Merge feature/event-invitations: full event invitation system

Adds event invitations with RSVP, per-occurrence overrides for recurring
events, display calendar assignment, can_modify toggle for granting
invitees edit access, active-invitee icon on owner's calendar, and
in-app notification integration. Three QA reviews and two penetration
tests passed. Includes field allowlist for invited editors, connection
validation, 20-invitation cap, and can_modify reset on decline.

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

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/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, shared_calendars as shared_calendars_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
 from app.jobs.notifications import run_notification_dispatch
 
 # Import models so Alembic's autogenerate can discover them
@@ -22,6 +22,7 @@ from app.models import connection_request as _connection_request_model  # noqa:
 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
 
 
 # ---------------------------------------------------------------------------
@@ -137,6 +138,8 @@ 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

@@ -20,6 +20,7 @@ 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
 
 __all__ = [
     "Settings",
@@ -44,4 +45,6 @@ __all__ = [
     "UserConnection",
     "CalendarMember",
     "EventLock",
+    "EventInvitation",
+    "EventInvitationOverride",
 ]

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/notification.py

@@ -8,6 +8,7 @@ from app.database import Base
 _NOTIFICATION_TYPES = (
     "connection_request", "connection_accepted", "connection_rejected",
     "calendar_invite", "calendar_invite_accepted", "calendar_invite_rejected",
+    "event_invite", "event_invite_response",
     "info", "warning", "reminder", "system",
 )
 

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_, case
+from sqlalchemy import false as sa_false, select, func, or_, case
 from datetime import datetime, date, timedelta
 from typing import Optional, List, Dict, Any
 
@@ -12,7 +12,8 @@ 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.services.calendar_sharing import get_accessible_calendar_ids
+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)
 
-    # Fetch all accessible calendar IDs (owned + accepted shared memberships)
-    user_calendar_ids = await get_accessible_calendar_ids(current_user.id, db)
+    # 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(
-        CalendarEvent.calendar_id.in_(user_calendar_ids),
+        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,
@@ -95,7 +116,11 @@ async def get_dashboard(
     # 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(
-        CalendarEvent.calendar_id.in_(user_calendar_ids),
+        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
         ],
@@ -169,8 +197,8 @@ async def get_upcoming(
     overdue_floor = today - timedelta(days=30)
     overdue_floor_dt = datetime.combine(overdue_floor, datetime.min.time())
 
-    # Fetch all accessible calendar IDs (owned + accepted shared memberships)
-    user_calendar_ids = await get_accessible_calendar_ids(current_user.id, db)
+    # Fetch all accessible calendar IDs + invited event IDs
+    user_calendar_ids, invited_event_ids = await get_accessible_event_scope(current_user.id, db)
 
     # Build queries — include overdue todos (up to 30 days back) and snoozed reminders
     todos_query = select(Todo).where(
@@ -182,7 +210,11 @@ async def get_upcoming(
     )
 
     events_query = select(CalendarEvent).where(
-        CalendarEvent.calendar_id.in_(user_calendar_ids),
+        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,
@@ -206,6 +238,20 @@ async def get_upcoming(
     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]] = []
 
@@ -223,6 +269,8 @@ async def get_upcoming(
 
     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,
@@ -233,6 +281,9 @@ async def get_upcoming(
             "all_day": event.all_day,
             "color": event.color,
             "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:

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
 
@@ -19,14 +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, require_permission
+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,
@@ -38,15 +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(
@@ -143,13 +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 + shared memberships
-    all_calendar_ids = await get_accessible_calendar_ids(current_user.id, db)
+    # 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_(all_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
@@ -171,7 +209,88 @@ async def get_events(
     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(
@@ -281,14 +400,20 @@ async def get_event(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user),
 ):
-    all_calendar_ids = await get_accessible_calendar_ids(current_user.id, db)
+    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_(all_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()
@@ -306,7 +431,11 @@ async def update_event(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user),
 ):
+    # 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)
@@ -319,14 +448,62 @@ async def update_event(
     event = result.scalar_one_or_none()
 
     if not event:
-        raise HTTPException(status_code=404, detail="Calendar event not found")
+        # 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])
 
-    # Shared calendar: require create_modify+ and check lock
-    await require_permission(db, event.calendar_id, current_user.id, "create_modify")
-    await check_lock_for_edit(db, event_id, current_user.id, event.calendar_id)
+        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)
 
@@ -335,23 +512,24 @@ 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
 
-    # SEC-04: if calendar_id is being changed, verify the target belongs to the user
-    # 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)
+    if not is_invited_editor:
+        # SEC-04: if calendar_id is being changed, verify the target belongs to the user
+        # 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",
+        # 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)
@@ -451,6 +629,9 @@ async def delete_event(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user),
 ):
+    # 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(

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/services/calendar_sharing.py

@@ -7,7 +7,7 @@ import logging
 from datetime import datetime, timedelta
 
 from fastapi import HTTPException
-from sqlalchemy import delete, select, text, update
+from sqlalchemy import delete, literal_column, select, text, union_all, update
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.models.calendar import Calendar
@@ -34,6 +34,42 @@ async def get_accessible_calendar_ids(user_id: int, db: AsyncSession) -> list[in
     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
@@ -220,6 +256,10 @@ async def cascade_on_disconnect(db: AsyncSession, user_a_id: int, user_b_id: int
             {"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:

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,
+        )
+    )

frontend/src/components/calendar/CalendarPage.tsx

@@ -10,7 +10,7 @@ import timeGridPlugin from '@fullcalendar/timegrid';
 import interactionPlugin from '@fullcalendar/interaction';
 import enAuLocale from '@fullcalendar/core/locales/en-au';
 import type { EventClickArg, DateSelectArg, EventDropArg, DatesSetArg, EventContentArg } from '@fullcalendar/core';
-import { ChevronLeft, ChevronRight, PanelLeft, Plus, Search, Repeat } from 'lucide-react';
+import { ChevronLeft, ChevronRight, PanelLeft, Plus, Search, Repeat, Users } from 'lucide-react';
 import api, { getErrorMessage } from '@/lib/api';
 import axios from 'axios';
 import type { CalendarEvent, EventTemplate, Location as LocationType, CalendarPermission } from '@/types';
@@ -229,9 +229,8 @@ export default function CalendarPage() {
       });
       return data;
     },
-    // AW-3: Reduce from 5s to 30s — personal organiser doesn't need 12 calls/min
-    refetchInterval: 30_000,
-    staleTime: 30_000,
+    refetchInterval: 5_000,
+    staleTime: 5_000,
   });
 
   const selectedEvent = useMemo(
@@ -242,9 +241,10 @@ export default function CalendarPage() {
   const selectedEventPermission = selectedEvent ? permissionMap.get(selectedEvent.calendar_id) ?? null : null;
   const selectedEventIsShared = selectedEvent ? sharedCalendarIds.has(selectedEvent.calendar_id) : false;
 
-  // Close panel if shared calendar was removed while viewing
+  // Close panel if shared calendar was removed while viewing (skip for invited events)
   useEffect(() => {
     if (!selectedEvent || allCalendarIds.size === 0) return;
+    if (selectedEvent.is_invited) return;
     if (!allCalendarIds.has(selectedEvent.calendar_id)) {
       handlePanelClose();
       toast.info('This calendar is no longer available');
@@ -331,7 +331,16 @@ export default function CalendarPage() {
 
   const filteredEvents = useMemo(() => {
     if (calendars.length === 0) return events;
-    return events.filter((e) => visibleCalendarIds.has(e.calendar_id));
+    // Invited events: if display_calendar_id is set, respect that calendar's visibility;
+    // otherwise (pending) always show
+    return events.filter((e) => {
+      if (e.is_invited) {
+        return e.display_calendar_id
+          ? visibleCalendarIds.has(e.display_calendar_id)
+          : true;
+      }
+      return visibleCalendarIds.has(e.calendar_id);
+    });
   }, [events, visibleCalendarIds, calendars.length]);
 
   const searchResults = useMemo(() => {
@@ -361,22 +370,28 @@ export default function CalendarPage() {
     }
   };
 
