Adds distributed locking using Nextcloud's ILockingProvider to prevent
race conditions between background job and on-demand token refresh.
Uses double-check locking pattern:
1. Quick check without lock - return immediately if token is valid
2. Acquire exclusive lock if token needs refresh
3. Re-check after lock - another process may have refreshed
4. Refresh only if still needed
5. Graceful degradation on LockedException
Changes:
- McpTokenStorage: add ILockingProvider, withTokenLock() method
- McpTokenStorage: update getAccessToken() with locking pattern
- RefreshUserTokens: wrap refresh in withTokenLock(), catch LockedException
- Add comprehensive unit tests for locking behavior
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Chris Coutinho
5b71ac3251