diff --git a/backend/internal/handler/gateway_handler_single_account_retry_test.go b/backend/internal/handler/gateway_handler_single_account_retry_test.go
new file mode 100644
index 00000000..96aa14c6
--- /dev/null
+++ b/backend/internal/handler/gateway_handler_single_account_retry_test.go
@@ -0,0 +1,51 @@
+package handler
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+// ---------------------------------------------------------------------------
+// sleepAntigravitySingleAccountBackoff 测试
+// ---------------------------------------------------------------------------
+
+func TestSleepAntigravitySingleAccountBackoff_ReturnsTrue(t *testing.T) {
+	ctx := context.Background()
+	start := time.Now()
+	ok := sleepAntigravitySingleAccountBackoff(ctx, 1)
+	elapsed := time.Since(start)
+
+	require.True(t, ok, "should return true when context is not canceled")
+	// 固定延迟 2s
+	require.GreaterOrEqual(t, elapsed, 1500*time.Millisecond, "should wait approximately 2s")
+	require.Less(t, elapsed, 5*time.Second, "should not wait too long")
+}
+
+func TestSleepAntigravitySingleAccountBackoff_ContextCanceled(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel() // 立即取消
+
+	start := time.Now()
+	ok := sleepAntigravitySingleAccountBackoff(ctx, 1)
+	elapsed := time.Since(start)
+
+	require.False(t, ok, "should return false when context is canceled")
+	require.Less(t, elapsed, 500*time.Millisecond, "should return immediately on cancel")
+}
+
+func TestSleepAntigravitySingleAccountBackoff_FixedDelay(t *testing.T) {
+	// 验证不同 retryCount 都使用固定 2s 延迟
+	ctx := context.Background()
+
+	start := time.Now()
+	ok := sleepAntigravitySingleAccountBackoff(ctx, 5)
+	elapsed := time.Since(start)
+
+	require.True(t, ok)
+	// 即使 retryCount=5，延迟仍然是固定的 2s
+	require.GreaterOrEqual(t, elapsed, 1500*time.Millisecond)
+	require.Less(t, elapsed, 5*time.Second)
+}
diff --git a/backend/internal/service/antigravity_single_account_retry_test.go b/backend/internal/service/antigravity_single_account_retry_test.go
new file mode 100644
index 00000000..0950b728
--- /dev/null
+++ b/backend/internal/service/antigravity_single_account_retry_test.go
@@ -0,0 +1,904 @@
+//go:build unit
+
+package service
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"net/http"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/Wei-Shaw/sub2api/internal/pkg/ctxkey"
+	"github.com/stretchr/testify/require"
+)
+
+// ---------------------------------------------------------------------------
+// 辅助函数：构造带 SingleAccountRetry 标记的 context
+// ---------------------------------------------------------------------------
+
+func ctxWithSingleAccountRetry() context.Context {
+	return context.WithValue(context.Background(), ctxkey.SingleAccountRetry, true)
+}
+
+// ---------------------------------------------------------------------------
+// 1. isSingleAccountRetry 测试
+// ---------------------------------------------------------------------------
+
+func TestIsSingleAccountRetry_True(t *testing.T) {
+	ctx := context.WithValue(context.Background(), ctxkey.SingleAccountRetry, true)
+	require.True(t, isSingleAccountRetry(ctx))
+}
+
+func TestIsSingleAccountRetry_False_NoValue(t *testing.T) {
+	require.False(t, isSingleAccountRetry(context.Background()))
+}
+
+func TestIsSingleAccountRetry_False_ExplicitFalse(t *testing.T) {
+	ctx := context.WithValue(context.Background(), ctxkey.SingleAccountRetry, false)
+	require.False(t, isSingleAccountRetry(ctx))
+}
+
+func TestIsSingleAccountRetry_False_WrongType(t *testing.T) {
+	ctx := context.WithValue(context.Background(), ctxkey.SingleAccountRetry, "true")
+	require.False(t, isSingleAccountRetry(ctx))
+}
+
+// ---------------------------------------------------------------------------
+// 2. 常量验证
+// ---------------------------------------------------------------------------
+
+func TestSingleAccountRetryConstants(t *testing.T) {
+	require.Equal(t, 3, antigravitySingleAccountSmartRetryMaxAttempts,
+		"单账号原地重试最多 3 次")
+	require.Equal(t, 15*time.Second, antigravitySingleAccountSmartRetryMaxWait,
+		"单次最大等待 15s")
+	require.Equal(t, 30*time.Second, antigravitySingleAccountSmartRetryTotalMaxWait,
+		"总累计等待不超过 30s")
+	require.Equal(t, 30*time.Second, antigravitySingleAccountMaxWait,
+		"预检查最大等待 30s")
+}
+
