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新增功能：
- 新增 TLS 指纹 Profile CRUD 管理（Ent schema + 迁移 + Admin API + 前端管理界面）
- 支持账号绑定数据库中的自定义 TLS Profile，或随机选择（profile_id=-1）
- HTTPUpstream.DoWithTLS 接口从 bool 改为 *tlsfingerprint.Profile，支持按账号指定 Profile
- AccountUsageService 注入 TLSFingerprintProfileService，统一 usage 场景与网关的 Profile 解析逻辑

代码优化：
- 删除已被 TLSFingerprintProfileService 完全取代的 registry.go 死代码（418 行）
- 提取 3 个 dialer 的重复 TLS 握手逻辑为 performTLSHandshake() 共用函数
- 修复 GetTLSFingerprintProfileID 缺少 json.Number 处理的 bug
- gateway_service.Forward 中 ResolveTLSProfile 从重试循环内重复调用改为预解析局部变量
- 删除冗余的 buildClientHelloSpec() 单行 wrapper 和 int64(e.ID) 无效转换
- tls_fingerprint_profile_cache.go 日志从 log.Printf 改为 slog 结构化日志
- dialer_capture_test.go 添加 //go:build integration 标签，防止 CI 失败
- 去重 TestProfileExpectation 类型至共享 test_types_test.go
- 修复 9 个测试文件缺少 tlsfingerprint import 的编译错误
- 修复 error_policy_integration_test.go 中 handleError 回调签名被错误替换的问题

feat: implement resolveCreditsOveragesModelKey function to stabilize model key resolution for credit overages

- Use mapped model (billingModel) instead of original request model for billing
- Use resolveFinalAntigravityModelKey for 429 rate limit model key,
  ensuring rate limit records match the actual upstream model
- Add regression tests for both fixes

MODEL_CAPACITY_EXHAUSTED (503) 表示模型容量不足，所有账号共享同一容量池，
切换账号无意义。改为固定1s间隔重试最多60次，重试耗尽后直接返回上游错误。

- 新增 antigravityModelCapacityRetryMaxAttempts=60 和 antigravityModelCapacityRetryWait=1s
- shouldTriggerAntigravitySmartRetry 新增 isModelCapacityExhausted 返回值
- handleSmartRetry 对 MODEL_CAPACITY_EXHAUSTED 使用独立重试策略
- handleModelRateLimit 对 MODEL_CAPACITY_EXHAUSTED 仅标记 Handled，不设限流
- 重试耗尽后不设置模型限流、不清除粘性会话、不切换账号

Merge functional changes from develop branch:
- Remove AntigravityQuotaScope system (claude/gemini_text/gemini_image)
- Replace with per-model rate limiting using resolveAntigravityModelKey
- Remove model load statistics (IncrModelCallCount/GetModelLoadBatch)
- Simplify account selection to unified priority→load→LRU algorithm
- Remove SetAntigravityQuotaScopeLimit from AccountRepository
- Clean up scope-related UI indicators and API fields

系统性地修复、补充和强化项目的自动化测试能力：

1. 测试基础设施修复
   - 修复 stubConcurrencyCache 缺失方法和构造函数参数不匹配
   - 创建 testutil 共享包（stubs.go, fixtures.go, httptest.go）
   - 为所有 Stub 添加编译期接口断言

2. 中间件测试补充
   - 新增 JWT 认证中间件测试（有效/过期/篡改/缺失 Token）
   - 补充 rate_limiter 和 recovery 中间件测试场景

3. 网关核心路径测试
   - 新增账户选择、等待队列、流式响应、并发控制、计费、Claude Code 检测测试
   - 覆盖负载均衡、粘性会话、SSE 转发、槽位管理等关键逻辑

4. 前端测试体系（11个新测试文件，163个测试用例）
   - Pinia stores: auth, app, subscriptions
   - API client: 请求拦截器、响应拦截器、401 刷新
   - Router guards: 认证重定向、管理员权限、简易模式限制
   - Composables: useForm, useTableLoader, useClipboard
   - Components: LoginForm, ApiKeyCreate, Dashboard

5. CI/CD 流水线重构
   - 重构 backend-ci.yml 为统一的 ci.yml
   - 前后端 4 个并行 Job + Postgres/Redis services
   - Race 检测、覆盖率收集与门禁、Docker 构建验证

6. E2E 自动化测试
   - e2e-test.sh 自动化脚本（Docker 启动→健康检查→测试→清理）
   - 用户注册→登录→API Key→网关调用完整链路测试
   - Mock 模式和 API Key 脱敏支持

7. 修复预存问题
   - tlsfingerprint dialer_test.go 缺失 build tag 导致集成测试编译冲突
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Remove threshold-based waiting in both sticky session and antigravity
pre-check paths. When a model is rate-limited, immediately clear the
sticky session and switch accounts instead of waiting for short durations.

- Add GetAccessToken upstream branch tests (success/failure/empty/nil)
- Add mapAntigravityModel wildcard-target-equals-request edge case tests
- Add upstream account smart retry test case
- Add GeminiMessagesCompatService custom model_mapping and empty model tests

- GetAccessToken: add upstream branch to read api_key from credentials
- shouldTriggerAntigravitySmartRetry: relax check from IsOAuth to Platform-based
- isModelSupportedByAccount/WithContext: replace IsAntigravityModelSupported
  whitelist with mapAntigravityModel for unified scheduling/forwarding logic
- mapAntigravityModel: fix edge case where wildcard target equals request model
- Update tests for new behavior and add custom model_mapping test cases

Key changes:
- Upgrade model mapping: Opus 4.5 → Opus 4.6-thinking with precise matching
- Unified rate limiting: scope-level → model-level with Redis snapshot sync
- Load-balanced scheduling by call count with smart retry mechanism
- Force cache billing support
- Model identity injection in prompts with leak prevention
- Thinking mode auto-handling (max_tokens/budget_tokens fix)
- Frontend: whitelist mode toggle, model mapping validation, status indicators
- Gemini session fallback with Redis Trie O(L) matching
- Ops: enhanced concurrency monitoring, account availability, retry logic
- Migration scripts: 049-051 for model mapping unification

- 新增 _token_version 版本号机制，防止过期 token 污染缓存
- TokenRefreshService 刷新成功后写入版本号并清除缓存
- TokenProvider 写入缓存前检查版本，过时则跳过
- ClearError 时同步清除 token 缓存