client: guard join_channel and send_text against stale ids

join_channel raises ValueError on missing channel instead of
KeyError. send_text handles missing channel_id gracefully.

src/tuimble/client.py

@@ -229,7 +229,12 @@ class MumbleClient:
     def send_text(self, message: str):
         """Send a text message to the current channel."""
         if self._mumble and self._connected:
-            ch = self._mumble.channels[self._mumble.users.myself["channel_id"]]
+            try:
+                cid = self._mumble.users.myself["channel_id"]
+                ch = self._mumble.channels[cid]
+            except (KeyError, AttributeError):
+                log.warning("send_text: channel unavailable")
+                return
             ch.send_text_message(message)
 
     def send_audio(self, pcm_data: bytes):
@@ -238,9 +243,16 @@ class MumbleClient:
             self._mumble.sound_output.add_sound(pcm_data)
 
     def join_channel(self, channel_id: int):
-        """Move to a different channel."""
+        """Move to a different channel.
+
+        Raises:
+            ValueError: If the channel no longer exists on the server.
+        """
         if self._mumble and self._connected:
-            self._mumble.channels[channel_id].move_in()
+            ch = self._mumble.channels.get(channel_id)
+            if ch is None:
+                raise ValueError(f"channel {channel_id} not found")
+            ch.move_in()
 
     def set_self_deaf(self, deaf: bool):
         """Toggle self-deafen on the server."""