+// ---------------------------------------------------------------------------
+// 3. handleSmartRetry + 503 + SingleAccountRetry → 走 handleSingleAccountRetryInPlace
+//    （而非设模型限流 + 切换账号）
+// ---------------------------------------------------------------------------
+
+// TestHandleSmartRetry_503_LongDelay_SingleAccountRetry_RetryInPlace
+// 核心场景：503 + retryDelay >= 7s + SingleAccountRetry 标记
+// → 不设模型限流、不切换账号，改为原地重试
+func TestHandleSmartRetry_503_LongDelay_SingleAccountRetry_RetryInPlace(t *testing.T) {
+	// 原地重试成功
+	successResp := &http.Response{
+		StatusCode: http.StatusOK,
+		Header:     http.Header{},
+		Body:       io.NopCloser(strings.NewReader(`{"result":"ok"}`)),
+	}
+	upstream := &mockSmartRetryUpstream{
+		responses: []*http.Response{successResp},
+		errors:    []error{nil},
+	}
+
+	repo := &stubAntigravityAccountRepo{}
+	account := &Account{
+		ID:          1,
+		Name:        "acc-single",
+		Type:        AccountTypeOAuth,
+		Platform:    PlatformAntigravity,
+		Concurrency: 1,
+	}
+
+	// 503 + 39s >= 7s 阈值 + MODEL_CAPACITY_EXHAUSTED
+	respBody := []byte(`{
+		"error": {
+			"code": 503,
+			"status": "UNAVAILABLE",
+			"details": [
+				{"@type": "type.googleapis.com/google.rpc.ErrorInfo", "metadata": {"model": "gemini-3-pro-high"}, "reason": "MODEL_CAPACITY_EXHAUSTED"},
+				{"@type": "type.googleapis.com/google.rpc.RetryInfo", "retryDelay": "39s"}
+			],
+			"message": "No capacity available for model gemini-3-pro-high on the server"
+		}
+	}`)
+	resp := &http.Response{
+		StatusCode: http.StatusServiceUnavailable,
+		Header:     http.Header{},
+		Body:       io.NopCloser(bytes.NewReader(respBody)),
+	}
+
+	params := antigravityRetryLoopParams{
+		ctx:          ctxWithSingleAccountRetry(), // 关键：设置单账号标记
+		prefix:       "[test]",
+		account:      account,
+		accessToken:  "token",
+		action:       "generateContent",
+		body:         []byte(`{"input":"test"}`),
+		httpUpstream: upstream,
+		accountRepo:  repo,
+		handleError: func(ctx context.Context, prefix string, account *Account, statusCode int, headers http.Header, body []byte, requestedModel string, groupID int64, sessionHash string, isStickySession bool) *handleModelRateLimitResult {
+			return nil
+		},
+	}
+
+	availableURLs := []string{"https://ag-1.test"}
+
+	svc := &AntigravityGatewayService{}
+	result := svc.handleSmartRetry(params, resp, respBody, "https://ag-1.test", 0, availableURLs)
+
+	require.NotNil(t, result)
+	require.Equal(t, smartRetryActionBreakWithResp, result.action)
+	// 关键断言：返回 resp（原地重试成功），而非 switchError（切换账号）
+	require.NotNil(t, result.resp, "should return successful response from in-place retry")
+	require.Equal(t, http.StatusOK, result.resp.StatusCode)
+	require.Nil(t, result.switchError, "should NOT return switchError in single account mode")
+	require.Nil(t, result.err)
+
+	// 验证未设模型限流（单账号模式不应设限流）
+	require.Len(t, repo.modelRateLimitCalls, 0,
+		"should NOT set model rate limit in single account retry mode")
+
+	// 验证确实调用了 upstream（原地重试）
+	require.GreaterOrEqual(t, len(upstream.calls), 1, "should have made at least one retry call")
+}
+
+// TestHandleSmartRetry_503_LongDelay_NoSingleAccountRetry_StillSwitches
+// 对照组：503 + retryDelay >= 7s + 无 SingleAccountRetry 标记
+// → 照常设模型限流 + 切换账号
+func TestHandleSmartRetry_503_LongDelay_NoSingleAccountRetry_StillSwitches(t *testing.T) {
+	repo := &stubAntigravityAccountRepo{}
+	account := &Account{
+		ID:       2,
+		Name:     "acc-multi",
+		Type:     AccountTypeOAuth,
+		Platform: PlatformAntigravity,
+	}
+
+	// 503 + 39s >= 7s 阈值
+	respBody := []byte(`{
+		"error": {
+			"code": 503,
+			"status": "UNAVAILABLE",
+			"details": [
+				{"@type": "type.googleapis.com/google.rpc.ErrorInfo", "metadata": {"model": "gemini-3-pro-high"}, "reason": "MODEL_CAPACITY_EXHAUSTED"},
+				{"@type": "type.googleapis.com/google.rpc.RetryInfo", "retryDelay": "39s"}
+			]
+		}
+	}`)
+	resp := &http.Response{
+		StatusCode: http.StatusServiceUnavailable,
+		Header:     http.Header{},
+		Body:       io.NopCloser(bytes.NewReader(respBody)),
+	}
+
+	params := antigravityRetryLoopParams{
+		ctx:         context.Background(), // 关键：无单账号标记
+		prefix:      "[test]",
+		account:     account,
+		accessToken: "token",
+		action:      "generateContent",
