Fix shutdown hang on session processor thread lock (#108)

* Initial plan

* Fix shutdown hang: wake session processor thread on stop() and mark daemon

Co-authored-by: lstein <111189+lstein@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: lstein <111189+lstein@users.noreply.github.com>

Author: Copilot

invokeai/app/services/session_processor/session_processor_default.py

@@ -355,6 +355,7 @@ def start(self, invoker: Invoker) -> None:
         self._thread = Thread(
             name="session_processor",
             target=self._process,
+            daemon=True,
             kwargs={
                 "stop_event": self._stop_event,
                 "poll_now_event": self._poll_now_event,
@@ -366,6 +367,9 @@ def start(self, invoker: Invoker) -> None:
 
     def stop(self, *args, **kwargs) -> None:
         self._stop_event.set()
+        # Wake the thread if it is sleeping in poll_now_event.wait() or blocked in resume_event.wait() (paused).
+        self._poll_now_event.set()
+        self._resume_event.set()
 
     def _poll_now(self) -> None:
         self._poll_now_event.set()