fix: antigravity 默认补全 gemini-3-flash 透传

backend/internal/service/account.go

@@ -372,6 +372,9 @@ func (a *Account) GetModelMapping() map[string]string {
 			}
 		}
 		if len(result) > 0 {
+			if a.Platform == domain.PlatformAntigravity {
+				ensureAntigravityDefaultPassthrough(result, "gemini-3-flash")
+			}
 			return result
 		}
 	}
@@ -382,6 +385,21 @@ func (a *Account) GetModelMapping() map[string]string {
 	return nil
 }
 
+func ensureAntigravityDefaultPassthrough(mapping map[string]string, model string) {
+	if mapping == nil || model == "" {
+		return
+	}
+	if _, exists := mapping[model]; exists {
+		return
+	}
+	for pattern := range mapping {
+		if matchWildcard(pattern, model) {
+			return
+		}
+	}
+	mapping[model] = model
+}
+
 // IsModelSupported 检查模型是否在 model_mapping 中（支持通配符）
 // 如果未配置 mapping，返回 true（允许所有模型）
 func (a *Account) IsModelSupported(requestedModel string) bool {

backend/internal/service/account_wildcard_test.go

@@ -267,3 +267,38 @@ func TestAccountGetMappedModel(t *testing.T) {
 		})
 	}
 }
+
+func TestAccountGetModelMapping_AntigravityEnsuresGemini3FlashPassthrough(t *testing.T) {
+	account := &Account{
+		Platform: PlatformAntigravity,
+		Credentials: map[string]any{
+			"model_mapping": map[string]any{
+				"gemini-3-pro-high": "gemini-3.1-pro-high",
+			},
+		},
+	}
+
+	mapping := account.GetModelMapping()
+	if mapping["gemini-3-flash"] != "gemini-3-flash" {
+		t.Fatalf("expected gemini-3-flash passthrough to be auto-filled, got: %q", mapping["gemini-3-flash"])
+	}
+}
+
+func TestAccountGetModelMapping_AntigravityRespectsWildcardOverride(t *testing.T) {
+	account := &Account{
+		Platform: PlatformAntigravity,
+		Credentials: map[string]any{
+			"model_mapping": map[string]any{
+				"gemini-3*": "gemini-3.1-pro-high",
+			},
+		},
+	}
+
+	mapping := account.GetModelMapping()
+	if _, exists := mapping["gemini-3-flash"]; exists {
+		t.Fatalf("did not expect explicit gemini-3-flash passthrough when wildcard already exists")
+	}
+	if mapped := account.GetMappedModel("gemini-3-flash"); mapped != "gemini-3.1-pro-high" {
+		t.Fatalf("expected wildcard mapping to stay effective, got: %q", mapped)
+	}
+}