fix httpx streaming: use client.stream() for async SSE

proxy/client.py

@@ -64,7 +64,20 @@ async def forward_request(provider: Provider, real_key: str, request: Request, b
 
     async with httpx.AsyncClient(timeout=_TIMEOUT, follow_redirects=True) as client:
         try:
-            upstream = await client.post(target_url, headers=headers, json=body, stream=stream)
+            if stream:
+                async with client.stream("POST", target_url, headers=headers, json=body) as upstream:
+                    if upstream.status_code >= 400:
+                        content = await upstream.aread()
+                        logger.warning("Upstream error from %s: %d %s", provider.name, upstream.status_code, content[:500])
+                        raise HTTPException(status_code=upstream.status_code, detail=content.decode("utf-8", errors="replace"))
+                    return StreamingResponse(
+                        _stream_chunks(upstream),
+                        status_code=upstream.status_code,
+                        media_type=upstream.headers.get("content-type", "text/event-stream"),
+                        headers={k: v for k, v in upstream.headers.items() if k.lower() in ("cache-control", "x-request-id")},
+                    )
+            else:
+                upstream = await client.post(target_url, headers=headers, json=body)
         except httpx.TimeoutException as exc:
             logger.warning("Upstream timeout for %s: %s", provider.name, exc)
             raise HTTPException(status_code=504, detail="Upstream provider timed out")
@@ -83,14 +96,6 @@ async def forward_request(provider: Provider, real_key: str, request: Request, b
             logger.warning("Upstream error from %s: %d %s", provider.name, upstream.status_code, content[:500])
             raise HTTPException(status_code=upstream.status_code, detail=content.decode("utf-8", errors="replace"))
 
-        if stream:
-            return StreamingResponse(
-                _stream_chunks(upstream),
-                status_code=upstream.status_code,
-                media_type=upstream.headers.get("content-type", "text/event-stream"),
-                headers={k: v for k, v in upstream.headers.items() if k.lower() in ("cache-control", "x-request-id")},
-            )
-
         return {
             "status_code": upstream.status_code,
             "headers": dict(upstream.headers),