chore: resolve merge conflicts with main

- deps.py: keep require_tenant_context + require_admin_db (RLS deps);
  drop unused get_tenant_context stub from Phase 0
- categories.py: keep both PLATFORM_ACCOUNT_ID and tenant_filter imports
  (body uses both)
- tenant-isolation spec: keep main's resolved TargetList/teams audit answers

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/api/endpoints/ai_sessions.py

@@ -519,11 +519,15 @@ async def save_task_lane(
     _: None = Depends(require_engineer_or_admin),
 ):
     """Save the current task lane state including user's in-progress responses."""
-    session = await db.get(AISession, session_id)
+    result = await db.execute(
+        select(AISession).where(
+            AISession.id == session_id,
+            AISession.user_id == current_user.id,
+        )
+    )
+    session = result.scalar_one_or_none()
     if not session:
         raise HTTPException(status_code=404, detail="Session not found")
-    if session.user_id != current_user.id:
-        raise HTTPException(status_code=403, detail="Not your session")
 
     payload = {
         "questions": [q.model_dump() for q in body.questions],
@@ -762,13 +766,13 @@ async def search_sessions(
     limit: int = Query(5, ge=1, le=20),
 ):
     """Search AI sessions by content using full-text search. Used by Command Palette."""
+    # Sessions are user-scoped. The list endpoint uses user_id only;
+    # search must be consistent. Cross-user access requires explicit
+    # escalation or session sharing — not ambient account membership.
     result = await db.execute(
         select(AISession)
         .where(
-            or_(
-                AISession.user_id == current_user.id,
-                AISession.account_id == current_user.account_id,
-            ),
+            AISession.user_id == current_user.id,
             text("ai_sessions.search_vector @@ plainto_tsquery('english', :q)"),
         )
         .params(q=q)
@@ -901,7 +905,7 @@ async def get_session(
     pkg = session.escalation_package or {}
     is_handler = pkg.get("picked_up_by") == str(current_user.id)
     if session.user_id != current_user.id and session.escalated_to_id != current_user.id and not is_handler:
-        raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail="Not authorized")
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Session not found")
 
     return _build_session_detail(session)
 
@@ -917,6 +921,18 @@ async def get_documentation(
     db: Annotated[AsyncSession, Depends(get_db)],
 ):
     """Get auto-generated documentation for a session."""
+    # Verify session ownership — owner only. Documentation endpoints require direct
+    # ownership; escalated_to_id / picked_up_by handlers use get_session (read-only).
+    # This is consistent with stream_documentation which has the same owner-only check.
+    result = await db.execute(
+        select(AISession).where(
+            AISession.id == session_id,
+            AISession.user_id == current_user.id,
+        )
+    )
+    if not result.scalar_one_or_none():
+        raise HTTPException(status_code=404, detail="Session not found")
+
     try:
         return await flowpilot_engine.get_session_documentation(
             session_id=session_id,
@@ -942,13 +958,14 @@ async def stream_documentation(
 
     # Verify session ownership
     result = await db.execute(
-        select(AISession).where(AISession.id == session_id)
+        select(AISession).where(
+            AISession.id == session_id,
+            AISession.user_id == current_user.id,
+        )
     )
     session = result.scalar_one_or_none()
     if not session:
         raise HTTPException(status_code=404, detail="Session not found")
-    if session.user_id != current_user.id:
-        raise HTTPException(status_code=403, detail="Not authorized")
 
     async def event_generator():
         try:
@@ -1043,6 +1060,19 @@ async def retry_psa_push_endpoint(
     """Manually retry a failed PSA documentation push."""
     from app.models.psa_post_log import PsaPostLog
 
+    # Verify the session belongs to the current user
+    session_result = await db.execute(
+        select(AISession).where(
+            AISession.id == session_id,
+            AISession.user_id == current_user.id,
+        )
+    )
+    if not session_result.scalar_one_or_none():
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="Session not found",
+        )
+
     # Find the latest failed push log for this session
     result = await db.execute(
         select(PsaPostLog)

backend/app/api/endpoints/analytics.py

@@ -7,6 +7,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.core.database import get_db
 from app.api.deps import get_current_active_user
+from app.core.filters import tenant_filter
 from app.models import User, Session, Tree, SessionRating
 from app.schemas.analytics import (
     TeamAnalyticsResponse, PersonalAnalyticsResponse, FlowAnalyticsResponse,
@@ -290,8 +291,13 @@ async def get_flow_analytics(
     current_user: User = Depends(get_current_active_user),
 ):
     """Analytics for a specific flow."""
-    # Verify tree exists
-    result = await db.execute(select(Tree).where(Tree.id == tree_id))
+    # Verify tree exists and belongs to the requesting user's account.
+    result = await db.execute(
+        select(Tree).where(
+            Tree.id == tree_id,
+            tenant_filter(Tree, current_user.account_id),
+        )
+    )
     tree = result.scalar_one_or_none()
     if not tree:
         raise HTTPException(status_code=404, detail="Flow not found")

backend/app/api/endpoints/categories.py

@@ -13,6 +13,7 @@ from app.schemas.category import CategoryCreate, CategoryUpdate, CategoryRespons
 from app.api.deps import get_current_active_user
 from app.core.permissions import can_manage_category, can_create_category
 from app.core.service_account import PLATFORM_ACCOUNT_ID
+from app.core.filters import tenant_filter
 
 router = APIRouter(prefix="/categories", tags=["categories"])
 
@@ -109,10 +110,12 @@ async def get_category(
             detail="You don't have access to this category"
         )
 
-    # Get tree count
+    # Get tree count — scoped to the requesting account so cross-account
+    # trees in shared categories are not counted.
     count_query = select(func.count(Tree.id)).where(
         Tree.category_id == category.id,
-        Tree.is_active == True
+        Tree.is_active == True,
+        tenant_filter(Tree, current_user.account_id),
     )
     count_result = await db.execute(count_query)
     tree_count = count_result.scalar() or 0

backend/app/api/endpoints/maintenance_schedules.py

@@ -29,8 +29,8 @@ def _compute_next_run(cron_expression: str, tz_name: str) -> datetime:
     return cron.get_next(datetime).astimezone(timezone.utc)
 
 
-async def _get_tree_or_403(tree_id: UUID, current_user: User, db: AsyncSession) -> "Tree":
-    """Fetch tree and verify the current user's team owns it."""
+async def _get_tree_or_404(tree_id: UUID, current_user: User, db: AsyncSession) -> "Tree":
+    """Fetch tree and verify the current user's team owns it. Raises 404 if not found or access denied."""
     result = await db.execute(select(Tree).where(Tree.id == tree_id))
     tree = result.scalar_one_or_none()
     if not tree:
@@ -38,7 +38,7 @@ async def _get_tree_or_403(tree_id: UUID, current_user: User, db: AsyncSession)
     # Super admins can access any tree; regular users must be on the same team
     if not getattr(current_user, 'is_super_admin', False):
         if tree.team_id != current_user.team_id:
-            raise HTTPException(status_code=403, detail="Access denied")
+            raise HTTPException(status_code=404, detail="Tree not found")
     return tree
 
 
@@ -51,7 +51,7 @@ async def create_schedule(
 ):
     """Create a cron schedule for a maintenance flow. One per flow."""
     # Verify user's team owns the tree
-    tree = await _get_tree_or_403(data.tree_id, current_user, db)
+    tree = await _get_tree_or_404(data.tree_id, current_user, db)
     if tree.tree_type != "maintenance":
         raise HTTPException(status_code=400, detail="Schedules are only supported for maintenance flows")
 
@@ -94,7 +94,7 @@ async def get_schedule_for_tree(
 ):
     """Get the schedule for a specific maintenance flow."""
     # Verify user's team owns the tree before returning schedule data
-    await _get_tree_or_403(tree_id, current_user, db)
+    await _get_tree_or_404(tree_id, current_user, db)
 
     result = await db.execute(
         select(MaintenanceSchedule).where(MaintenanceSchedule.tree_id == tree_id)
@@ -122,7 +122,7 @@ async def update_schedule(
         raise HTTPException(status_code=404, detail="Schedule not found")
 
     # Verify user's team owns the tree this schedule belongs to
-    await _get_tree_or_403(schedule.tree_id, current_user, db)
+    await _get_tree_or_404(schedule.tree_id, current_user, db)
 
     update_fields = data.model_fields_set
     was_active = schedule.is_active

backend/app/api/endpoints/sessions.py

@@ -143,8 +143,8 @@ async def get_session(
 
     if session.user_id != current_user.id and session.assigned_to_id != current_user.id:
         raise HTTPException(
-            status_code=status.HTTP_403_FORBIDDEN,
-            detail="You don't have access to this session"
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="Session not found"
         )
 
     return session
@@ -234,8 +234,8 @@ async def update_session(
 
     if session.user_id != current_user.id and session.assigned_to_id != current_user.id:
         raise HTTPException(
-            status_code=status.HTTP_403_FORBIDDEN,
-            detail="You don't have access to this session"
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="Session not found"
         )
 
     if session.completed_at:
@@ -281,8 +281,8 @@ async def complete_session(
 
     if session.user_id != current_user.id and session.assigned_to_id != current_user.id:
         raise HTTPException(
-            status_code=status.HTTP_403_FORBIDDEN,
-            detail="You don't have access to this session"
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="Session not found"
         )
 
     if session.completed_at:
@@ -319,8 +319,8 @@ async def update_scratchpad(
 
     if session.user_id != current_user.id and session.assigned_to_id != current_user.id:
         raise HTTPException(
-            status_code=status.HTTP_403_FORBIDDEN,
-            detail="You don't have access to this session"
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="Session not found"
         )
 
     session.scratchpad = data.scratchpad
@@ -348,8 +348,8 @@ async def update_session_variables(
 
     if session.user_id != current_user.id and session.assigned_to_id != current_user.id:
         raise HTTPException(
-            status_code=status.HTTP_403_FORBIDDEN,
-            detail="You don't have access to this session"
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="Session not found"
         )
 
     if session.completed_at:
@@ -387,8 +387,8 @@ async def export_session(
 
     if session.user_id != current_user.id and session.assigned_to_id != current_user.id:
         raise HTTPException(
-            status_code=status.HTTP_403_FORBIDDEN,
-            detail="You don't have access to this session"
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="Session not found"
         )
 
     # PDF export — separate path with binary response
@@ -830,8 +830,8 @@ async def link_ticket(
     if session.user_id != current_user.id and session.assigned_to_id != current_user.id:
         if not current_user.is_super_admin:
             raise HTTPException(
-                status_code=status.HTTP_403_FORBIDDEN,
-                detail="You don't have access to this session",
+                status_code=status.HTTP_404_NOT_FOUND,
+                detail="Session not found",
             )
 
     # Unlink

backend/app/api/endpoints/shares.py

@@ -72,8 +72,8 @@ async def create_share(
 
     if session.user_id != current_user.id and not current_user.is_super_admin:
         raise HTTPException(
-            status_code=status.HTTP_403_FORBIDDEN,
-            detail="Only the session owner can create share links"
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="Session not found"
         )
 
     # Require account_id for account-scoped shares
@@ -170,8 +170,8 @@ async def revoke_share(
 
     if share.created_by != current_user.id and not current_user.is_super_admin:
         raise HTTPException(
-            status_code=status.HTTP_403_FORBIDDEN,
-            detail="Only the share creator can revoke it"
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="Share not found"
         )
 
     share.is_active = False

backend/app/api/endpoints/step_categories.py

@@ -95,8 +95,8 @@ async def get_step_category(
     # Check access: global categories visible to all, account categories only to account members
     if category.account_id and category.account_id != current_user.account_id and not current_user.is_super_admin:
         raise HTTPException(
-            status_code=status.HTTP_403_FORBIDDEN,
-            detail="You don't have access to this step category"
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="Step category not found"
         )
 
     return StepCategoryResponse(

backend/app/api/endpoints/steps.py

@@ -47,10 +47,10 @@ async def get_step_or_404(
         raise HTTPException(status_code=404, detail="Step not found")
 
     if check_view and not can_view_step(current_user, step):
-        raise HTTPException(status_code=403, detail="Not authorized to view this step")
+        raise HTTPException(status_code=404, detail="Step not found")
 
     if check_edit and not can_edit_step(current_user, step):
-        raise HTTPException(status_code=403, detail="Not authorized to modify this step")
+        raise HTTPException(status_code=404, detail="Step not found")
 
     return step
 

backend/app/api/endpoints/tags.py

@@ -106,8 +106,8 @@ async def get_tag(
     # Check access: global tags visible to all, account tags only to account members
     if tag.account_id and tag.account_id != current_user.account_id and not current_user.is_super_admin:
         raise HTTPException(
-            status_code=status.HTTP_403_FORBIDDEN,
-            detail="You don't have access to this tag"
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="Tag not found"
         )
 
     return TagResponse.model_validate(tag)

backend/app/api/endpoints/trees.py

@@ -612,9 +612,17 @@ async def update_tree(
         )
 
     if not can_edit_tree(current_user, tree):
+        # If the user can see this tree (same account, team visibility), give a 403 with
+        # a clear message — returning 404 here would be confusing since GET returns 200.
+        # For truly inaccessible trees (cross-account), return 404 to avoid confirming existence.
+        if can_access_tree(current_user, tree):
+            raise HTTPException(
+                status_code=status.HTTP_403_FORBIDDEN,
+                detail="You do not have permission to edit this flow"
+            )
         raise HTTPException(
-            status_code=status.HTTP_403_FORBIDDEN,
-            detail="You can only edit your own trees"
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="Tree not found"
         )
 
     # Extract tags for separate handling
@@ -1146,9 +1154,17 @@ async def update_tree_visibility(
         )
 
     if not can_edit_tree(current_user, tree):
+        # If the user can see this tree (same account, team visibility), give a 403 with
+        # a clear message — returning 404 here would be confusing since GET returns 200.
+        # For truly inaccessible trees (cross-account), return 404 to avoid confirming existence.
+        if can_access_tree(current_user, tree):
+            raise HTTPException(
+                status_code=status.HTTP_403_FORBIDDEN,
+                detail="You do not have permission to edit this flow"
+            )
         raise HTTPException(
-            status_code=status.HTTP_403_FORBIDDEN,
-            detail="You can only edit your own trees"
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="Tree not found"
         )
 
