feat: 所有 Provider 失败时透传上游错误信息

- FallbackOrchestrator 在所有候选组合失败后保留最后的错误信息
- 从 httpx.HTTPStatusError 提取上游状态码和响应内容
- ProviderNotAvailableException 携带上游错误信息
- ErrorResponse 在返回错误时透传上游状态码和响应

src/core/exceptions.py

@@ -547,11 +547,19 @@ class ErrorResponse:
         - 所有错误都记录到日志，通过错误 ID 关联
         """
         if isinstance(e, ProxyException):
+            details = e.details.copy() if e.details else {}
+            status_code = e.status_code
+            message = e.message
+            # 如果是 ProviderNotAvailableException 且有上游错误，直接透传上游信息
+            if isinstance(e, ProviderNotAvailableException) and e.upstream_response:
+                if e.upstream_status:
+                    status_code = e.upstream_status
+                message = e.upstream_response
             return ErrorResponse.create(
                 error_type=e.error_type,
-                message=e.message,
+                message=message,
-                status_code=e.status_code,
+                status_code=status_code,
-                details=e.details,
+                details=details if details else None,
             )
         elif isinstance(e, HTTPException):
             return ErrorResponse.create(

src/services/orchestration/fallback_orchestrator.py

@@ -543,7 +543,9 @@ class FallbackOrchestrator:
                 raise last_error
 
         # 所有组合都已尝试完毕，全部失败
-        self._raise_all_failed_exception(request_id, max_attempts, last_candidate, model_name, api_format_enum)
+        self._raise_all_failed_exception(
+            request_id, max_attempts, last_candidate, model_name, api_format_enum, last_error
+        )
 
     async def _try_candidate_with_retries(
         self,
@@ -565,6 +567,7 @@ class FallbackOrchestrator:
         provider = candidate.provider
         endpoint = candidate.endpoint
         max_retries_for_candidate = int(endpoint.max_retries) if candidate.is_cached else 1
+        last_error: Optional[Exception] = None
 
         for retry_index in range(max_retries_for_candidate):
             attempt_counter += 1
@@ -599,6 +602,7 @@ class FallbackOrchestrator:
                 return {"success": True, "response": response}
 
             except ExecutionError as exec_err:
+                last_error = exec_err.cause
                 action = await self._handle_candidate_error(
                     exec_err=exec_err,
                     candidate=candidate,
@@ -630,6 +634,7 @@ class FallbackOrchestrator:
             "success": False,
             "attempt_counter": attempt_counter,
             "max_attempts": max_attempts,
+            "error": last_error,
         }
 
     def _attach_metadata_to_error(
@@ -678,6 +683,7 @@ class FallbackOrchestrator:
         last_candidate: Optional[ProviderCandidate],
         model_name: str,
         api_format_enum: APIFormat,
+        last_error: Optional[Exception] = None,
     ) -> NoReturn:
         """所有组合都失败时抛出异常"""
         logger.error(f"  [{request_id}] 所有 {max_attempts} 个组合均失败")
@@ -693,9 +699,28 @@ class FallbackOrchestrator:
                 "api_format": api_format_enum.value,
             }
 
+        # 提取上游错误响应
+        upstream_status: Optional[int] = None
+        upstream_response: Optional[str] = None
+        if last_error:
+            # 从 httpx.HTTPStatusError 提取
+            if isinstance(last_error, httpx.HTTPStatusError):
+                upstream_status = last_error.response.status_code
+                try:
+                    upstream_response = last_error.response.text
+                except Exception:
+                    pass
+            # 从异常属性提取
+            elif hasattr(last_error, "upstream_status"):
+                upstream_status = getattr(last_error, "upstream_status", None)
+            if hasattr(last_error, "upstream_response"):
+                upstream_response = getattr(last_error, "upstream_response", None)
+
         raise ProviderNotAvailableException(
             f"所有Provider均不可用，已尝试{max_attempts}个组合",
             request_metadata=request_metadata,
+            upstream_status=upstream_status,
+            upstream_response=upstream_response,
         )
 
     async def execute_with_fallback(