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/model-usage/scripts/test_model_usage.py

@@ -0,0 +1,40 @@
+#!/usr/bin/env python3
+"""
+Tests for model_usage helpers.
+"""
+
+import argparse
+from datetime import date, timedelta
+from unittest import TestCase, main
+
+from model_usage import filter_by_days, positive_int
+
+
+class TestModelUsage(TestCase):
+    def test_positive_int_accepts_valid_numbers(self):
+        self.assertEqual(positive_int("1"), 1)
+        self.assertEqual(positive_int("7"), 7)
+
+    def test_positive_int_rejects_zero_and_negative(self):
+        with self.assertRaises(argparse.ArgumentTypeError):
+            positive_int("0")
+        with self.assertRaises(argparse.ArgumentTypeError):
+            positive_int("-3")
+
+    def test_filter_by_days_keeps_recent_entries(self):
+        today = date.today()
+        entries = [
+            {"date": (today - timedelta(days=5)).strftime("%Y-%m-%d"), "modelBreakdowns": []},
+            {"date": (today - timedelta(days=1)).strftime("%Y-%m-%d"), "modelBreakdowns": []},
+            {"date": today.strftime("%Y-%m-%d"), "modelBreakdowns": []},
+        ]
+
+        filtered = filter_by_days(entries, 2)
+
+        self.assertEqual(len(filtered), 2)
+        self.assertEqual(filtered[0]["date"], (today - timedelta(days=1)).strftime("%Y-%m-%d"))
+        self.assertEqual(filtered[1]["date"], today.strftime("%Y-%m-%d"))
+
+
+if __name__ == "__main__":
+    main()