diff --git a/backend/internal/pkg/antigravity/client_test.go b/backend/internal/pkg/antigravity/client_test.go
index d3e2fd94..394b6128 100644
--- a/backend/internal/pkg/antigravity/client_test.go
+++ b/backend/internal/pkg/antigravity/client_test.go
@@ -400,7 +400,9 @@ func TestShouldFallbackToNextURL_无错误且200(t *testing.T) {
 // ---------------------------------------------------------------------------
 
 func TestClient_ExchangeCode_成功(t *testing.T) {
-	t.Setenv(AntigravityOAuthClientSecretEnv, "test-secret")
+	old := defaultClientSecret
+	defaultClientSecret = "test-secret"
+	t.Cleanup(func() { defaultClientSecret = old })
 
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		// 验证请求方法
@@ -493,7 +495,9 @@ func TestClient_ExchangeCode_成功(t *testing.T) {
 }
 
 func TestClient_ExchangeCode_无ClientSecret(t *testing.T) {
-	t.Setenv(AntigravityOAuthClientSecretEnv, "")
+	old := defaultClientSecret
+	defaultClientSecret = ""
+	t.Cleanup(func() { defaultClientSecret = old })
 
 	client := NewClient("")
 	_, err := client.ExchangeCode(context.Background(), "code", "verifier")
@@ -506,7 +510,9 @@ func TestClient_ExchangeCode_无ClientSecret(t *testing.T) {
 }
 
 func TestClient_ExchangeCode_服务器返回错误(t *testing.T) {
-	t.Setenv(AntigravityOAuthClientSecretEnv, "test-secret")
+	old := defaultClientSecret
+	defaultClientSecret = "test-secret"
+	t.Cleanup(func() { defaultClientSecret = old })
 
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusBadRequest)
@@ -531,7 +537,9 @@ func TestClient_ExchangeCode_服务器返回错误(t *testing.T) {
 // ---------------------------------------------------------------------------
 
 func TestClient_RefreshToken_MockServer(t *testing.T) {
-	t.Setenv(AntigravityOAuthClientSecretEnv, "test-secret")
+	old := defaultClientSecret
+	defaultClientSecret = "test-secret"
+	t.Cleanup(func() { defaultClientSecret = old })
 
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.Method != http.MethodPost {
@@ -590,7 +598,9 @@ func TestClient_RefreshToken_MockServer(t *testing.T) {
 }
 
 func TestClient_RefreshToken_无ClientSecret(t *testing.T) {
-	t.Setenv(AntigravityOAuthClientSecretEnv, "")
+	old := defaultClientSecret
+	defaultClientSecret = ""
+	t.Cleanup(func() { defaultClientSecret = old })
 
 	client := NewClient("")
 	_, err := client.RefreshToken(context.Background(), "refresh-tok")
@@ -784,7 +794,9 @@ func newTestClientWithRedirect(redirects map[string]string) *Client {
 // ---------------------------------------------------------------------------
 
 func TestClient_ExchangeCode_Success_RealCall(t *testing.T) {
-	t.Setenv(AntigravityOAuthClientSecretEnv, "test-secret")
+	old := defaultClientSecret
+	defaultClientSecret = "test-secret"
+	t.Cleanup(func() { defaultClientSecret = old })
 
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.Method != http.MethodPost {
@@ -853,7 +865,9 @@ func TestClient_ExchangeCode_Success_RealCall(t *testing.T) {
 }
 
 func TestClient_ExchangeCode_ServerError_RealCall(t *testing.T) {
-	t.Setenv(AntigravityOAuthClientSecretEnv, "test-secret")
+	old := defaultClientSecret
+	defaultClientSecret = "test-secret"
+	t.Cleanup(func() { defaultClientSecret = old })
 
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusBadRequest)
@@ -878,7 +892,9 @@ func TestClient_ExchangeCode_ServerError_RealCall(t *testing.T) {
 }
 
 func TestClient_ExchangeCode_InvalidJSON_RealCall(t *testing.T) {
-	t.Setenv(AntigravityOAuthClientSecretEnv, "test-secret")
+	old := defaultClientSecret
+	defaultClientSecret = "test-secret"
+	t.Cleanup(func() { defaultClientSecret = old })
 
