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>

scala/test/M09Runtime.test.scala

@@ -2,12 +2,15 @@ package snake
 
 import scala.collection.mutable.ListBuffer
 
-/** A fake platform: records every call and lets the test fire events by hand. */
-class FakePlatform(seed: Long = 42) extends Platform:
+/** A fake platform: records every call and lets the test fire events by hand. `best` answers loadBest (m10). */
+class FakePlatform(seed: Long = 42, best: Int = 0) extends Platform:
   val calls: ListBuffer[List[Any]] = ListBuffer.empty
   private var onTime: Long => Unit = _ => ()
   private var onDown: String => Unit = _ => ()
   private var onUp: String => Unit = _ => ()
+  private var onClickCb: (Int, Int) => Unit = (_, _) => ()
+  // Which callbacks the runtime registered, by name: "click", "down", "time", "up" (m13).
+  private var handlers: Set[String] = Set.empty
 
   def fillRect(x: Int, y: Int, w: Int, h: Int, color: String): Unit = calls += List("fillRect", x, y, w, h, color)
   def fillText(x: Int, y: Int, text: String, color: String, size: Int, align: String): Unit =
@@ -15,13 +18,29 @@ class FakePlatform(seed: Long = 42) extends Platform:
   def randomSeed(): Long =
     calls += List("randomSeed")
     seed
-  def startClock(cb: Long => Unit): Unit = onTime = cb
-  def onKeyDown(cb: String => Unit): Unit = onDown = cb
-  def onKeyUp(cb: String => Unit): Unit = onUp = cb
+  def loadBest(): Int =
+    calls += List("loadBest")
+    best
+  def saveBest(score: Int): Unit = calls += List("saveBest", score)
+  def startClock(cb: Long => Unit): Unit =
+    onTime = cb
+    handlers += "time"
+  def onKeyDown(cb: String => Unit): Unit =
+    onDown = cb
+    handlers += "down"
+  def onKeyUp(cb: String => Unit): Unit =
+    onUp = cb
+    handlers += "up"
+  // m13: a runtime from Module 9 does not register this yet; nothing in m09-m12 fires a click.
+  def onClick(cb: (Int, Int) => Unit): Unit =
+    onClickCb = cb
+    handlers += "click"
 
   def fireTime(t: Long): Unit = onTime(t)
   def fireKey(key: String): Unit = onDown(key)
   def fireKeyUp(key: String): Unit = onUp(key)
+  def fireClick(x: Int, y: Int): Unit = onClickCb(x, y)
+  def registered: List[String] = handlers.toList.sorted
 
 class M09RuntimeSuite extends munit.FunSuite:
   // The m09 program (classicMain) ticks every 150 ms; the shipped `main` uses speedActions after m10.