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/solutions/pong/app.js

@@ -3,7 +3,9 @@ import { initialPong, PongAction } from './model.js'
 import { pongUpdate } from './rules.js'
 import { pongView } from './view.js'
 import { map as mapIO, randomSeed, drawScene } from '../io.js'
-import { keyDowns, keyUps, interval, map, filterMap, merge, scan, startWith } from '../stream.js'
+import { keyDowns, keyUps, interval, map, filterMap, merge, scan, startWith, clampTime } from '../stream.js'
+import { MAX_GAP_MS } from '../app.js'
+/** @import { PongState, Stream, Program } from '../types' */
 
 export const FRAME_MS_PONG = 30
 
@@ -13,19 +15,23 @@ const keys = {
 }
 
 // hasOwn, not `key in keys`: "constructor" and "toString" are inherited, not keys we mapped.
+/** @type {(isDown: boolean, key: string) => PongAction | null} */
 export const pongKey = (isDown, key) =>
   Object.hasOwn(keys, key) ? (isDown ? PongAction.Press : PongAction.Release)(keys[key])
     : (key === 'r' || key === 'R') && isDown ? PongAction.Restart
     : null
 
+/** @type {Stream<PongAction>} */
 export const pongActions = merge(
   map(interval(FRAME_MS_PONG), () => PongAction.Frame),
   merge(
     filterMap(keyDowns, (key) => pongKey(true, key)),
     filterMap(keyUps, (key) => pongKey(false, key))))
 
+/** @type {(seed: number, actions: Stream<PongAction>) => Stream<PongState>} */
 export const pongStates = (seed, actions) =>
   startWith(scan(actions, pongUpdate, initialPong(seed)), initialPong(seed))
 
+/** @type {Program} */
 export const pongMain = mapIO(randomSeed, (seed) =>
-  map(pongStates(seed, pongActions), (state) => drawScene(pongView(state))))
+  clampTime(map(pongStates(seed, pongActions), (state) => drawScene(pongView(state))), MAX_GAP_MS))