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/json")
@@ -901,7 +917,9 @@ func TestClient_ExchangeCode_InvalidJSON_RealCall(t *testing.T) {
 }
 
 func TestClient_ExchangeCode_ContextCanceled_RealCall(t *testing.T) {
-	t.Setenv(AntigravityOAuthClientSecretEnv, "test-secret")
+	old := defaultClientSecret
+	defaultClientSecret = "test-secret"
+	t.Cleanup(func() { defaultClientSecret = old })
 
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		time.Sleep(5 * time.Second) // 模拟慢响应
@@ -927,7 +945,9 @@ func TestClient_ExchangeCode_ContextCanceled_RealCall(t *testing.T) {
 // ---------------------------------------------------------------------------
 
 func TestClient_RefreshToken_Success_RealCall(t *testing.T) {
-	t.Setenv(AntigravityOAuthClientSecretEnv, "test-secret")
+	old := defaultClientSecret
+	defaultClientSecret = "test-secret"
+	t.Cleanup(func() { defaultClientSecret = old })
 
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.Method != http.MethodPost {
@@ -976,7 +996,9 @@ func TestClient_RefreshToken_Success_RealCall(t *testing.T) {
 }
 
 func TestClient_RefreshToken_ServerError_RealCall(t *testing.T) {
-	t.Setenv(AntigravityOAuthClientSecretEnv, "test-secret")
+	old := defaultClientSecret
+	defaultClientSecret = "test-secret"
+	t.Cleanup(func() { defaultClientSecret = old })
 
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusUnauthorized)
@@ -998,7 +1020,9 @@ func TestClient_RefreshToken_ServerError_RealCall(t *testing.T) {
 }
 
 func TestClient_RefreshToken_InvalidJSON_RealCall(t *testing.T) {
-	t.Setenv(AntigravityOAuthClientSecretEnv, "test-secret")
+	old := defaultClientSecret
+	defaultClientSecret = "test-secret"
+	t.Cleanup(func() { defaultClientSecret = old })
 
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/json")
@@ -1021,7 +1045,9 @@ func TestClient_RefreshToken_InvalidJSON_RealCall(t *testing.T) {
 }
 
 func TestClient_RefreshToken_ContextCanceled_RealCall(t *testing.T) {
-	t.Setenv(AntigravityOAuthClientSecretEnv, "test-secret")
+	old := defaultClientSecret
+	defaultClientSecret = "test-secret"
+	t.Cleanup(func() { defaultClientSecret = old })
 
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		time.Sleep(5 * time.Second)
diff --git a/backend/internal/pkg/antigravity/oauth_test.go b/backend/internal/pkg/antigravity/oauth_test.go
index d8f2b098..da7d3fca 100644
--- a/backend/internal/pkg/antigravity/oauth_test.go
+++ b/backend/internal/pkg/antigravity/oauth_test.go
@@ -7,6 +7,7 @@ import (
 	"encoding/base64"
 	"encoding/hex"
 	"net/url"
+	"os"
 	"strings"
 	"testing"
 	"time"
@@ -17,8 +18,14 @@ import (
 // ---------------------------------------------------------------------------
 
 func TestGetClientSecret_环境变量设置(t *testing.T) {
+	old := defaultClientSecret
+	defaultClientSecret = ""
+	t.Cleanup(func() { defaultClientSecret = old })
 	t.Setenv(AntigravityOAuthClientSecretEnv, "my-secret-value")
 
+	// 需要重新触发 init 逻辑：手动从环境变量读取
+	defaultClientSecret = os.Getenv(AntigravityOAuthClientSecretEnv)
+
 	secret, err := getClientSecret()
 	if err != nil {
 		t.Fatalf("获取 client_secret 失败: %v", err)
@@ -29,11 +36,13 @@ func TestGetClientSecret_环境变量设置(t *testing.T) {
 }
 
 func TestGetClientSecret_环境变量为空(t *testing.T) {
-	t.Setenv(AntigravityOAuthClientSecretEnv, "")
+	old := defaultClientSecret
+	defaultClientSecret = ""
+	t.Cleanup(func() { defaultClientSecret = old })
 
