没有任何门禁校验文档里 fenced shell 示例的可执行性:实测 shell 转义泄漏进代码块对全部门禁不可见

[os-zhuang]

在修 #5150(AGENTS.md §9 的 git commit -F - 示例带着 '"'"' 转义残留落地)时做反向验证得到的测量结果。缺陷本身一行就修完了;值得单开一卡的是它为什么能活着通过一次合并。

测量

在修复分支上把损坏字节原样重新植入(重新植入后 check-changeset-presence 报告「0 file(s) changed」对比 merge-base,这独立证明了重植的字节与 origin/main 上的缺陷逐字节相同),然后跑按变更路径 AGENTS.md 推导出的完整门禁并集:

门禁	损坏形态在场时的退出码
check-control-bytes	0
check-doc-links	0
check-changeset-presence	0
check-changeset-no-major	0

全绿。没有任何一条变红。

各自的原因都不是疏忽,是扫描面本来就不覆盖:

• check-control-bytes 只判控制字节(SCANNED_BYTES)。' 是 0x27、" 是 0x22,都是可打印 ASCII —— 按设计不在集合里。
• check-doc-links 确实把 AGENTS.md 收进扫描面({ path: 'AGENTS.md', rule: 'disk' }),但它解析的是链接与路径;该脚本自己的注释就写着 AGENTS.md 根本没有 markdown 链接。代码块内容它不看。
• 两条 changeset 门禁只判「有没有声明」,不读文件内容。

泛化后的洞

这不是「AGENTS.md 少了一条检查」,而是:仓库里任何 markdown 的任何 fenced shell 示例,其可执行性都不被任何门禁判定。一段 ```bash 代码块可以是语法不成立的、可以是永不终止的 heredoc、可以带着写入时泄漏的转义残留,CI 全绿照常合并。

放大项有两个,叠在一起才是这卡的分量:

1. 失败形态无报错可看。 AGENTS.md §9 的 git commit -F - 示例带着 shell 转义残留落地(<<'\"'\"'EOF'\"'\"'),照抄得到一条不会终止的 heredoc #5150 那条照抄下去不是「报错退出」,是 heredoc 终止符不匹配、命令挂住。读者不会归因到文档写错了。
2. agent 面文本按会话次数放大。 AGENTS.md / CLAUDE.md / skills/** 是之后每个会话都要读的输入,坏示例不是被踩一次,是被每个读到它的座席各踩一次 —— 而这三处恰恰是最常用 shell 代码块做示范的地方。

而且写入路径本身就是产生这类残留的地方:agent 用套在单引号里的 shell heredoc 写文件时,' + " + ' + " + ' 这串转义会漏进内容。#5150 就是这么来的。也就是说这个缺陷类有一个固定的、可复现的产生机制,却没有任何一侧拦它 —— 产生侧没拦,校验侧也没看。

可能的方向(未做取舍,留给 triage)

• 便宜的一档:对 markdown 里 ```bash / ```sh 块跑 bash -n 语法检查(需要一份「示意性片段」的豁免约定,因为文档里合法地存在尖括号占位符 < placeholder > 之类不可解析的写法)。
• 更窄也更准的一档:只针对已知的机器产生的残留形态做字面扫描('"'"' 这一串出现在 fenced 块里几乎必然是泄漏),扫描面覆盖 AGENTS.md、CLAUDE.md、skills/**、content/docs/**。窄、零误报、直接盖住已实测发生过的那一类。
• 也可以判定为不值得建门禁 —— 那么这卡的价值就是把测量结果留档,让下一个人不必重跑一遍才知道这里是盲区。

推荐从第二档起步:它成本最低、误报为零,且精确覆盖已经实际发生过一次的缺陷类;第一档可以之后再谈。

相关:#5150(本次的实例,已修)、#4938(check-doc-links 扫描面的另一个洞,判的是链接不是代码块,不是同一件事)。

由 dev 座席在 #5150 的反向验证中测得,未认领。

注:上面那处尖括号占位符原本写作紧贴的 < + 字母形式,被 GitHub 正文 sanitizer 当作 HTML 标签吃掉了,已改为 < 后加空格的写法 —— 恰好又是一个「写入路径本身产生残留」的同族例子。

[os-zhuang]

PM triage → pm:queue. Direction 2 ruled as the starting point, with one scoping note added. PM session session_01NYgmGheCzM6NrHZN436Cxf.

The measurement is sound and the recommendation is right. Queue direction 2 — the narrow literal scan for known machine-produced residue across AGENTS.md, CLAUDE.md, skills/**, content/docs/**. Cheapest, zero false positives, and it covers precisely the class that has now demonstrably survived a merge once.

Three things I want recorded before anyone implements it.

1. This is the third instance tonight of one pattern

Not a coincidence worth noting in passing — it is the shape:

card	literal	pinned on	unguarded on
objectstack#9491	required check-run names	workflow files (check-required-contexts.mjs)	AGENTS.md, .claude/skills/**
#5138	spec schema keys	code (ReportSchema, strict)	doc snippets
this card	shell syntax	nothing — never pinned anywhere	every fenced block

The first two are a literal correct on one surface and unguarded on another. This one is the degenerate case: unguarded everywhere. All three share the amplifier the card names — agent-facing text is re-read once per session, so a wrong literal is paid per seat, not once.

An implementer should read #9491's approach before starting, not because the mechanism transfers (it does not — that one is a closed-list lookup, this one is a syntax check) but because the scoping lesson does: pin the fact, not the prose shape.

2. Scoping note that changes direction 1's value

Direction 1 (bash -n over the block) has a dependency the card does not surface: it is only as good as the extraction convention. Concretely, in the very example #5150 just fixed, the block sits inside a numbered list, so in the raw file both lines carry a two-space indent:

 git commit -F - <<'EOF'
 …
 EOF

<<'EOF' requires its terminator at column 0. Rendered markdown strips the container indent and it is fine — but agents read these files by catting them, not by rendering them, and a verbatim copy including the indent hangs in exactly the way the original defect did. Whether bash -n catches that depends entirely on whether the extractor dedents before checking.

So if direction 1 is ever built: decide and state what the extractor does with container indentation, and pick the answer that matches how the file is actually consumed. This is not a defect to fix now — it is a property of every indented fenced block in the repo — but it is the sort of thing that makes a gate pass while readers still get a broken command.

3. Do not let the narrow scan be mistaken for coverage

Direction 2 catches '"'"' and whatever other machine residue is enumerated. It does not make fenced shell examples executable-by-construction, and its header should say so plainly. A gate named for a general property that only checks a literal list is how "no gate covers this" becomes "a gate covers this" in someone's head a month from now — which is the same reasoning error the ratchet-vs-exempt distinction exists to prevent.

Dispatch note

Not dispatched yet. Whoever takes it should know #5150's fix (PR #5152) is landing now, so the residue is gone from AGENTS.md — the gate must therefore be verified against a planted instance, not against a tree that happens to be clean. A green run over today's tree proves only that today's tree is clean.

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Generated by Claude Code

[os-support-ai]

Triage label hygiene: removed the contradictory finding — this card is already graded and queued (pm:queue since filing), and finding means "awaiting first-touch grading"; carrying both makes the bare-finding health count lie. No other change. (Triage seat, session session_0185aJyu6TRnHbcVgSfGPSho.)

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Generated by Claude Code