Add final SSE error events for streaming endpoints when retries are exhausted

* Initial plan

* Add final SSE error events for all streaming services

Co-authored-by: bbbugg <80089841+bbbugg@users.noreply.github.com>

* revert openai

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: bbbugg <80089841+bbbugg@users.noreply.github.com>
Co-authored-by: bbbugg <daming20120101@163.com>

Enhance error handling by extracting nested JSON from error messages in SSE events

Enhance error handling for content generation and streaming endpoints

Enhance error handling for content generation and streaming endpoints

Enhance error handling for content generation and streaming endpoints

Enhance error handling for content generation and streaming endpoints

还原vertex和openai的更改，只保留gemini

app/router/gemini_routes.py

@@ -1,6 +1,7 @@
 from fastapi import APIRouter, Depends, HTTPException
 from fastapi.responses import StreamingResponse, JSONResponse
 from copy import deepcopy
+import json
 import asyncio
 from app.config.config import settings
 from app.log.logger import get_gemini_logger
@@ -159,7 +160,6 @@ async def generate_content(
         )
         return response
 
-
 @router.post("/models/{model_name}:streamGenerateContent")
 @router_v1beta.post("/models/{model_name}:streamGenerateContent")
 @RetryHandler(key_arg="api_key")
@@ -181,12 +181,42 @@ async def stream_generate_content(
         if not await model_service.check_model_support(model_name):
             raise HTTPException(status_code=400, detail=f"Model {model_name} is not supported")
 
-        response_stream = chat_service.stream_generate_content(
+        raw_stream = chat_service.stream_generate_content(
             model=model_name,
             request=request,
             api_key=api_key
         )
-        return StreamingResponse(response_stream, media_type="text/event-stream")
+        try:
+            # 尝试获取第一条数据，判断是正常 SSE（data: 前缀）还是错误 JSON
+            first_chunk = await raw_stream.__anext__()
+        except StopAsyncIteration:
+            # 如果流直接结束，退回标准 SSE 输出
+            return StreamingResponse(raw_stream, media_type="text/event-stream")
+        except Exception as e:
+            # 初始化流异常，直接返回 500 错误
+            return JSONResponse(
+                content={"error": {"code": 500, "message": str(e)}},
+                status_code=500
+            )
+
+        # 如果以 "data:" 开头，代表正常 SSE，将首块和后续块一起发送
+        if isinstance(first_chunk, str) and first_chunk.startswith("data:"):
+            async def combined():
+                yield first_chunk
+                async for chunk in raw_stream:
+                    yield chunk
+
+            return StreamingResponse(combined(), media_type="text/event-stream")
+
+        # 否则把首块当作错误 JSON 处理
+        try:
+            err = json.loads(first_chunk)
+            code = err.get("error", {}).get("code", 500)
+        except json.JSONDecodeError:
+            err = {"error": {"code": 500, "message": first_chunk}}
+            code = 500
+
+        return JSONResponse(content=err, status_code=code)
 
 
 @router.post("/models/{model_name}:countTokens")