
-                className="h-6 text-xs py-0 px-1.5 w-auto min-w-[120px]"
+                className="h-6 text-xs py-0 px-1.5 w-auto min-w-[100px] sm:min-w-[120px]"
                 disabled={updateRole.isPending}
               >
                 <option value="admin">Admin</option>
@@ -192,6 +193,18 @@ export default function UserDetailSection({ userId, onClose }: UserDetailSection
               />
             }
           />
+          <DetailRow
+            label="Passwordless"
+            value={
+              user.passwordless_enabled ? (
+                <span className="text-[9px] px-1.5 py-0.5 rounded font-medium uppercase tracking-wide bg-green-500/15 text-green-400">
+                  Enabled
+                </span>
+              ) : (
+                <span className="text-xs text-muted-foreground">Off</span>
+              )
+            }
+          />
           <DetailRow
             label="Must Change Pwd"
             value={user.must_change_password ? 'Yes' : 'No'}
@@ -218,6 +231,24 @@ export default function UserDetailSection({ userId, onClose }: UserDetailSection
           />
         </CardContent>
       </Card>
+
+      {/* Sharing Stats */}
+      <Card>
+        <CardHeader className="pb-3">
+          <div className="flex items-center gap-2">
+            <div className="p-1.5 rounded-md bg-accent/10">
+              <Share2 className="h-3.5 w-3.5 text-accent" />
+            </div>
+            <CardTitle className="text-sm">Sharing</CardTitle>
+          </div>
+        </CardHeader>
+        <CardContent className="pt-0 space-y-0.5">
+          <DetailRow label="Calendars Shared" value={String(sharingStats?.shared_calendars_owned ?? 0)} />
+          <DetailRow label="Member Of" value={String(sharingStats?.calendars_member_of ?? 0)} />
+          <DetailRow label="Invites Sent" value={String(sharingStats?.pending_invites_sent ?? 0)} />
+          <DetailRow label="Invites Received" value={String(sharingStats?.pending_invites_received ?? 0)} />
+        </CardContent>
+      </Card>
     </div>
   );
 }

frontend/src/components/auth/LockScreen.tsx

@@ -1,7 +1,7 @@
 import { useState, FormEvent } from 'react';
 import { Navigate } from 'react-router-dom';
 import { toast } from 'sonner';
-import { AlertTriangle, Copy, Lock, Loader2, ShieldCheck, UserPlus } from 'lucide-react';
+import { AlertTriangle, Copy, Fingerprint, Lock, Loader2, ShieldCheck, UserPlus } from 'lucide-react';
 import { useAuth } from '@/hooks/useAuth';
 import api, { getErrorMessage } from '@/lib/api';
 import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card';
@@ -10,6 +10,7 @@ import { DatePicker } from '@/components/ui/date-picker';
 import { Button } from '@/components/ui/button';
 import { Label } from '@/components/ui/label';
 import { cn } from '@/lib/utils';
+import { Separator } from '@/components/ui/separator';
 import AmbientBackground from './AmbientBackground';
 import type { TotpSetupResponse } from '@/types';
 
@@ -47,6 +48,8 @@ export default function LockScreen() {
     isRegisterPending,
     isSetupPending,
     isTotpPending,
+    passkeyLogin,
+    isPasskeyLoginPending,
   } = useAuth();
 
   // ── Shared credential fields ──
@@ -83,6 +86,31 @@ export default function LockScreen() {
   const [forcedConfirmPassword, setForcedConfirmPassword] = useState('');
   const [isForcePwPending, setIsForcePwPending] = useState(false);
 
