.

hf_backend.py

@@ -112,3 +112,13 @@ class HFChatBackend(ChatBackend):
                 {"index": 0, "delta": {"content": text}, "finish_reason": "stop"}
             ],
         }
+class StubImagesBackend(ImagesBackend):
+    """
+    Stub backend for images since HFChatBackend is text-only.
+    Returns a transparent 1x1 PNG placeholder.
+    """
+    async def generate_b64(self, request: Dict[str, Any]) -> str:
+        logger.warning("Image generation not supported in HF backend.")
+        return (
+            "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR4nGP4BwQACfsD/etCJH0AAAAASUVORK5CYII="
+        )