diff --git a/backend/app/routers/projects.py b/backend/app/routers/projects.py
index 06ebde6..cd2b1f2 100644
--- a/backend/app/routers/projects.py
+++ b/backend/app/routers/projects.py
@@ -4,7 +4,7 @@ from sqlalchemy import select
 from sqlalchemy.orm import selectinload
 from typing import List, Optional
 from datetime import date, timedelta
-from pydantic import BaseModel
+from pydantic import BaseModel, ConfigDict
 
 from app.database import get_db
 from app.models.project import Project
@@ -20,6 +20,7 @@ router = APIRouter()
 
 
 class ReorderItem(BaseModel):
+    model_config = ConfigDict(extra="forbid")
     id: int
     sort_order: int
 
diff --git a/frontend/src/hooks/useCalendars.ts b/frontend/src/hooks/useCalendars.ts
index b5e74ed..ee2fa4d 100644
--- a/frontend/src/hooks/useCalendars.ts
+++ b/frontend/src/hooks/useCalendars.ts
@@ -1,4 +1,4 @@
-import { useMemo, useRef } from 'react';
+import { useState, useMemo } from 'react';
 import { useQuery } from '@tanstack/react-query';
 import api from '@/lib/api';
 import type { Calendar, SharedCalendarMembership } from '@/types';
@@ -18,10 +18,11 @@ export function useCalendars({ pollingEnabled = false }: UseCalendarsOptions = {
 
   // AS-4: Gate shared-calendar polling on whether user participates in sharing.
   // Saves ~12 API calls/min for personal-only users.
-  // Use a ref to latch "has sharing" once discovered, so polling doesn't flicker.
-  const hasSharingRef = useRef(false);
+  // Uses useState (not useRef) so changes trigger a re-render and the
+  // refetchInterval picks up the new value immediately.
+  const [hasSharing, setHasSharing] = useState(false);
   const ownsShared = (ownedQuery.data ?? []).some((c) => c.is_shared);
-  if (ownsShared) hasSharingRef.current = true;
+  if (ownsShared && !hasSharing) setHasSharing(true);
 
   const sharedQuery = useQuery({
     queryKey: ['calendars', 'shared'],
@@ -29,12 +30,12 @@ export function useCalendars({ pollingEnabled = false }: UseCalendarsOptions = {
       const { data } = await api.get<SharedCalendarMembership[]>('/shared-calendars');
       return data;
     },
-    refetchInterval: pollingEnabled && hasSharingRef.current ? 5_000 : false,
+    refetchInterval: pollingEnabled && hasSharing ? 5_000 : false,
     staleTime: 3_000,
   });
 
   // Also latch if user is a member of others' shared calendars
-  if ((sharedQuery.data ?? []).length > 0) hasSharingRef.current = true;
+  if ((sharedQuery.data ?? []).length > 0 && !hasSharing) setHasSharing(true);
 
   const allCalendarIds = useMemo(() => {
     const owned = (ownedQuery.data ?? []).map((c) => c.id);