* fix(mcp): synchronize session pool singleton lifecycle
Parity follow-up to #3778 (skill storage) and #3730 (sandbox provider).
get_session_pool() already serialised creation with _pool_lock, but its
fast-path check and final return read the global separately, and
reset_session_pool() cleared it with no lock. A reset_mcp_tools_cache()
(reachable via the /api/mcp/cache/reset admin endpoint) racing a
concurrent get could null the singleton between the None-check and the
return, handing the caller None despite the -> MCPSessionPool annotation.
Build and return the pool inside _pool_lock with a double check, and
clear it under the same lock in reset_session_pool(). The critical
section is tiny and never awaits, so holding the threading.Lock is safe
from both the async and sync/worker-thread paths. No behavior change for
single-threaded callers.
Signed-off-by: Yufeng He <40085740+he-yufeng@users.noreply.github.com>
* Apply suggestions from code review
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
---------
Signed-off-by: Yufeng He <40085740+he-yufeng@users.noreply.github.com>
Co-authored-by: Willem Jiang <willem.jiang@gmail.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
