Fix skill frontmatter parsing

tests/test_skill_loading.py

@@ -2,15 +2,18 @@ import importlib.util
 import os
 import sys
 import tempfile
+import time
 import types
 from pathlib import Path
 
 
 ROOT = Path(__file__).resolve().parents[1]
 LESSON = ROOT / "s07_skill_loading" / "code.py"
+INTEGRATED_LESSON = ROOT / "s15_integrated_harness" / "code.py"
+SKILL_LESSONS = (LESSON, INTEGRATED_LESSON)
 
 
-def load_lesson(workdir: Path):
+def load_lesson(workdir: Path, lesson_path: Path = LESSON):
     fake_anthropic = types.ModuleType("anthropic")
     fake_dotenv = types.ModuleType("dotenv")
 
@@ -28,12 +31,14 @@ def load_lesson(workdir: Path):
     previous_cwd = Path.cwd()
     previous_model = os.environ.get("MODEL_ID")
 
-    spec = importlib.util.spec_from_file_location("s07_skill_test", LESSON)
+    module_name = f"skill_loading_test_{lesson_path.parent.name}_{time.time_ns()}"
+    spec = importlib.util.spec_from_file_location(module_name, lesson_path)
     assert spec is not None and spec.loader is not None
     module = importlib.util.module_from_spec(spec)
 
     sys.modules["anthropic"] = fake_anthropic
     sys.modules["dotenv"] = fake_dotenv
+    sys.modules[module_name] = module
     try:
         os.chdir(workdir)
         os.environ["MODEL_ID"] = "test-model"
@@ -50,6 +55,13 @@ def load_lesson(workdir: Path):
                 sys.modules.pop(name, None)
             else:
                 sys.modules[name] = previous
+        sys.modules.pop(module_name, None)
+
+
+def parse_frontmatter(lesson, text: str) -> tuple[dict, str]:
+    if hasattr(lesson, "SkillLoader"):
+        return lesson.SkillLoader.parse_frontmatter(text)
+    return lesson._parse_frontmatter(text)
 
 
 def test_catalog_stays_small_and_load_skill_returns_the_full_file() -> None:
@@ -93,3 +105,60 @@ def test_s07_exposes_only_base_tools_and_load_skill() -> None:
             "glob",
             "load_skill",
         ]
+
+
+def test_skill_frontmatter_requires_standalone_delimiters() -> None:
+    invalid_opening = "---not frontmatter\n---\n# Body"
+    block_scalar = """---
+name: demo
+description: |
+  before
+  ---
+  after
+---
+# Body
+"""
+    for lesson_path in SKILL_LESSONS:
+        with tempfile.TemporaryDirectory() as tmp:
+            lesson = load_lesson(Path(tmp), lesson_path)
+            assert parse_frontmatter(lesson, invalid_opening) == ({}, invalid_opening)
+            for text in (block_scalar, block_scalar.replace("\n", "\r\n")):
+                metadata, body = parse_frontmatter(lesson, text)
+                assert metadata["description"] == "before\n---\nafter\n"
+                assert body == "# Body"
+
+
+def test_skill_frontmatter_falls_back_for_invalid_or_empty_metadata() -> None:
+    manifest = "---\nname:\ndescription:\n---\n# Body description\n"
+    for lesson_path in SKILL_LESSONS:
+        with tempfile.TemporaryDirectory() as tmp:
+            root = Path(tmp)
+            skill_dir = root / "skills" / "fallback-skill"
+            skill_dir.mkdir(parents=True)
+            (skill_dir / "SKILL.md").write_text(manifest)
+            empty_dir = root / "skills" / "empty-skill"
+            empty_dir.mkdir()
+            (empty_dir / "SKILL.md").write_text("---\nname: empty-skill\n---\n")
+            typed_dir = root / "skills" / "typed-fallback"
+            typed_dir.mkdir()
+            (typed_dir / "SKILL.md").write_text(
+                "---\nname: [bad]\ndescription: [bad]\n---\n# Typed fallback\n"
+            )
+            outside = root / "outside-skill.md"
+            outside.write_text("# External skill\n\nDO_NOT_LOAD")
+            linked_dir = root / "skills" / "linked-skill"
+            linked_dir.mkdir()
+            (linked_dir / "SKILL.md").symlink_to(outside)
+            lesson = load_lesson(root, lesson_path)
+            registry = (lesson.SKILL_LOADER.skills if hasattr(lesson, "SKILL_LOADER")
+                        else lesson.SKILL_REGISTRY)
+            assert registry["fallback-skill"]["description"] == "Body description"
+            assert registry["empty-skill"]["description"] == ""
+            assert registry["typed-fallback"]["description"] == "Typed fallback"
+            assert "linked-skill" not in registry
+
+            metadata, body = parse_frontmatter(
+                lesson, "---\n- not\n- a mapping\n---\nBody"
+            )
+            assert metadata == {}
+            assert body == "Body"