+  // ── Passkey support (U-01: browser feature detection, not per-user) ──
+  const [supportsWebAuthn] = useState(() => !!window.PublicKeyCredential);
+
+  const handlePasskeyLogin = async () => {
+    setLoginError(null);
+    try {
+      const result = await passkeyLogin();
+      if (result?.must_change_password) {
+        setMode('force_pw');
+      }
+    } catch (error: unknown) {
+      if (error instanceof Error) {
+        if (error.name === 'NotAllowedError') {
+          toast.info('Passkey not recognized. Try your password.');
+        } else if (error.name === 'AbortError') {
+          // User cancelled — silent
+        } else {
+          toast.error(getErrorMessage(error, 'Passkey login failed. Try your password.'));
+        }
+      } else {
+        toast.error(getErrorMessage(error, 'Passkey login failed. Try your password.'));
+      }
+    }
+  };
+
   // Redirect authenticated users (no pending MFA flows)
   if (!isLoading && authStatus?.authenticated && !mfaSetupRequired && mode !== 'force_pw') {
     return <Navigate to="/dashboard" replace />;
@@ -127,11 +155,10 @@ export default function LockScreen() {
       // mfaSetupRequired / mfaRequired handled by hook state → activeMode switches automatically
     } catch (error: any) {
       const status = error?.response?.status;
-      if (status === 423) {
-        setLoginError(error.response.data?.detail || 'Account locked. Try again later.');
-      } else if (status === 403) {
+      if (status === 403) {
         setLoginError(error.response.data?.detail || 'Account is disabled. Contact an administrator.');
       } else {
+        // 401 covers both wrong password and account lockout (backend embeds detail string)
         setLoginError(getErrorMessage(error, 'Invalid username or password'));
       }
     }
@@ -491,18 +518,28 @@ export default function LockScreen() {
         </div>
       </CardHeader>
       <CardContent>
-        {loginError && (
+        {loginError && (() => {
+          const isLockWarning =
+            loginError.includes('remaining') || loginError.includes('temporarily locked');
+          return (
             <div
               role="alert"
               className={cn(
-              'flex items-center gap-2 rounded-md border border-red-500/30',
-              'bg-red-500/10 px-3 py-2 mb-4'
+                'flex items-center gap-2 rounded-md border px-3 py-2 mb-4',
+                isLockWarning
+                  ? 'bg-amber-500/10 border-amber-500/30'
+                  : 'bg-red-500/10 border-red-500/30'
               )}
             >
-            <AlertTriangle className="h-4 w-4 text-red-400 shrink-0" aria-hidden="true" />
-            <p className="text-xs text-red-400">{loginError}</p>
+              {isLockWarning
+                ? <Lock className="h-4 w-4 text-amber-400 shrink-0" aria-hidden="true" />
+                : <AlertTriangle className="h-4 w-4 text-red-400 shrink-0" aria-hidden="true" />}
+              <p className={cn('text-xs', isLockWarning ? 'text-amber-400' : 'text-red-400')}>
+                {loginError}
+              </p>
             </div>
-        )}
+          );
+        })()}
         <form onSubmit={handleCredentialSubmit} className="space-y-4">
           <div className="space-y-2">
             <Label htmlFor="username" required>Username</Label>
@@ -561,6 +598,30 @@ export default function LockScreen() {
           </Button>
         </form>
 
+        {/* Passkey login — shown when browser supports WebAuthn (U-01) */}
+        {!isSetup && supportsWebAuthn && (
+          <>
+            <div className="relative my-4">
+              <Separator />
+              <span className="absolute left-1/2 top-1/2 -translate-x-1/2 -translate-y-1/2 bg-card px-2 text-xs text-muted-foreground">
+                or
+              </span>
+            </div>
+            <Button
+              variant="outline"
+              className="w-full gap-2"
+              onClick={handlePasskeyLogin}
+              disabled={isPasskeyLoginPending}
+              aria-label="Sign in with a passkey"
+            >
+              {isPasskeyLoginPending
+                ? <Loader2 className="h-4 w-4 animate-spin" />
+                : <Fingerprint className="h-4 w-4" />}
+              Sign in with a passkey
+            </Button>
+          </>
+        )}
+
         {/* Open registration link — only shown on login screen when enabled */}
         {!isSetup && registrationOpen && (
           <div className="mt-4 text-center">

