docs(agents): point os-dev.md at AGENTS.md's body-mutation clause instead of a narrow local copy (#9838)

The sanitizer's shape was described twice: AGENTS.md carries the binding
body-mutation clause ("GitHub mutates body BYTES - spell poison-shaped
tokens out in words, never literally"), which names the two measured
mutation shapes and points at the pm-dispatch reading ledger for their
triggers. os-dev.md carried an older, narrower restatement that knew only
one member of that family, so the local copy was already drifting behind
its authoritative home.

Replace the local shape description with a one-line pointer at AGENTS.md's
clause - one rule, one home. The operative os-dev-specific instructions
around it are untouched: the attribution-footer form and its code block
stay, as does the separate instruction to read back your own report comment
after posting it.


Claude-Session: https://claude.ai/code/session_01AeA3nU1B5Q2pgxqxgUrexd

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

Author: os-warren

.claude/agents/os-dev.md

@@ -338,10 +338,9 @@ Your recommendation must be justified on all four axes;四轴冲突时如实呈
 `scripts/check-nul-bytes.mjs` 头部 —— 引用它,别重推。push 前跑它;改动哪怕只是提到控制
 字符,就在门禁之外自扫(`grep -naP '[\x00-\x08\x0b\x0c\x0e-\x1f\x7f]' <files>`)。
 
-GitHub 正文 sanitizer 是同一纪律的另一半:它把 `<` 后跟字母当 HTML 标签剥掉,**落库时**
-生效,issue 与 PR 正文一视同仁 —— 摧毁 TypeScript 泛型,并在裸 `<word` 之后静默截断散
-文。泛型在每个 `<` 后加空格,PR/issue 散文避开 `<`+字母,片段承重时读回落库后的正文。署
-名页脚必须用 **session-URL** 形式:
+GitHub 正文 sanitizer 是同一纪律的另一半 —— 形状、触发条件与作者纪律都归 AGENTS.md 的
+「GitHub mutates body BYTES」条款(一条规则一个家;此处不再复制窄版)。署名页脚必须用
+**session-URL** 形式:
 
 ```text
 _Generated by [Claude Code](https://claude.ai/code)_                ← stripped on every edit