     # Update visibility

backend/app/api/endpoints/uploads.py

@@ -255,9 +255,9 @@ async def get_upload_url(
     if upload is None:
         raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Upload not found")
 
-    # Verify the upload belongs to the user's account
+    # Verify the upload belongs to the user's account — 404 to avoid revealing existence
     if upload.account_id != current_user.account_id and not current_user.is_super_admin:
-        raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail="Access denied")
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Upload not found")
 
     url = storage_service.get_presigned_url(upload.storage_key)
     return {"url": url}
@@ -311,9 +311,9 @@ async def delete_upload(
     if upload is None:
         raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Upload not found")
 
-    # Verify ownership
+    # Verify ownership — 404 to avoid revealing existence
     if upload.uploaded_by != current_user.id and not current_user.is_super_admin:
-        raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail="Access denied")
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Upload not found")
 
     # Delete from S3
     await storage_service.delete_file(upload.storage_key)

backend/app/core/filters.py

@@ -1,10 +1,12 @@
 """
 Centralized query filters for ResolutionFlow.
 
-Provides reusable SQLAlchemy filter builders for tree access control
-and step visibility, used across multiple endpoint modules.
+Provides reusable SQLAlchemy filter builders for tree access control,
+step visibility, and the canonical tenant_filter used by all queries
+on tenant-scoped tables.
 """
 from __future__ import annotations
+import uuid
 from typing import TYPE_CHECKING
 
 from sqlalchemy import or_, and_, true as sa_true
@@ -13,6 +15,18 @@ if TYPE_CHECKING:
     from app.models.user import User
 
 
+def tenant_filter(model, account_id: uuid.UUID):
+    """Primary app-layer tenant filter.
+
+    MUST be used in every SELECT/UPDATE/DELETE on tenant tables.
+    RLS (Phase 2) is the safety net — this is the primary enforcement.
+
+    Usage:
+        stmt = select(Tree).where(tenant_filter(Tree, current_user.account_id), ...)
+    """
+    return model.account_id == account_id
+
+
 def build_tree_access_filter(current_user: User):
     """Build the access filter for trees based on user permissions.
 
@@ -36,10 +50,11 @@ def build_tree_access_filter(current_user: User):
         Tree.author_id == current_user.id,
     ]
     if current_user.account_id:
+        # Team-visible trees: use tenant_filter as the account match
         conditions.append(
             and_(
                 Tree.visibility == 'team',
-                Tree.account_id == current_user.account_id
+                tenant_filter(Tree, current_user.account_id),
             )
         )
     return or_(*conditions)
@@ -58,11 +73,14 @@ def build_step_visibility_filter(current_user: User):
     if current_user.account_id:
         return or_(
             StepLibrary.visibility == 'public',
-            and_(StepLibrary.visibility == 'team', StepLibrary.account_id == current_user.account_id),
-            StepLibrary.created_by == current_user.id  # Own private steps
+            and_(
+                StepLibrary.visibility == 'team',
+                tenant_filter(StepLibrary, current_user.account_id),
+            ),
+            StepLibrary.created_by == current_user.id,
         )
     else:
         return or_(
             StepLibrary.visibility == 'public',
-            StepLibrary.created_by == current_user.id
+            StepLibrary.created_by == current_user.id,
         )

backend/app/services/copilot_service.py

@@ -8,7 +8,7 @@ from datetime import datetime, timezone, timedelta
 from typing import Optional, Any
 from uuid import UUID
 
-from sqlalchemy import select
+from sqlalchemy import select, or_
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy.orm import selectinload
 
@@ -103,13 +103,23 @@ async def start_conversation(
 
     Returns (conversation, greeting_message).
     """
-    # Load tree
+    # Load tree — must be accessible to this account.
+    # Allows own account's trees, default trees, and public trees.
+    # Raises ValueError (caught by endpoint as 404) if not found or not accessible.
     result = await db.execute(
-        select(Tree).options(selectinload(Tree.tags)).where(Tree.id == tree_id)
+        select(Tree).options(selectinload(Tree.tags)).where(
+            Tree.id == tree_id,
+            or_(
+                Tree.account_id == account_id,
+                Tree.author_id == user_id,
+                Tree.is_default == True,
+                Tree.is_public == True,
+            ),
+        )
     )
     tree = result.scalar_one_or_none()
     if not tree:
-        raise ValueError(f"Tree {tree_id} not found")
+        raise ValueError(f"Tree {tree_id} not found or not accessible")
 
     conversation = CopilotConversation(
         user_id=user_id,