* fix(frontend): replace invalid "context" select field with "metadata" in threads.search
The LangGraph API server does not support "context" as a select field for
threads/search, causing a 422 Unprocessable Entity error introduced by
commit 60e0abf (#1771).
- Replace "context" with "metadata" in the default select list
- Persist agent_name into thread metadata on creation so search results
carry the agent identity
- Update pathOfThread() to fall back to metadata.agent_name when
context is unavailable from search results
- Add regression tests for metadata-based agent routing
Fixes#2037
Made-with: Cursor
* fix: apply Copilot suggestions
* style: fix the lint error