+		body:        []byte(`{"input":"test"}`),
+		accountRepo: repo,
+		handleError: func(ctx context.Context, prefix string, account *Account, statusCode int, headers http.Header, body []byte, requestedModel string, groupID int64, sessionHash string, isStickySession bool) *handleModelRateLimitResult {
+			return nil
+		},
+	}
+
+	availableURLs := []string{"https://ag-1.test"}
+
+	svc := &AntigravityGatewayService{}
+	result := svc.handleSmartRetry(params, resp, respBody, "https://ag-1.test", 0, availableURLs)
+
+	require.NotNil(t, result)
+	require.Equal(t, smartRetryActionBreakWithResp, result.action)
+	// 对照：多账号模式返回 switchError
+	require.NotNil(t, result.switchError, "multi-account mode should return switchError for 503")
+	require.Nil(t, result.resp, "should not return resp when switchError is set")
+
+	// 对照：多账号模式应设模型限流
+	require.Len(t, repo.modelRateLimitCalls, 1,
+		"multi-account mode SHOULD set model rate limit")
+}
+
+// TestHandleSmartRetry_429_LongDelay_SingleAccountRetry_StillSwitches
+// 边界情况：429（非 503）+ SingleAccountRetry 标记
+// → 单账号原地重试仅针对 503，429 依然走切换账号逻辑
+func TestHandleSmartRetry_429_LongDelay_SingleAccountRetry_StillSwitches(t *testing.T) {
+	repo := &stubAntigravityAccountRepo{}
+	account := &Account{
+		ID:       3,
+		Name:     "acc-429",
+		Type:     AccountTypeOAuth,
+		Platform: PlatformAntigravity,
+	}
+
+	// 429 + 15s >= 7s 阈值
+	respBody := []byte(`{
+		"error": {
+			"status": "RESOURCE_EXHAUSTED",
+			"details": [
+				{"@type": "type.googleapis.com/google.rpc.ErrorInfo", "metadata": {"model": "claude-sonnet-4-5"}, "reason": "RATE_LIMIT_EXCEEDED"},
+				{"@type": "type.googleapis.com/google.rpc.RetryInfo", "retryDelay": "15s"}
+			]
+		}
+	}`)
+	resp := &http.Response{
+		StatusCode: http.StatusTooManyRequests, // 429，不是 503
+		Header:     http.Header{},
+		Body:       io.NopCloser(bytes.NewReader(respBody)),
+	}
+
+	params := antigravityRetryLoopParams{
+		ctx:         ctxWithSingleAccountRetry(), // 有单账号标记
+		prefix:      "[test]",
+		account:     account,
+		accessToken: "token",
+		action:      "generateContent",
+		body:        []byte(`{"input":"test"}`),
+		accountRepo: repo,
+		handleError: func(ctx context.Context, prefix string, account *Account, statusCode int, headers http.Header, body []byte, requestedModel string, groupID int64, sessionHash string, isStickySession bool) *handleModelRateLimitResult {
+			return nil
+		},
+	}
+
+	availableURLs := []string{"https://ag-1.test"}
+
+	svc := &AntigravityGatewayService{}
+	result := svc.handleSmartRetry(params, resp, respBody, "https://ag-1.test", 0, availableURLs)
+
+	require.NotNil(t, result)
+	require.Equal(t, smartRetryActionBreakWithResp, result.action)
+	// 429 即使有单账号标记，也应走切换账号
+	require.NotNil(t, result.switchError, "429 should still return switchError even with SingleAccountRetry")
+	require.Len(t, repo.modelRateLimitCalls, 1,
+		"429 should still set model rate limit even with SingleAccountRetry")
+}
+
+// ---------------------------------------------------------------------------
+// 4. handleSmartRetry + 503 + 短延迟 + SingleAccountRetry → 智能重试耗尽后不设限流
+// ---------------------------------------------------------------------------
+
+// TestHandleSmartRetry_503_ShortDelay_SingleAccountRetry_NoRateLimit
+// 503 + retryDelay < 7s + SingleAccountRetry → 智能重试耗尽后直接返回 503，不设限流
+func TestHandleSmartRetry_503_ShortDelay_SingleAccountRetry_NoRateLimit(t *testing.T) {
+	// 智能重试也返回 503
+	failRespBody := `{
+		"error": {
+			"code": 503,
+			"status": "UNAVAILABLE",
+			"details": [
+				{"@type": "type.googleapis.com/google.rpc.ErrorInfo", "metadata": {"model": "gemini-3-flash"}, "reason": "MODEL_CAPACITY_EXHAUSTED"},
+				{"@type": "type.googleapis.com/google.rpc.RetryInfo", "retryDelay": "0.1s"}
+			]
+		}
+	}`
+	failResp := &http.Response{
+		StatusCode: http.StatusServiceUnavailable,
+		Header:     http.Header{},
+		Body:       io.NopCloser(strings.NewReader(failRespBody)),
+	}
+	upstream := &mockSmartRetryUpstream{
+		responses: []*http.Response{failResp},
+		errors:    []error{nil},
+	}
+
+	repo := &stubAntigravityAccountRepo{}
+	account := &Account{
+		ID:       4,
+		Name:     "acc-short-503",
+		Type:     AccountTypeOAuth,
+		Platform: PlatformAntigravity,
+	}
+
+	// 0.1s < 7s 阈值
+	respBody := []byte(`{
