docs(pm-dispatch): forbid the seat post's updated_at as a liveness proxy; add the runnable liveness reading

[os-support-ai]

Fixes#9790

What

.claude/skills/pm-dispatch/references/seat-post-protocol.md, the 无心跳/活性判定 bullet — two additions, per the card:

1. Explicit ban: ⛔ never infer liveness or death from the seat post's updated_at/title. The write side refreshes only at round boundaries by design, so a mid-round seat is stale-by-design on the post — the busiest seat looks deadest. The measured incident is described without card ids: a post 18h stale was reported "possibly dead" while the seat had 15 cards in flight with minutes-fresh outputs.
2. Runnable reading: liveness = the seat's latest platform-stamped output — one search of the lane's pm:dispatched cards sorted by updated_at desc, or the latest claim/ACCEPT/audit comment timestamp; minutes-fresh card churn = alive, whatever the post says.

Ratchet payment (file was 101/101, headroom 0 — every added line paid in the same file)

Net addition: the 活性判定 bullet grew 5 → 8 lines (+3). Paid by three 1-line true-dedup cuts; reflow happened only at cut points, no untouched bullet was re-wrapped.

Cut (content removed)	Lines	Surviving copy (named)
Intro: 「多写手共编一个 body 机制上防不住互吞,所以架构是每个座位一张登记贴(维护者 2026-08-06 拍板)」 — the intro keeps its pointer that principles live in the main file, now naming the ruling date	−1	SKILL.md §座位贴协议 first sentence, verbatim incl. the 2026-08-06 ruling
写侧刷新点 bullet: 「中途状态由卡上 claim/ACCEPT 评论承载(本就是 state of record),⛔ 不逐事件回写贴正文」 — replaced by a one-clause pointer	−1	SKILL.md §座位贴协议 carries the clause verbatim; the ⛔ 不逐事件 norm also survives in this file's own 班次叙事 bullet
交接收尾清单 ⑥ʹ/⑦: the account-scope not found explanation (kept: the norm + 账号作用域 + runbook pointer); 「零建议是好班次」 trimmed to a main-file pointer; minor compression of the 欠账 clause	−1	dispatch-runbook.md §监控与转向 (「对另一账号建的会话一律 not found」); SKILL.md 换班报告默认零建议 + 三类上报纪律
In-bullet (part of the +3 accounting): 「子树/批次里在飞的认领仍由原认领者跟完」 cut; 「分诊 Routine 每 fire 附带的座位贴活性巡查,同一 >24h 判据」 compressed to 「分诊轮的座位贴活性巡查,同一判据」	in-bullet	dispatch-runbook.md §座位贴活性巡查 (「在飞认领照认领协议由原认领者跟完」; fire cadence + the >24h criterion 「与既有回收线同一条」); this file's own Epic section carries the in-flight-claims rule too

Result: 101/101, headroom 0.

Gates (all at final head 780cbb5, exits captured)

Derived with node scripts/pm/dispatch-gates.mjs (no paths passed; changeset from merge base ca19ee81f) — 6 families matched, all run locally, all exit 0:

• pnpm check:pm-skill-ratchet — exit 0 (seat-post-protocol.md is 101 lines (ceiling 101; headroom 0))
• pnpm check:pm-skill-id-lint — exit 0 (9 files clean; no issue-ID citations added)
• pnpm check:doc-authoring — exit 0 (377 files clean)
• pnpm --filter @objectstack/lint run check:doc-formula-expressions — exit 0 (after building @objectstack/formula deps)
• pnpm check:pm-governed-merges — exit 0 (self-test, 77 assertions)
• pnpm check:skill-frame-sync — exit 0
• node scripts/check-nul-bytes.mjs — exit 0 (6245 files, no raw control bytes)

Governed surface

This PR touches .claude/skills/** — DRAFT, human merge only (Prime Directive #14). Do not queue, arm auto-merge, or flip out of draft.

Tests-/protocol-text-only change: skip-changeset label applied.

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