subagent: carry inherited policy overrides in the child session header

Review fix (ds-review-bot critical #2 on #623): the first-turn event stamp
had a durability hole no turn anchoring can close — an idle SessionStart-
style injection persists a complete one-shot turn before any prompt turn
opens, so a crash in that window left a resumable-looking child with no
inherited policy, falling back to a possibly wider deployment default.

The captured overrides now ride the child's creation meta into its
immutable SessionHeader (sandboxMode/approvalPolicy, neutral strings at the
session boundary — the delegationDepth precedent), durable from the moment
the session exists: no listener ordering can starve the baseline and no
crash window can lose it. overrideOf(session) on both policy services
resolves fold(events past header.seedLength) ?? header baseline, validating
against the closed vocabulary on read; stampOverride and the prompt-submit
listener machinery are deleted. The header field rides both persistence
backends (JSONL header line; SQLite sessions columns, SCHEMA_VERSION 11 —
pre-release, no migration). pty-local reads through overrideOf so PTY
spawns see the baseline too.

Red-first: header-durability-before-any-turn test (the injection crash
window shape), baseline/seed-boundary/closed-vocabulary contract tests in
both service suites; the real-wall suite (race, veto, fork stale-seed,
grandchild) re-anchored on header assertions and green. The Agent Note's
Alternatives now records the superseded event-stamping iteration with the
review evidence; bilingual docs updated.

packages/ui/user-approval/README.zh.md

@@ -8,7 +8,7 @@
 
 应答者是 `approval/request` waterfall（瀑布式事件）监听器。要回答所拥有 agent 的请求，请返回一个结果；否则调用 `next()` 委托。限定到 agent 的监听器只接收该 agent 的请求；每项部署应当组合一个终端应答者，因为同级监听器的顺序不是策略优先级机制。ACP（Agent Client Protocol）自动化桥接层为其拥有的会话提供一次性机器决定。
 
-`ApprovalPolicy` 为 `'ask'` 或 `'never'`。实际值取最后一条 `approval/policy` 事件，并回退到配置；`setApprovalPolicy()` 是写入路径。`'never'` 会在交互式分发之前拒绝请求，也是提示词中唯一声明的策略。切换最多产生一条合并通知：如果覆盖发生在最后一个 `request/header` 之后，则归因于用户；否则归因于操作方／配置。`ctx.approval.overrideOf(session)`／`ctx.approval.stampOverride(child, policy)` 是委派继承的两半：仅折叠本身（绝不包含配置默认值），以及通过该写入路径写入捕获的覆盖项；进程内 subagent 驱动器在委派时捕获，并在子 agent 的第一个轮次内盖章，使 `'never'` 父级无法造出会弹出提示的子 agent（参见[设计原理](../../../.agents/notes/implemented/feature/2026-07-25-subagent-policy-inheritance.md)）。
+`ApprovalPolicy` 为 `'ask'` 或 `'never'`。实际值取最后一条 `approval/policy` 事件，并回退到配置；`setApprovalPolicy()` 是写入路径。`'never'` 会在交互式分发之前拒绝请求，也是提示词中唯一声明的策略。切换最多产生一条合并通知：如果覆盖发生在最后一个 `request/header` 之后，则归因于用户；否则归因于操作方／配置。`ctx.approval.overrideOf(session)` 解析会话的覆盖链，绝不包含配置默认值：先折叠会话自己的切换（`SessionHeader.seedLength` 之后的事件），否则取会话头中继承的 `approvalPolicy` 委派基线，读取时按封闭词汇校验；进程内 subagent 驱动器在委派时捕获该值，并写入每个子 agent 创建时的会话头，使 `'never'` 父级无法造出会弹出提示的子 agent，且不存在任何第一轮次的时序窗口（参见[设计原理](../../../.agents/notes/implemented/feature/2026-07-25-subagent-policy-inheritance.md)）。
 
 工具流水线通过此 seam 路由 `ask` 决定，并在该 seam 缺失时以拒绝方式关闭；沙箱 bash 工具也会将它用于升权重试。ACP 自动化桥接层根据客户端的机器策略，回答其自有 agent 的调用。审计事件仍只写入日志，因此模型只会看到发起请求的消费方所返回的结果。详见[审批 seam Agent Note（agent 决策记录）](../../../.agents/notes/implemented/feature/2026-07-06-approval-seam.md)和[沙箱 Agent Note](../../../.agents/notes/implemented/feature/2026-07-06-sandbox.md)。