+		"error": {
+			"code": 503,
+			"status": "UNAVAILABLE",
+			"details": [
+				{"@type": "type.googleapis.com/google.rpc.ErrorInfo", "metadata": {"model": "gemini-3-flash"}, "reason": "MODEL_CAPACITY_EXHAUSTED"},
+				{"@type": "type.googleapis.com/google.rpc.RetryInfo", "retryDelay": "0.1s"}
+			]
+		}
+	}`)
+	resp := &http.Response{
+		StatusCode: http.StatusServiceUnavailable,
+		Header:     http.Header{},
+		Body:       io.NopCloser(bytes.NewReader(respBody)),
+	}
+
+	params := antigravityRetryLoopParams{
+		ctx:          ctxWithSingleAccountRetry(),
+		prefix:       "[test]",
+		account:      account,
+		accessToken:  "token",
+		action:       "generateContent",
+		body:         []byte(`{"input":"test"}`),
+		httpUpstream: upstream,
+		accountRepo:  repo,
+		handleError: func(ctx context.Context, prefix string, account *Account, statusCode int, headers http.Header, body []byte, requestedModel string, groupID int64, sessionHash string, isStickySession bool) *handleModelRateLimitResult {
+			return nil
+		},
+	}
+
+	availableURLs := []string{"https://ag-1.test"}
+
+	svc := &AntigravityGatewayService{}
+	result := svc.handleSmartRetry(params, resp, respBody, "https://ag-1.test", 0, availableURLs)
+
+	require.NotNil(t, result)
+	require.Equal(t, smartRetryActionBreakWithResp, result.action)
+	// 关键断言：单账号 503 模式下，智能重试耗尽后直接返回 503 响应，不切换
+	require.NotNil(t, result.resp, "should return 503 response directly for single account mode")
+	require.Equal(t, http.StatusServiceUnavailable, result.resp.StatusCode)
+	require.Nil(t, result.switchError, "should NOT switch account in single account mode")
+
+	// 关键断言：不设模型限流
+	require.Len(t, repo.modelRateLimitCalls, 0,
+		"should NOT set model rate limit for 503 in single account mode")
+}
+
+// TestHandleSmartRetry_503_ShortDelay_NoSingleAccountRetry_SetsRateLimit
+// 对照组：503 + retryDelay < 7s + 无 SingleAccountRetry → 智能重试耗尽后照常设限流
+func TestHandleSmartRetry_503_ShortDelay_NoSingleAccountRetry_SetsRateLimit(t *testing.T) {
+	failRespBody := `{
+		"error": {
+			"code": 503,
+			"status": "UNAVAILABLE",
+			"details": [
+				{"@type": "type.googleapis.com/google.rpc.ErrorInfo", "metadata": {"model": "gemini-3-flash"}, "reason": "MODEL_CAPACITY_EXHAUSTED"},
+				{"@type": "type.googleapis.com/google.rpc.RetryInfo", "retryDelay": "0.1s"}
+			]
+		}
+	}`
+	failResp := &http.Response{
+		StatusCode: http.StatusServiceUnavailable,
+		Header:     http.Header{},
+		Body:       io.NopCloser(strings.NewReader(failRespBody)),
+	}
+	upstream := &mockSmartRetryUpstream{
+		responses: []*http.Response{failResp},
+		errors:    []error{nil},
+	}
+
+	repo := &stubAntigravityAccountRepo{}
+	account := &Account{
+		ID:       5,
+		Name:     "acc-multi-503",
+		Type:     AccountTypeOAuth,
+		Platform: PlatformAntigravity,
+	}
+
+	respBody := []byte(`{
+		"error": {
+			"code": 503,
+			"status": "UNAVAILABLE",
+			"details": [
+				{"@type": "type.googleapis.com/google.rpc.ErrorInfo", "metadata": {"model": "gemini-3-flash"}, "reason": "MODEL_CAPACITY_EXHAUSTED"},
+				{"@type": "type.googleapis.com/google.rpc.RetryInfo", "retryDelay": "0.1s"}
+			]
+		}
+	}`)
+	resp := &http.Response{
+		StatusCode: http.StatusServiceUnavailable,
+		Header:     http.Header{},
+		Body:       io.NopCloser(bytes.NewReader(respBody)),
+	}
+
+	params := antigravityRetryLoopParams{
+		ctx:          context.Background(), // 无单账号标记
+		prefix:       "[test]",
+		account:      account,
+		accessToken:  "token",
+		action:       "generateContent",
+		body:         []byte(`{"input":"test"}`),
+		httpUpstream: upstream,
+		accountRepo:  repo,
+		handleError: func(ctx context.Context, prefix string, account *Account, statusCode int, headers http.Header, body []byte, requestedModel string, groupID int64, sessionHash string, isStickySession bool) *handleModelRateLimitResult {
+			return nil
+		},
+	}
+
+	availableURLs := []string{"https://ag-1.test"}
+
+	svc := &AntigravityGatewayService{}
+	result := svc.handleSmartRetry(params, resp, respBody, "https://ag-1.test", 0, availableURLs)
+
+	require.NotNil(t, result)
+	require.Equal(t, smartRetryActionBreakWithResp, result.action)
+	// 对照：多账号模式应返回 switchError
+	require.NotNil(t, result.switchError, "multi-account mode should return switchError for 503")
