fix(agent): keep file search off the gateway event loop

[louiseboo]

Summary

• offload FindTool filesystem traversal and result formatting to a worker thread
• give FindTool an explicit 30-second execution ceiling
• add deterministic regressions for event-loop responsiveness and registry timeouts

Root cause: FindTool.execute() performed synchronous Path.glob() traversal inside an async method. A slow filesystem walk blocked the gateway event loop, so channel polling and the surrounding asyncio.wait_for() timeout could not run until traversal returned.

Type

• Bug fix
• Feature
• Refactor
• Documentation

Verification

• uv run pytest tests/test_search_tools.py tests/test_file_search_traversal_guard.py tests/test_tool_registry_timeout.py -q — 29 passed
• make test-python — 59 passed
• make lint-python — passed
• uv run pre-commit run --files raven/agent/tools/file_search.py tests/test_search_tools.py — passed

A broader local suite attempt reached 4,477 passing tests, with 124 failures and 19 errors in environment-dependent EverOS, Boxlite, tui-use, and TUI integration tests unavailable on this machine. The focused search, traversal-guard, timeout, lint, and repository CI smoke suites above all pass.

Risk and rollback

• Public tool schema, matching behavior, path guards, ordering, and output format are unchanged.
• A timed-out worker may finish its current filesystem traversal in the background, but it no longer stalls the event loop or channel polling.
• Rollback: revert the single fix commit.

Privacy

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Fixes #193