-  const calendarEvents = filteredEvents.map((event) => ({
-    id: String(event.id),
-    title: event.title,
-    start: event.start_datetime,
-    end: event.end_datetime || undefined,
-    allDay: event.all_day,
-    color: 'transparent',
-    editable: permissionMap.get(event.calendar_id) !== 'read_only',
-    extendedProps: {
-      is_virtual: event.is_virtual,
-      is_recurring: event.is_recurring,
-      parent_event_id: event.parent_event_id,
-      calendar_id: event.calendar_id,
-      calendarColor: event.calendar_color || 'hsl(var(--accent-color))',
-    },
-  }));
+  const calendarEvents = filteredEvents
+    // Exclude declined invited events from calendar display
+    .filter((event) => !(event.is_invited && event.invitation_status === 'declined'))
+    .map((event) => ({
+      id: String(event.id),
+      title: event.title,
+      start: event.start_datetime,
+      end: event.end_datetime || undefined,
+      allDay: event.all_day,
+      color: 'transparent',
+      editable: (event.is_invited && !!event.can_modify) || (!event.is_invited && permissionMap.get(event.calendar_id) !== 'read_only'),
+      extendedProps: {
+        is_virtual: event.is_virtual,
+        is_recurring: event.is_recurring,
+        parent_event_id: event.parent_event_id,
+        calendar_id: event.calendar_id,
+        calendarColor: event.calendar_color || 'hsl(var(--accent-color))',
+        is_invited: event.is_invited,
+        can_modify: event.can_modify,
+        has_active_invitees: event.has_active_invitees,
+      },
+    }));
 
   const handleEventClick = (info: EventClickArg) => {
     const event = events.find((e) => String(e.id) === info.event.id);
@@ -516,29 +531,44 @@ export default function CalendarPage() {
     const isMonth = arg.view.type === 'dayGridMonth';
     const isAllDay = arg.event.allDay;
     const isRecurring = arg.event.extendedProps.is_recurring || arg.event.extendedProps.parent_event_id;
+    const isInvited = arg.event.extendedProps.is_invited;
+    const hasActiveInvitees = arg.event.extendedProps.has_active_invitees;
+    const calColor = arg.event.extendedProps.calendarColor as string;
 
-    const repeatIcon = isRecurring ? (
-      <Repeat className="h-2.5 w-2.5 shrink-0 opacity-50" />
-    ) : null;
+    // Sync --event-color on the parent FC element so CSS rules (background, hover)
+    // pick up color changes without requiring a full remount (eventDidMount only fires once).
+    const syncColor = (el: HTMLElement | null) => {
+      if (el && calColor) {
+        const fcEl = el.closest('.umbra-event');
+        if (fcEl) (fcEl as HTMLElement).style.setProperty('--event-color', calColor);
+      }
+    };
+
+    const icons = (
+      <>
+        {(isInvited || hasActiveInvitees) && <Users className="h-2.5 w-2.5 shrink-0 opacity-60" />}
+        {isRecurring && <Repeat className="h-2.5 w-2.5 shrink-0 opacity-50" />}
+      </>
+    );
 
     if (isMonth) {
       if (isAllDay) {
         return (
-          <div className="flex items-center gap-1 truncate px-1">
+          <div ref={syncColor} className="flex items-center gap-1 truncate px-1">
             <span className="text-[11px] font-medium truncate">{arg.event.title}</span>
-            {repeatIcon}
+            {icons}
           </div>
         );
       }
       // Timed events in month: dot + title + time right-aligned
       return (
-        <div className="flex items-center gap-1.5 truncate w-full">
+        <div ref={syncColor} className="flex items-center gap-1.5 truncate w-full">
           <span
             className="fc-daygrid-event-dot"
-            style={{ borderColor: 'var(--event-color)' }}
+            style={{ borderColor: calColor || 'var(--event-color)' }}
           />
           <span className="text-[11px] font-medium truncate">{arg.event.title}</span>
-          {repeatIcon}
+          {icons}
           <span className="umbra-event-time text-[10px] opacity-50 shrink-0 ml-auto tabular-nums">{arg.timeText}</span>
         </div>
       );
@@ -546,10 +576,10 @@ export default function CalendarPage() {
 
     // Week/day view — title on top, time underneath
     return (
-      <div className="flex flex-col overflow-hidden h-full">
+      <div ref={syncColor} className="flex flex-col overflow-hidden h-full">
         <div className="flex items-center gap-1">
           <span className="text-[12px] font-medium truncate">{arg.event.title}</span>
-          {repeatIcon}
+          {icons}
         </div>
         <span className="text-[10px] opacity-50 leading-tight tabular-nums">{arg.timeText}</span>
       </div>

frontend/src/components/calendar/EventDetailPanel.tsx

@@ -1,9 +1,9 @@
-import { useState, useEffect, useCallback } from 'react';
+import { useState, useEffect, useCallback, useMemo } from 'react';
 import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query';
 import { toast } from 'sonner';
 import { format, parseISO } from 'date-fns';
 import {
-  X, Pencil, Trash2, Save, Clock, MapPin, AlignLeft, Repeat, Star, Calendar, Loader2,
+  X, Pencil, Trash2, Save, Clock, MapPin, AlignLeft, Repeat, Star, Calendar, Loader2, LogOut,
 } from 'lucide-react';
 import axios from 'axios';
 import api, { getErrorMessage } from '@/lib/api';
@@ -11,9 +11,12 @@ import type { CalendarEvent, Location as LocationType, RecurrenceRule, CalendarP
 import { useCalendars } from '@/hooks/useCalendars';
 import { useConfirmAction } from '@/hooks/useConfirmAction';
 import { useEventLock } from '@/hooks/useEventLock';
+import { useEventInvitations, useConnectedUsersSearch } from '@/hooks/useEventInvitations';
 import { formatUpdatedAt } from '@/components/shared/utils';
 import CopyableField from '@/components/shared/CopyableField';
 import EventLockBanner from './EventLockBanner';
+import { InviteeList, InviteSearch, RsvpButtons } from './InviteeSection';
+import LeaveEventDialog from './LeaveEventDialog';
 import { Button } from '@/components/ui/button';
 import { Input } from '@/components/ui/input';
 import { DatePicker } from '@/components/ui/date-picker';
@@ -234,6 +237,7 @@ export default function EventDetailPanel({
       .filter((m) => m.permission === 'create_modify' || m.permission === 'full_access')
       .map((m) => ({ id: m.calendar_id, name: m.calendar_name, color: m.local_color || m.calendar_color, is_default: false })),
   ];
+  const ownedCalendars = calendars.filter((c) => !c.is_system);
   const defaultCalendar = calendars.find((c) => c.is_default);
 
   const { data: locations = [] } = useQuery({
@@ -251,6 +255,24 @@ export default function EventDetailPanel({
   const [lockInfo, setLockInfo] = useState<EventLockInfo | null>(null);
 
 
+  // Event invitation hooks
+  const eventNumericId = event && typeof event.id === 'number' ? event.id : null;
+  const parentEventId = event?.parent_event_id ?? eventNumericId;
+  const {
+    invitees, invite, isInviting, respond: respondInvitation,
+    isResponding, override: overrideInvitation, updateDisplayCalendar,
+    isUpdatingDisplayCalendar, leave: leaveInvitation, isLeaving,
+    toggleCanModify, togglingInvitationId,
+  } = useEventInvitations(parentEventId);
+  const { connections } = useConnectedUsersSearch();
+  const [showLeaveDialog, setShowLeaveDialog] = useState(false);
+
+  const isInvitedEvent = !!event?.is_invited;
+  const canModifyAsInvitee = isInvitedEvent && !!event?.can_modify;
+  const existingInviteeIds = useMemo(() => new Set(invitees.map((i) => i.user_id)), [invitees]);
+  const myInvitationStatus = event?.invitation_status ?? null;
+  const myInvitationId = event?.invitation_id ?? null;
+
   const [isEditing, setIsEditing] = useState(isCreating);
   const [editState, setEditState] = useState<EditState>(() =>
     isCreating
@@ -294,7 +316,7 @@ export default function EventDetailPanel({
   const isRecurring = !!(event?.is_recurring || event?.parent_event_id);
 
