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>

scripts/check-stubs.sh

@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 # Usage: scripts/check-stubs.sh <js|scala|fsharp>
-# Runs each module M01..M11 that has tests against the stubs in src/. Fails if any module's tests pass,
+# Runs each module M01..M13 (and the optional M07b) that has tests against the stubs in src/. Fails if any module's tests pass,
 # and also fails (exit 2) on tooling/build errors, so a broken toolchain can never look like "stubs fail".
 set -uo pipefail
 track="${1:?usage: check-stubs.sh <js|scala|fsharp>}"
@@ -32,11 +32,39 @@ tests_failed() {
   esac
 }
 
+# Modules in course order; "07b" is the optional Module 7b.
+modules="01 02 03 04 05 06 07 07b 08 09 10 11 12 13"
+
+# Scala's `./test.sh M07` (munit glob "*M07*") and F#'s (Expecto --filter-test-list, a substring) also select the
+# M07b tests. Their failures would hide an M07 that wrongly passes, so for such a module run the tests in a temp
+# copy without the longer-tagged modules' test files (F#: also without their line in tests/Snake.Tests.fsproj).
+run_module() {
+  local n="$1" longer="" t f tmp
+  if [ "$track" != js ]; then
+    for t in $modules; do [[ "$t" == "$n"?* ]] && has "$t" && longer="$longer $t"; done
+  fi
+  if [ -z "$longer" ]; then (cd "$dir" && ./test.sh "M$n" 2>&1); return; fi
+  tmp="$(mktemp -d)"
+  tar -C "$repo" --exclude=.git --exclude=node_modules --exclude=bin --exclude=obj \
+      --exclude=.scala-build --exclude=.bsp --exclude=.superpowers -cf - . | tar -C "$tmp" -xf -
+  for t in $longer; do
+    case "$track" in
+      scala)  rm -f "$tmp"/scala/test/M"$t"*.test.scala ;;
+      fsharp) for f in "$tmp"/fsharp/tests/M"$t"*.fs; do
+                rm -f "$f"; sed -i "/Include=\"$(basename "$f")\"/d" "$tmp/fsharp/tests/Snake.Tests.fsproj"
+              done ;;
+    esac
+  done
+  (cd "$tmp/$track" && ./test.sh "M$n" 2>&1); local rc=$?
+  rm -rf "$tmp"
+  return $rc
+}
+
 status=0
-for n in 01 02 03 04 05 06 07 08 09 10 11; do
+for n in $modules; do
   m="M$n"
   if ! has "$n"; then echo "$m: no tests"; continue; fi
-  out="$(cd "$dir" && ./test.sh "$m" 2>&1)"; rc=$?
+  out="$(run_module "$n")"; rc=$?
   out="$(sed $'s/\x1b\\[[0-9;?]*[A-Za-z]//g' <<<"$out")"
   if [ $rc -eq 0 ]; then
     echo "$m: FAIL (tests pass against stubs)"; status=1