feat(course): audit fixes and twelve extensions (Modules 7b, 12, 13)

Audit pass:
- Frame rule counts frames since the last move, so every step lasts
  exactly movesEvery(score) frames, also right after a speed-up
- clampTime + MAX_GAP_MS: a hidden tab no longer replays the whole gap
- Pong Restart keeps held keys
- Fact corrections (mulberry32 output coverage, Haskell IO, uniform)
- New fixture cases from a mutation analysis

Extensions (all three tracks, shared fixtures, course text):
- Turn queue (Exercise 10.6), persisted high score (10.7),
  replay viewer (10.8), play() end-to-end helper (9.5)
- Optional State (4.7) and optional Module 7b, stack-safe IO
- Module 12, property-based testing with generators, shrinking,
  invariants and a model-based oracle
- Module 13, Conway's Life with a Click event
- JS type checking via jsconfig, JSDoc and types.d.ts
- Maintainer tools: scripts/mutate.mjs, scripts/typecheck-js.sh,
  Playwright end-to-end suite (e2e/, scripts/e2e.sh)

Docs: docs/contract.md is the canonical contract; specs and build log
under docs/superpowers.

Verified: JS 728, Scala 689, F# 691 unit tests; stubs and progression
M01-M13 and M07b; 176 end-to-end tests on Chromium and WebKit.

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>

js/test/purity.test.js

@@ -7,7 +7,8 @@ import { dirname, join, basename } from 'node:path'
 const srcDir = join(dirname(fileURLToPath(import.meta.url)), '..', 'src')
 
 // Files that are allowed to touch the outside world.
-const excluded = (file) => ['runtime.js', 'browser.js', 'main.js'].includes(basename(file))
+// The entry files (main.js, life/main.js, pong/main.js and the replay viewer's replay-main.js) are given browser glue.
+const excluded = (file) => ['runtime.js', 'browser.js', 'main.js', 'replay-main.js'].includes(basename(file))
 
 const banned = [
   ['let', /\blet\b/],
@@ -32,6 +33,7 @@ const banned = [
 const stripComments = (code) => code.replace(/\/\*[\s\S]*?\*\//g, '').replace(/\/\/.*$/gm, '')
 const violations = (code) => banned.filter(([, re]) => re.test(stripComments(code))).map(([name]) => name)
 
+// Only JavaScript is scanned. src/types.d.ts (the optional type declarations) holds no code that runs, so it is skipped.
 const jsFiles = (dir) =>
   readdirSync(dir, { withFileTypes: true }).flatMap((e) =>
     e.isDirectory() ? jsFiles(join(dir, e.name)) : e.name.endsWith('.js') ? [join(dir, e.name)] : [])
@@ -74,6 +76,9 @@ jsFiles(srcDir)
     test(`purity: ${f.slice(srcDir.length + 1)} has no banned constructs`, () =>
       assert.deepEqual(violations(readFileSync(f, 'utf8')), [])))
 
+test('the purity audit skips .d.ts files', () =>
+  assert.deepEqual(jsFiles(srcDir).filter((f) => f.endsWith('.d.ts')), []))
+
 // helpers.js is loaded by every test file; importing src/ there would make all tests fail at load time against the stubs.
 test('test/helpers.js imports nothing from src/', () =>
   assert.doesNotMatch(readFileSync(join(dirname(fileURLToPath(import.meta.url)), 'helpers.js'), 'utf8'), /from\s+['"][^'"]*src\//))