+	// 对照：多账号模式应设模型限流
+	require.Len(t, repo.modelRateLimitCalls, 1,
+		"multi-account mode should set model rate limit")
+}
+
+// ---------------------------------------------------------------------------
+// 5. handleSingleAccountRetryInPlace 直接测试
+// ---------------------------------------------------------------------------
+
+// TestHandleSingleAccountRetryInPlace_Success 原地重试成功
+func TestHandleSingleAccountRetryInPlace_Success(t *testing.T) {
+	successResp := &http.Response{
+		StatusCode: http.StatusOK,
+		Header:     http.Header{},
+		Body:       io.NopCloser(strings.NewReader(`{"result":"ok"}`)),
+	}
+	upstream := &mockSmartRetryUpstream{
+		responses: []*http.Response{successResp},
+		errors:    []error{nil},
+	}
+
+	account := &Account{
+		ID:          10,
+		Name:        "acc-inplace-ok",
+		Type:        AccountTypeOAuth,
+		Platform:    PlatformAntigravity,
+		Concurrency: 1,
+	}
+
+	resp := &http.Response{
+		StatusCode: http.StatusServiceUnavailable,
+		Header:     http.Header{},
+	}
+
+	params := antigravityRetryLoopParams{
+		ctx:          ctxWithSingleAccountRetry(),
+		prefix:       "[test]",
+		account:      account,
+		accessToken:  "token",
+		action:       "generateContent",
+		body:         []byte(`{"input":"test"}`),
+		httpUpstream: upstream,
+	}
+
+	svc := &AntigravityGatewayService{}
+	result := svc.handleSingleAccountRetryInPlace(params, resp, nil, "https://ag-1.test", 1*time.Second, "gemini-3-pro")
+
+	require.NotNil(t, result)
+	require.Equal(t, smartRetryActionBreakWithResp, result.action)
+	require.NotNil(t, result.resp, "should return successful response")
+	require.Equal(t, http.StatusOK, result.resp.StatusCode)
+	require.Nil(t, result.switchError, "should not switch account on success")
+	require.Nil(t, result.err)
+}
+
+// TestHandleSingleAccountRetryInPlace_AllRetriesFail 所有重试都失败，返回 503（不设限流）
+func TestHandleSingleAccountRetryInPlace_AllRetriesFail(t *testing.T) {
+	// 构造 3 个 503 响应（对应 3 次原地重试）
+	var responses []*http.Response
+	var errors []error
+	for i := 0; i < antigravitySingleAccountSmartRetryMaxAttempts; i++ {
+		responses = append(responses, &http.Response{
+			StatusCode: http.StatusServiceUnavailable,
+			Header:     http.Header{},
+			Body: io.NopCloser(strings.NewReader(`{
+				"error": {
+					"code": 503,
+					"status": "UNAVAILABLE",
+					"details": [
+						{"@type": "type.googleapis.com/google.rpc.ErrorInfo", "metadata": {"model": "gemini-3-pro"}, "reason": "MODEL_CAPACITY_EXHAUSTED"},
+						{"@type": "type.googleapis.com/google.rpc.RetryInfo", "retryDelay": "0.1s"}
+					]
+				}
+			}`)),
+		})
+		errors = append(errors, nil)
+	}
+	upstream := &mockSmartRetryUpstream{
+		responses: responses,
+		errors:    errors,
+	}
+
+	account := &Account{
+		ID:          11,
+		Name:        "acc-inplace-fail",
+		Type:        AccountTypeOAuth,
+		Platform:    PlatformAntigravity,
+		Concurrency: 1,
+	}
+
+	origBody := []byte(`{"error":{"code":503,"status":"UNAVAILABLE"}}`)
+	resp := &http.Response{
+		StatusCode: http.StatusServiceUnavailable,
+		Header:     http.Header{"X-Test": {"original"}},
+	}
+
+	params := antigravityRetryLoopParams{
+		ctx:          ctxWithSingleAccountRetry(),
+		prefix:       "[test]",
+		account:      account,
+		accessToken:  "token",
+		action:       "generateContent",
+		body:         []byte(`{"input":"test"}`),
+		httpUpstream: upstream,
+	}
+
+	svc := &AntigravityGatewayService{}
+	result := svc.handleSingleAccountRetryInPlace(params, resp, origBody, "https://ag-1.test", 1*time.Second, "gemini-3-pro")
+
+	require.NotNil(t, result)
+	require.Equal(t, smartRetryActionBreakWithResp, result.action)
+	// 关键：返回 503 resp，不返回 switchError
+	require.NotNil(t, result.resp, "should return 503 response directly")
+	require.Equal(t, http.StatusServiceUnavailable, result.resp.StatusCode)
+	require.Nil(t, result.switchError, "should NOT return switchError - let Handler handle it")
+	require.Nil(t, result.err)
+
+	// 验证确实重试了指定次数
+	require.Len(t, upstream.calls, antigravitySingleAccountSmartRetryMaxAttempts,
+		"should have made exactly maxAttempts retry calls")
+}
+
+// TestHandleSingleAccountRetryInPlace_WaitDurationClamped 等待时间被限制在 [min, max] 范围
+func TestHandleSingleAccountRetryInPlace_WaitDurationClamped(t *testing.T) {
