feat(relay): hosted-tool conversion fidelity, reasoning normalization, and billing usage integrity (#7137)

* feat(relaykit): preserve hosted tools across conversions

- add protocol-neutral hosted-tool DTOs, conversion metadata, and loss policies
- bridge citations, grounding metadata, and hosted-tool stream lifecycles
- document the public conversion behavior and channel policy controls

* refactor(relaykit): normalize reasoning and thinking intent

- centralize provider-neutral reasoning intent, effort, and budget mappings
- parse model suffixes at the host entry boundary while preserving provider-owned tails
- keep adaptive Claude thinking and explicit zero-token compatibility consistent

* fix(billing): preserve authoritative usage across relay hops

- carry native BillingUsage sidecars through direct and streamed protocol bridges
- merge partial and terminal usage monotonically with safe fallback settlement
- retain cache metadata, penultimate usage, and per-call Gemini tool surcharges

* feat(relay): bridge Responses with Claude and Gemini protocols

- add direct request, response, and stream converters across supported relay formats
- expose Claude count_tokens and Chat-to-Responses compatibility endpoints
- carry conversion diagnostics through the host while retaining the curated public goldens

* fix(relay): wire relaykit conversions into host channels

- connect handlers, adaptors, and channel settings to the standalone conversion layer
- keep model mapping, pricing identity, retries, and provider-specific suffix behavior aligned
- ignore local audit artifacts and retain focused public regression coverage

relaykit/README.md

@@ -199,6 +199,9 @@ meta := &convmeta.Values{
 - OpenAI Chat 或 OpenAI Responses 转 Claude 时，Claude 请求必须具有 `max_tokens`。源请求未提供时，需要配置 `Claude.DefaultMaxTokens`，否则转换会返回错误。
 - RelayKit 不负责选择渠道或映射模型名。调用转换前，应将请求中的 `Model` 设置为目标上游使用的模型名。
 - 自定义 `convmeta.Meta` 的指针实现必须保证所有方法对 nil receiver 安全，完整约束见 `convmeta.Meta` 的接口注释。
+- 工具损耗策略默认是 `allow`：跨协议转换会成功，损耗以诊断形式返回。`safe` / `strict` 只在请求阶段 opt-in 拒绝；响应和流式转换无论策略如何都不会因损耗失败。
+- `ThinkingAdapterEnabled` 只控制是否把已解析的推理意图渲染到 Claude / Gemini 请求上。`-thinking` / `-nothinking` / effort 尾缀等命名约定不再由转换器自动解释。
+- 若你的入口仍使用这些模型名后缀，请在调用转换前自行调用 `relayconvert/reasoning` 的 `Parse*` 帮助函数，把结果写成 `dto.ReasoningConversionState`，并通过 `convmeta.Meta.ReasoningState()`（`convmeta.Values.ReasoningConversion`）传入。同时把发给上游的模型名裁成无后缀基础名。
 
 ## 多模态内容