   // Permission helpers
-  const canEdit = !isSharedEvent || myPermission === 'owner' || myPermission === 'create_modify' || myPermission === 'full_access';
+  const canEdit = canModifyAsInvitee || !isSharedEvent || myPermission === 'owner' || myPermission === 'create_modify' || myPermission === 'full_access';
   const canDelete = !isSharedEvent || myPermission === 'owner' || myPermission === 'full_access';
 
   // Reset state when event changes
@@ -345,10 +367,13 @@ export default function EventDetailPanel({
         end_datetime: endDt,
         all_day: data.all_day,
         location_id: data.location_id ? parseInt(data.location_id) : null,
-        calendar_id: data.calendar_id ? parseInt(data.calendar_id) : null,
         is_starred: data.is_starred,
         recurrence_rule: rule,
       };
+      // Invited editors cannot change calendars — omit calendar_id from payload
+      if (!canModifyAsInvitee) {
+        payload.calendar_id = data.calendar_id ? parseInt(data.calendar_id) : null;
+      }
 
       if (event && !isCreating) {
         if (editScope) payload.edit_scope = editScope;
@@ -418,7 +443,14 @@ export default function EventDetailPanel({
     }
 
     if (isRecurring) {
-      setScopeStep('edit');
+      // Invited editors can only edit "this" occurrence — skip scope step
+      if (canModifyAsInvitee) {
+        setEditScope('this');
+        if (event) setEditState(buildEditStateFromEvent(event));
+        setIsEditing(true);
+      } else {
+        setScopeStep('edit');
+      }
     } else {
       if (event) setEditState(buildEditStateFromEvent(event));
       setIsEditing(true);
@@ -579,7 +611,8 @@ export default function EventDetailPanel({
               <>
                 {!event?.is_virtual && (
                   <>
-                    {canEdit && (
+                    {/* Edit button — own events, shared with edit permission, or can_modify invitees */}
+                    {canEdit && (!isInvitedEvent || canModifyAsInvitee) && (
                       <Button
                         variant="ghost"
                         size="icon"
@@ -591,7 +624,20 @@ export default function EventDetailPanel({
                         {isAcquiringLock ? <Loader2 className="h-3.5 w-3.5 animate-spin" /> : <Pencil className="h-3.5 w-3.5" />}
                       </Button>
                     )}
-                    {canDelete && (
+                    {/* Leave button for invited events */}
+                    {isInvitedEvent && myInvitationId && (
+                      <Button
+                        variant="ghost"
+                        size="icon"
+                        className="h-7 w-7 text-muted-foreground hover:text-destructive"
+                        onClick={() => setShowLeaveDialog(true)}
+                        title="Leave event"
+                      >
+                        <LogOut className="h-3.5 w-3.5" />
+                      </Button>
+                    )}
+                    {/* Delete button for own events */}
+                    {canDelete && !isInvitedEvent && (
                       confirmingDelete ? (
                         <Button
                           variant="ghost"
@@ -743,20 +789,22 @@ export default function EventDetailPanel({
               </div>
             </div>
 
-            <div className="grid grid-cols-2 gap-3">
-              <div className="space-y-1">
-                <Label htmlFor="panel-calendar">Calendar</Label>
-                <Select
-                  id="panel-calendar"
-                  value={editState.calendar_id}
-                  onChange={(e) => updateField('calendar_id', e.target.value)}
-                  className="text-xs"
-                >
-                  {selectableCalendars.map((cal) => (
-                    <option key={cal.id} value={cal.id}>{cal.name}</option>
-                  ))}
-                </Select>
-              </div>
+            <div className={`grid ${canModifyAsInvitee ? 'grid-cols-1' : 'grid-cols-2'} gap-3`}>
+              {!canModifyAsInvitee && (
+                <div className="space-y-1">
+                  <Label htmlFor="panel-calendar">Calendar</Label>
+                  <Select
+                    id="panel-calendar"
+                    value={editState.calendar_id}
+                    onChange={(e) => updateField('calendar_id', e.target.value)}
+                    className="text-xs"
+                  >
+                    {selectableCalendars.map((cal) => (
+                      <option key={cal.id} value={cal.id}>{cal.name}</option>
+                    ))}
+                  </Select>
+                </div>
+              )}
               <div className="space-y-1">
                 <Label htmlFor="panel-location">Location</Label>
                 <LocationPicker
@@ -789,22 +837,24 @@ export default function EventDetailPanel({
               </div>
             </div>
 
-            {/* Recurrence */}
-            <div className="space-y-1">
-              <Label htmlFor="panel-recurrence">Recurrence</Label>
-              <Select
-                id="panel-recurrence"
-                value={editState.recurrence_type}
-                onChange={(e) => updateField('recurrence_type', e.target.value)}
-                className="text-xs"
-              >
-                <option value="">None</option>
-                <option value="every_n_days">Every X days</option>
-                <option value="weekly">Weekly</option>
-                <option value="monthly_nth_weekday">Monthly (nth weekday)</option>
-                <option value="monthly_date">Monthly (date)</option>
-              </Select>
-            </div>
+            {/* Recurrence — hidden for invited editors (they can only edit "this" occurrence) */}
+            {!canModifyAsInvitee && (
+              <div className="space-y-1">
+                <Label htmlFor="panel-recurrence">Recurrence</Label>
+                <Select
+                  id="panel-recurrence"
+                  value={editState.recurrence_type}
+                  onChange={(e) => updateField('recurrence_type', e.target.value)}
+                  className="text-xs"
+                >
+                  <option value="">None</option>
+                  <option value="every_n_days">Every X days</option>
+                  <option value="weekly">Weekly</option>
+                  <option value="monthly_nth_weekday">Monthly (nth weekday)</option>
+                  <option value="monthly_date">Monthly (date)</option>
+                </Select>
+              </div>
+            )}
 
             {editState.recurrence_type === 'every_n_days' && (
               <div className="space-y-1">
@@ -898,19 +948,47 @@ export default function EventDetailPanel({
           <>
             {/* 2-column grid: Calendar, Starred, Start, End, Location, Recurrence */}
             <div className="grid grid-cols-2 gap-3">
-              {/* Calendar */}
+              {/* Calendar — for invited events with accepted/tentative, show picker */}
               <div className="space-y-1">
                 <div className="flex items-center gap-1.5 text-[11px] text-muted-foreground uppercase tracking-wider">
                   <Calendar className="h-3 w-3" />
                   Calendar
                 </div>
-                <div className="flex items-center gap-2">
-                  <div
-                    className="w-2 h-2 rounded-full shrink-0"
-                    style={{ backgroundColor: event?.calendar_color || 'hsl(var(--accent-color))' }}
-                  />
-                  <span className="text-sm">{event?.calendar_name}</span>
-                </div>
+                {isInvitedEvent && myInvitationId && (myInvitationStatus === 'accepted' || myInvitationStatus === 'tentative') ? (
+                  <div className="flex items-center gap-2">
+                    <div
+                      className="w-2 h-2 rounded-full shrink-0"
+                      style={{ backgroundColor: event?.calendar_color || '#6B7280' }}
+                    />
+                    <Select
+                      aria-label="Display calendar"
+                      value={event?.display_calendar_id?.toString() || ''}
+                      onChange={(e) => {
+                        const calId = parseInt(e.target.value);
+                        if (calId && myInvitationId) {
+                          updateDisplayCalendar({ invitationId: myInvitationId, calendarId: calId });
+                        }
+                      }}
+                      className="text-xs h-8 py-1"
+                      disabled={isUpdatingDisplayCalendar}
+                    >
+                      {!event?.display_calendar_id && (
+                        <option value="" disabled>Assign to calendar...</option>
+                      )}
+                      {ownedCalendars.map((cal) => (
+                        <option key={cal.id} value={cal.id}>{cal.name}</option>
+                      ))}
+                    </Select>
+                  </div>
+                ) : (
+                  <div className="flex items-center gap-2">
+                    <div
+                      className="w-2 h-2 rounded-full shrink-0"
+                      style={{ backgroundColor: event?.calendar_color || 'hsl(var(--accent-color))' }}
+                    />
+                    <span className="text-sm">{event?.calendar_name}</span>
+                  </div>
+                )}
               </div>
 
