[renrenmimi]

Branches from #9 (commit 2148ad8), so it can be merged before or after it, and independently of #10–#17.

It touches chapter 02 (app/functions/page.tsx, viz.tsx, lib/functions-data.tsx) and chapter 03 (app/narrowing/page.tsx, viz.tsx, lib/narrowing-data.tsx). It does not touch the three ORDER_* presets, which #14 owns.

Summary

Fixes from the 2026-10-09 content audit (04-TSer-内容.md):

• B3 (high)
  • What the chapter taught: a callback keeps narrowing only if the variable is "never reassigned anywhere in the function". This applied to the code note, the callout, the key point and the quiz.
  • Why that is wrong: it is the TypeScript 5.3 rule. Since 5.4, a callback created after the last assignment keeps the narrowing.
• B6: inferred type predicates (TS 5.5) were described as working "only for a short callback with one parameter". In fact a block-bodied declaration and a two-parameter arrow both get o is Paid.
• B12:
  • The claim: "TypeScript never adds behavior to the output. Type erasure is absolute." / 「类型擦除是铁律」.
  • Where it conflicts: chapter 08 teaches parameter properties, which do generate code.
• B15: "typeof never throws" is false for a let or const in its temporal dead zone.
• B23 (the ! operator): ! was called "a TypeScript annotation", while the term non-null assertion appeared only in the quiz.
• B21 (quiz titles): the quiz titles used 通关测验.
• B22 (register): colloquial Chinese, including 坑人, 一声不吭, 一刀切, 老老实实, 一场被夸大的战争, 吃的就是 and 挺过.
• A26 (these chapters): the signature segments, the guard cells and the order-status buttons did not expose their selected state.

Changes

• Chapter 03
  • Code note, callout and key point: they state the TS 5.4 rule. A callback keeps outside narrowing only if the variable is not assigned again after the callback is created.
  • Quiz: the question now places x = 42 after the if, at the end of the function, and every explanation follows the 5.4 rule.
  • Inferred predicates: the note and the task solution list the real conditions: no return type annotation, a single return, the parameter not modified, and true exactly when narrowed.
  • typeof: the explanation mentions the temporal dead zone.
  • !: it is introduced as 非空断言(non-null assertion).
• Chapter 02: the readonly explanation now says readonly is erased like every type annotation and adds no code.
• Both chapters: formal Chinese, 本章测验 / Chapter quiz, and aria-pressed on .fn-sig-seg, .nr-gx-cell and .nr-os-btn.

Verification

• npx tsc --noEmit --incremental false: clean.
• npm test: 6 files, 38 tests pass, including zh-copy-spacing.
• npm run build: succeeds.
• Rules checked with the lab worker on TypeScript 5.9.3 (during the audit):
  • An assignment before the callback gives no error.
  • The page's example, with value = 42 after the callback, reports TS2339 on string | number.
  • A function isPaidDecl(o) { const ok = …; return ok; } declaration and a (o, i) => … arrow are both inferred as o is Paid.
  • Two returns, or a non-iff test, give boolean.
  • typeof on a let before its declaration throws ReferenceError in Node 22.
• Headless Chrome against a local next start, both languages:
  • The new text is on the page, the old rule statements are gone, and there are 0 console errors.
  • Two of the new strings sit in wrong-answer explanations that appear only after a quiz answer. They were checked in the source.

🤖 Generated with Claude Code

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