 	_, err := getClientSecret()
 	if err == nil {
-		t.Fatal("环境变量为空时应返回错误")
+		t.Fatal("defaultClientSecret 为空时应返回错误")
 	}
 	if !strings.Contains(err.Error(), AntigravityOAuthClientSecretEnv) {
 		t.Errorf("错误信息应包含环境变量名: got %s", err.Error())
@@ -41,30 +50,31 @@ func TestGetClientSecret_环境变量为空(t *testing.T) {
 }
 
 func TestGetClientSecret_环境变量未设置(t *testing.T) {
-	// t.Setenv 会在测试结束时恢复，但我们需要确保它不存在
-	// 注意：如果 ClientSecret 常量非空，这个测试会直接返回常量值
-	// 当前代码中 ClientSecret = ""，所以会走环境变量逻辑
-
-	// 明确设置再取消，确保环境变量不存在
-	t.Setenv(AntigravityOAuthClientSecretEnv, "")
+	old := defaultClientSecret
+	defaultClientSecret = ""
+	t.Cleanup(func() { defaultClientSecret = old })
 
 	_, err := getClientSecret()
 	if err == nil {
-		t.Fatal("环境变量未设置时应返回错误")
+		t.Fatal("defaultClientSecret 为空时应返回错误")
 	}
 }
 
 func TestGetClientSecret_环境变量含空格(t *testing.T) {
-	t.Setenv(AntigravityOAuthClientSecretEnv, "   ")
+	old := defaultClientSecret
+	defaultClientSecret = "   "
+	t.Cleanup(func() { defaultClientSecret = old })
 
 	_, err := getClientSecret()
 	if err == nil {
-		t.Fatal("环境变量仅含空格时应返回错误")
+		t.Fatal("defaultClientSecret 仅含空格时应返回错误")
 	}
 }
 
 func TestGetClientSecret_环境变量有前后空格(t *testing.T) {
-	t.Setenv(AntigravityOAuthClientSecretEnv, "  valid-secret  ")
+	old := defaultClientSecret
+	defaultClientSecret = "  valid-secret  "
+	t.Cleanup(func() { defaultClientSecret = old })
 
 	secret, err := getClientSecret()
 	if err != nil {
@@ -671,7 +681,14 @@ func TestConstants_值正确(t *testing.T) {
 		t.Errorf("ClientID 不匹配: got %s", ClientID)
 	}
 	if ClientSecret != "" {
-		t.Error("ClientSecret 应为空字符串")
+		t.Error("ClientSecret 常量应为空字符串（默认值已移至 defaultClientSecret）")
+	}
+	secret, err := getClientSecret()
+	if err != nil {
+		t.Fatalf("getClientSecret 应返回默认值，但报错: %v", err)
+	}
+	if secret != "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" {
+		t.Errorf("默认 client_secret 不匹配: got %s", secret)
 	}
 	if RedirectURI != "http://localhost:8085/callback" {
 		t.Errorf("RedirectURI 不匹配: got %s", RedirectURI)
diff --git a/backend/migrations/058_add_sonnet46_to_model_mapping.sql b/backend/migrations/058_add_sonnet46_to_model_mapping.sql
index aa7657d7..93e7b39d 100644
--- a/backend/migrations/058_add_sonnet46_to_model_mapping.sql
+++ b/backend/migrations/058_add_sonnet46_to_model_mapping.sql
@@ -27,11 +27,11 @@ SET credentials = jsonb_set(
         "gemini-2.5-flash-thinking": "gemini-2.5-flash-thinking",
         "gemini-2.5-pro": "gemini-2.5-pro",
         "gemini-3-flash": "gemini-3-flash",
-        "gemini-3-pro-high": "gemini-3-pro-high",
-        "gemini-3-pro-low": "gemini-3-pro-low",
+        "gemini-3-pro-high": "gemini-3.1-pro-high",
+        "gemini-3-pro-low": "gemini-3.1-pro-low",
         "gemini-3-pro-image": "gemini-3-pro-image",
         "gemini-3-flash-preview": "gemini-3-flash",
-        "gemini-3-pro-preview": "gemini-3-pro-high",
+        "gemini-3-pro-preview": "gemini-3.1-pro-high",
         "gemini-3-pro-image-preview": "gemini-3-pro-image",
         "gpt-oss-120b-medium": "gpt-oss-120b-medium",
         "tab_flash_lite_preview": "tab_flash_lite_preview"