diff --git a/python/mujoco/experimental/studio/launch_passive.py b/python/mujoco/experimental/studio/launch_passive.py
index 5ecd17ae..215c940f 100644
--- a/python/mujoco/experimental/studio/launch_passive.py
+++ b/python/mujoco/experimental/studio/launch_passive.py
@@ -149,6 +149,7 @@ def launch_passive(
   handle = viewer_handle.ViewerHandle(
       sim_endpoint,
       is_alive_fn=thread.is_alive,
+      shutdown_fn=thread.join,
       handlers=sim_handlers,
   )
   return handle
diff --git a/python/mujoco/experimental/studio/native_viewer.py b/python/mujoco/experimental/studio/native_viewer.py
index dceaba8f..f7f444d5 100644
--- a/python/mujoco/experimental/studio/native_viewer.py
+++ b/python/mujoco/experimental/studio/native_viewer.py
@@ -99,11 +99,12 @@ class NativeViewer(viewer_protocol.Viewer):
       self._viewer.InitRenderer(model)
       self._renderer_model_id = id(model)
 
-  def is_running(self) -> bool:
-    """Poll for a new frame; returns ``False`` when the window is closed."""
-    if super().is_running() and not self._viewer.NewFrame():
-      self.close()
-    return super().is_running()
+  def prepare_next_frame(self) -> bool:
+    """Advances to the next frame; returns False when the window is closed."""
+    if not self._viewer.NewFrame():
+      self._is_running = False
+      return False
+    return True
 
   def sync(self) -> None:
     """Render the scene and present it to the window."""
diff --git a/python/mujoco/experimental/studio/viewer_handle.py b/python/mujoco/experimental/studio/viewer_handle.py
index f87241a6..ef910c0e 100644
--- a/python/mujoco/experimental/studio/viewer_handle.py
+++ b/python/mujoco/experimental/studio/viewer_handle.py
@@ -21,6 +21,15 @@ from mujoco.experimental.studio import messages
 from mujoco.experimental.studio import sim as _sim
 import numpy as np
 
+# Launcher-owned liveness check: returns True while the viewer is still alive.
+# This enables the handle to notice a viewer died without sending ExitEvent.
+IsAliveFn = Callable[[], bool]
+
+# Launcher-owned shutdown function: waits up to the given timeout (seconds) for
+# the viewer to finish after close() has sent the ExitEvent. Waiting lets the
+# viewer release its resources before the interpreter tears itself down.
+ShutdownFn = Callable[[float], None]
+
 
 class ViewerHandle:
   """A handle for interacting with a running Studio application from the sim."""
@@ -30,7 +39,8 @@ class ViewerHandle:
       sim_endpoint: endpoints.SimEndpoint,
       *,
       handlers: list[Any] | None = None,
-      is_alive_fn: Callable[[], bool] | None = None,
+      is_alive_fn: IsAliveFn | None = None,
+      shutdown_fn: ShutdownFn | None = None,
   ) -> None:
     """Initializes the ViewerHandle.
 
@@ -38,14 +48,15 @@ class ViewerHandle:
       sim_endpoint: The endpoint to use for communication with the viewer.
       handlers: Optional list of handler instances for sim-side processing,
         which are classes with methods decorated with ``@handler``.
-      is_alive_fn: Optional function called to check if the viewer is still
-        alive/responsive. If not provided, the viewer is assumed to be running
-        until ``close()`` is called.
+      is_alive_fn: Optional liveness check; without one the viewer is assumed to
+        be running until ``close()`` is called.
+      shutdown_fn: Optional launcher-owned shutdown hook, called by ``close()``.
     """
 
     self._sim_endpoint = sim_endpoint
     self._is_running = True
     self._is_alive_fn = is_alive_fn
+    self._shutdown_fn = shutdown_fn
     self.model: mujoco.MjModel | None = None
     self.data: mujoco.MjData | None = None
     self.step_control: _sim.StepControl | None = None
@@ -56,13 +67,15 @@ class ViewerHandle:
     self._handlers = handler_registry.HandlerRegistry(all_handlers)
 
