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Giles Odigwe 7d23582e2b Python: fix: prevent MCP message_handler deadlock on notification reload (#4866 )

* fix(python): prevent MCP message_handler deadlock on notification reload

When an MCP server sends a notifications/tools/list_changed or
notifications/prompts/list_changed notification, the message_handler
previously awaited load_tools()/load_prompts() directly. Since the
handler runs on the MCP SDK's single-threaded receive loop, this
caused a deadlock: load_tools() sends a list_tools request and waits
for its response, but the receive loop cannot deliver that response
while blocked in the handler.

This manifested as a timeout in call_tool(), which then surfaced as
"Error: Function failed." to the model instead of the real tool
output. The MATLAB MCP server reliably triggers this because it sends
a tools/list_changed notification during tool execution.

Fix: schedule reloads as background asyncio.Tasks via a new
_schedule_reload() helper, freeing the receive loop immediately.

Fixes #4828

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Address PR review feedback: fix exc_info, coalesce reloads, shutdown cleanup, tests

- Fix exc_info=exc -> exc_info=True in _schedule_reload and message_handler
- Tighten _schedule_reload param type from Any to Coroutine[Any, Any, None]
- Coalesce reloads: cancel-and-replace per reload kind to prevent unbounded growth
- Cancel pending reload tasks in _close_on_owner before tearing down session
- Re-raise CancelledError in _safe_reload to respect task cancellation
- Replace flaky asyncio.sleep(0) with asyncio.wait_for/gather in tests
- Add caplog assertions to verify reload failure is actually logged
- Assert _pending_reload_tasks cleanup on error path

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: address review comments on MCP reload handling

- Fix exc_info=True -> exc_info=message in message_handler error logging,
  since the handler is not called from an except block
- Await cancelled reload tasks in _close_on_owner before tearing down
  the session to avoid 'Task was destroyed but pending' warnings
- Add cancel-and-replace test verifying duplicate notifications cancel
  the first reload task and only keep one in flight

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: remove Task.cancelling() call for Python 3.10 compat

Task.cancelling() was added in Python 3.11. Replace with awaiting
the task and checking cancelled() instead.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Add debug log when cancelling superseded reload task

Log at DEBUG level when a new notification cancels an in-flight reload
task, improving observability of the cancel-and-replace behavior.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot <copilot@github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>