test(lint-skills): cover check_skill and check_command, not just settings

The linter's main job - frontmatter keys, allowed-tools targets, the
command title rule - had zero assertions; deleting the missing-
allowed-tools error left the suite green. The fixture's yaml stub now
parses the flat frontmatter the fixtures write instead of returning a
canned mapping, and four new cases pin both check functions.
Mutation-verified against the real linter. Review finding F23
(2026-08-19).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -15,6 +15,12 @@ per-file diff commands.
 
 ### Added
 
+- **Tests for `lint_skills.py`'s skill and command checks** - only `check_settings()`
+  had coverage; the linter's main job (frontmatter keys, `allowed-tools` targets
+  existing, the `# /<name>` command title rule) was unasserted, so deleting the
+  missing-allowed-tools error survived the whole suite. Four new cases in
+  `tests/test_lint_skills.py`, with the fixture's yaml stub upgraded to parse the real
+  frontmatter. Mutation-verified.
 - **Discriminating tests for `robots_check`'s tie-break and browser-UA fallback** - the
   existing tie test put Disallow first, the one ordering that cannot detect deletion of
   the tie-break clause; and the browser-readback recovery that `09-web-research.md`

tests/test_lint_skills.py

@@ -29,11 +29,19 @@ class LinterRepoFixture(unittest.TestCase):
         shutil.copy(LINTER_SCRIPT, tools / "lint_skills.py")
         # The Python-test CI job does not install PyYAML; the separate lint job
         # does. These settings-focused tests only need a valid frontmatter map.
+        # The stub parses simple "key: value" lines, enough for the flat
+        # frontmatter these fixtures write, so the checks under test see the
+        # actual file content instead of a canned mapping.
         (tools / "yaml.py").write_text(
             "class YAMLError(Exception):\n"
             "    pass\n\n"
-            "def safe_load(_text):\n"
-            "    return {'name': 'example', 'description': 'Example skill'}\n",
+            "def safe_load(text):\n"
+            "    result = {}\n"
+            "    for line in (text or '').splitlines():\n"
+            "        if ':' in line:\n"
+            "            key, _, value = line.partition(':')\n"
+            "            result[key.strip()] = value.strip()\n"
+            "    return result\n",
             encoding="utf-8",
         )
 
@@ -103,5 +111,63 @@ class SettingsShapeTests(LinterRepoFixture):
                 self.assertEqual(result.returncode, 1)
                 self.assertIn("expected permissions.allow to be a list", result.stdout)
                 self.assertNotIn("Traceback", result.stderr)
+class SkillAndCommandCheckTests(LinterRepoFixture):
+    """check_skill()/check_command() are the linter's main job and were
+    previously untested - only check_settings() had coverage, so deleting
+    e.g. the missing-allowed-tools error survived the whole suite (review
+    finding F23, 2026-08-19)."""
+
+    def write_skill(self, frontmatter: str):
+        skill = self.root / ".claude" / "skills" / "example" / "SKILL.md"
+        skill.write_text(frontmatter, encoding="utf-8")
+
+    def test_allowed_tools_referencing_a_missing_file_fails(self):
+        self.write_skill(
+            "---\n"
+            "name: example\n"
+            "description: Example skill\n"
+            "allowed-tools: Bash(bun run .claude/skills/example/DOES_NOT_EXIST.ts *)\n"
+            "---\n"
+        )
+
+        result = run_linter(self.root)
+
+        self.assertEqual(result.returncode, 1, result.stdout + result.stderr)
+        self.assertIn("allowed-tools references a missing file", result.stdout)
+        self.assertIn("DOES_NOT_EXIST.ts", result.stdout)
+
+    def test_allowed_tools_referencing_an_existing_file_passes(self):
+        target = self.root / ".claude" / "skills" / "example" / "cli.ts"
+        target.write_text("// present\n", encoding="utf-8")
+        self.write_skill(
+            "---\n"
+            "name: example\n"
+            "description: Example skill\n"
+            "allowed-tools: Bash(bun run .claude/skills/example/cli.ts *)\n"
+            "---\n"
+        )
+
+        result = run_linter(self.root)
+
+        self.assertEqual(result.returncode, 0, result.stdout + result.stderr)
+
+    def test_frontmatter_missing_description_fails(self):
+        self.write_skill("---\nname: example\ndescription:\n---\n")
+
+        result = run_linter(self.root)
+
+        self.assertEqual(result.returncode, 1)
+        self.assertIn("missing required key 'description'", result.stdout)
+
+    def test_command_without_slash_title_fails(self):
+        command = self.root / ".claude" / "commands" / "setup.md"
+        command.write_text("# setup - missing the slash\n", encoding="utf-8")
+
+        result = run_linter(self.root)
+
+        self.assertEqual(result.returncode, 1)
+        self.assertIn("must start with a '# /<name>' title", result.stdout)
+
+
 if __name__ == "__main__":
     unittest.main()