fix(tools): stage course cards from M5, audit noun words without flagging identifiers, Node<24.2 main guard, rename-proof expansion-check, safe check-links

- cardDirs: course/cards only from Module 5 (spec 6.2a); fixture modules 04/05 and tests
- coupling-audit: noun words match as UPPERCASE, PascalCase or a whole string literal;
  lowercase identifiers like key/flag pass; card names keep every variant
- isMain() argv guard replaces import.meta.main in coupling-audit and verify-references;
  engines.node >=22
- expansion-check: git diff --no-renames so moving engine code into content fails
- start-module and other tools: clear error when .course.json is missing
- check-links: malformed URLs reported as invalid URL instead of throwing

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/test/start-module.test.mjs

@@ -14,9 +14,23 @@ test("start_module_copies_tests", () => {
   assert.match(r.out, /newGame, summon, play/);
 });
 
-test("start_module_copies_course_cards", () => {
+test("start_module_copies_course_cards_from_module_5", () => {
+  // Spec §6.2a: Modules 1-4 keep their cards in the learner's code; course/cards
+  // (with the M3/M4 drop answers and the M5 data format) arrives with Module 5.
+  for (const [num, prev] of [["01", null], ["04", "m03.rs"]]) {
+    const ws = copyFixture("ws-start");
+    if (prev) {
+      mkdirSync(join(ws, "tests"), { recursive: true });
+      writeFileSync(join(ws, "tests", prev), "");
+    }
+    const r = run("start-module.mjs", [num, ws], env);
+    assert.equal(r.code, 0, r.out);
+    assert.ok(!existsSync(join(ws, "cards/test-fixture.json")), `module ${num} gets no course cards`);
+  }
   const ws = copyFixture("ws-start");
-  const r = run("start-module.mjs", ["01", ws], env);
+  mkdirSync(join(ws, "tests"), { recursive: true });
+  writeFileSync(join(ws, "tests/m04.rs"), "");
+  const r = run("start-module.mjs", ["05", ws], env);
   assert.equal(r.code, 0, r.out);
   assert.ok(existsSync(join(ws, "cards/test-fixture.json")));
 });
@@ -24,17 +38,25 @@ test("start_module_copies_course_cards", () => {
 test("start_module_copies_module_cards_up_to_the_module", () => {
   const early = copyFixture("ws-start");
   assert.equal(run("start-module.mjs", ["01", early], env).code, 0);
-  assert.ok(existsSync(join(early, "cards/test-fixture.json")));
   assert.ok(!existsSync(join(early, "cards/module-fixture.json")));
   const later = copyFixture("ws-start");
   mkdirSync(join(later, "tests"), { recursive: true });
   writeFileSync(join(later, "tests/m02.rs"), "");
   const r = run("start-module.mjs", ["03", later], env);
   assert.equal(r.code, 0, r.out);
-  assert.ok(existsSync(join(later, "cards/test-fixture.json")));
+  assert.ok(!existsSync(join(later, "cards/test-fixture.json")));
   assert.ok(existsSync(join(later, "cards/module-fixture.json")));
 });
 
+test("start_module_explains_missing_course_json", () => {
+  const ws = copyFixture("ws-content-only");
+  const r = run("start-module.mjs", ["01", join(ws, "no-such-dir")], env);
+  assert.equal(r.code, 1);
+  assert.match(r.out, /No \.course\.json/);
+  assert.match(r.out, /workspace-template/);
+  assert.doesNotMatch(r.out, /ENOENT|at .*\.mjs:\d+/);
+});
+
 test("start_module_copies_module_levels", () => {
   const ws = copyFixture("ws-start");
   mkdirSync(join(ws, "tests"), { recursive: true });