   def close(self) -> None:
-    """Signals the viewer to exit and closes the sim endpoint."""
+    """Signals the viewer to exit and waits for it to shut down."""
     if self._is_running:
       self._is_running = False
       try:
         self.send_to_viewer(messages.ExitEvent())
       except Exception:  # pylint: disable=broad-exception-caught
         pass  # Ignore exceptions, the viewer may have already closed.
+      if self._shutdown_fn is not None:
+        self._shutdown_fn(5.0)
     self._sim_endpoint.close()
 
   def __enter__(self) -> 'ViewerHandle':
diff --git a/python/mujoco/experimental/studio/viewer_protocol.py b/python/mujoco/experimental/studio/viewer_protocol.py
index 9dc83cca..e6193d90 100644
--- a/python/mujoco/experimental/studio/viewer_protocol.py
+++ b/python/mujoco/experimental/studio/viewer_protocol.py
@@ -58,6 +58,9 @@ class ViewerConfig:
   height: int = 800
   gfx: str = ''
   viewer_mode: ViewerMode = ViewerMode.NATIVE
+  # Web viewer only: public port. 0 picks the first free port starting at 8080,
+  # so several viewers can run side by side.
+  http_port: int = 0
 
 
 # Legacy message types kept for backward compatibility.
@@ -141,6 +144,7 @@ class Viewer(abc.ABC):
     self.config = config
     self._endpoint = endpoint
     self._is_running = True
+    self._closed = False
 
     # Viewer-owned model and data.
     if model is None:
@@ -169,13 +173,21 @@ class Viewer(abc.ABC):
 
   def close(self) -> None:
     """Closes the viewer, sends an exit event and shuts down the endpoint."""
-    if self._is_running:
-      self._is_running = False
-      try:
-        self.send_to_sim(messages.ExitEvent())
-      except Exception:  # pylint: disable=broad-exception-caught
-        pass  # Ignore exceptions, the sim may have already closed.
-      self._endpoint.close()
+    if self._closed:
+      return
+    self._closed = True
+    self._is_running = False
+    try:
+      self.send_to_sim(messages.ExitEvent())
+    except Exception:  # pylint: disable=broad-exception-caught
+      pass  # Ignore exceptions, the sim may have already closed.
+    self._endpoint.close()
+
+  @messages.handler(priority=messages.Priority.CRITICAL)
+  def _on_exit(self, _: messages.ExitEvent) -> bool:
+    """Stops the viewer loop when the sim side requests an exit."""
+    self._is_running = False
+    return False  # Do not consume; app handlers may want cleanup too.
 
   def is_running(self) -> bool:
     """Returns True while the viewer has not been closed."""
@@ -221,6 +233,11 @@ class Viewer(abc.ABC):
       mujoco.mj_forward(self.model, self.data)
     return False  # Do not consume; let other handlers see the event.
 
+  @abc.abstractmethod
+  def prepare_next_frame(self) -> bool:
+    """Advances to the next frame; returns whether one is ready to render."""
+    ...
+
   @abc.abstractmethod
   def sync(self) -> None:
     """Renders the scene using the viewer's current model and data."""
@@ -251,18 +268,30 @@ def run_viewer_loop(viewer: Viewer) -> None:
   Args:
     viewer: A Viewer that owns the endpoint and handler registry.
   """
-  while viewer.is_running():
-    # Process incoming messages.
+  while True:
+    # Get the next frame; this also gets the frame's mouse/keyboard events.
+    frame = viewer.prepare_next_frame()
+
+    # Process incoming simulation events.
     for event in viewer.get_sim_events():
       viewer.dispatch(event)
+
+    # Stop the loop if the viewer is not running (endpoint will be closed).
+    if not viewer.is_running():
+      break
+
+    # Process incoming simulation snapshots.
     for snapshot in viewer.get_sim_snapshots():
       viewer.dispatch(snapshot)
 
-    # Dispatch lifecycle events.
-    viewer.dispatch(messages.UpdateEvent())
-    viewer.dispatch(messages.BuildGuiEvent())
+    # Skip rendering when prepare_next_frame returned no active frame.
+    # e.g., no browser is connected to the web viewer.
+    if frame:
+      # Dispatch lifecycle events.
+      viewer.dispatch(messages.UpdateEvent())
+      viewer.dispatch(messages.BuildGuiEvent())
 
-    # Render the scene.
-    viewer.sync()
+      # Render the scene.
+      viewer.sync()
 
   viewer.close()