               {/* Starred */}
@@ -988,6 +1066,54 @@ export default function EventDetailPanel({
               </div>
             )}
 
+            {/* Invitee section — view mode */}
+            {event && !event.is_virtual && (
+              <>
+                {/* RSVP buttons for invitees */}
+                {isInvitedEvent && myInvitationId && (
+                  <div className="space-y-1">
+                    <div className="flex items-center gap-1.5 text-[11px] text-muted-foreground uppercase tracking-wider">
+                      Your RSVP
+                    </div>
+                    <RsvpButtons
+                      currentStatus={myInvitationStatus || 'pending'}
+                      onRespond={(status) => {
+                        if (event.parent_event_id && eventNumericId) {
+                          overrideInvitation({ invitationId: myInvitationId, occurrenceId: eventNumericId, status });
+                        } else {
+                          respondInvitation({ invitationId: myInvitationId, status });
+                        }
+                      }}
+                      isResponding={isResponding}
+                    />
+                  </div>
+                )}
+
+                {/* Invitee list */}
+                {invitees.length > 0 && (
+                  <InviteeList
+                    invitees={invitees}
+                    isRecurringChild={!!event.parent_event_id}
+                    isOwner={myPermission === 'owner'}
+                    onToggleCanModify={(invitationId, canModify) =>
+                      toggleCanModify({ invitationId, canModify })
+                    }
+                    togglingInvitationId={togglingInvitationId}
+                  />
+                )}
+
+                {/* Invite search for event owner/editor */}
+                {!isInvitedEvent && canEdit && (
+                  <InviteSearch
+                    connections={connections}
+                    existingInviteeIds={existingInviteeIds}
+                    onInvite={(userIds) => invite(userIds)}
+                    isInviting={isInviting}
+                  />
+                )}
+              </>
+            )}
+
             {/* Updated at */}
             {event && !event.is_virtual && (
               <div className="pt-2 border-t border-border">
@@ -996,6 +1122,23 @@ export default function EventDetailPanel({
                 </span>
               </div>
             )}
+
+            {/* Leave event dialog */}
+            {event && isInvitedEvent && myInvitationId && (
+              <LeaveEventDialog
+                open={showLeaveDialog}
+                onClose={() => setShowLeaveDialog(false)}
+                onConfirm={() => {
+                  leaveInvitation(myInvitationId)
+                    .then(() => onClose())
+                    .catch(() => {})
+                    .finally(() => setShowLeaveDialog(false));
+                }}
+                eventTitle={event.title}
+                isRecurring={!!(event.is_recurring || event.parent_event_id)}
+                isLeaving={isLeaving}
+              />
+            )}
           </>
         )}
       </div>

frontend/src/components/calendar/InviteeSection.tsx

@@ -0,0 +1,264 @@
+import { useState, useMemo } from 'react';
+import { Users, UserPlus, Search, X, Pencil, PencilOff } from 'lucide-react';
+import { Input } from '@/components/ui/input';
+import { Button } from '@/components/ui/button';
+import type { EventInvitation, Connection } from '@/types';
+
+// ── Status display helpers ──
+
+const STATUS_CONFIG = {
+  accepted: { label: 'Going', dotClass: 'bg-green-400', textClass: 'text-green-400' },
+  tentative: { label: 'Tentative', dotClass: 'bg-amber-400', textClass: 'text-amber-400' },
+  declined: { label: 'Declined', dotClass: 'bg-red-400', textClass: 'text-red-400' },
+  pending: { label: 'Pending', dotClass: 'bg-neutral-500', textClass: 'text-muted-foreground' },
+} as const;
+
+function StatusBadge({ status }: { status: string }) {
+  const config = STATUS_CONFIG[status as keyof typeof STATUS_CONFIG] ?? STATUS_CONFIG.pending;
+  return (
+    <div className="flex items-center gap-1.5">
+      <span className={`w-[7px] h-[7px] rounded-full ${config.dotClass}`} />
+      <span className={`text-xs ${config.textClass}`}>{config.label}</span>
+    </div>
+  );
+}
+
+function AvatarCircle({ name }: { name: string }) {
+  const letter = name?.charAt(0)?.toUpperCase() || '?';
+  return (
+    <div className="w-7 h-7 rounded-full bg-muted flex items-center justify-center shrink-0">
+      <span className="text-xs font-medium text-muted-foreground">{letter}</span>
+    </div>
+  );
+}
+
+// ── View Mode: InviteeList ──
+
+interface InviteeListProps {
+  invitees: EventInvitation[];
+  isRecurringChild?: boolean;
+  isOwner?: boolean;
+  onToggleCanModify?: (invitationId: number, canModify: boolean) => void;
+  togglingInvitationId?: number | null;
+}
+
+export function InviteeList({ invitees, isRecurringChild, isOwner, onToggleCanModify, togglingInvitationId }: InviteeListProps) {
+  if (invitees.length === 0) return null;
+
+  const goingCount = invitees.filter((i) => i.status === 'accepted').length;
+  const countLabel = goingCount > 0 ? `${goingCount} going` : null;
+
+  return (
+    <div className="space-y-1">
+      <div className="flex items-center justify-between">
+        <div className="flex items-center gap-1.5 text-[11px] text-muted-foreground uppercase tracking-wider">
+          <Users className="h-3 w-3" />
+          Invitees
+        </div>
+        {countLabel && (
+          <span className="text-[11px] text-muted-foreground">{countLabel}</span>
+        )}
+      </div>
+      <div className="space-y-1">
+        {invitees.map((inv) => (
+          <div key={inv.id} className="flex items-center gap-2 py-1">
+            <AvatarCircle name={inv.invitee_name} />
+            <span className="text-sm flex-1 truncate">{inv.invitee_name}</span>
+            {isOwner && onToggleCanModify && (
+              <button
+                type="button"
+                onClick={() => onToggleCanModify(inv.id, !inv.can_modify)}
+                disabled={togglingInvitationId === inv.id}
+                title={inv.can_modify ? 'Remove edit access' : 'Allow editing'}
+                className={`p-1 rounded transition-colors ${
+                  inv.can_modify
+                    ? 'text-accent bg-accent/10'
+                    : 'text-muted-foreground hover:text-foreground hover:bg-card-elevated'
+                }`}
+                style={inv.can_modify ? { color: 'hsl(var(--accent-color))', backgroundColor: 'hsl(var(--accent-color) / 0.1)' } : undefined}
+              >
+                {inv.can_modify ? <Pencil className="h-3 w-3" /> : <PencilOff className="h-3 w-3" />}
+              </button>
+            )}
+            <StatusBadge status={inv.status} />
+          </div>
+        ))}
+      </div>
+      {isRecurringChild && (
+        <p className="text-[11px] text-muted-foreground mt-1">
+          Status shown for this occurrence
+        </p>
+      )}
+    </div>
+  );
+}
+
+// ── Edit Mode: InviteSearch ──
+
+interface InviteSearchProps {
+  connections: Connection[];
+  existingInviteeIds: Set<number>;
+  onInvite: (userIds: number[]) => void;
+  isInviting: boolean;
+}
+
+export function InviteSearch({ connections, existingInviteeIds, onInvite, isInviting }: InviteSearchProps) {
+  const [search, setSearch] = useState('');
+  const [selectedIds, setSelectedIds] = useState<number[]>([]);
+
+  const searchResults = useMemo(() => {
+    if (!search.trim()) return [];
+    const q = search.toLowerCase();
+    return connections
+      .filter((c) =>
+        !existingInviteeIds.has(c.connected_user_id) &&
+        !selectedIds.includes(c.connected_user_id) &&
+        (
+          (c.connected_preferred_name?.toLowerCase().includes(q)) ||
+          c.connected_umbral_name.toLowerCase().includes(q)
+        )
+      )
+      .slice(0, 6);
+  }, [search, connections, existingInviteeIds, selectedIds]);
+
+  const selectedConnections = connections.filter((c) => selectedIds.includes(c.connected_user_id));
+
+  const handleAdd = (userId: number) => {
+    setSelectedIds((prev) => [...prev, userId]);
+    setSearch('');
+  };
+
+  const handleRemove = (userId: number) => {
+    setSelectedIds((prev) => prev.filter((id) => id !== userId));
+  };
+
+  const handleSend = () => {
+    if (selectedIds.length === 0) return;
+    onInvite(selectedIds);
+    setSelectedIds([]);
+  };
+
+  return (
+    <div className="space-y-2">
+      <div className="flex items-center gap-1.5 text-[11px] text-muted-foreground uppercase tracking-wider">
+        <UserPlus className="h-3 w-3" />
+        Invite People
+      </div>
+
+      <div className="relative">
+        <Search className="absolute left-2.5 top-1/2 -translate-y-1/2 h-3.5 w-3.5 text-muted-foreground" />
+        <Input
+          value={search}
+          onChange={(e) => setSearch(e.target.value)}
+          onBlur={() => setTimeout(() => setSearch(''), 200)}
+          placeholder="Search connections..."
+          className="h-8 pl-8 text-xs"
+        />
+        {search.trim() && searchResults.length > 0 && (
+          <div className="absolute z-50 mt-1 w-full rounded-lg border border-border bg-card shadow-lg overflow-hidden">
+            {searchResults.map((conn) => (
+              <button
+                key={conn.connected_user_id}
+                type="button"
+                onClick={() => handleAdd(conn.connected_user_id)}
+                className="flex items-center gap-2 w-full px-3 py-2 text-sm text-left hover:bg-accent/10 transition-colors"
+              >
+                <AvatarCircle name={conn.connected_preferred_name || conn.connected_umbral_name} />
+                <div className="flex-1 min-w-0">
+                  <span className="text-sm truncate block">{conn.connected_preferred_name || conn.connected_umbral_name}</span>
+                  {conn.connected_preferred_name && (
+                    <span className="text-[11px] text-muted-foreground">@{conn.connected_umbral_name}</span>
+                  )}
+                </div>
+                <UserPlus className="h-3.5 w-3.5 text-muted-foreground" />
+              </button>
+            ))}
+          </div>
+        )}
+        {search.trim() && searchResults.length === 0 && (
+          <div className="absolute z-50 mt-1 w-full rounded-lg border border-border bg-card shadow-lg p-3">
+            <p className="text-xs text-muted-foreground text-center">No connections found</p>
+          </div>
+        )}
+      </div>
+
+      {/* Selected invitees */}
+      {selectedConnections.length > 0 && (
+        <div className="space-y-1">
+          {selectedConnections.map((conn) => (
+            <div key={conn.connected_user_id} className="flex items-center gap-2 py-1">
+              <AvatarCircle name={conn.connected_preferred_name || conn.connected_umbral_name} />
+              <span className="text-sm flex-1 truncate">{conn.connected_preferred_name || conn.connected_umbral_name}</span>
+              <button
+                type="button"
+                onClick={() => handleRemove(conn.connected_user_id)}
+                className="p-0.5 rounded hover:bg-card-elevated text-muted-foreground"
+              >
+                <X className="h-3.5 w-3.5" />
+              </button>
+            </div>
+          ))}
+          <Button
+            size="sm"
+            onClick={handleSend}
+            disabled={isInviting}
+            className="w-full mt-1"
+          >
+            {isInviting ? 'Sending...' : `Send ${selectedIds.length === 1 ? 'Invite' : `${selectedIds.length} Invites`}`}
+          </Button>
+        </div>
+      )}
+    </div>
+  );
+}
+
+// ── RSVP Buttons (for invitee view) ──
+
+interface RsvpButtonsProps {
+  currentStatus: string;
+  onRespond: (status: 'accepted' | 'tentative' | 'declined') => void;
+  isResponding: boolean;
+}
+
+export function RsvpButtons({ currentStatus, onRespond, isResponding }: RsvpButtonsProps) {
+  return (
+    <div className="flex items-center gap-1.5">
+      <button
+        type="button"
+        onClick={() => onRespond('accepted')}
+        disabled={isResponding}
+        className={`px-2.5 py-1 text-xs font-medium rounded-md transition-colors ${
+          currentStatus === 'accepted'
+            ? 'bg-green-500/20 text-green-400'
+            : 'text-muted-foreground hover:bg-card-elevated'
+        }`}
+      >
+        Going
+      </button>
+      <button
+        type="button"
+        onClick={() => onRespond('tentative')}
+        disabled={isResponding}
+        className={`px-2.5 py-1 text-xs font-medium rounded-md transition-colors ${
+          currentStatus === 'tentative'
+            ? 'bg-amber-500/20 text-amber-400'
+            : 'text-muted-foreground hover:bg-card-elevated'
+        }`}
+      >
+        Maybe
+      </button>
+      <button
+        type="button"
+        onClick={() => onRespond('declined')}
+        disabled={isResponding}
+        className={`px-2.5 py-1 text-xs font-medium rounded-md transition-colors ${
+          currentStatus === 'declined'
+            ? 'bg-red-500/20 text-red-400'
+            : 'text-muted-foreground hover:bg-card-elevated'
+        }`}
+      >
+        Decline
+      </button>
+    </div>
+  );
+}

frontend/src/components/calendar/LeaveEventDialog.tsx

@@ -0,0 +1,48 @@
+import { Dialog, DialogContent, DialogHeader, DialogTitle, DialogFooter } from '@/components/ui/dialog';
+import { Button } from '@/components/ui/button';
+
+interface LeaveEventDialogProps {
+  open: boolean;
+  onClose: () => void;
+  onConfirm: () => void;
+  eventTitle: string;
+  isRecurring: boolean;
+  isLeaving: boolean;
+}
+
+export default function LeaveEventDialog({
+  open,
+  onClose,
+  onConfirm,
+  eventTitle,
+  isRecurring,
+  isLeaving,
+}: LeaveEventDialogProps) {
+  return (
+    <Dialog open={open} onOpenChange={(v) => !v && onClose()}>
+      <DialogContent>
+        <DialogHeader>
+          <DialogTitle>Leave Event</DialogTitle>
+        </DialogHeader>
+        <div className="space-y-2 py-2">
+          <p className="text-sm text-foreground">
+            This will remove you from &ldquo;{eventTitle}&rdquo;. You won&rsquo;t see it on your calendar anymore.
+          </p>
+          {isRecurring && (
+            <p className="text-sm text-muted-foreground">
+              For recurring events: removed from all future occurrences.
+            </p>
+          )}
+        </div>
+        <DialogFooter>
+          <Button variant="outline" onClick={onClose} disabled={isLeaving}>
+            Cancel
+          </Button>
+          <Button variant="destructive" onClick={onConfirm} disabled={isLeaving}>
+            {isLeaving ? 'Leaving...' : 'Leave Event'}
+          </Button>
+        </DialogFooter>
+      </DialogContent>
+    </Dialog>
+  );
+}

frontend/src/components/notifications/NotificationToaster.tsx

@@ -1,12 +1,12 @@
 import { useEffect, useRef, useCallback } from 'react';
 import { toast } from 'sonner';
-import { Check, X, Bell, UserPlus, Calendar } from 'lucide-react';
+import { Check, X, Bell, UserPlus, Calendar, Clock } from 'lucide-react';
 import { useQueryClient } from '@tanstack/react-query';
 import { useNotifications } from '@/hooks/useNotifications';
 import { useConnections } from '@/hooks/useConnections';
 import { useSharedCalendars } from '@/hooks/useSharedCalendars';
 import axios from 'axios';
-import { getErrorMessage } from '@/lib/api';
+import api, { getErrorMessage } from '@/lib/api';
 import type { AppNotification } from '@/types';
 
 export default function NotificationToaster() {
@@ -18,7 +18,7 @@ export default function NotificationToaster() {
   const initializedRef = useRef(false);
   const prevUnreadRef = useRef(0);
   // Track in-flight request IDs so repeated clicks are blocked
-  const respondingRef = useRef<Set<number>>(new Set());
+  const respondingRef = useRef<Set<string>>(new Set());
   // Always call the latest respond — Sonner toasts capture closures at creation time
   const respondInviteRef = useRef(respondInvite);
   const respondRef = useRef(respond);
@@ -30,8 +30,9 @@ export default function NotificationToaster() {
   const handleConnectionRespond = useCallback(
     async (requestId: number, action: 'accept' | 'reject', toastId: string | number, notificationId: number) => {
       // Guard against double-clicks (Sonner toasts are static, no disabled prop)
-      if (respondingRef.current.has(requestId)) return;
-      respondingRef.current.add(requestId);
+      const key = `conn-${requestId}`;
+      if (respondingRef.current.has(key)) return;
+      respondingRef.current.add(key);
 
       // Immediately dismiss the custom toast and show a loading indicator
       toast.dismiss(toastId);
@@ -54,7 +55,7 @@ export default function NotificationToaster() {
           toast.error(getErrorMessage(err, 'Failed to respond to request'));
         }
       } finally {
-        respondingRef.current.delete(requestId);
+        respondingRef.current.delete(key);
       }
     },
     [],
@@ -63,8 +64,9 @@ export default function NotificationToaster() {
 
   const handleCalendarInviteRespond = useCallback(
     async (inviteId: number, action: 'accept' | 'reject', toastId: string | number, notificationId: number) => {
-      if (respondingRef.current.has(inviteId + 100000)) return;
-      respondingRef.current.add(inviteId + 100000);
+      const key = `cal-${inviteId}`;
+      if (respondingRef.current.has(key)) return;
+      respondingRef.current.add(key);
 
       toast.dismiss(toastId);
       const loadingId = toast.loading(
@@ -83,11 +85,44 @@ export default function NotificationToaster() {
           toast.error(getErrorMessage(err, 'Failed to respond to invite'));
         }
       } finally {
-        respondingRef.current.delete(inviteId + 100000);
+        respondingRef.current.delete(key);
       }
     },
     [],
   );
+  const handleEventInviteRespond = useCallback(
+    async (invitationId: number, status: 'accepted' | 'tentative' | 'declined', toastId: string | number, notificationId: number) => {
+      const key = `event-${invitationId}`;
+      if (respondingRef.current.has(key)) return;
+      respondingRef.current.add(key);
+
+      toast.dismiss(toastId);
+      const statusLabel = { accepted: 'Accepting', tentative: 'Setting tentative', declined: 'Declining' };
+      const loadingId = toast.loading(`${statusLabel[status]}…`);
+
+      try {
+        await api.put(`/event-invitations/${invitationId}/respond`, { status });
+        toast.dismiss(loadingId);
+        const successLabel = { accepted: 'Going', tentative: 'Tentative', declined: 'Declined' };
+        toast.success(`Marked as ${successLabel[status]}`);
+        markReadRef.current([notificationId]).catch(() => {});
+        queryClient.invalidateQueries({ queryKey: ['calendar-events'] });
+        queryClient.invalidateQueries({ queryKey: ['event-invitations'] });
+      } catch (err) {
+        toast.dismiss(loadingId);
+        if (axios.isAxiosError(err) && err.response?.status === 409) {
+          toast.success('Already responded');
+          markReadRef.current([notificationId]).catch(() => {});
+        } else {
+          toast.error(getErrorMessage(err, 'Failed to respond'));
+        }
+      } finally {
+        respondingRef.current.delete(key);
+      }
+    },
+    [],
+  );
+
   // Track unread count changes to force-refetch the list
   useEffect(() => {
     if (unreadCount > prevUnreadRef.current && initializedRef.current) {
@@ -100,10 +135,28 @@ export default function NotificationToaster() {
   useEffect(() => {
     if (!notifications.length) return;
 
-    // On first load, record the max ID without toasting
+    // On first load, record the max ID — but still toast actionable unread items
     if (!initializedRef.current) {
       maxSeenIdRef.current = Math.max(...notifications.map((n) => n.id));
       initializedRef.current = true;
+
+      // Toast actionable unread notifications on login so the user can act immediately
+      const actionableTypes = new Set(['connection_request', 'calendar_invite', 'event_invite']);
+      const actionable = notifications.filter(
+        (n) => !n.is_read && actionableTypes.has(n.type),
+      );
+      if (actionable.length === 0) return;
+      // Show at most 3 toasts on first load to avoid flooding
+      const toShow = actionable.slice(0, 3);
+      toShow.forEach((notification) => {
+        if (notification.type === 'connection_request' && notification.source_id) {
+          showConnectionRequestToast(notification);
+        } else if (notification.type === 'calendar_invite' && notification.source_id) {
+          showCalendarInviteToast(notification);
+        } else if (notification.type === 'event_invite' && notification.data) {
+          showEventInviteToast(notification);
+        }
+      });
       return;
     }
 
@@ -126,6 +179,10 @@ export default function NotificationToaster() {
     if (newNotifications.some((n) => n.type === 'calendar_invite')) {
       queryClient.invalidateQueries({ queryKey: ['calendar-invites', 'incoming'] });
     }
+    if (newNotifications.some((n) => n.type === 'event_invite')) {
+      queryClient.invalidateQueries({ queryKey: ['calendar-events'] });
+      queryClient.invalidateQueries({ queryKey: ['event-invitations'] });
+    }
 
     // Show toasts
     newNotifications.forEach((notification) => {
@@ -133,6 +190,8 @@ export default function NotificationToaster() {
         showConnectionRequestToast(notification);
       } else if (notification.type === 'calendar_invite' && notification.source_id) {
         showCalendarInviteToast(notification);
+      } else if (notification.type === 'event_invite' && notification.data) {
+        showEventInviteToast(notification);
       } else {
         toast(notification.title || 'New Notification', {
           description: notification.message || undefined,
@@ -141,7 +200,7 @@ export default function NotificationToaster() {
         });
       }
     });
-  }, [notifications, handleConnectionRespond, handleCalendarInviteRespond]);
+  }, [notifications, handleConnectionRespond, handleCalendarInviteRespond, handleEventInviteRespond]);
 