frontend/src/components/calendar/CalendarForm.tsx

@@ -1,8 +1,8 @@
-import { useState, FormEvent } from 'react';
-import { useMutation, useQueryClient } from '@tanstack/react-query';
+import { useState, FormEvent, useCallback } from 'react';
+import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query';
 import { toast } from 'sonner';
 import api, { getErrorMessage } from '@/lib/api';
-import type { Calendar } from '@/types';
+import type { Calendar, CalendarMemberInfo, CalendarPermission, Connection } from '@/types';
 import {
   Dialog,
   DialogContent,
@@ -14,6 +14,11 @@ import {
 import { Input } from '@/components/ui/input';
 import { Label } from '@/components/ui/label';
 import { Button } from '@/components/ui/button';
+import PermissionToggle from './PermissionToggle';
+import { useConnections } from '@/hooks/useConnections';
+import { useSharedCalendars } from '@/hooks/useSharedCalendars';
+import CalendarMemberSearch from './CalendarMemberSearch';
+import CalendarMemberList from './CalendarMemberList';
 
 interface CalendarFormProps {
   calendar: Calendar | null;
@@ -21,14 +26,8 @@ interface CalendarFormProps {
 }
 
 const colorSwatches = [
-  '#3b82f6', // blue
-  '#ef4444', // red
-  '#f97316', // orange
-  '#eab308', // yellow
-  '#22c55e', // green
-  '#8b5cf6', // purple
-  '#ec4899', // pink
-  '#06b6d4', // cyan
+  '#3b82f6', '#ef4444', '#f97316', '#eab308',
+  '#22c55e', '#8b5cf6', '#ec4899', '#06b6d4',
 ];
 
 export default function CalendarForm({ calendar, onClose }: CalendarFormProps) {
@@ -36,6 +35,23 @@ export default function CalendarForm({ calendar, onClose }: CalendarFormProps) {
   const [name, setName] = useState(calendar?.name || '');
   const [color, setColor] = useState(calendar?.color || '#3b82f6');
 
+  const [pendingInvite, setPendingInvite] = useState<{ conn: Connection; permission: CalendarPermission } | null>(null);
+
+  const { connections } = useConnections();
+  const { invite, isInviting, updateMember, removeMember } = useSharedCalendars();
+
+  const membersQuery = useQuery({
+    queryKey: ['calendar-members', calendar?.id],
+    queryFn: async () => {
+      const { data } = await api.get<CalendarMemberInfo[]>(
+        `/shared-calendars/${calendar!.id}/members`
+      );
+      return data;
+    },
+    enabled: !!calendar?.is_shared,
+  });
+  const members = membersQuery.data ?? [];
+
   const mutation = useMutation({
     mutationFn: async () => {
       if (calendar) {
@@ -78,11 +94,42 @@ export default function CalendarForm({ calendar, onClose }: CalendarFormProps) {
     mutation.mutate();
   };
 
+  const handleSelectConnection = useCallback((conn: Connection) => {
+    setPendingInvite({ conn, permission: 'read_only' });
+  }, []);
+
+  const handleSendInvite = async () => {
+    if (!calendar || !pendingInvite) return;
+    await invite({
+      calendarId: calendar.id,
+      connectionId: pendingInvite.conn.id,
+      permission: pendingInvite.permission,
+      canAddOthers: false,
+    });
+    setPendingInvite(null);
+  };
+
+  const handleUpdatePermission = async (memberId: number, permission: CalendarPermission) => {
+    if (!calendar) return;
+    await updateMember({ calendarId: calendar.id, memberId, permission });
+  };
+
+  const handleUpdateCanAddOthers = async (memberId: number, canAddOthers: boolean) => {
+    if (!calendar) return;
+    await updateMember({ calendarId: calendar.id, memberId, canAddOthers });
+  };
+
+  const handleRemoveMember = async (memberId: number) => {
+    if (!calendar) return;
+    await removeMember({ calendarId: calendar.id, memberId });
+  };
+
   const canDelete = calendar && !calendar.is_default && !calendar.is_system;
+  const showSharing = calendar && !calendar.is_system;
 
