Handle broken resource error gracefully

# Conflicts:
#	src/exo/master/api.py

src/exo/master/api.py

@@ -654,14 +654,17 @@ class API:
                 for idx, event in self.event_buffer.drain_indexed():
                     self._event_log.append(event)
                     self.state = apply(self.state, IndexedEvent(event=event, idx=idx))
-                    if isinstance(event, ChunkGenerated):
+                    if (
+                        isinstance(event, ChunkGenerated)
+                        and event.command_id in self._chat_completion_queues
+                    ):
                         assert isinstance(event.chunk, TokenChunk)
-                        queue = self._chat_completion_queues.get(event.command_id)
-                        if queue is not None:
-                            try:
-                                await queue.send(event.chunk)
-                            except BrokenResourceError:
-                                self._chat_completion_queues.pop(event.command_id, None)
+                        try:
+                            await self._chat_completion_queues[event.command_id].send(
+                                event.chunk
+                            )
+                        except BrokenResourceError:
+                            del self._chat_completion_queues[event.command_id]
 
     async def _pause_on_new_election(self):
         with self.election_receiver as ems: