docs(pm): make the merged-PR read the primary leg of the stale-claim test (#13968)

The dead-claim reclaim paragraph established staleness from two proxies
(promised branch absent + no PR), and both fail toward "nothing landed"
in a squash-merging, delete-on-merge repo family. The primary leg is now
the direct read: search PRs that reference the card and read their
merged/merged_at — not the closes-list, which is empty exactly when a
partial PR deliberately wrote Refs instead of Fixes. Branch absence and
commit-message scans demote to corroboration that can only support a
stale verdict, never establish one alone; zero referencing PRs means
stop and ask, never "nothing landed". Rescue-first precondition, the
message-boundary clause and the live-branch never-reclaim rule are
untouched.


Claude-Session: https://claude.ai/code/session_01Msg17tAHJ3jVTYFgHydCm2

Co-authored-by: Claude <noreply@anthropic.com>

Author: os-sam

.claude/skills/pm-dispatch/SKILL.md

@@ -551,7 +551,10 @@ pin 前置等运维细则见 `references/seat-post-protocol.md`)。** 判据二
    依赖路径、已确认的坑、在飞同文件PR、区域申报、串行约束),赢家不必重扫。
 
 dev 侧早推分支 —— 远程分支是在飞工作最硬的证据。**死认领回收(stale-claim reclaim)**:
-认领 >~24h、承诺分支不存在、无 PR ⇒ 死认领 —— **回收前先救工作树**:
+认领 >~24h ⇒ 疑死;**判死主腿 = 搜引用本卡的 PR、读其 `merged`/`merged_at`** —— ⛔ 不读
+closes-list:部分交付 PR 特意写 Refs 而非 Fixes 时它恰为空,正是两条代理读数同漏的形状。
+承诺分支缺席与提交扫描失效同向「没落地」,只能支持判死、永不单独确立;零引用 PR ⇒
+停下发问,⛔ 不判「什么都没落地」。判死后 —— **回收前先救工作树**:
 **存活前置**:向任何派发 worktree 提交前(任何 actor)先过存活/所有权检查,
 或对树最新 mtime 过明确年龄阈值;⛔ 不凭 GitHub 侧静默动手 —— 零提交、零推送、无 PR,
 在干活但未推的席位给出同一组信号:未提交改动是在飞工作的证据,不是死亡的证据。