   return (
     <Dialog open={true} onOpenChange={onClose}>
-      <DialogContent>
+      <DialogContent className={calendar?.is_shared && showSharing ? 'max-w-3xl' : undefined}>
         <DialogClose onClick={onClose} />
         <DialogHeader>
           <DialogTitle>{calendar ? 'Edit Calendar' : 'New Calendar'}</DialogTitle>
@@ -108,7 +155,7 @@ export default function CalendarForm({ calendar, onClose }: CalendarFormProps) {
                   key={c}
                   type="button"
                   onClick={() => setColor(c)}
-                  className="h-8 w-8 rounded-full border-2 transition-all duration-150 hover:scale-110"
+                  className="h-6 w-6 rounded-full border-2 transition-all duration-150 hover:scale-110"
                   style={{
                     backgroundColor: c,
                     borderColor: color === c ? 'hsl(0 0% 98%)' : 'transparent',
@@ -119,6 +166,72 @@ export default function CalendarForm({ calendar, onClose }: CalendarFormProps) {
             </div>
           </div>
 
+          {showSharing && (
+            <>
+              {calendar?.is_shared && (
+                <div className="space-y-3">
+                  <div className="flex items-center justify-between">
+                    <Label className="mb-0">Members</Label>
+                    <span className="text-[11px] text-muted-foreground">
+                      You (Owner)
+                    </span>
+                  </div>
+
+                  {pendingInvite ? (
+                    <div
+                      className="rounded-lg border border-border bg-card-elevated p-4 space-y-3 animate-fade-in"
+                      style={{ borderLeftWidth: '3px', borderLeftColor: 'hsl(var(--accent-color) / 0.5)' }}
+                    >
+                      <div className="flex items-center justify-between">
+                        <span className="text-sm font-medium text-foreground">
+                          {pendingInvite.conn.connected_preferred_name || pendingInvite.conn.connected_umbral_name}
+                        </span>
+                        <button
+                          type="button"
+                          onClick={() => setPendingInvite(null)}
+                          className="text-xs text-muted-foreground hover:text-foreground transition-colors"
+                        >
+                          Cancel
+                        </button>
+                      </div>
+                      <div className="flex items-center gap-3">
+                        <PermissionToggle
+                          value={pendingInvite.permission}
+                          onChange={(p) => setPendingInvite((prev) => prev ? { ...prev, permission: p } : null)}
+                        />
+                        <div className="flex-1" />
+                        <Button
+                          type="button"
+                          size="sm"
+                          onClick={handleSendInvite}
+                          disabled={isInviting}
+                        >
+                          {isInviting ? 'Sending...' : 'Send Invite'}
+                        </Button>
+                      </div>
+                    </div>
+                  ) : (
+                    <CalendarMemberSearch
+                      connections={connections}
+                      existingMembers={members}
+                      onSelect={handleSelectConnection}
+                      isLoading={isInviting}
+                    />
+                  )}
+
+                  <CalendarMemberList
+                    members={members}
+                    isLoading={membersQuery.isLoading}
+                    isOwner={true}
+                    onUpdatePermission={handleUpdatePermission}
+                    onUpdateCanAddOthers={handleUpdateCanAddOthers}
+                    onRemove={handleRemoveMember}
+                  />
+                </div>
+              )}
+            </>
+          )}
+
           <DialogFooter>
             {canDelete && (
               <Button

frontend/src/components/calendar/CalendarMemberList.tsx

@@ -0,0 +1,55 @@
+import { Loader2 } from 'lucide-react';
+import type { CalendarMemberInfo, CalendarPermission } from '@/types';
+import CalendarMemberRow from './CalendarMemberRow';
+
+interface CalendarMemberListProps {
+  members: CalendarMemberInfo[];
+  isLoading?: boolean;
+  isOwner: boolean;
+  readOnly?: boolean;
+  onUpdatePermission?: (memberId: number, permission: CalendarPermission) => void;
+  onUpdateCanAddOthers?: (memberId: number, canAddOthers: boolean) => void;
+  onRemove?: (memberId: number) => void;
+}
+
+export default function CalendarMemberList({
+  members,
+  isLoading = false,
+  isOwner,
+  readOnly = false,
+  onUpdatePermission,
+  onUpdateCanAddOthers,
+  onRemove,
+}: CalendarMemberListProps) {
+  if (isLoading) {
+    return (
+      <div className="flex items-center justify-center py-4">
+        <Loader2 className="h-5 w-5 animate-spin text-muted-foreground" />
+      </div>
+    );
+  }
+
+  if (members.length === 0) {
+    return (
+      <p className="text-xs text-muted-foreground py-2">
+        Search your connections to add members
+      </p>
+    );
+  }
+
+  return (
+    <div className="space-y-2 max-h-72 overflow-y-auto">
+      {members.map((member) => (
+        <CalendarMemberRow
+          key={member.id}
+          member={member}
+          isOwner={isOwner}
+          readOnly={readOnly}
+          onUpdatePermission={onUpdatePermission}
+          onUpdateCanAddOthers={onUpdateCanAddOthers}
+          onRemove={onRemove}
+        />
+      ))}
+    </div>
+  );
+}

