- Add VALID_TOPICS whitelist to WS handler, reject unknown topic subscriptions - Add per-connection rate limit (50 topic changes/min) and max 20 subscriptions - Remove wildcard "*" subscription (security risk) - Add tracing::info! audit logging to all 8 mutation handlers - Add 30s AbortController timeout to frontend API calls - Fix clippy: rename _claims → claims in handlers that now use it Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>