fix(security_guards): reject un-allowlisted .gitignore negations (#195)

check_gitignore() verified each required personal-data rule was present via set membership, but .gitignore is order-sensitive: a later !pattern re-includes a file an earlier rule excluded, so the required line stays physically present while the file is no longer ignored - the guard failed open on exactly the weakening its docstring claims to catch. Keeps the required-rules-present check and additionally rejects any negation line outside a small reviewed ALLOWED_IGNORE_NEGATIONS allowlist (same explicit-widening pattern as ALLOWED_PERMISSIONS). Fixes #194.

By @thejesh23. Verified: allowlist matches the four negations currently in .gitignore; guard test suite passes locally (17 tests) and in CI.

Closes #194

tests/test_security_guards.py

@@ -125,6 +125,29 @@ class GitignoreGuardTests(GuardRepoFixture):
         self.assertEqual(result.returncode, 0, result.stdout + result.stderr)
 
 
+class GitignoreNegationTests(GuardRepoFixture):
+    def test_negation_reincluding_personal_data_fails(self):
+        # .gitignore is order-sensitive: `!salary_data.json` after the
+        # `salary_data.json` rule re-includes the file, so the required rule is
+        # still present but no longer takes effect. Set membership on the
+        # required rules cannot see this, so the negation must be rejected.
+        self.write_gitignore(list(security_guards.REQUIRED_IGNORE_RULES) + ["!salary_data.json"])
+        result = run_guards(self.root)
+        self.assertEqual(result.returncode, 1, result.stdout + result.stderr)
+        self.assertIn("negation rule not in the reviewed allowlist", result.stdout)
+        self.assertIn("!salary_data.json", result.stdout)
+
+    def test_allowlisted_negations_pass(self):
+        # The template's own benign negations (example CV/cover letter, fonts,
+        # .gitkeep placeholders) must keep passing.
+        self.write_gitignore(
+            list(security_guards.REQUIRED_IGNORE_RULES)
+            + sorted(security_guards.ALLOWED_IGNORE_NEGATIONS)
+        )
+        result = run_guards(self.root)
+        self.assertEqual(result.returncode, 0, result.stdout + result.stderr)
+
+
 class ManifestGuardTests(GuardRepoFixture):
     def test_each_lifecycle_script_fails(self):
         for script in sorted(security_guards.FORBIDDEN_SCRIPTS):