Improve Python reliability in channel retries and thread typing (#1776)

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backend/app/channels/feishu.py

@@ -206,7 +206,9 @@ class FeishuChannel(Channel):
                     await asyncio.sleep(delay)
 
         logger.error("[Feishu] send failed after %d attempts: %s", _max_retries, last_exc)
-        raise last_exc  # type: ignore[misc]
+        if last_exc is None:
+            raise RuntimeError("Feishu send failed without an exception from any attempt")
+        raise last_exc
 
     async def send_file(self, msg: OutboundMessage, attachment: ResolvedAttachment) -> bool:
         if not self._api_client: