docs(skill): counting a proxy is the twin of a substring search

The previous commit corrected the record and the rule it drew did not reach the
skill, because the anchor had shifted. It is there now, as item 7 beside "a
criterion must not be a substring search":

  counting code blocks to decide whether alternatives are offered at equal
  weight; counting headings that contain a word to decide which chapter owns a
  topic. The number is real and the thing counted is not the property -- and
  because the number is real, review does not catch it.

With the three instances from this batch recorded beside it, so the shape is
recognisable rather than abstract.

Author: speak-agent

.agents/skills/mcpp-docs-style/SKILL.md

@@ -260,6 +260,14 @@ docs/specs/    ──▶ docs/              允许
 6. **过期的判据不要用子串搜索。** 「grep 到这个词就算讲过了」会在有人改一次
    措辞时静默变空转。要判断一份文档是否覆盖某个能力,读**结构化的东西** ——
    示例的 `mcpp.toml`、源码里的键表、`print_usage()` 的正文。
+7. **也不要数一个代理量。** 子串搜索的孪生形态:数**代码块个数**来判断「是不是把
+   几种做法并列了」、数**含某词的标题**来判断「哪一章拥有这个主题」。数字是真的,
+   而被量的对象不是那个性质 —— **正因为数字是真的,评审很难发现**。判据要直接指向
+   性质:并列的替代由「alternatively / 也可以 / 等价写法」这类**并列标记**识别,
+   主题归属由「这一节是不是在解释它」识别。
+   
+   本轮三次同形:用含 test 的标题数「哪几章解释测试」、用字面拼写查反查索引、用
+   代码块数量查并列替代。三次的数字都对,三次量的都不是那个性质。
 
 ## 九、梯度:一个主题的五级台阶,以及只链接相邻级