- Add creator ownership verification on chat session endpoints (get, archive, send, list messages)
- Add CancelTaskByUser handler with ownership check instead of unrestricted CancelTask
- Show user messages optimistically before server response
- Remove unused streamingContent from chat store and sendMessage mutation import
- Make QueryProvider devtools flag a prop instead of reading process.env in core package
- Add proper FK constraint on chat_session.creator_id → user(id)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>