+	// 用短延迟的成功响应，只验证不 panic
+	successResp := &http.Response{
+		StatusCode: http.StatusOK,
+		Header:     http.Header{},
+		Body:       io.NopCloser(strings.NewReader(`{"result":"ok"}`)),
+	}
+	upstream := &mockSmartRetryUpstream{
+		responses: []*http.Response{successResp},
+		errors:    []error{nil},
+	}
+
+	account := &Account{
+		ID:          12,
+		Name:        "acc-clamp",
+		Type:        AccountTypeOAuth,
+		Platform:    PlatformAntigravity,
+		Concurrency: 1,
+	}
+
+	resp := &http.Response{
+		StatusCode: http.StatusServiceUnavailable,
+		Header:     http.Header{},
+	}
+
+	params := antigravityRetryLoopParams{
+		ctx:          ctxWithSingleAccountRetry(),
+		prefix:       "[test]",
+		account:      account,
+		accessToken:  "token",
+		action:       "generateContent",
+		body:         []byte(`{"input":"test"}`),
+		httpUpstream: upstream,
+	}
+
+	svc := &AntigravityGatewayService{}
+
+	// 等待时间过大应被 clamp 到 antigravitySingleAccountSmartRetryMaxWait
+	result := svc.handleSingleAccountRetryInPlace(params, resp, nil, "https://ag-1.test", 999*time.Second, "gemini-3-pro")
+	require.NotNil(t, result)
+	require.Equal(t, smartRetryActionBreakWithResp, result.action)
+	require.NotNil(t, result.resp)
+	require.Equal(t, http.StatusOK, result.resp.StatusCode)
+}
+
+// TestHandleSingleAccountRetryInPlace_ContextCanceled context 取消时立即返回
+func TestHandleSingleAccountRetryInPlace_ContextCanceled(t *testing.T) {
+	upstream := &mockSmartRetryUpstream{
+		responses: []*http.Response{nil},
+		errors:    []error{nil},
+	}
+
+	account := &Account{
+		ID:          13,
+		Name:        "acc-cancel",
+		Type:        AccountTypeOAuth,
+		Platform:    PlatformAntigravity,
+		Concurrency: 1,
+	}
+
+	resp := &http.Response{
+		StatusCode: http.StatusServiceUnavailable,
+		Header:     http.Header{},
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	ctx = context.WithValue(ctx, ctxkey.SingleAccountRetry, true)
+	cancel() // 立即取消
+
+	params := antigravityRetryLoopParams{
+		ctx:          ctx,
+		prefix:       "[test]",
+		account:      account,
+		accessToken:  "token",
+		action:       "generateContent",
+		body:         []byte(`{"input":"test"}`),
+		httpUpstream: upstream,
+	}
+
+	svc := &AntigravityGatewayService{}
+	result := svc.handleSingleAccountRetryInPlace(params, resp, nil, "https://ag-1.test", 1*time.Second, "gemini-3-pro")
+
+	require.NotNil(t, result)
+	require.Equal(t, smartRetryActionBreakWithResp, result.action)
+	require.Error(t, result.err, "should return context error")
+	// 不应调用 upstream（因为在等待阶段就被取消了）
+	require.Len(t, upstream.calls, 0, "should not call upstream when context is canceled")
+}
+
+// TestHandleSingleAccountRetryInPlace_NetworkError_ContinuesRetry 网络错误时继续重试
+func TestHandleSingleAccountRetryInPlace_NetworkError_ContinuesRetry(t *testing.T) {
+	successResp := &http.Response{
+		StatusCode: http.StatusOK,
+		Header:     http.Header{},
+		Body:       io.NopCloser(strings.NewReader(`{"result":"ok"}`)),
+	}
+	upstream := &mockSmartRetryUpstream{
+		// 第1次网络错误（nil resp），第2次成功
+		responses: []*http.Response{nil, successResp},
+		errors:    []error{nil, nil},
+	}
+
+	account := &Account{
+		ID:          14,
+		Name:        "acc-net-retry",
+		Type:        AccountTypeOAuth,
+		Platform:    PlatformAntigravity,
+		Concurrency: 1,
+	}
+
+	resp := &http.Response{
+		StatusCode: http.StatusServiceUnavailable,
+		Header:     http.Header{},
+	}
+
+	params := antigravityRetryLoopParams{
+		ctx:          ctxWithSingleAccountRetry(),
+		prefix:       "[test]",
+		account:      account,
+		accessToken:  "token",
+		action:       "generateContent",
+		body:         []byte(`{"input":"test"}`),
+		httpUpstream: upstream,
+	}
+
+	svc := &AntigravityGatewayService{}
+	result := svc.handleSingleAccountRetryInPlace(params, resp, nil, "https://ag-1.test", 1*time.Second, "gemini-3-pro")
+
+	require.NotNil(t, result)
+	require.Equal(t, smartRetryActionBreakWithResp, result.action)
+	require.NotNil(t, result.resp, "should return successful response after network error recovery")
+	require.Equal(t, http.StatusOK, result.resp.StatusCode)
+	require.Len(t, upstream.calls, 2, "first call fails (network error), second succeeds")
+}
+
+// ---------------------------------------------------------------------------
