Exact Web per-Turn token usage
Web 单轮次精确 token 用量
Web Chat exposes cumulative session token usage near the composer, but that value cannot explain the cost of one completed Turn. A paged history window may begin inside a Turn, retries may consume several model calls, streaming and final events may repeat one attempt's usage, and optional cache fields do not prove an exact total. Displaying a partial subtotal as Turn usage would make recorded provider facts look more
English
Problem
Web Chat exposes cumulative session token usage near the composer, but that value cannot explain the cost of one completed Turn. A paged history window may begin inside a Turn, retries may consume several model calls, streaming and final events may repeat one attempt's usage, and optional cache fields do not prove an exact total. Displaying a partial subtotal as Turn usage would make recorded provider facts look more complete than they are.
Decision
The shared TokenUsage value carries optional totalTokens for one model call. Adapters publish it only from an exact provider total or authoritative aggregate prompt and output counters. DeepSeek checks its prompt-plus-completion aggregate against any wire total, and pi-ai preserves its provided total.
Token-meter owns a browser-safe pure Turn-local fold over durable session events, shared with its retry-aware cumulative usage projection. step/start and llm/retry-started open actual attempts; a final assistant message replaces the same attempt's streaming sample; terminal failures, retries, and step boundaries close attempts without double counting. Every started attempt must close with safe non-negative integer usage and an exact total. Optional cache, reasoning, and route aggregates appear only when every contributing attempt reports them, and reasoning remains a subset of output.
Web Chat selects a Turn only when its loaded match window includes turn/start, passes that complete durable-event window to the token-meter fold, and renders the result. A complete, exact result appears through a local-state DisclosureRow above the existing actions; incomplete or contradictory evidence produces no row. Chat owns no token-accounting state machine.
Alternatives considered
Subtract neighboring cumulative session values. Rejected because pagination, compaction, retry coverage, and projection completeness can make adjacent values incomparable; subtraction would infer data that no call reported.
Publish historical per-Turn values through a new client session projection. Rejected because the loaded per-Turn view already has the durable attempt events it needs, while a history-growing projection would add transport, persistence, and versioning costs. Reusing token-meter's pure fold keeps one accounting owner without adding another wire value.
Show known buckets without an exact total. Rejected because a lower-bound subtotal presented in a completed Turn footer is indistinguishable from a complete bill.
Consequences
New provider records can expose exact per-Turn accounting without a new transport or persisted UI state. Older sessions and adapters without enough evidence simply omit the disclosure. Model routes disappear as a group when any billed attempt lacks attribution, while trustworthy token totals remain visible.
Focused adapter, token-meter fold/projection, component, pagination, and assembled Web replay tests pin total preservation, retry-attempt separation, fail-closed validation, optional-field omission, interaction, and full-window publication. The cumulative projection and exact Turn fold now share token-meter ownership; the projection remains a whole-log bucket view, while the fold alone makes the stricter exactness and completeness claim required by the disclosure.
中文
Problem
Web Chat 在编辑框附近显示会话累计 token 用量，但该值无法解释一个已完成轮次的消耗。分页历史窗口可能从轮次中间开始，重试可能消耗多次模型调用，流式事件与最终事件可能重复携带同一次 attempt 的用量，而可选 cache 字段也不能证明精确总量。将局部小计显示成轮次用量，会让已记录的提供方事实显得比实际更完整。
Decision
共享 TokenUsage 值为一次模型调用携带可选的 totalTokens。适配器只从提供方精确总量，或权威的提示词与输出聚合计数发布该字段。DeepSeek 会将提示词加输出的聚合值与协议提供的总量核对，pi-ai 则保留其提供的总量。
token-meter 拥有一份可安全用于浏览器的纯轮次局部 fold，并与其具备重试感知能力的累计用量投影共享记账所有权。step/start 与 llm/retry-started 打开真实 attempt；最终 assistant 消息替换同一 attempt 的流式样本；终止失败、重试与步骤边界关闭 attempt，且不会重复计数。每个已开始的 attempt 都必须以安全的非负整数用量和精确总量关闭。只有每个参与聚合的 attempt 都报告时，才会显示可选的 cache、推理与路由聚合值；推理仍是输出的子集。
Web Chat 只选择已加载匹配窗口包含 turn/start 的 Turn，将该完整的持久事件窗口交给 token-meter fold，再渲染结果。完整且精确的结果通过现有 actions 上方、仅保留本地状态的 DisclosureRow 显示；证据不完整或矛盾时不显示该行。Chat 不拥有 token 记账状态机。
Alternatives considered
对相邻的会话累计值做减法。 不采用，因为分页、压缩、重试覆盖范围与投影完整性可能让相邻值无法比较；减法会推断任何调用都未报告的数据。
通过新的客户端会话投影发布历史单轮次值。 不采用，因为已加载的单轮次视图已经拥有所需的持久 attempt 事件，而随历史增长的投影会增加传输、持久化与版本成本。复用 token-meter 的纯 fold，可以在不新增 wire 值的前提下保持唯一记账所有方。
缺少精确总量时仍显示已知 bucket。 不采用，因为在已完成轮次 footer 中展示的下界小计与完整账单无法区分。
Consequences
新的提供方记录无需新增传输接口或持久化 UI 状态，即可显示精确的单轮次记账。证据不足的旧会话与适配器只会省略 disclosure。任一计费 attempt 缺少归属时，模型路由会整体消失，可信 token 总量仍可显示。
定向的适配器、token-meter fold／投影、组件、分页与组装 Web 回放测试固定了总量保留、重试 attempt 分离、fail-closed 校验、可选字段省略、交互与完整窗口发布。累计投影与精确 Turn fold 现在同归 token-meter 所有；投影仍是完整日志的 bucket 视图，只有 fold 会作出 disclosure 所需的更严格精确性与完整性声明。