Skills/Python: harden script edge cases and add regression tests (#24277)

* Skill creator: skip self-including .skill output

* Skill creator tests: cover output-dir-inside-skill case

* Skill validator: parse frontmatter robustly across newlines

* Skill validator tests: add CRLF and malformed frontmatter coverage

* Model usage: require positive --days value

* Model usage tests: cover --days validation and filtering

* Nano banana: close input image handles after loading

* Skill validator: keep type hints compatible with older python

* Changelog: credit @vincentkoc for Python skills hardening

skills/skill-creator/scripts/test_quick_validate.py

@@ -0,0 +1,46 @@
+#!/usr/bin/env python3
+"""
+Regression tests for quick skill validation.
+"""
+
+import tempfile
+from pathlib import Path
+from unittest import TestCase, main
+
+from quick_validate import validate_skill
+
+
+class TestQuickValidate(TestCase):
+    def setUp(self):
+        self.temp_dir = Path(tempfile.mkdtemp(prefix="test_quick_validate_"))
+
+    def tearDown(self):
+        import shutil
+
+        if self.temp_dir.exists():
+            shutil.rmtree(self.temp_dir)
+
+    def test_accepts_crlf_frontmatter(self):
+        skill_dir = self.temp_dir / "crlf-skill"
+        skill_dir.mkdir(parents=True, exist_ok=True)
+        content = "---\r\nname: crlf-skill\r\ndescription: ok\r\n---\r\n# Skill\r\n"
+        (skill_dir / "SKILL.md").write_text(content, encoding="utf-8")
+
+        valid, message = validate_skill(skill_dir)
+
+        self.assertTrue(valid, message)
+
+    def test_rejects_missing_frontmatter_closing_fence(self):
+        skill_dir = self.temp_dir / "bad-skill"
+        skill_dir.mkdir(parents=True, exist_ok=True)
+        content = "---\nname: bad-skill\ndescription: missing end\n# no closing fence\n"
+        (skill_dir / "SKILL.md").write_text(content, encoding="utf-8")
+
+        valid, message = validate_skill(skill_dir)
+
+        self.assertFalse(valid)
+        self.assertEqual(message, "Invalid frontmatter format")
+
+
+if __name__ == "__main__":
+    main()