   const showConnectionRequestToast = (notification: AppNotification) => {
     const requestId = notification.source_id!;
@@ -222,5 +281,84 @@ export default function NotificationToaster() {
       { id: `calendar-invite-${inviteId}`, duration: 30000 },
     );
   };
+  const resolveInvitationId = async (notification: AppNotification): Promise<number | null> => {
+    const data = notification.data as Record<string, unknown> | undefined;
+    // Prefer invitation_id from notification data (populated after flush fix)
+    if (data?.invitation_id) return data.invitation_id as number;
+    // Fallback: fetch pending invitations to resolve by event_id
+    const eventId = data?.event_id as number | undefined;
+    if (!eventId) return null;
+    try {
+      const { data: pending } = await api.get('/event-invitations/pending');
+      const inv = (pending as Array<{ id: number; event_id: number }>).find(
+        (p) => p.event_id === eventId,
+      );
+      return inv?.id ?? null;
+    } catch {
+      return null;
+    }
+  };
+
+  const handleEventToastClick = async (
+    notification: AppNotification,
+    status: 'accepted' | 'tentative' | 'declined',
+    toastId: string | number,
+  ) => {
+    const invId = await resolveInvitationId(notification);
+    if (invId) {
+      handleEventInviteRespond(invId, status, toastId, notification.id);
+    } else {
+      toast.dismiss(toastId);
+      markReadRef.current([notification.id]).catch(() => {});
+      toast.success('Already responded');
+    }
+  };
+
+  const showEventInviteToast = (notification: AppNotification) => {
+    const inviteKey = `event-invite-${notification.id}`;
+
+    toast.custom(
+      (id) => (
+        <div className="w-[356px] rounded-lg border border-border bg-card p-4 shadow-lg">
+          <div className="flex items-start gap-3">
+            <div className="h-9 w-9 rounded-full bg-purple-500/15 flex items-center justify-center shrink-0">
+              <Calendar className="h-4 w-4 text-purple-400" />
+            </div>
+            <div className="flex-1 min-w-0">
+              <p className="text-sm font-medium text-foreground">Event Invitation</p>
+              <p className="text-xs text-muted-foreground mt-0.5">
+                {notification.message || 'You were invited to an event'}
+              </p>
+              <div className="flex items-center gap-2 mt-3">
+                <button
+                  onClick={() => handleEventToastClick(notification, 'accepted', id)}
+                  className="flex items-center gap-1 px-3 py-1.5 text-xs font-medium rounded-md bg-accent text-accent-foreground hover:bg-accent/90 transition-colors"
+                >
+                  <Check className="h-3.5 w-3.5" />
+                  Accept
+                </button>
+                <button
+                  onClick={() => handleEventToastClick(notification, 'tentative', id)}
+                  className="flex items-center gap-1 px-3 py-1.5 text-xs font-medium rounded-md bg-amber-500/15 text-amber-400 hover:bg-amber-500/25 transition-colors"
+                >
+                  <Clock className="h-3.5 w-3.5" />
+                  Tentative
+                </button>
+                <button
+                  onClick={() => handleEventToastClick(notification, 'declined', id)}
+                  className="flex items-center gap-1 px-3 py-1.5 text-xs font-medium rounded-md text-muted-foreground hover:bg-card-elevated transition-colors"
+                >
+                  <X className="h-3.5 w-3.5" />
+                  Decline
+                </button>
+              </div>
+            </div>
+          </div>
+        </div>
+      ),
+      { id: inviteKey, duration: 30000 },
+    );
+  };
+
   return null;
 }

frontend/src/components/notifications/NotificationsPage.tsx

@@ -1,7 +1,7 @@
 import { useState, useMemo, useEffect } from 'react';
 import { useNavigate } from 'react-router-dom';
 import { useQueryClient } from '@tanstack/react-query';
-import { Bell, Check, CheckCheck, Trash2, UserPlus, Info, AlertCircle, X, Loader2, Calendar } from 'lucide-react';
+import { Bell, Check, CheckCheck, Trash2, UserPlus, Info, AlertCircle, X, Loader2, Calendar, Clock } from 'lucide-react';
 import { formatDistanceToNow } from 'date-fns';
 import { toast } from 'sonner';
 import { useNotifications } from '@/hooks/useNotifications';
@@ -10,7 +10,7 @@ import { useSharedCalendars } from '@/hooks/useSharedCalendars';
 import { Button } from '@/components/ui/button';
 import { cn } from '@/lib/utils';
 import axios from 'axios';
-import { getErrorMessage } from '@/lib/api';
+import api, { getErrorMessage } from '@/lib/api';
 import { ListSkeleton } from '@/components/ui/skeleton';
 import type { AppNotification } from '@/types';
 
@@ -20,6 +20,8 @@ const typeIcons: Record<string, { icon: typeof Bell; color: string }> = {
   calendar_invite: { icon: Calendar, color: 'text-purple-400' },
   calendar_invite_accepted: { icon: Calendar, color: 'text-green-400' },
   calendar_invite_rejected: { icon: Calendar, color: 'text-muted-foreground' },
+  event_invite: { icon: Calendar, color: 'text-purple-400' },
+  event_invite_response: { icon: Calendar, color: 'text-green-400' },
   info: { icon: Info, color: 'text-blue-400' },
   warning: { icon: AlertCircle, color: 'text-amber-400' },
 };
@@ -41,6 +43,7 @@ export default function NotificationsPage() {
   const queryClient = useQueryClient();
   const navigate = useNavigate();
   const [filter, setFilter] = useState<Filter>('all');
+  const [respondingEventInvite, setRespondingEventInvite] = useState<number | null>(null);
 
   // Build a set of pending connection request IDs for quick lookup
   const pendingInviteIds = useMemo(
@@ -60,6 +63,10 @@ export default function NotificationsPage() {
     if (notifications.some((n) => n.type === 'calendar_invite' && !n.is_read)) {
       queryClient.invalidateQueries({ queryKey: ['calendar-invites', 'incoming'] });
     }
+    // Refresh event invitations
+    if (notifications.some((n) => n.type === 'event_invite' && !n.is_read)) {
+      queryClient.invalidateQueries({ queryKey: ['event-invitations'] });
+    }
     const hasMissing = notifications.some(
       (n) => n.type === 'connection_request' && n.source_id && !n.is_read && !pendingRequestIds.has(n.source_id),
     );
@@ -141,6 +148,52 @@ export default function NotificationsPage() {
       }
     }
   };
+  const handleEventInviteRespond = async (
+    notification: AppNotification,
+    status: 'accepted' | 'tentative' | 'declined',
+  ) => {
+    const data = notification.data as Record<string, unknown> | undefined;
+    const eventId = data?.event_id as number | undefined;
+    if (!eventId) return;
+
+    setRespondingEventInvite(notification.id);
+    try {
+      // Prefer invitation_id from notification data; fallback to pending fetch
+      let invitationId = data?.invitation_id as number | undefined;
+      if (!invitationId) {
+        const { data: pending } = await api.get('/event-invitations/pending');
+        const inv = (pending as Array<{ id: number; event_id: number }>).find(
+          (p) => p.event_id === eventId,
+        );
+        invitationId = inv?.id;
+      }
+
+      if (invitationId) {
+        await api.put(`/event-invitations/${invitationId}/respond`, { status });
+        const successLabel = { accepted: 'Going', tentative: 'Tentative', declined: 'Declined' };
+        toast.success(`Marked as ${successLabel[status]}`);
+        queryClient.invalidateQueries({ queryKey: ['calendar-events'] });
+        queryClient.invalidateQueries({ queryKey: ['event-invitations'] });
+      } else {
+        toast.success('Already responded');
+      }
+      if (!notification.is_read) {
+        await markRead([notification.id]).catch(() => {});
+      }
+    } catch (err) {
+      if (axios.isAxiosError(err) && err.response?.status === 409) {
+        toast.success('Already responded');
+        if (!notification.is_read) {
+          await markRead([notification.id]).catch(() => {});
+        }
+      } else {
+        toast.error(getErrorMessage(err, 'Failed to respond'));
+      }
+    } finally {
+      setRespondingEventInvite(null);
+    }
+  };
+
   const handleNotificationClick = async (notification: AppNotification) => {
     // Don't navigate for pending connection requests — let user act inline
     if (
@@ -150,6 +203,10 @@ export default function NotificationsPage() {
     ) {
       return;
     }
+    // Don't navigate for unread event invites — let user act inline
+    if (notification.type === 'event_invite' && !notification.is_read) {
+      return;
+    }
     if (!notification.is_read) {
       await markRead([notification.id]).catch(() => {});
     }
@@ -157,6 +214,10 @@ export default function NotificationsPage() {
     if (notification.type === 'connection_request' || notification.type === 'connection_accepted') {
       navigate('/people');
     }
+    // Navigate to Calendar for event-related notifications
+    if (notification.type === 'event_invite' || notification.type === 'event_invite_response') {
+      navigate('/calendar');
+    }
   };
 
