fix(gateway): /v1/responses 转 Anthropic 时统一以去空白的请求模型兜底映射

forwardResponsesViaNativeAnthropic 的 defaultMappedModel 是账号 model_mapping
未命中时的兜底模型。此前按模型分流的账号（OpenCode）传空串、其余账号传
reqModel，源自两处分支各自实现。映射未命中且请求模型带首尾空白时，前者的
计费模型名保留空白（上游模型名因 normalizeOpenAIModelForUpstream 已去空白，
两者不一致，定价查找可能落空），后者为去空白的名字。

统一传 reqModel，并移除入口里最后一处 routesByModel 分支。仅影响按模型
分流账号收到带首尾空白模型名的请求：计费模型名改为去空白后的名字；发往
上游的请求不变。新增测试覆盖 OpenCode 与 Kimi 两类账号。

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/internal/service/openai_gateway_forward.go

@@ -187,12 +187,8 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 	case APIProtocolAnthropic:
 		// Responses 客户端 × Anthropic 上游：转成 Anthropic 请求走原生端点。不能落到
 		// raw-CC 分支——其 URL 构造会把 anthropic base 当 CC base 用。
-		// 按模型分流的账号不以请求模型兜底模型映射。
-		defaultMappedModel := reqModel
-		if account.routesByModel() {
-			defaultMappedModel = ""
-		}
-		return s.forwardResponsesViaNativeAnthropic(ctx, c, account, body, defaultMappedModel)
+		// 账号映射未命中时以去除首尾空白的请求模型兜底，计费名与上游模型名一致。
+		return s.forwardResponsesViaNativeAnthropic(ctx, c, account, body, reqModel)
 	case APIProtocolChatCompletions:
 		return s.forwardResponsesViaRawChatCompletions(ctx, c, account, body)
 	}

backend/internal/service/upstream_protocol_routing_test.go

@@ -3,10 +3,14 @@
 package service
 
 import (
+	"context"
+	"strings"
 	"testing"
 
 	"github.com/Wei-Shaw/sub2api/internal/pkg/openai_compat"
+	"github.com/gin-gonic/gin"
 	"github.com/stretchr/testify/require"
+	"github.com/tidwall/gjson"
 )
 
 func routingTestAccount(platform, accountType string, credentials, extra map[string]any) *Account {
@@ -117,3 +121,44 @@ func TestUpstreamRoutingModelOnlyForModelRoutedAccounts(t *testing.T) {
 	require.Equal(t, "glm-5.3", upstreamRoutingModel(openCode, body, ""))
 	require.Empty(t, upstreamRoutingModel(routingTestAccount(PlatformKimi, AccountTypeAPIKey, nil, nil), body, ""))
 }
+
+// /v1/responses 转 Anthropic 上游时，计费模型名与上游模型名都应是去除首尾空白的
+// 请求模型；按模型分流（OpenCode）与显式 anthropic 协议（Kimi）账号行为一致。
+func TestResponsesToNativeAnthropicTrimsBillingModel(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	openCode := &Account{
+		ID:          703,
+		Name:        "opencode-go",
+		Platform:    PlatformOpenCodeGo,
+		Type:        AccountTypeAPIKey,
+		Concurrency: 1,
+		Credentials: map[string]any{
+			"api_key":      "sk-test",
+			"account_mode": AccountModeGo,
+			"api_base_urls": map[string]any{
+				APIProtocolAnthropic: "http://anthropic.example",
+			},
+		},
+	}
+	for _, tc := range []struct {
+		name    string
+		account *Account
+		model   string
+	}{
+		{"opencode by model", openCode, "minimax-m3"},
+		{"kimi pinned anthropic", nativeAnthropicTestAccount(), "kimi-k2"},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			body := []byte(`{"model":" ` + tc.model + ` ","input":"hello","stream":false}`)
+			upstream := &httpUpstreamRecorder{resp: nativeAnthropicStreamResponse()}
+			svc := &OpenAIGatewayService{cfg: rawChatCompletionsTestConfig(), httpUpstream: upstream}
+
+			result, err := svc.Forward(context.Background(), adaptiveProtocolTestContext("/v1/responses", body), tc.account, body)
+			require.NoError(t, err)
+			require.True(t, strings.HasSuffix(upstream.lastReq.URL.Path, "/v1/messages"), upstream.lastReq.URL.String())
+			require.Equal(t, tc.model, gjson.GetBytes(upstream.lastBody, "model").String())
+			require.Equal(t, tc.model, result.BillingModel)
+		})
+	}
+}