docs(pm-skills): the strip prescription costs the session id — name it on the write-side footer cell

The write-side footer cell already carries the mechanism on both sides: a bare
REST `PATCH /pulls` appends a bare footer and keeps an existing session-URL one
(+58 B), and sending a footer-less body the same way stores back exactly one —
the platform's bare form. What it did not carry is what that costs: the bare
form has no session id, so a body stripped per this cell's own prescription no
longer records which session wrote it. One row, paid in place.

Retired to pay for it: the note that the footer-deleting reading is the only
observation off the criterion and its channel is denied. Its content survives in
the same cell — the denied channel and its history reading one row up, and the
read-back-after-every-write obligation two rows down.

Claude-Session: https://claude.ai/code/session_01Gqi43smmqjJ5sUrhfoPeKu
Co-authored-by: Claude <noreply@anthropic.com>

Author: os-justin

.claude/skills/pm-dispatch/references/platform-readings.md

@@ -345,12 +345,12 @@
 - 裸 REST `PATCH /pulls` 追加一个裸页脚并保留既有 session-URL 页脚,差恰 58 字节。
 - 同路送无页脚正文存回恰一条(平台裸形)⇒ 该格处方是不送页脚,⛔ 不是不重送正文。
 - 页脚两拼写:裸版与 session-URL 版都要剥,漏剥的卡在正文中段,而 58 字节差照常。
+- ⇒ 代价是归属:裸形无 session id,按此剥净的 PR 正文不载明哪个会话写的;另置见 AGENTS.md。
 - 第四形:建 PR 两通道同判 —— 送出体尾部不是 `---` 加页脚块时,追加一条同形页脚。
 - 该追加带前置横线、恰 90 字节,送出体是存储体的严格前缀。
 - 尾部已是该块则一字不追加,两通道各实测两向 ⇒ 建侧通道不是变量,判据是送出体尾部。
 - ⛔ 无受控对照(同通道只差该块两送)⇒ 是拟合不是定论,⛔ 不外推到别的动作。
 - 调用不带 `body` 参数则页脚状态不动:`draft` 或 `title` 单字段更新既不删也不合成。
-- 删页脚那条读数是唯一不合此判据的观察,通道已拒 ⇒ 活通道无反例,写后仍必回读。
 - 正文把 harness 两行块叠在页脚之上,存回是三条署名块;单块形态才复现成一条。
 - ⇒ 形态随动作与送出体尾部变,改侧还随通道变;⛔ 不由任一条推其余,写后必回读。
 - 平台在尾部 `---` 前后正反两向归一空行:比对正文只按首个差异偏移,⛔ 不按长度。