- Populate watcher_* routing fields for watch-only processes (not just
notify_on_complete), so watch-pattern events carry direct metadata
instead of relying solely on session_key parsing fallback
- Extract _parse_session_key() helper to dedupe session key parsing
at two call sites in gateway/run.py
- Add negative test proving cross-thread leakage doesn't happen
- Add edge-case tests for _build_process_event_source returning None
(empty evt, invalid platform, short session_key)
- Add unit tests for _parse_session_key helper