frontend/src/components/calendar/CalendarMemberRow.tsx

@@ -0,0 +1,86 @@
+import { X, UserPlus } from 'lucide-react';
+import type { CalendarMemberInfo, CalendarPermission } from '@/types';
+import { Checkbox } from '@/components/ui/checkbox';
+import { useConfirmAction } from '@/hooks/useConfirmAction';
+import PermissionBadge from './PermissionBadge';
+import PermissionToggle from './PermissionToggle';
+
+interface CalendarMemberRowProps {
+  member: CalendarMemberInfo;
+  isOwner: boolean;
+  readOnly?: boolean;
+  onUpdatePermission?: (memberId: number, permission: CalendarPermission) => void;
+  onUpdateCanAddOthers?: (memberId: number, canAddOthers: boolean) => void;
+  onRemove?: (memberId: number) => void;
+}
+
+export default function CalendarMemberRow({
+  member,
+  isOwner,
+  readOnly = false,
+  onUpdatePermission,
+  onUpdateCanAddOthers,
+  onRemove,
+}: CalendarMemberRowProps) {
+  const { confirming, handleClick: handleRemoveClick } = useConfirmAction(
+    () => onRemove?.(member.id)
+  );
+
+  const displayName = member.preferred_name || member.umbral_name;
+  const initial = displayName.charAt(0).toUpperCase();
+
+  return (
+    <div className="flex items-center gap-3 rounded-lg border border-border p-3 transition-all duration-200 hover:border-border/80">
+      <div className="h-8 w-8 rounded-full bg-violet-500/15 flex items-center justify-center shrink-0">
+        <span className="text-sm text-violet-400 font-medium">{initial}</span>
+      </div>
+
+      <div className="flex items-center gap-2 min-w-0 flex-1 truncate">
+        <span className="text-sm font-medium truncate">{displayName}</span>
+        {member.preferred_name && (
+          <span className="text-xs text-violet-400 truncate shrink-0">{member.umbral_name}</span>
+        )}
+        {member.status === 'pending' && (
+          <span className="text-[9px] px-1.5 py-0.5 rounded-full bg-orange-500/10 text-orange-400 font-medium shrink-0">
+            Pending
+          </span>
+        )}
+      </div>
+
+      {readOnly ? (
+        <PermissionBadge permission={member.permission} />
+      ) : isOwner ? (
+        <div className="flex items-center gap-2.5 shrink-0">
+          <PermissionToggle
+            value={member.permission}
+            onChange={(p) => onUpdatePermission?.(member.id, p)}
+          />
+          {(member.permission === 'create_modify' || member.permission === 'full_access') && (
+            <label className="flex items-center gap-1.5 cursor-pointer shrink-0" title="Can add others">
+              <Checkbox
+                checked={member.can_add_others}
+                onChange={() => onUpdateCanAddOthers?.(member.id, !member.can_add_others)}
+                className="h-3.5 w-3.5"
+              />
+              <UserPlus className="h-3.5 w-3.5 text-muted-foreground" />
+            </label>
+          )}
+          <button
+            type="button"
+            onClick={handleRemoveClick}
+            className="text-muted-foreground hover:text-destructive transition-colors"
+            title={confirming ? 'Click again to confirm' : 'Remove member'}
+          >
+            {confirming ? (
+              <span className="text-[10px] text-destructive font-medium px-1">Sure?</span>
+            ) : (
+              <X className="h-4 w-4" />
+            )}
+          </button>
+        </div>
+      ) : (
+        <PermissionBadge permission={member.permission} />
+      )}
+    </div>
+  );
+}

