📝 Pull Request Template

1. Related Issue

Closes # (issue number)

2. Type of Change (select one)

Bug Fix

3. Description

Problem

Using asyncio.to_thread(_resolve_local_agent_class, spec) occasionally hangs on Windows during request handling.

Root cause (short)

• CPython serializes imports with a global import lock.
• asyncio.to_thread runs import_module in a worker thread; if the main thread (or another thread) is also importing or holding resources, the worker can block waiting for the import lock while the main thread waits for the worker — producing a deadlock-like hang.
• Windows scheduling, platform-specific init in some libraries, and antivirus/file-scanner delays make this race more likely there.

Why it shows up in this codepath

• The threaded import is performed during request handling (_build_local_agent), so any blocking stalls the request pipeline between “Resolved prompt” and “Launching in-process agent”.

Short mitigations

• Add timeout + synchronous fallback (applied): try asyncio.to_thread with asyncio.wait_for(..., timeout=5s) and fall back to sync _resolve_local_agent_class on timeout.

4. Testing

• I have tested this locally.
• I have updated or added relevant tests.

5. Checklist

• I have read the Code of Conduct
• I have followed the Contributing Guidelines
• My changes follow the project's coding style