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/m10-replay.test.js

@@ -0,0 +1,106 @@
+import test from 'node:test'
+import assert from 'node:assert/strict'
+import {
+  REPLAY_MS, frames, viewerStart, ViewerAction, viewerUpdate, viewerKey, viewerView, replayActions, viewerStates, replayMain,
+} from '../src/replay.js'
+import { history } from '../src/game.js'
+import { newGame } from '../src/spawn.js'
+import { view } from '../src/view.js'
+import { run } from '../src/stream.js'
+import { trace } from '../src/io.js'
+import { loadFixture, freeze } from './helpers.js'
+
+const fixtureTests = (name, f) => {
+  const fx = loadFixture(name)
+  fx.cases.forEach((c) =>
+    test(`m10 ${fx.function}: ${c.name}`, () => assert.deepStrictEqual(f(...freeze(c.args)), c.expected)))
+}
+
+fixtureTests('m10-viewer-update', viewerUpdate)
+fixtureTests('m10-viewer-key', viewerKey)
+fixtureTests('m10-viewer-view', viewerView)
+
+// The sample recording, as the page loads it. Not a fixture of cases: a recording `{seed, actions}`.
+const sample = freeze(loadFixture('replay-sample'))
+
+const time = (t) => ({ tag: 'Time', t })
+const key = (k) => ({ tag: 'KeyDown', key: k })
+const shapes = (io) => trace(io, 0).ops.map((o) => o.shape)
+
+test('m10 the sample recording is worth watching: Tick and Turn only, under 400 actions, at least five apples, then game over', () => {
+  assert.ok(sample.actions.every((a) => a.tag === 'Tick' || a.tag === 'Turn'))
+  assert.ok(sample.actions.length >= 150 && sample.actions.length <= 400, `${sample.actions.length} actions`)
+  const fs = history(newGame(sample.seed), sample.actions)
+  assert.ok(fs.at(-1).score >= 5, `score ${fs.at(-1).score}`)
+  assert.equal(fs.at(-1).status, 'GameOver')
+  assert.equal(fs.at(-2).status, 'Playing')
+})
+
+test('m10 frames replays the recording with history, from the new game of its seed', () => {
+  const recording = freeze({ seed: 42, actions: [{ tag: 'Tick' }, { tag: 'Turn', dir: 'Up' }, { tag: 'Tick' }] })
+  assert.deepStrictEqual(frames(recording), history(newGame(42), recording.actions))
+  assert.equal(frames(sample).length, sample.actions.length + 1)
+})
+
+test('m10 viewerStart is the first frame, not playing', () =>
+  assert.deepStrictEqual(viewerStart(12), { index: 0, last: 12, playing: false }))
+
+test('m10 ViewerAction has the six actions as plain values', () =>
+  assert.deepStrictEqual(
+    [ViewerAction.Next, ViewerAction.Prev, ViewerAction.First, ViewerAction.Last, ViewerAction.TogglePlay, ViewerAction.Beat],
+    [{ tag: 'Next' }, { tag: 'Prev' }, { tag: 'First' }, { tag: 'Last' }, { tag: 'TogglePlay' }, { tag: 'Beat' }]))
+
+test('m10 viewerUpdate keeps the index in [0, last] whatever the actions', () => {
+  const actions = [ViewerAction.Prev, ViewerAction.Next, ViewerAction.Last, ViewerAction.Next, ViewerAction.TogglePlay,
+    ViewerAction.Beat, ViewerAction.Beat, ViewerAction.First, ViewerAction.Prev, ViewerAction.Beat]
+  const viewers = actions.reduce((acc, a) => [...acc, viewerUpdate(acc.at(-1), a)], [freeze(viewerStart(3))])
+  assert.ok(viewers.every((v) => v.index >= 0 && v.index <= 3 && !(v.playing && v.index === 3)))
+})
+
+test('m10 the autoplay clock beats every 100 ms', () => assert.equal(REPLAY_MS, 100))
+
+test('m10 replayActions turns the clock into Beats and keys into viewer actions', () =>
+  assert.deepStrictEqual(
+    run(replayActions, freeze([time(100), key('ArrowRight'), key('x'), key(' '), time(300)])),
+    [ViewerAction.Beat, ViewerAction.Next, ViewerAction.TogglePlay, ViewerAction.Beat, ViewerAction.Beat]))
+
+test('m10 autoplay: Space, then the clock steps one frame per 100 ms and stops at the end', () => {
+  const out = run(viewerStates(3, replayActions), freeze([time(0), key(' '), time(100), time(200), time(300), time(400), time(500)]))
+  assert.deepStrictEqual(out.map((v) => v.index), [0, 0, 1, 2, 3, 3, 3])
+  assert.deepStrictEqual(out.map((v) => v.playing), [false, true, true, true, false, false, false])
+})
+
+test('m10 without Space nothing plays: the clock alone never moves the viewer', () =>
+  assert.ok(run(viewerStates(3, replayActions), freeze([time(0), time(1000), time(2000)])).every((v) => v.index === 0)))
+
+test('m10 replayMain asks for nothing and draws the first frame of the recording first', () => {
+  const { ops, result: stream } = trace(replayMain(sample), 0)
+  assert.deepStrictEqual(ops, [])
+  const [drawings] = stream.step(time(0))
+  assert.equal(drawings.length, 1)
+  assert.deepStrictEqual(shapes(drawings[0]), viewerView(frames(sample), viewerStart(sample.actions.length)))
+  assert.deepStrictEqual(shapes(drawings[0]).slice(0, view(newGame(sample.seed)).length), view(newGame(sample.seed)))
+})
+
+test('m10 replayMain: End shows the last frame of the game, the game over', () => {
+  const out = run(trace(replayMain(sample), 0).result, freeze([time(0), key('End')]))
+  const fs = frames(sample)
+  assert.deepStrictEqual(shapes(out.at(-1)), viewerView(fs, { index: fs.length - 1, last: fs.length - 1, playing: false }))
+  assert.ok(shapes(out.at(-1)).some((s) => s.tag === 'Text' && s.text === 'Game Over'))
+})
+
+test('m10 stepping back shows exactly the earlier scene', () => {
+  const out = run(trace(replayMain(sample), 0).result,
+    freeze([time(0), key('ArrowRight'), key('ArrowRight'), key('ArrowRight'), key('ArrowLeft'), key('d'), key('a'), key('a')]))
+  const scenes = out.map(shapes)
+  assert.deepStrictEqual(scenes[4], scenes[2])
+  assert.deepStrictEqual(scenes[6], scenes[4])
+  assert.deepStrictEqual(scenes[7], scenes[1])
+  assert.notDeepStrictEqual(scenes[3], scenes[2])
+})
+
+test('m10 replayMain: after ten seconds in a background tab autoplay moves 2 frames (250 ms), not 100', () => {
+  const [, afterPlay] = trace(replayMain(sample), 0).result.step(key(' '))
+  const [, afterFirst] = afterPlay.step(time(0))
+  assert.equal(afterFirst.step(time(10000))[0].length, 2)
+})