Fix three critical bugs causing bash/tmux session leaks

1. EventService.close() fire-and-forget (CRITICAL): Added missing await
   to ensure LocalConversation.close() actually runs during shutdown

2. No tmux session cleanup on startup (MEDIUM): Added cleanup_stale_tmux_sessions()
   to kill orphaned sessions from previous server runs on startup

3. Task manager sub-conversations use delete_on_close=False (MEDIUM): Changed
   to delete_on_close=True in both locations to ensure tool cleanup runs

These fixes prevent unbounded accumulation of orphaned tmux sessions and
their bash children processes that were never being terminated.

Co-authored-by: openhands <openhands@all-hands.dev>

Author: rbren

openhands-agent-server/openhands/agent_server/api.py

@@ -49,8 +49,50 @@
 logger = get_logger(__name__)
 
 
+async def cleanup_stale_tmux_sessions() -> None:
+    """Clean up any stale tmux sessions on server startup.
+
+    Tmux sessions live in a separate process that survives agent-server restarts.
+    This function kills all existing sessions on the openhands socket to prevent
+    accumulation of orphaned sessions. Reconnecting conversations will create
+    fresh sessions as needed.
+    """
+    try:
+        import libtmux
+
+        # Connect to the dedicated OpenHands tmux server
+        server = libtmux.Server(socket_name="openhands")
+
+        # Get all sessions on this server
+        sessions = server.sessions
+        if not sessions:
+            logger.debug("No tmux sessions found on openhands socket")
+            return
+
+        logger.info("Cleaning up %d stale tmux session(s) on startup", len(sessions))
+
+        # Kill all sessions - they're all stale since we're starting up
+        for session in sessions:
+            try:
+                logger.debug("Killing tmux session: %s", session.name)
+                session.kill()
+            except Exception as e:
+                logger.warning("Failed to kill tmux session %s: %s", session.name, e)
+
+        logger.info("Tmux cleanup completed")
+
+    except ImportError:
+        logger.debug("libtmux not available, skipping tmux cleanup")
+    except Exception as e:
+        # Don't let tmux cleanup failures prevent server startup
+        logger.warning("Failed to cleanup tmux sessions: %s", e)
+
+
 @asynccontextmanager
 async def api_lifespan(api: FastAPI) -> AsyncIterator[None]:
+    # Clean up stale tmux sessions from previous server runs
+    await cleanup_stale_tmux_sessions()
+
     service = get_default_conversation_service()
     vscode_service = get_vscode_service()
     desktop_service = get_desktop_service()

openhands-tools/openhands/tools/task/manager.py

@@ -198,7 +198,7 @@ def _resume_task(self, resume: str, subagent_type: str) -> Task:
                 persistence_dir=self._persistence_dir,
                 conversation_id=conversation_id,
                 hook_config=factory.definition.hooks,
-                delete_on_close=False,
+                delete_on_close=True,
             )
 
             self._set_confirmation_policy(
@@ -285,7 +285,7 @@ def _get_conversation(
             conversation_id=conversation_id,
             max_iteration_per_run=max_iteration_per_run,
             hook_config=hook_config,
-            delete_on_close=False,
+            delete_on_close=True,
         )
 
     def _get_sub_agent(self, subagent_type: str) -> Agent: