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When custom error codes are enabled and the upstream error code is NOT
in the configured list, return HTTP 500 to the client instead of
transparently forwarding the original status code.

Also adds integration test TestCustomErrorCode599 verifying that 429,
500, 503, 401, 403 all return 500 without triggering SetRateLimited
or SetError.

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

Without this routing guard, ForwardUpstream is never called because
Forward() always proceeds with the standard OAuth/cookie flow.

- In handleSmartRetry, use the actual upstream retryDelay to set model
  rate limit duration instead of always using the 30s default
- Return info.RetryDelay from shouldTriggerAntigravitySmartRetry when
  shouldRateLimitModel=true, so callers know the actual delay
- Extract getDefaultRateLimitDuration() and resolveResetTime() helpers
  to reduce duplication in handleUpstreamError 429 handling
- Improve debug logging with upstream_retry_delay and response body

Upstream accounts now use the standard APIKey type instead of a dedicated
upstream type. GetBaseURL() and new GetGeminiBaseURL() automatically append
/antigravity for Antigravity platform APIKey accounts, eliminating the need
for separate upstream forwarding methods.

- Remove ForwardUpstream, ForwardUpstreamGemini, testUpstreamConnection
- Remove upstream branch guards in Forward/ForwardGemini/TestConnection
- Add migration 052 to convert existing upstream accounts to apikey
- Update frontend CreateAccountModal to create apikey type
- Add unit tests for GetBaseURL and GetGeminiBaseURL

ForwardUpstream/ForwardUpstreamGemini should pipe the upstream response
directly to the client (headers + body), not parse it as SSE stream.

Replace manual header setting (Content-Type, anthropic-version, anthropic-beta)
with full client header passthrough in ForwardUpstream/ForwardUpstreamGemini.
Only authentication headers (Authorization, x-api-key) are overridden with
upstream account credentials. Hop-by-hop headers are excluded.

Add unit tests covering header passthrough, auth override, and hop-by-hop filtering.

v0.1.74 merged upstream accounts into the OAuth path, causing requests
to hit the wrong protocol and endpoint. Add three upstream-specific
methods (testUpstreamConnection, ForwardUpstream, ForwardUpstreamGemini)
that use base_url + apiKey auth and passthrough the original body, while
reusing the existing response handling and error/retry logic.

- Change antigravitySmartRetryMaxAttempts from 3 to 1 to prevent
  repeated rate limiting and long waits
- Clear sticky session binding (DeleteSessionAccountID) after smart
  retry exhaustion, so subsequent requests don't hit the same
  rate-limited account
- Add flow diagrams to Forward/ForwardGemini doc comments
- Add comprehensive unit tests covering:
  - Sticky session cleared on retry failure (429, 503, network error)
  - Sticky session NOT cleared on retry success
  - Sticky session NOT cleared for non-sticky requests (empty hash)
  - Sticky session NOT cleared on long delay path (handled by handler)
  - Nil cache safety (no panic)
  - MaxAttempts constant verification
  - End-to-end retryLoop → switchError propagation with session clear

- avoid panic by using safe UUID prefix truncation in Gemini digest fallback logs\n- remove unconditional Antigravity 429 full-body debug logs and honor log truncation config\n- align Antigravity quick preset mappings to opus 4.6-thinking targets only\n- restore scope rate-limit aggregation/output in ops availability stats

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.

1. Frontend: replace hardcoded antigravityDefaultMappings with async
   fetch from GET /admin/accounts/antigravity/default-model-mapping,
   eliminating the duplicate data source that caused frontend/backend
   mapping inconsistency.

2. Backend: convert handleSmartRetry and antigravityRetryLoop from
   standalone functions to AntigravityGatewayService methods, enabling
   Redis cache sync (updateAccountModelRateLimitInCache) after both
   rate-limit write paths — long-delay branch and retry-exhausted branch.

- 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

The default fallback cooldown when rate limit reset time cannot be
parsed was 5 minutes, which is too aggressive and causes accounts
to be unnecessarily locked out. Reduce to 30 seconds for faster
recovery. Config override still works (unit remains minutes).

支持管理员配置上游错误如何返回给客户端：
- 新增 ErrorPassthroughRule 数据模型和 Ent Schema
- 实现规则的 CRUD API（/admin/error-passthrough-rules）
- 支持按错误码、关键词匹配，支持 any/all 匹配模式
- 支持按平台过滤（anthropic/openai/gemini/antigravity）
- 支持透传或自定义响应状态码和错误消息
- 实现两级缓存（Redis + 本地内存）和多实例同步
- 集成到 gateway_handler 的错误处理流程
- 新增前端管理界面组件
- 新增单元测试覆盖核心匹配逻辑

优化：
- 移除 refreshLocalCache 中的冗余排序（数据库已排序）
- 后端 Validate() 增加匹配条件非空校验

问题描述：
使用扩展思考功能时，偶现以下错误：
"thinking or redacted_thinking blocks in the latest assistant message cannot be modified"

根因分析：
当代理服务修改请求体中的某些字段时（如 metadata.user_id、model），
使用 map[string]any 解析整个 JSON 后重新序列化，导致：
1. 字段顺序改变（Go map 序列化按字母排序）
2. 数字格式变化（如 1.0 → 1）
3. Unicode 转义变化

Claude API 对 thinking 块进行字节级验证，任何变化都会触发错误。

修复内容：
1. identity_service.go - RewriteUserID/RewriteUserIDWithMasking
   使用 json.RawMessage 保留其他字段的原始字节

2. gateway_service.go - replaceModelInBody
   使用 json.RawMessage 保留其他字段的原始字节

3. gateway_service.go - normalizeClaudeOAuthRequestBody
   保留 messages 的原始字节，跳过包含 thinking 块的消息修改

4. gateway_service.go - isThinkingBlockSignatureError
   添加 "cannot be modified" 错误检测，触发自动重试

5. antigravity_gateway_service.go - isSignatureRelatedError
   添加 "cannot be modified" 错误检测
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

将 GATEWAY_ANTIGRAVITY_429_SCOPE_LIMIT 的默认值从关闭改为开启。
当 Gemini 模型触发 429 限流时，只会限制对应的配额域（gemini_text），
而 Claude 和 gemini_image 仍可继续使用，提高账号利用率。

Antigravity 上游不再支持 gemini-2.5 系列，统一映射到 gemini-3：
- gemini-2.5-flash → gemini-3-flash
- gemini-2.5-flash-lite → gemini-3-flash
- gemini-2.5-flash-thinking → gemini-3-flash
- gemini-2.5-flash-image → gemini-3-pro-image
- gemini-2.5-pro → gemini-3-pro-high
- gemini-2.5-pro-preview → gemini-3-pro-high
- gemini-2.5-pro-exp → gemini-3-pro-high

Add prefix mapping rules for gemini-2.5-pro variants:
- gemini-2.5-pro -> gemini-3-pro-high
- gemini-2.5-pro-preview -> gemini-3-pro-high
- gemini-2.5-pro-exp -> gemini-3-pro-high

Gemini API 不接受 contents 数组中 parts 为空的消息，会返回 400 INVALID_ARGUMENT 错误。
添加 filterEmptyPartsFromGeminiRequest 函数在转发前过滤这类消息。

影响范围：ForwardGemini (antigravity) 和 ForwardNative (gemini)

- Group 新增 mcp_xml_inject 字段，控制 Antigravity 平台的 MCP XML 协议注入
- 默认启用，可在分组设置中关闭
- 修复 GetByKeyForAuth 遗漏查询 mcp_xml_inject 字段导致认证缓存值始终为 false 的问题

- 修复 TransformGeminiToClaude 的 JSON 解析逻辑，当 V1InternalResponse
  解析成功但 candidates 为空时，尝试直接解析为 GeminiResponse 格式
- 修复 handleClaudeStreamToNonStreaming 收集流式响应的逻辑，累积所有
  chunks 的内容而不是只保留最后一个（最后一个 chunk 通常 text 为空）
- 新增 mergeCollectedPartsToResponse 函数，合并所有类型的 parts
  （text、thinking、functionCall、inlineData），保持原始顺序
- 连续的普通 text parts 合并为一个，thinking/functionCall/inlineData 保持原样

新增环境变量：
- GATEWAY_ANTIGRAVITY_MAX_RETRIES_CLAUDE
- GATEWAY_ANTIGRAVITY_MAX_RETRIES_GEMINI_TEXT
- GATEWAY_ANTIGRAVITY_MAX_RETRIES_GEMINI_IMAGE

未设置时回退到平台级 GATEWAY_ANTIGRAVITY_MAX_RETRIES

主要变更：
1. 重构代码结构：
   - 将 CleanJSONSchema 及其相关辅助函数从 request_transformer.go 提取到独立的 schema_cleaner.go 文件中，实现逻辑解耦。

2. 逻辑优化与修正：
   - 参考 Antigravity-Manager (json_schema.rs) 的实现逻辑，修正了 Schema 清洗策略。

主要变更：
1. 重构代码结构：
   - 将 CleanJSONSchema 及其相关辅助函数从 request_transformer.go 提取到独立的 schema_cleaner.go 文件中，实现逻辑解耦。

2. 逻辑优化与修正：
   - 参考 Antigravity-Manager (json_schema.rs) 的实现逻辑，修正了 Schema 清洗策略。