fix(lint): report malformed settings shapes without crashing (#146)

Valid JSON such as [] or {"permissions": []} caused lint_skills.py to raise AttributeError because it assumed both values were objects.

Validate the top-level settings value and permissions object before reading nested keys. Malformed settings now produce clear lint errors and exit 1 without a traceback.

Add subprocess regression tests covering invalid JSON, malformed root values, invalid permissions values, and non-list permissions.allow values.

tests/test_lint_skills.py

@@ -0,0 +1,107 @@
+import json
+import shutil
+import subprocess
+import sys
+import tempfile
+import unittest
+from pathlib import Path
+
+
+REPO_ROOT = Path(__file__).resolve().parent.parent
+LINTER_SCRIPT = REPO_ROOT / "tools" / "lint_skills.py"
+
+
+def run_linter(root: Path) -> subprocess.CompletedProcess:
+    return subprocess.run(
+        [sys.executable, str(root / "tools" / "lint_skills.py")],
+        capture_output=True,
+        text=True,
+    )
+
+
+class LinterRepoFixture(unittest.TestCase):
+    def setUp(self):
+        self.root = Path(tempfile.mkdtemp())
+        self.addCleanup(shutil.rmtree, self.root, ignore_errors=True)
+
+        tools = self.root / "tools"
+        tools.mkdir()
+        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.
+        (tools / "yaml.py").write_text(
+            "class YAMLError(Exception):\n"
+            "    pass\n\n"
+            "def safe_load(_text):\n"
+            "    return {'name': 'example', 'description': 'Example skill'}\n",
+            encoding="utf-8",
+        )
+
+        command = self.root / ".claude" / "commands" / "setup.md"
+        command.parent.mkdir(parents=True)
+        command.write_text("# /setup - Test setup command\n", encoding="utf-8")
+
+        skill = self.root / ".claude" / "skills" / "example" / "SKILL.md"
+        skill.parent.mkdir(parents=True)
+        skill.write_text(
+            "---\nname: example\ndescription: Example skill\n---\n",
+            encoding="utf-8",
+        )
+
+        self.settings = self.root / ".claude" / "settings.json"
+        self.write_settings({"permissions": {"allow": []}})
+
+    def write_settings(self, data):
+        self.settings.write_text(json.dumps(data), encoding="utf-8")
+
+
+class SettingsShapeTests(LinterRepoFixture):
+    def test_valid_settings_pass(self):
+        result = run_linter(self.root)
+
+        self.assertEqual(result.returncode, 0, result.stdout + result.stderr)
+        self.assertIn("lint_skills: OK", result.stdout)
+
+    def test_invalid_json_fails_cleanly(self):
+        self.settings.write_text("{not json", encoding="utf-8")
+
+        result = run_linter(self.root)
+
+        self.assertEqual(result.returncode, 1)
+        self.assertIn(".claude/settings.json", result.stdout)
+        self.assertNotIn("Traceback", result.stderr)
+
+    def test_non_object_root_fails_cleanly(self):
+        for data in ([], "settings", 1, None):
+            with self.subTest(data=data):
+                self.write_settings(data)
+
+                result = run_linter(self.root)
+
+                self.assertEqual(result.returncode, 1)
+                self.assertIn("top-level JSON value to be an object", result.stdout)
+                self.assertNotIn("Traceback", result.stderr)
+
+    def test_non_object_permissions_fails_cleanly(self):
+        for permissions in ([], "permissions", 1, None):
+            with self.subTest(permissions=permissions):
+                self.write_settings({"permissions": permissions})
+
+                result = run_linter(self.root)
+
+                self.assertEqual(result.returncode, 1)
+                self.assertIn("expected permissions to be an object", result.stdout)
+                self.assertNotIn("Traceback", result.stderr)
+
+    def test_non_list_allow_fails_cleanly(self):
+        for allow in ({}, "Bash(bun run:*)", 1, None):
+            with self.subTest(allow=allow):
+                self.write_settings({"permissions": {"allow": allow}})
+
+                result = run_linter(self.root)
+
+                self.assertEqual(result.returncode, 1)
+                self.assertIn("expected permissions.allow to be a list", result.stdout)
+                self.assertNotIn("Traceback", result.stderr)
+if __name__ == "__main__":
+    unittest.main()

tools/lint_skills.py

@@ -84,7 +84,14 @@ def check_settings() -> None:
     except (OSError, json.JSONDecodeError) as exc:
         errors.append(f".claude/settings.json: {exc}")
         return
-    if not isinstance(data.get("permissions", {}).get("allow"), list):
+    if not isinstance(data, dict):
+        errors.append(".claude/settings.json: expected top-level JSON value to be an object")
+        return
+    permissions = data.get("permissions", {})
+    if not isinstance(permissions, dict):
+        errors.append(".claude/settings.json: expected permissions to be an object")
+        return
+    if not isinstance(permissions.get("allow"), list):
         errors.append(".claude/settings.json: expected permissions.allow to be a list")