fix: YAML frontmatter and GPT-5 model fallback

- Fix invalid YAML in SKILL.md argument-hint (closes #8)
  Wrapped value in single quotes to properly escape double quotes

- Add automatic model fallback for GPT-5 access errors (closes #9)
  When OpenAI returns 400 for unverified orgs, retry with gpt-4o

- Add tests for model fallback logic

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/test_openai_reddit.py

@@ -0,0 +1,77 @@
+"""Tests for openai_reddit module."""
+
+import sys
+import unittest
+from pathlib import Path
+
+# Add scripts directory to path
+sys.path.insert(0, str(Path(__file__).parent.parent / "scripts"))
+
+from lib import http
+from lib.openai_reddit import _is_model_access_error, MODEL_FALLBACK_ORDER
+
+
+class TestIsModelAccessError(unittest.TestCase):
+    """Tests for _is_model_access_error function."""
+
+    def test_returns_false_for_non_400_error(self):
+        """Non-400 errors should not trigger fallback."""
+        error = http.HTTPError("Server error", status_code=500, body="Internal error")
+        self.assertFalse(_is_model_access_error(error))
+
+    def test_returns_false_for_400_without_body(self):
+        """400 without body should not trigger fallback."""
+        error = http.HTTPError("Bad request", status_code=400, body=None)
+        self.assertFalse(_is_model_access_error(error))
+
+    def test_returns_true_for_verification_error(self):
+        """Verification error should trigger fallback."""
+        error = http.HTTPError(
+            "Bad request",
+            status_code=400,
+            body='{"error": {"message": "Your organization must be verified to use the model \'gpt-5.2\'"}}'
+        )
+        self.assertTrue(_is_model_access_error(error))
+
+    def test_returns_true_for_access_error(self):
+        """Access denied error should trigger fallback."""
+        error = http.HTTPError(
+            "Bad request",
+            status_code=400,
+            body='{"error": {"message": "Your account does not have access to this model"}}'
+        )
+        self.assertTrue(_is_model_access_error(error))
+
+    def test_returns_true_for_model_not_found(self):
+        """Model not found error should trigger fallback."""
+        error = http.HTTPError(
+            "Bad request",
+            status_code=400,
+            body='{"error": {"message": "The model gpt-5.2 was not found"}}'
+        )
+        self.assertTrue(_is_model_access_error(error))
+
+    def test_returns_false_for_unrelated_400(self):
+        """Unrelated 400 errors should not trigger fallback."""
+        error = http.HTTPError(
+            "Bad request",
+            status_code=400,
+            body='{"error": {"message": "Invalid JSON in request body"}}'
+        )
+        self.assertFalse(_is_model_access_error(error))
+
+
+class TestModelFallbackOrder(unittest.TestCase):
+    """Tests for MODEL_FALLBACK_ORDER constant."""
+
+    def test_contains_gpt4o(self):
+        """Fallback list should include gpt-4o."""
+        self.assertIn("gpt-4o", MODEL_FALLBACK_ORDER)
+
+    def test_gpt4o_is_first(self):
+        """gpt-4o should be the first fallback option."""
+        self.assertEqual(MODEL_FALLBACK_ORDER[0], "gpt-4o")
+
+
+if __name__ == "__main__":
+    unittest.main()