Fix Space SSE stream proxy startup

brain_app.py

@@ -254,13 +254,25 @@ async def api_stream(model: str, request: Request):
     url = MODELS[_m(model)]["stream"]
     body = await request.body()
 
-    async def gen():
-        async with httpx.AsyncClient(timeout=300) as client:
-            async with client.stream("POST", url, content=body,
-                                     headers={"Content-Type": "application/json"}) as r:
-                async for chunk in r.aiter_raw():
-                    if chunk:
-                        yield chunk
+    def gen():
+        # Send one SSE comment immediately so HF/Gradio/browser proxies open the
+        # response before the upstream Modal stream produces its first token.
+        yield b": connected\n\n"
+        timeout = httpx.Timeout(600.0, connect=30.0, read=None, write=30.0, pool=30.0)
+        headers = {"Content-Type": "application/json", "Accept": "text/event-stream"}
+        try:
+            with httpx.Client(timeout=timeout, follow_redirects=True) as client:
+                with client.stream("POST", url, content=body, headers=headers) as r:
+                    if r.status_code >= 400:
+                        msg = json.dumps({"type": "error", "message": f"Upstream stream failed: {r.status_code}"})
+                        yield f"data: {msg}\n\n".encode()
+                        return
+                    for chunk in r.iter_raw():
+                        if chunk:
+                            yield chunk
+        except Exception as e:
+            msg = json.dumps({"type": "error", "message": str(e)})
+            yield f"data: {msg}\n\n".encode()
 
     return StreamingResponse(gen(), media_type="text/event-stream",
                              headers={"Cache-Control": "no-cache",