fix(provider): 修正媒体请求转换与上游错误透传

按上游协议能力延迟处理媒体资源：OpenAI 兼容平台默认使用 multipart，显式配置后才发送 JSON URL；Gemini 官方协议使用 Files API，兼容协议使用内嵌 Base64，并同步覆盖相关媒体客户端。\n\n安全的上游 400/422 原始错误会作为下游 message 返回，同时保留结构化诊断信息和历史任务兼容。\n\n验证：API 全量无缓存测试、go vet、pnpm lint、pnpm test、pnpm build、pnpm openapi、git diff --check。

apps/api/internal/httpapi/public_errors.go

@@ -11,9 +11,7 @@ import (
 func publicGatewayTask(task store.GatewayTask) store.GatewayTask {
 	if task.Status == "failed" || task.Status == "cancelled" || task.ErrorCode != "" || task.ErrorMessage != "" {
 		value := publicerror.FromFields(task.ErrorCode, firstNonEmpty(task.ErrorMessage, task.Error), taskErrorHTTPStatus(task), false)
-		if task.PublicError != nil && task.PublicError.Code != "" && task.PublicError.Source != "" {
-			value = *task.PublicError
-		}
+		value = mergeStoredPublicError(task.PublicError, value)
 		value = publicerror.WithIDs(value, task.RequestID, task.ID)
 		publicerror.Observe(value)
 		task.PublicError = &value
@@ -32,9 +30,7 @@ func publicGatewayTask(task store.GatewayTask) store.GatewayTask {
 			status = http.StatusBadGateway
 		}
 		value := publicerror.FromFields(attempt.ErrorCode, attempt.ErrorMessage, status, attempt.Retryable)
-		if attempt.PublicError != nil && attempt.PublicError.Code != "" && attempt.PublicError.Source != "" {
-			value = *attempt.PublicError
-		}
+		value = mergeStoredPublicError(attempt.PublicError, value)
 		value = publicerror.WithIDs(value, attempt.RequestID, task.ID)
 		attempt.PublicError = &value
 		attempt.ErrorCode = value.Code
@@ -44,14 +40,33 @@ func publicGatewayTask(task store.GatewayTask) store.GatewayTask {
 }
 
 func publicTaskError(task store.GatewayTask) publicerror.Error {
-	if task.PublicError != nil && task.PublicError.Code != "" && task.PublicError.Source != "" {
-		return publicerror.WithIDs(*task.PublicError, task.RequestID, task.ID)
-	}
 	status := taskErrorHTTPStatus(task)
 	if status <= 0 {
 		status = http.StatusBadGateway
 	}
-	return publicerror.WithIDs(publicerror.FromFields(task.ErrorCode, firstNonEmpty(task.ErrorMessage, task.Error, task.Message), status, false), task.RequestID, task.ID)
+	value := publicerror.FromFields(task.ErrorCode, firstNonEmpty(task.ErrorMessage, task.Error, task.Message), status, false)
+	value = mergeStoredPublicError(task.PublicError, value)
+	return publicerror.WithIDs(value, task.RequestID, task.ID)
+}
+
+func mergeStoredPublicError(stored *publicerror.Error, derived publicerror.Error) publicerror.Error {
+	if stored == nil || stored.Code == "" || stored.Source == "" {
+		return derived
+	}
+	value := *stored
+	if len(value.Details) == 0 && len(derived.Details) > 0 {
+		value.Details = derived.Details
+	}
+	if message := safeDerivedUpstreamMessage(derived); message != "" {
+		value.Message = message
+	}
+	return value
+}
+
+func safeDerivedUpstreamMessage(value publicerror.Error) string {
+	upstream, _ := value.Details["upstreamError"].(map[string]any)
+	message, _ := upstream["message"].(string)
+	return strings.TrimSpace(message)
 }
 
 func taskErrorHTTPStatus(task store.GatewayTask) int {
@@ -109,6 +124,9 @@ func publicErrorMap(value publicerror.Error) map[string]any {
 	if taskID := strings.TrimSpace(value.TaskID); taskID != "" {
 		out["taskId"] = taskID
 	}
+	if len(value.Details) > 0 {
+		out["details"] = value.Details
+	}
 	return out
 }
 
@@ -146,6 +164,11 @@ func safePublicErrorDetails(details map[string]any, value publicerror.Error, inc
 			}
 		}
 	}
+	for key, item := range value.Details {
+		if item != nil {
+			out[key] = item
+		}
+	}
 	if includePublicError {
 		out["publicError"] = value
 	}