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>

e2e/tests/pong.spec.mjs

@@ -0,0 +1,75 @@
+// Pong (pong.html) on every track, judged against the pure model.
+import { test, expect, TRACKS } from '../lib/app.mjs'
+
+// The player's paddle is the white 8 x 64 rect in column 2 (x = 16); its top row in cells is y / 8.
+const lastScene = (shapes) => shapes.slice(Math.max(0, shapes.findLastIndex((s) => s.tag === 'Rect' && s.w === 640)))
+const paddleOf = (shapes) => lastScene(shapes).find((s) => s.tag === 'Rect' && s.x === 16 && s.h === 64).y / 8
+const textsOf = (shapes) => lastScene(shapes).filter((s) => s.tag === 'Text').map((s) => s.text)
+
+for (const track of TRACKS) {
+  test.describe(`${track}: pong`, () => {
+    test('holding and releasing keys moves the paddle as the model says', async ({ app }) => {
+      const a = await (await app(track, 'pong')).start()
+      const p0 = paddleOf(await a.expectInSync())
+      await a.down('ArrowUp')
+      await a.advance(300)
+      const p1 = paddleOf(await a.expectInSync('holding ArrowUp'))
+      await a.up('ArrowUp')
+      await a.advance(300)
+      const p2 = paddleOf(await a.expectInSync('released'))
+      await a.down('ArrowDown')
+      await a.advance(600)
+      const p3 = paddleOf(await a.expectInSync('holding ArrowDown'))
+      await a.up('ArrowDown')
+      await a.advance(100)
+      await a.expectInSync('released again')
+      // One cell per 30 ms game frame while held, none after release.
+      expect(p0).toBe(21)
+      expect(p1).toBeLessThan(p0)
+      expect(p2).toBe(p1)
+      expect(p3).toBeGreaterThan(p2)
+    })
+
+    test('a whole match on the fake clock ends with the model\'s score and the right winner text', async ({ app }) => {
+      const a = await (await app(track, 'pong')).start()
+      // A simple player: every 90 ms, hold the key that brings the paddle's middle toward the ball.
+      let held = null
+      for (let i = 0; i < 1000 && a.state.status === 'Playing'; i++) {
+        const { ball, player } = a.state
+        const want = player + 4 < ball.y - 1 ? 'ArrowDown' : player + 4 > ball.y + 1 ? 'ArrowUp' : null
+        if (want !== held) {
+          if (held) await a.up(held)
+          if (want) await a.down(want)
+          held = want
+        }
+        await a.advance(90)
+        if (i % 10 === 0) await a.expectInSync(`match, ${i * 90} ms`)
+      }
+      if (held) await a.up(held)
+      await a.advance(500)
+      const end = await a.expectInSync('match over')
+      const { score } = a.state
+      expect(a.state.status).toBe('Over')
+      expect(Math.max(score.player, score.cpu)).toBe(5)
+      expect(textsOf(end)).toEqual(expect.arrayContaining([`${score.player}   ${score.cpu}`,
+        score.player > score.cpu ? 'You Win!' : 'CPU Wins', 'Press R to restart']))
+    })
+
+    test('R restarts and keeps a held key', async ({ app }) => {
+      const a = await (await app(track, 'pong')).start()
+      await a.advance(300)
+      await a.down('ArrowDown')
+      await a.advance(150)
+      const before = paddleOf(await a.expectInSync('holding ArrowDown'))
+      await a.press('r')
+      const restarted = paddleOf(await a.expectInSync('after R'))
+      await a.advance(300)
+      const after = paddleOf(await a.expectInSync('after R, still holding'))
+      await a.up('ArrowDown')
+      await a.expectInSync('released')
+      expect(before).toBeGreaterThan(21)
+      expect(restarted).toBe(21)
+      expect(after).toBeGreaterThan(21)
+    })
+  })
+}