frontend/src/components/calendar/CalendarMemberSearch.tsx

@@ -0,0 +1,103 @@
+import { useState, useRef, useEffect } from 'react';
+import { Search, Loader2 } from 'lucide-react';
+import { Input } from '@/components/ui/input';
+import type { Connection, CalendarMemberInfo } from '@/types';
+
+interface CalendarMemberSearchProps {
+  connections: Connection[];
+  existingMembers: CalendarMemberInfo[];
+  onSelect: (connection: Connection) => void;
+  isLoading?: boolean;
+}
+
+export default function CalendarMemberSearch({
+  connections,
+  existingMembers,
+  onSelect,
+  isLoading = false,
+}: CalendarMemberSearchProps) {
+  const [query, setQuery] = useState('');
+  const [focused, setFocused] = useState(false);
+  const containerRef = useRef<HTMLDivElement>(null);
+
+  useEffect(() => {
+    const handler = (e: MouseEvent) => {
+      if (containerRef.current && !containerRef.current.contains(e.target as Node)) {
+        setFocused(false);
+      }
+    };
+    document.addEventListener('mousedown', handler);
+    return () => document.removeEventListener('mousedown', handler);
+  }, []);
+
+  const existingUserIds = new Set(existingMembers.map((m) => m.user_id));
+
+  const filtered = connections.filter((c) => {
+    if (existingUserIds.has(c.connected_user_id)) return false;
+    if (!query.trim()) return true;
+    const q = query.toLowerCase();
+    return (
+      c.connected_umbral_name.toLowerCase().includes(q) ||
+      (c.connected_preferred_name?.toLowerCase().includes(q) ?? false)
+    );
+  });
+
+  const handleSelect = (connection: Connection) => {
+    onSelect(connection);
+    setQuery('');
+    setFocused(false);
+  };
+
+  return (
+    <div ref={containerRef} className="relative">
+      <div className="relative">
+        {isLoading ? (
+          <Loader2 className="absolute left-2.5 top-1/2 -translate-y-1/2 h-3.5 w-3.5 text-muted-foreground animate-spin" />
+        ) : (
+          <Search className="absolute left-2.5 top-1/2 -translate-y-1/2 h-3.5 w-3.5 text-muted-foreground" />
+        )}
+        <Input
+          placeholder="Search connections to invite..."
+          value={query}
+          onChange={(e) => setQuery(e.target.value)}
+          onFocus={() => setFocused(true)}
+          className="pl-8 h-9 text-sm"
+        />
+      </div>
+
+      {focused && filtered.length > 0 && (
+        <div className="absolute z-50 mt-1 w-full rounded-md border bg-popover shadow-lg overflow-hidden max-h-40 overflow-y-auto">
+          {filtered.map((conn) => {
+            const displayName = conn.connected_preferred_name || conn.connected_umbral_name;
+            const initial = displayName.charAt(0).toUpperCase();
+            return (
+              <button
+                key={conn.id}
+                type="button"
+                onMouseDown={(e) => e.preventDefault()}
+                onClick={() => handleSelect(conn)}
+                className="flex items-center gap-2.5 w-full px-3 py-2 text-sm text-left hover:bg-accent/10 transition-colors"
+              >
+                <div className="h-6 w-6 rounded-full bg-violet-500/15 flex items-center justify-center shrink-0">
+                  <span className="text-xs text-violet-400 font-medium">{initial}</span>
+                </div>
+                <div className="min-w-0 flex-1">
+                  <span className="font-medium truncate block">{displayName}</span>
+                  {conn.connected_preferred_name && (
+                    <span className="text-xs text-muted-foreground">{conn.connected_umbral_name}</span>
+                  )}
+                </div>
+              </button>
+            );
+          })}
+        </div>
+      )}
+
+      {focused && query.trim() && filtered.length === 0 && (
+        <div className="absolute z-50 mt-1 w-full rounded-md border bg-popover shadow-lg p-3">
+          <p className="text-xs text-muted-foreground text-center">No matching connections</p>
+        </div>
+      )}
+    </div>
+  );
+}