diff --git a/engine/core/transports.py b/engine/core/transports.py
index 3df04ba..31e398c 100644
--- a/engine/core/transports.py
+++ b/engine/core/transports.py
@@ -69,6 +69,13 @@ class SocketTransport(BaseTransport):
         self.lock = asyncio.Lock()  # Prevent frame interleaving
         self._closed = False
 
+    def _ws_disconnected(self) -> bool:
+        """Best-effort check for websocket disconnection state."""
+        return (
+            self.ws.client_state == WebSocketState.DISCONNECTED
+            or self.ws.application_state == WebSocketState.DISCONNECTED
+        )
+
     async def send_event(self, event: dict) -> None:
         """
         Send a JSON event via WebSocket.
@@ -76,17 +83,27 @@ class SocketTransport(BaseTransport):
         Args:
             event: Event data as dictionary
         """
-        if self._closed:
+        if self._closed or self._ws_disconnected():
             logger.warning("Attempted to send event on closed transport")
+            self._closed = True
             return
 
         async with self.lock:
             try:
                 await self.ws.send_text(json.dumps(event))
                 logger.debug(f"Sent event: {event.get('event', 'unknown')}")
-            except Exception as e:
-                logger.error(f"Error sending event: {e}")
+            except RuntimeError as e:
                 self._closed = True
+                if self._ws_disconnected() or "close message has been sent" in str(e):
+                    logger.debug(f"Skip sending event on closed websocket: {e!r}")
+                    return
+                logger.error(f"Error sending event: {e!r}")
+            except Exception as e:
+                self._closed = True
+                if self._ws_disconnected():
+                    logger.debug(f"Skip sending event on disconnected websocket: {e!r}")
+                    return
+                logger.error(f"Error sending event: {e!r}")
 
     async def send_audio(self, pcm_bytes: bytes) -> None:
         """
@@ -95,16 +112,26 @@ class SocketTransport(BaseTransport):
         Args:
             pcm_bytes: PCM audio data (16-bit, mono, 16kHz)
         """
-        if self._closed:
+        if self._closed or self._ws_disconnected():
             logger.warning("Attempted to send audio on closed transport")
+            self._closed = True
             return
 
         async with self.lock:
             try:
                 await self.ws.send_bytes(pcm_bytes)
-            except Exception as e:
-                logger.error(f"Error sending audio: {e}")
+            except RuntimeError as e:
                 self._closed = True
+                if self._ws_disconnected() or "close message has been sent" in str(e):
+                    logger.debug(f"Skip sending audio on closed websocket: {e!r}")
+                    return
+                logger.error(f"Error sending audio: {e!r}")
+            except Exception as e:
+                self._closed = True
+                if self._ws_disconnected():
+                    logger.debug(f"Skip sending audio on disconnected websocket: {e!r}")
+                    return
+                logger.error(f"Error sending audio: {e!r}")
 
     async def close(self) -> None:
         """Close the WebSocket connection."""
@@ -112,10 +139,7 @@ class SocketTransport(BaseTransport):
             return
 
         self._closed = True
-        if (
-            self.ws.client_state == WebSocketState.DISCONNECTED
-            or self.ws.application_state == WebSocketState.DISCONNECTED
-        ):
+        if self._ws_disconnected():
             return
 
         try: