fix: address PR #589 review feedback (round 2)

Consolidate three independent RefreshTokenStorage lazy singletons into a
single lock-protected get_shared_storage() function, eliminating race
conditions on concurrent first-access. Remove blanket try/except in
_get_stored_scopes so storage errors propagate as proper MCP errors
instead of silently triggering "please provision" messages. Handle
declined/cancelled elicitation results in Login Flow tools by cleaning up
sessions and returning clear status. Add update_app_password_scopes() to
avoid unnecessary decrypt/re-encrypt when only scopes change. Add
unprovisioned-user early exit and no-op detection to nc_auth_update_scopes.
Remove four dead config fields and misleading NEXTCLOUD_PASSWORD deprecation
warning. Add periodic login flow session cleanup task. Generate separate
Fernet keys per service. Add board cleanup in deck integration test. Gate
CI unit tests on linting and skip Astrolabe build for single-user profile.
Fix test markers from oauth to multi_user_basic for astrolabe integration
tests. Update login_flow.py docstrings to document outbound HTTP calls.

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

nextcloud_mcp_server/auth/storage.py

@@ -1614,6 +1614,40 @@ class RefreshTokenStorage:
             )
             return None
 
+    async def update_app_password_scopes(self, user_id: str, scopes: list[str]) -> bool:
+        """Update only the scopes for an existing app password (no decrypt/re-encrypt).
+
+        Args:
+            user_id: MCP user ID
+            scopes: New scope list
+
+        Returns:
+            True if a row was updated, False if user not found
+        """
+        if not self._initialized:
+            await self.initialize()
+
+        scopes_json = json.dumps(scopes)
+        now = int(time.time())
+        start_time = time.time()
+        try:
+            async with aiosqlite.connect(self.db_path) as db:
+                cursor = await db.execute(
+                    "UPDATE app_passwords SET scopes = ?, updated_at = ? WHERE user_id = ?",
+                    (scopes_json, now, user_id),
+                )
+                await db.commit()
+                updated = cursor.rowcount > 0
+
+            duration = time.time() - start_time
+            record_db_operation("sqlite", "update", duration, "success")
+            return updated
+
+        except Exception:
+            duration = time.time() - start_time
+            record_db_operation("sqlite", "update", duration, "error")
+            raise
+
     # ── Login Flow v2: Session Tracking ──────────────────────────────────
 
     async def store_login_flow_session(
@@ -1811,6 +1845,25 @@ class RefreshTokenStorage:
             raise
 
 
+_shared_instance: RefreshTokenStorage | None = None
+_shared_lock = anyio.Lock()
+
+
+async def get_shared_storage() -> RefreshTokenStorage:
+    """Get the process-wide RefreshTokenStorage singleton (lock-protected).
+
+    All modules that need storage should use this function instead of
+    creating their own lazy singletons. The lock ensures thread-safe
+    initialization on concurrent first-access.
+    """
+    global _shared_instance
+    async with _shared_lock:
+        if _shared_instance is None:
+            _shared_instance = RefreshTokenStorage.from_env()
+            await _shared_instance.initialize()
+    return _shared_instance
+
+
 async def generate_encryption_key() -> str:
     """
     Generate a new Fernet encryption key.