   return (
@@ -311,6 +372,42 @@ export default function NotificationsPage() {
                         </Button>
                       </div>
                     )}
+
+                  {/* Event invite actions (inline) */}
+                  {notification.type === 'event_invite' &&
+                    !notification.is_read && (
+                      <div className="flex items-center gap-1.5 shrink-0">
+                        <Button
+                          size="sm"
+                          onClick={(e) => { e.stopPropagation(); handleEventInviteRespond(notification, 'accepted'); }}
+                          disabled={respondingEventInvite === notification.id}
+                          className="gap-1 h-7 text-xs"
+                        >
+                          {respondingEventInvite === notification.id ? <Loader2 className="h-3 w-3 animate-spin" /> : <Check className="h-3 w-3" />}
+                          Going
+                        </Button>
+                        <Button
+                          variant="ghost"
+                          size="sm"
+                          onClick={(e) => { e.stopPropagation(); handleEventInviteRespond(notification, 'tentative'); }}
+                          disabled={respondingEventInvite === notification.id}
+                          className="h-7 text-xs gap-1 text-amber-400 hover:text-amber-300"
+                        >
+                          <Clock className="h-3 w-3" />
+                          Maybe
+                        </Button>
+                        <Button
+                          variant="ghost"
+                          size="sm"
+                          onClick={(e) => { e.stopPropagation(); handleEventInviteRespond(notification, 'declined'); }}
+                          disabled={respondingEventInvite === notification.id}
+                          className="h-7 text-xs"
+                        >
+                          <X className="h-3 w-3" />
+                        </Button>
+                      </div>
+                    )}
+
                   {/* Timestamp + actions */}
                   <div className="flex items-center gap-1.5 shrink-0">
                     <span className="text-[11px] text-muted-foreground tabular-nums">

frontend/src/hooks/useEventInvitations.ts

@@ -0,0 +1,144 @@
+import { useState } from 'react';
+import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
+import { toast } from 'sonner';
+import api, { getErrorMessage } from '@/lib/api';
+import type { EventInvitation, Connection } from '@/types';
+
+export function useEventInvitations(eventId: number | null) {
+  const queryClient = useQueryClient();
+
+  const inviteesQuery = useQuery({
+    queryKey: ['event-invitations', eventId],
+    queryFn: async () => {
+      const { data } = await api.get<EventInvitation[]>(`/events/${eventId}/invitations`);
+      return data;
+    },
+    enabled: !!eventId,
+  });
+
+  const inviteMutation = useMutation({
+    mutationFn: async (userIds: number[]) => {
+      const { data } = await api.post(`/events/${eventId}/invitations`, { user_ids: userIds });
+      return data;
+    },
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ['event-invitations', eventId] });
+      queryClient.invalidateQueries({ queryKey: ['calendar-events'] });
+      toast.success('Invitation sent');
+    },
+    onError: (error) => {
+      toast.error(getErrorMessage(error, 'Failed to send invitation'));
+    },
+  });
+
+  const respondMutation = useMutation({
+    mutationFn: async ({ invitationId, status }: { invitationId: number; status: 'accepted' | 'tentative' | 'declined' }) => {
+      const { data } = await api.put(`/event-invitations/${invitationId}/respond`, { status });
+      return data;
+    },
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ['event-invitations'] });
+      queryClient.invalidateQueries({ queryKey: ['calendar-events'] });
+      queryClient.invalidateQueries({ queryKey: ['notifications'] });
+    },
+    onError: (error) => {
+      toast.error(getErrorMessage(error, 'Failed to respond to invitation'));
+    },
+  });
+
+  const overrideMutation = useMutation({
+    mutationFn: async ({ invitationId, occurrenceId, status }: { invitationId: number; occurrenceId: number; status: 'accepted' | 'tentative' | 'declined' }) => {
+      const { data } = await api.put(`/event-invitations/${invitationId}/respond/${occurrenceId}`, { status });
+      return data;
+    },
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ['event-invitations'] });
+      queryClient.invalidateQueries({ queryKey: ['calendar-events'] });
+    },
+    onError: (error) => {
+      toast.error(getErrorMessage(error, 'Failed to update status'));
+    },
+  });
+
+  const updateDisplayCalendarMutation = useMutation({
+    mutationFn: async ({ invitationId, calendarId }: { invitationId: number; calendarId: number }) => {
+      const { data } = await api.put(`/event-invitations/${invitationId}/display-calendar`, { calendar_id: calendarId });
+      return data;
+    },
+    onSuccess: () => {
+      queryClient.refetchQueries({ queryKey: ['calendar-events'] });
+      queryClient.invalidateQueries({ queryKey: ['event-invitations'] });
+      toast.success('Display calendar updated');
+    },
+    onError: (error) => {
+      toast.error(getErrorMessage(error, 'Failed to update display calendar'));
+    },
+  });
+
+  const [togglingInvitationId, setTogglingInvitationId] = useState<number | null>(null);
+  const toggleCanModifyMutation = useMutation({
+    mutationFn: async ({ invitationId, canModify }: { invitationId: number; canModify: boolean }) => {
+      setTogglingInvitationId(invitationId);
+      const { data } = await api.put(`/event-invitations/${invitationId}/can-modify`, { can_modify: canModify });
+      return data;
+    },
+    onSuccess: () => {
+      setTogglingInvitationId(null);
+      queryClient.invalidateQueries({ queryKey: ['event-invitations', eventId] });
+      queryClient.invalidateQueries({ queryKey: ['calendar-events'] });
+    },
+    onError: (error) => {
+      setTogglingInvitationId(null);
+      toast.error(getErrorMessage(error, 'Failed to update edit access'));
+    },
+  });
+
+  const leaveMutation = useMutation({
+    mutationFn: async (invitationId: number) => {
+      await api.delete(`/event-invitations/${invitationId}`);
+    },
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ['event-invitations'] });
+      queryClient.invalidateQueries({ queryKey: ['calendar-events'] });
+      queryClient.invalidateQueries({ queryKey: ['dashboard'] });
+      queryClient.invalidateQueries({ queryKey: ['upcoming'] });
+      toast.success('Left event');
+    },
+    onError: (error) => {
+      toast.error(getErrorMessage(error, 'Failed to leave event'));
+    },
+  });
+
+  return {
+    invitees: inviteesQuery.data ?? [],
+    isLoadingInvitees: inviteesQuery.isLoading,
+    invite: inviteMutation.mutateAsync,
+    isInviting: inviteMutation.isPending,
+    respond: respondMutation.mutateAsync,
+    isResponding: respondMutation.isPending,
+    override: overrideMutation.mutateAsync,
+    updateDisplayCalendar: updateDisplayCalendarMutation.mutateAsync,
+    isUpdatingDisplayCalendar: updateDisplayCalendarMutation.isPending,
+    leave: leaveMutation.mutateAsync,
+    isLeaving: leaveMutation.isPending,
+    toggleCanModify: toggleCanModifyMutation.mutateAsync,
+    isTogglingCanModify: toggleCanModifyMutation.isPending,
+    togglingInvitationId,
+  };
+}
+
+export function useConnectedUsersSearch() {
+  const connectionsQuery = useQuery({
+    queryKey: ['connections'],
+    queryFn: async () => {
+      const { data } = await api.get<Connection[]>('/connections');
+      return data;
+    },
+    staleTime: 30_000,
+  });
+
+  return {
+    connections: connectionsQuery.data ?? [],
+    isLoading: connectionsQuery.isLoading,
+  };
+}

frontend/src/types/index.ts

@@ -112,6 +112,12 @@ export interface CalendarEvent {
   parent_event_id?: number | null;
   is_recurring?: boolean;
   original_start?: string | null;
+  is_invited?: boolean;
+  invitation_status?: 'pending' | 'accepted' | 'tentative' | 'declined' | null;
+  invitation_id?: number | null;
+  display_calendar_id?: number | null;
+  can_modify?: boolean;
+  has_active_invitees?: boolean;
   created_at: string;
   updated_at: string;
 }
@@ -486,6 +492,31 @@ export interface CalendarInvite {
   invited_at: string;
 }
 
+// ── Event Invitations ─────────────────────────────────────────────
+
+export interface EventInvitation {
+  id: number;
+  event_id: number;
+  user_id: number;
+  invited_by: number | null;
+  status: 'pending' | 'accepted' | 'tentative' | 'declined';
+  invited_at: string;
+  responded_at: string | null;
+  invitee_name: string;
+  invitee_umbral_name: string;
+  can_modify: boolean;
+}
+
+export interface PendingEventInvitation {
+  id: number;
+  event_id: number;
+  event_title: string;
+  event_start: string;
+  invited_by_name: string;
+  invited_at: string;
+  status: string;
+}
+
 export interface EventLockInfo {
   locked: boolean;
   locked_by_name: string | null;