feat(dashboard): auto-stop server after 5 minutes idle

Replace pause-on-idle with full server shutdown after IDLE_SHUTDOWN_SECONDS
(default 5 minutes). Next visitor gets a fresh simulation instance.

- Idle checker stops server and clears st.cache_resource
- init_session_state detects stopped server and recreates fresh state
- Clears instruments and history for clean restart

Configurable via IDLE_SHUTDOWN_SECONDS environment variable.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/py_dvt_ate/app/dashboard/app.py

@@ -28,26 +28,49 @@ from py_dvt_ate.tests.thermal.tempco import TempCoTest
 _test_executor = ThreadPoolExecutor(max_workers=1, thread_name_prefix="test_runner")
 
 
-# Idle pause configuration
-# Physics engine pauses after IDLE_PAUSE_SECONDS of no activity (default: 30s)
-IDLE_PAUSE_SECONDS = int(os.environ.get("IDLE_PAUSE_SECONDS", "30"))
+# Idle shutdown configuration
+# Server stops after IDLE_SHUTDOWN_SECONDS of no activity (default: 5 minutes)
+# Next visitor gets a fresh simulation instance
+IDLE_SHUTDOWN_SECONDS = int(os.environ.get("IDLE_SHUTDOWN_SECONDS", "300"))
 _last_activity_time: float = time.time()
 _idle_checker_started = False
 _server_ref: SimulationServer | None = None  # Reference for idle checker thread
 
 
 def _idle_checker() -> None:
-    """Background thread that pauses physics when idle."""
+    """Background thread that stops server when idle."""
     global _last_activity_time, _server_ref
     while True:
-        time.sleep(5)  # Check every 5 seconds
+        time.sleep(10)  # Check every 10 seconds
         if _server_ref is None:
             continue
 
         idle_seconds = time.time() - _last_activity_time
-        if idle_seconds > IDLE_PAUSE_SECONDS and not _server_ref.paused:
-            _server_ref.paused = True
-            print(f"Physics engine paused (idle for {idle_seconds:.0f}s)")
+        if idle_seconds > IDLE_SHUTDOWN_SECONDS:
+            print(f"Stopping server (idle for {idle_seconds:.0f}s)")
+            _stop_server()
+            break  # Exit checker thread - new one starts with new server
+
+
+def _stop_server() -> None:
+    """Stop the server and clear caches for fresh restart."""
+    global _server_ref, _idle_checker_started
+    if _server_ref is not None:
+        # Stop the server
+        loop = asyncio.new_event_loop()
+        try:
+            loop.run_until_complete(_server_ref.stop())
+        except Exception:
+            pass
+        finally:
+            loop.close()
+        _server_ref = None
+
+    # Clear Streamlit's cached server so next visitor gets fresh instance
+    get_or_create_server.clear()
+
+    # Reset idle checker flag so new one can start
+    _idle_checker_started = False
 
 
 def _start_idle_checker(server: SimulationServer) -> None:
@@ -161,19 +184,21 @@ def get_or_create_server() -> SimulationServer:
 
 
 def _update_activity() -> None:
-    """Update activity timestamp and resume physics if paused."""
+    """Update activity timestamp to prevent idle shutdown."""
     global _last_activity_time
     _last_activity_time = time.time()
 
-    # Resume physics if it was paused
-    server = st.session_state.get("server")
-    if server is not None and server.paused:
-        server.paused = False
-        print("Physics engine resumed (user activity detected)")
-
 
 def init_session_state() -> None:
     """Initialise Streamlit session state."""
+    # Check if existing server was stopped by idle checker
+    if "server" in st.session_state and st.session_state.server is not None:
+        if not st.session_state.server.is_running:
+            # Server was stopped - clear stale state for fresh start
+            st.session_state.server = None
+            st.session_state.pop("instruments", None)
+            st.session_state.pop("history", None)
+
     # Get or create the server singleton (survives Streamlit reruns via st.cache_resource)
     if "server" not in st.session_state or st.session_state.server is None:
         with st.spinner("Starting simulation server..."):
@@ -189,7 +214,7 @@ def init_session_state() -> None:
             st.error("Failed to start simulation server. Please refresh the page.")
             st.stop()
 
-        # Start idle checker to pause physics when no one's viewing
+        # Start idle checker to stop server when no one's viewing
         _start_idle_checker(st.session_state.server)
 
     if "instruments" not in st.session_state: