Handle transport errors

server.py

@@ -277,6 +277,8 @@ def preview_url(
                     e.response.status_code,
                     f"Failed to fetch {e.response.url} - HTTP {e.response.status_code}: {e.response.text}"
                 )
+            except httpx.NetworkError as e:
+                raise HTTPException(502, f"Failed to fetch {url} - {e}")
 
             if "text/html" not in response.headers.get("content-type", ""):
                 return {}