Ensure runtime IM channels are ready after restart

backend/tests/test_channels.py

@@ -3504,6 +3504,51 @@ class TestChannelService:
             "app_token": "xapp-ui",
         }
 
+    def test_start_retries_configured_channel_until_ready(self, monkeypatch):
+        from app.channels.service import ChannelService
+
+        class FlakyReadyChannel(Channel):
+            starts = 0
+
+            def __init__(self, bus, config):
+                super().__init__(name="slack", bus=bus, config=config)
+
+            async def start(self):
+                type(self).starts += 1
+                self._running = type(self).starts >= 2
+
+            async def stop(self):
+                self._running = False
+
+            async def send(self, msg):
+                return None
+
+        monkeypatch.setattr(
+            "deerflow.reflection.resolve_class",
+            lambda import_path, base_class=None: FlakyReadyChannel,
+        )
+
+        async def go():
+            service = ChannelService(
+                channels_config={
+                    "slack": {
+                        "enabled": True,
+                        "bot_token": "xoxb-ui",
+                        "app_token": "xapp-ui",
+                    },
+                }
+            )
+
+            try:
+                await service.start()
+
+                assert FlakyReadyChannel.starts == 2
+                assert service.get_status()["channels"]["slack"]["running"] is True
+            finally:
+                await service.stop()
+
+        _run(go())
+
     def test_connection_repo_is_forwarded_to_manager(self):
         from app.channels.service import ChannelService