+// 6. antigravityRetryLoop 预检查：单账号模式跳过限流
+// ---------------------------------------------------------------------------
+
+// TestAntigravityRetryLoop_PreCheck_SingleAccountRetry_SkipsRateLimit
+// 预检查中，如果有 SingleAccountRetry 标记，即使账号已限流也跳过直接发请求
+func TestAntigravityRetryLoop_PreCheck_SingleAccountRetry_SkipsRateLimit(t *testing.T) {
+	// 创建一个已设模型限流的账号
+	upstream := &recordingOKUpstream{}
+	account := &Account{
+		ID:          20,
+		Name:        "acc-rate-limited",
+		Type:        AccountTypeOAuth,
+		Platform:    PlatformAntigravity,
+		Schedulable: true,
+		Status:      StatusActive,
+		Concurrency: 1,
+		Extra: map[string]any{
+			modelRateLimitsKey: map[string]any{
+				"claude-sonnet-4-5": map[string]any{
+					"rate_limit_reset_at": time.Now().Add(30 * time.Second).Format(time.RFC3339),
+				},
+			},
+		},
+	}
+
+	svc := &AntigravityGatewayService{}
+	result, err := svc.antigravityRetryLoop(antigravityRetryLoopParams{
+		ctx:            ctxWithSingleAccountRetry(),
+		prefix:         "[test]",
+		account:        account,
+		accessToken:    "token",
+		action:         "generateContent",
+		body:           []byte(`{"input":"test"}`),
+		httpUpstream:   upstream,
+		requestedModel: "claude-sonnet-4-5",
+		handleError: func(ctx context.Context, prefix string, account *Account, statusCode int, headers http.Header, body []byte, requestedModel string, groupID int64, sessionHash string, isStickySession bool) *handleModelRateLimitResult {
+			return nil
+		},
+	})
+
+	require.NoError(t, err, "should not return error")
+	require.NotNil(t, result, "should return result")
+	require.NotNil(t, result.resp, "should have response")
+	require.Equal(t, http.StatusOK, result.resp.StatusCode)
+	// 关键：尽管限流了，有 SingleAccountRetry 标记时仍然到达了 upstream
+	require.Equal(t, 1, upstream.calls, "should have reached upstream despite rate limit")
+}
+
+// TestAntigravityRetryLoop_PreCheck_NoSingleAccountRetry_SwitchesOnRateLimit
+// 对照组：无 SingleAccountRetry + 已限流 → 预检查返回 switchError
+func TestAntigravityRetryLoop_PreCheck_NoSingleAccountRetry_SwitchesOnRateLimit(t *testing.T) {
+	upstream := &recordingOKUpstream{}
+	account := &Account{
+		ID:          21,
+		Name:        "acc-rate-limited-multi",
+		Type:        AccountTypeOAuth,
+		Platform:    PlatformAntigravity,
+		Schedulable: true,
+		Status:      StatusActive,
+		Concurrency: 1,
+		Extra: map[string]any{
+			modelRateLimitsKey: map[string]any{
+				"claude-sonnet-4-5": map[string]any{
+					"rate_limit_reset_at": time.Now().Add(30 * time.Second).Format(time.RFC3339),
+				},
+			},
+		},
+	}
+
+	svc := &AntigravityGatewayService{}
+	result, err := svc.antigravityRetryLoop(antigravityRetryLoopParams{
+		ctx:            context.Background(), // 无单账号标记
+		prefix:         "[test]",
+		account:        account,
+		accessToken:    "token",
+		action:         "generateContent",
+		body:           []byte(`{"input":"test"}`),
+		httpUpstream:   upstream,
+		requestedModel: "claude-sonnet-4-5",
+		handleError: func(ctx context.Context, prefix string, account *Account, statusCode int, headers http.Header, body []byte, requestedModel string, groupID int64, sessionHash string, isStickySession bool) *handleModelRateLimitResult {
+			return nil
+		},
+	})
+
+	require.Nil(t, result, "should not return result on rate limit switch")
+	require.NotNil(t, err, "should return error")
+
+	var switchErr *AntigravityAccountSwitchError
+	require.ErrorAs(t, err, &switchErr, "should return AntigravityAccountSwitchError")
+	require.Equal(t, account.ID, switchErr.OriginalAccountID)
+	require.Equal(t, "claude-sonnet-4-5", switchErr.RateLimitedModel)
+
+	// upstream 不应被调用（预检查就短路了）
+	require.Equal(t, 0, upstream.calls, "upstream should NOT be called when pre-check blocks")
+}
+
+// ---------------------------------------------------------------------------
+// 7. 端到端集成场景测试
+// ---------------------------------------------------------------------------
+
+// TestHandleSmartRetry_503_SingleAccount_RetryInPlace_ThenSuccess_E2E
+// 端到端场景：503 + 单账号 + 原地重试第2次成功
+func TestHandleSmartRetry_503_SingleAccount_RetryInPlace_ThenSuccess_E2E(t *testing.T) {
+	// 第1次原地重试仍返回 503，第2次成功
+	fail503Body := `{
+		"error": {
+			"code": 503,
+			"status": "UNAVAILABLE",
+			"details": [
+				{"@type": "type.googleapis.com/google.rpc.ErrorInfo", "metadata": {"model": "gemini-3-pro"}, "reason": "MODEL_CAPACITY_EXHAUSTED"},
+				{"@type": "type.googleapis.com/google.rpc.RetryInfo", "retryDelay": "0.1s"}
+			]
+		}
+	}`
+	resp503 := &http.Response{
+		StatusCode: http.StatusServiceUnavailable,
+		Header:     http.Header{},
+		Body:       io.NopCloser(strings.NewReader(fail503Body)),
+	}
+	successResp := &http.Response{
+		StatusCode: http.StatusOK,
+		Header:     http.Header{},
+		Body:       io.NopCloser(strings.NewReader(`{"result":"ok"}`)),
+	}
+
+	upstream := &mockSmartRetryUpstream{
+		responses: []*http.Response{resp503, successResp},
+		errors:    []error{nil, nil},
+	}
+
+	account := &Account{
+		ID:          30,
+		Name:        "acc-e2e",
+		Type:        AccountTypeOAuth,
+		Platform:    PlatformAntigravity,
+		Concurrency: 1,
+	}
+
+	resp := &http.Response{
+		StatusCode: http.StatusServiceUnavailable,
+		Header:     http.Header{},
+	}
+
+	params := antigravityRetryLoopParams{
+		ctx:          ctxWithSingleAccountRetry(),
+		prefix:       "[test]",
+		account:      account,
+		accessToken:  "token",
+		action:       "generateContent",
+		body:         []byte(`{"input":"test"}`),
+		httpUpstream: upstream,
+	}
+
+	svc := &AntigravityGatewayService{}
+	result := svc.handleSingleAccountRetryInPlace(params, resp, nil, "https://ag-1.test", 1*time.Second, "gemini-3-pro")
+
+	require.NotNil(t, result)
+	require.Equal(t, smartRetryActionBreakWithResp, result.action)
+	require.NotNil(t, result.resp, "should return successful response after 2nd attempt")
+	require.Equal(t, http.StatusOK, result.resp.StatusCode)
+	require.Nil(t, result.switchError)
+	require.Len(t, upstream.calls, 2, "first 503, second OK")
+}
+
+// TestAntigravityRetryLoop_503_SingleAccount_InPlaceRetryUsed_E2E
+// 通过 antigravityRetryLoop → handleSmartRetry → handleSingleAccountRetryInPlace 完整链路
+func TestAntigravityRetryLoop_503_SingleAccount_InPlaceRetryUsed_E2E(t *testing.T) {
+	// 初始请求返回 503 + 长延迟
+	initial503Body := []byte(`{
+		"error": {
+			"code": 503,
+			"status": "UNAVAILABLE",
+			"details": [
+				{"@type": "type.googleapis.com/google.rpc.ErrorInfo", "metadata": {"model": "gemini-3-pro"}, "reason": "MODEL_CAPACITY_EXHAUSTED"},
+				{"@type": "type.googleapis.com/google.rpc.RetryInfo", "retryDelay": "10s"}
+			],
+			"message": "No capacity available"
+		}
+	}`)
+	initial503Resp := &http.Response{
+		StatusCode: http.StatusServiceUnavailable,
+		Header:     http.Header{},
+		Body:       io.NopCloser(bytes.NewReader(initial503Body)),
+	}
+
+	// 原地重试成功
+	successResp := &http.Response{
+		StatusCode: http.StatusOK,
+		Header:     http.Header{},
+		Body:       io.NopCloser(strings.NewReader(`{"result":"ok"}`)),
+	}
+
+	upstream := &mockSmartRetryUpstream{
+		// 第1次调用（retryLoop 主循环）返回 503
+		// 第2次调用（handleSingleAccountRetryInPlace 原地重试）返回 200
+		responses: []*http.Response{initial503Resp, successResp},
+		errors:    []error{nil, nil},
+	}
+
+	repo := &stubAntigravityAccountRepo{}
+	account := &Account{
+		ID:          31,
+		Name:        "acc-e2e-loop",
+		Type:        AccountTypeOAuth,
+		Platform:    PlatformAntigravity,
+		Schedulable: true,
+		Status:      StatusActive,
+		Concurrency: 1,
+	}
+
+	svc := &AntigravityGatewayService{}
+	result, err := svc.antigravityRetryLoop(antigravityRetryLoopParams{
+		ctx:          ctxWithSingleAccountRetry(),
+		prefix:       "[test]",
+		account:      account,
+		accessToken:  "token",
+		action:       "generateContent",
+		body:         []byte(`{"input":"test"}`),
+		httpUpstream: upstream,
+		accountRepo:  repo,
+		handleError: func(ctx context.Context, prefix string, account *Account, statusCode int, headers http.Header, body []byte, requestedModel string, groupID int64, sessionHash string, isStickySession bool) *handleModelRateLimitResult {
+			return nil
+		},
+	})
+
+	require.NoError(t, err, "should not return error on successful retry")
+	require.NotNil(t, result, "should return result")
+	require.NotNil(t, result.resp, "should return response")
+	require.Equal(t, http.StatusOK, result.resp.StatusCode)
+
+	// 验证未设模型限流
+	require.Len(t, repo.modelRateLimitCalls, 0,
+		"should NOT set model rate limit in single account retry mode")
+}