fix(12): resolve critical code review findings (CR-01 through CR-04)

- CR-01: fix browse URL from /folders/{id} to /items?parent_ref= (broken feature)
- CR-02: remove raw provider exception text from _TerminalProviderError messages
- CR-03: add user_id predicate to get_or_create_folder_state query (ownership boundary)
- CR-04: add max_length=255 to ConnectionRenameRequest.display_name

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

backend/api/cloud/schemas.py

@@ -9,7 +9,7 @@ from __future__ import annotations
 from datetime import datetime
 from typing import List, Optional
 
-from pydantic import BaseModel, field_validator
+from pydantic import BaseModel, Field, field_validator
 
 
 # ── Capability / item schemas ─────────────────────────────────────────────────
@@ -75,7 +75,7 @@ class ConnectionRenameRequest(BaseModel):
     Only display_name is accepted — mass assignment prevention.
     """
 
-    display_name: str
+    display_name: str = Field(..., max_length=255)
 
     @field_validator("display_name")
     @classmethod

backend/services/cloud_items.py

@@ -229,6 +229,7 @@ async def get_or_create_folder_state(
     uid_fs = user_id if isinstance(user_id, uuid.UUID) else uuid.UUID(str(user_id))
     result = await session.execute(
         select(CloudFolderState).where(
+            CloudFolderState.user_id == uid_fs,
             CloudFolderState.connection_id == cid_fs,
             CloudFolderState.parent_ref == parent_ref,
         )

backend/tasks/cloud_tasks.py

@@ -107,7 +107,7 @@ async def _run(user_id: str, connection_id: str, parent_ref: str | None) -> dict
                 error_message="Credential decryption failed. Re-connect the account.",
             )
             await session.commit()
-            raise _TerminalProviderError(f"Credential decryption failed: {exc}") from exc
+            raise _TerminalProviderError("Credential decryption failed. Re-connect the account.") from exc
 
         # Build adapter and fetch listing
         try:
@@ -133,9 +133,9 @@ async def _run(user_id: str, connection_id: str, parent_ref: str | None) -> dict
                     error_message="Authentication failed. Re-connect the account.",
                 )
                 await session.commit()
-                raise _TerminalProviderError(f"Auth error: {exc}") from exc
+                raise _TerminalProviderError("Authentication failed. Re-connect the account.") from exc
             # Transient failure — let Celery retry
-            raise _TransientProviderError(f"Provider error: {exc}") from exc
+            raise _TransientProviderError("Provider error. Will retry.") from exc
 
         # Reconcile listing into durable cloud_items rows
         await reconcile_cloud_listing(

frontend/src/api/cloud.js

@@ -30,11 +30,12 @@ export function updateDefaultStorage(backend) {
 }
 
 /**
- * Browse a cloud folder by connection UUID and folder path.
- * connectionId is always a UUID; folderId is a path string (default 'root').
+ * Browse a cloud folder by connection UUID and optional parent_ref.
+ * connectionId is always a UUID; parentRef is a provider path string (default '').
  */
-export function getCloudFoldersByConnectionId(connectionId, folderId) {
-  return request(`/api/cloud/connections/${connectionId}/folders/${folderId}`)
+export function getCloudFoldersByConnectionId(connectionId, parentRef = '') {
+  const qs = parentRef ? `?parent_ref=${encodeURIComponent(parentRef)}` : ''
+  return request(`/api/cloud/connections/${connectionId}/items${qs}`)
 }
 
 /** @deprecated Use getCloudFoldersByConnectionId instead. */