diff --git a/backend/app/routers/projects.py b/backend/app/routers/projects.py
index 2f85ce0..32cd0e7 100644
--- a/backend/app/routers/projects.py
+++ b/backend/app/routers/projects.py
@@ -54,7 +54,7 @@ def _task_load_options():
     """All load options needed for task responses."""
     return [
         selectinload(ProjectTask.comments).selectinload(TaskComment.user),
-        selectinload(ProjectTask.subtasks).selectinload(ProjectTask.comments),
+        selectinload(ProjectTask.subtasks).selectinload(ProjectTask.comments).selectinload(TaskComment.user),
         selectinload(ProjectTask.subtasks).selectinload(ProjectTask.subtasks),
         selectinload(ProjectTask.assignments).selectinload(ProjectTaskAssignment.user),
         selectinload(ProjectTask.subtasks).selectinload(ProjectTask.assignments).selectinload(ProjectTaskAssignment.user),
@@ -375,7 +375,7 @@ async def update_project_task(
     current_user: User = Depends(get_current_user)
 ):
     """Update a project task. Permission checked at project and task level."""
-    perm = await get_effective_task_permission(db, current_user.id, task_id, project_id)
+    perm, project_perm = await get_effective_task_permission(db, current_user.id, task_id, project_id)
     if perm is None:
         raise HTTPException(status_code=404, detail="Project not found")
     if perm == "read_only":
@@ -395,7 +395,6 @@ async def update_project_task(
     update_data = task_update.model_dump(exclude_unset=True)
 
     # SEC-P02: Assignees (non-owner, non-project-member with create_modify) restricted to content fields
-    project_perm = await get_project_permission(db, project_id, current_user.id)
     if project_perm not in ("owner", "create_modify"):
         # This user's create_modify comes from task assignment — enforce allowlist
         disallowed = set(update_data.keys()) - ASSIGNEE_ALLOWED_FIELDS
diff --git a/backend/app/services/project_sharing.py b/backend/app/services/project_sharing.py
index e56602d..6f6360d 100644
--- a/backend/app/services/project_sharing.py
+++ b/backend/app/services/project_sharing.py
@@ -110,19 +110,19 @@ async def validate_project_connections(
 
 async def get_effective_task_permission(
     db: AsyncSession, user_id: int, task_id: int, project_id: int
-) -> str | None:
+) -> tuple[str | None, str | None]:
     """
-    Returns effective permission for a specific task:
+    Returns (effective_permission, project_level_permission) for a specific task.
     1. Get project-level permission (owner/create_modify/read_only)
     2. If user is assigned to THIS task → max(project_perm, create_modify)
     3. If task has parent and user assigned to PARENT → same as above
-    4. Return effective permission
+    4. Return (effective, project_level)
     """
     project_perm = await get_project_permission(db, project_id, user_id)
     if project_perm is None:
-        return None
+        return None, None
     if project_perm == "owner":
-        return "owner"
+        return "owner", "owner"
 
     # Check direct assignment on this task
     task_result = await db.execute(
@@ -130,7 +130,7 @@ async def get_effective_task_permission(
     )
     task_row = task_result.one_or_none()
     if not task_row:
-        return project_perm
+        return project_perm, project_perm
 
     parent_task_id = task_row[0]
 
@@ -148,10 +148,10 @@ async def get_effective_task_permission(
     if assignment_result.scalar_one_or_none() is not None:
         # Assignment grants at least create_modify
         if PERMISSION_RANK.get(project_perm, 0) >= PERMISSION_RANK["create_modify"]:
-            return project_perm
-        return "create_modify"
+            return project_perm, project_perm
+        return "create_modify", project_perm
 
-    return project_perm
+    return project_perm, project_perm
 
 
 async def ensure_auto_membership(
diff --git a/frontend/src/components/projects/ProjectDetail.tsx b/frontend/src/components/projects/ProjectDetail.tsx
index 5908930..235a182 100644
--- a/frontend/src/components/projects/ProjectDetail.tsx
+++ b/frontend/src/components/projects/ProjectDetail.tsx
@@ -165,7 +165,12 @@ export default function ProjectDetail() {
     },
     enabled: !!id,
   });
-  const acceptedMembers = members.filter((m) => m.status === 'accepted');
+  const acceptedMembers = useMemo(() => members.filter((m) => m.status === 'accepted'), [members]);
+  const myPermission = useMemo(
+    () => acceptedMembers.find((m) => m.user_id === currentUserId)?.permission ?? null,
+    [acceptedMembers, currentUserId]
+  );
+  const canEditTasks = isOwner || myPermission === 'create_modify';
 
   const toggleTaskMutation = useMutation({
     mutationFn: async ({ taskId, status }: { taskId: number; status: string }) => {
@@ -425,7 +430,7 @@ export default function ProjectDetail() {
         {/* Permission badge for non-owners */}
         {isShared && (
           <Badge className="shrink-0 bg-blue-500/10 text-blue-400 border-0">
-            {acceptedMembers.find((m) => m.user_id === currentUserId)?.permission === 'create_modify' ? 'Editor' : 'Viewer'}
+            {myPermission === 'create_modify' ? 'Editor' : 'Viewer'}
           </Badge>
         )}
         {canManageProject && (
@@ -602,7 +607,7 @@ export default function ProjectDetail() {
               </div>
             )}
 
-            {(isOwner || acceptedMembers.find((m) => m.user_id === currentUserId)?.permission === 'create_modify') && (
+            {canEditTasks && (
               <Button size="sm" onClick={() => openTaskForm(null, null)}>
                 <Plus className="mr-2 h-3.5 w-3.5" />
                 Add Task
@@ -713,7 +718,7 @@ export default function ProjectDetail() {
                   members={acceptedMembers}
                   currentUserId={currentUserId}
                   ownerId={project?.user_id ?? 0}
-                  canAssign={isOwner || acceptedMembers.some(m => m.user_id === currentUserId && m.permission === 'create_modify')}
+                  canAssign={canEditTasks}
                   onDelete={handleDeleteTask}
                   onAddSubtask={(parentId) => openTaskForm(null, parentId)}
                   onClose={() => setSelectedTaskId(null)}
diff --git a/frontend/src/hooks/useDeltaPoll.ts b/frontend/src/hooks/useDeltaPoll.ts
index 86c5572..67a9b9c 100644
--- a/frontend/src/hooks/useDeltaPoll.ts
+++ b/frontend/src/hooks/useDeltaPoll.ts
@@ -22,6 +22,10 @@ export function useDeltaPoll(
 ) {
   const queryClient = useQueryClient();
   const sinceRef = useRef<string>(toLocalDatetime());
+  // Store key in ref to decouple from useEffect deps (prevents infinite loop
+  // if caller passes an inline array literal instead of a memoized one)
+  const keyRef = useRef(queryKeyToInvalidate);
+  keyRef.current = queryKeyToInvalidate;
 
   const { data } = useQuery<PollResponse>({
     queryKey: ['delta-poll', endpoint],
@@ -39,10 +43,10 @@ export function useDeltaPoll(
 
   useEffect(() => {
     if (data?.has_changes) {
-      queryClient.invalidateQueries({ queryKey: queryKeyToInvalidate });
+      queryClient.invalidateQueries({ queryKey: keyRef.current });
       sinceRef.current = toLocalDatetime();
     }
-  }, [data, queryClient, queryKeyToInvalidate]);
+  }, [data, queryClient]);
 
   const updateSince = (timestamp: string) => {
     sinceRef.current = timestamp;