fix(google): buffer non-streaming JSON, convert to fake SSE chunks

Google streaming through HF Spaces HTTP/2 edge causes
ERR_HTTP2_PROTOCOL_ERROR regardless of content. Workaround:
force stream=false upstream, buffer full JSON response, convert
to OpenAI SSE format (role + content + final + [DONE]),
return as plain Response with text/event-stream Content-Type.
No StreamingResponse involved = no HTTP/2 streaming edge case.

proxy/client.py

@@ -5,7 +5,7 @@ from typing import Any, AsyncIterator
 
 import httpx
 from fastapi import HTTPException
-from fastapi.responses import StreamingResponse
+from fastapi.responses import Response, StreamingResponse
 from starlette.requests import Request
 
 from config import POLL_INTERVAL, POLL_MAX_ATTEMPTS
@@ -111,6 +111,47 @@ def _strip_extra_content_json(content: bytes) -> bytes:
         return content
 
 
+def _json_to_sse(content: bytes) -> bytes:
+    """Convert a non-streaming OpenAI JSON response into SSE chunks."""
+    try:
+        obj = json.loads(content)
+        base = {
+            "id": obj.get("id", "chatcmpl-proxy"),
+            "object": "chat.completion.chunk",
+            "created": obj.get("created", 0),
+            "model": obj.get("model", ""),
+        }
+        events = []
+        for choice in obj.get("choices", []):
+            idx = choice.get("index", 0)
+            message = choice.get("message", {})
+            content_text = message.get("content", "")
+            finish_reason = choice.get("finish_reason", None)
+
+            role_chunk = dict(base)
+            role_chunk["choices"] = [{"index": idx, "delta": {"role": message.get("role", "assistant")}}]
+            if finish_reason:
+                role_chunk["choices"][0]["finish_reason"] = finish_reason
+            events.append(f"data: {json.dumps(role_chunk, ensure_ascii=False)}\n\n")
+
+            if content_text:
+                content_chunk = dict(base)
+                content_chunk["choices"] = [{"index": idx, "delta": {"content": content_text}}]
+                if finish_reason:
+                    content_chunk["choices"][0]["finish_reason"] = finish_reason
+                events.append(f"data: {json.dumps(content_chunk, ensure_ascii=False)}\n\n")
+
+            if finish_reason:
+                final_chunk = dict(base)
+                final_chunk["choices"] = [{"index": idx, "delta": {}, "finish_reason": finish_reason}]
+                events.append(f"data: {json.dumps(final_chunk, ensure_ascii=False)}\n\n")
+
+        events.append("data: [DONE]\n\n")
+        return "".join(events).encode("utf-8")
+    except (json.JSONDecodeError, KeyError, TypeError, UnicodeDecodeError):
+        return content
+
+
 async def _stream_response(provider: Provider, real_key: str, body: dict[str, Any]) -> AsyncIterator[bytes]:
     """Async generator that manages its own httpx client for streaming."""
     target_url = f"{provider.base_url}/v1/chat/completions"
@@ -140,12 +181,12 @@ async def forward_request(provider: Provider, real_key: str, request: Request, b
     body = _sanitize_body(provider, body)
     target_url = f"{provider.base_url}/v1/chat/completions"
     headers = _build_headers(provider, real_key, dict(request.headers))
+    original_stream = bool(body.get("stream"))
 
-    if bool(body.get("stream")):
-        if provider.name == "google":
-            body["stream"] = False
-        else:
-            return StreamingResponse(_stream_response(provider, real_key, body), media_type="text/event-stream")
+    if original_stream and provider.name == "google":
+        body["stream"] = False
+    elif original_stream:
+        return StreamingResponse(_stream_response(provider, real_key, body), media_type="text/event-stream")
 
     async with httpx.AsyncClient(timeout=_TIMEOUT, follow_redirects=True) as client:
         try:
@@ -172,6 +213,11 @@ async def forward_request(provider: Provider, real_key: str, request: Request, b
         content = upstream.content
         if provider.name == "google":
             content = _strip_extra_content_json(content)
+            if original_stream:
+                content = _json_to_sse(content)
+
+        if original_stream and provider.name == "google":
+            return Response(content=content, media_type="text/event-stream")
 
         return {
             "status_code": upstream.status_code,