Remove unused endpoint and fix stale slot retry problems

app/radio.py

@@ -306,6 +306,15 @@ class RadioManager:
         self._channel_slot_by_key.move_to_end(normalized_key)
         self._channel_key_by_slot[slot] = normalized_key
 
+    def invalidate_cached_channel_slot(self, channel_key: str) -> None:
+        """Drop any cached slot assignment for a channel key."""
+        normalized_key = channel_key.upper()
+        slot = self._channel_slot_by_key.pop(normalized_key, None)
+        if slot is None:
+            return
+        if self._channel_key_by_slot.get(slot) == normalized_key:
+            self._channel_key_by_slot.pop(slot, None)
+
     def get_channel_send_cache_snapshot(self) -> list[tuple[str, int]]:
         """Return the current channel send cache contents in LRU order."""
         return list(self._channel_slot_by_key.items())

app/services/message_send.py

@@ -112,7 +112,10 @@ async def send_channel_message_with_effective_scope(
             msg=text,
             timestamp=timestamp_bytes,
         )
-        radio_manager.note_channel_slot_used(channel_key)
+        if send_result.type == EventType.ERROR:
+            radio_manager.invalidate_cached_channel_slot(channel_key)
+        else:
+            radio_manager.note_channel_slot_used(channel_key)
         return send_result
     finally:
         if override_scope and override_scope != baseline_scope:

tests/test_send_messages.py

@@ -475,6 +475,32 @@ class TestOutgoingChannelBroadcast:
         assert mc.commands.set_channel.await_count == 2
         assert radio_manager.get_cached_channel_slot(chan_key) is None
 
+    @pytest.mark.asyncio
+    async def test_send_channel_msg_error_invalidates_cached_slot(self, test_db):
+        mc = _make_mc(name="MyNode")
+        chan_key = "f1" * 16
+        await ChannelRepository.upsert(key=chan_key, name="#stale")
+        radio_manager.max_channels = 4
+        radio_manager._connection_info = "Serial: /dev/ttyUSB0"
+
+        mc.commands.send_chan_msg = AsyncMock(
+            return_value=MagicMock(type=EventType.ERROR, payload="bad slot")
+        )
+
+        with (
+            patch("app.routers.messages.require_connected", return_value=mc),
+            patch.object(radio_manager, "_meshcore", mc),
+            patch("app.decoder.calculate_channel_hash", return_value="abcd"),
+            patch("app.routers.messages.broadcast_event"),
+            pytest.raises(HTTPException) as exc_info,
+        ):
+            await send_channel_message(
+                SendChannelMessageRequest(channel_key=chan_key, text="this will fail")
+            )
+
+        assert exc_info.value.status_code == 500
+        assert radio_manager.get_cached_channel_slot(chan_key) is None
+
 
 class TestResendChannelMessage:
     """Test the user-triggered resend endpoint."""