fix(skill_engine): read block-scalar values in get_frontmatter_field

Line-oriented lookup returned the literal "|" for description: | blocks.
Delegate to parse_frontmatter so indented body lines are kept.

.gitignore

@@ -51,6 +51,7 @@ tests/skill_engine/*
 !tests/skill_engine/test_evolver_length_recovery.py
 !tests/skill_engine/test_evolution_retry_idempotency.py
 !tests/skill_engine/test_analyzer_length_recovery.py
+!tests/skill_engine/test_get_frontmatter_block_scalar.py
 !tests/skill_engine/decision/
 tests/skill_engine/decision/*
 !tests/skill_engine/decision/test_analysis_adapter.py

openspace/skill_engine/skill_utils.py

@@ -113,18 +113,15 @@ def get_frontmatter_field(content: str, field_name: str) -> Optional[str]:
     """Extract a single field value from YAML frontmatter.
 
     Returns ``None`` if the field is absent or content has no frontmatter.
+    Uses :func:`parse_frontmatter` so block scalars (``|`` / ``>``) round-trip.
     """
-    if not content.startswith("---"):
+    fm = parse_frontmatter(content)
+    if field_name not in fm:
         return None
-    match = _FRONTMATTER_RE.match(content)
-    if not match:
+    value = fm[field_name]
+    if value is None:
         return None
-    for line in match.group(1).split("\n"):
-        if ":" in line:
-            key, value = line.split(":", 1)
-            if key.strip() == field_name:
-                return _yaml_unquote(value.strip())
-    return None
+    return value if isinstance(value, str) else str(value)
 
 
 def set_frontmatter_field(content: str, field_name: str, value: str) -> str:

tests/skill_engine/test_get_frontmatter_block_scalar.py

@@ -0,0 +1,15 @@
+"""Regression: get_frontmatter_field must read YAML block scalars."""
+
+from __future__ import annotations
+
+from openspace.skill_engine.skill_utils import get_frontmatter_field
+
+
+def test_get_frontmatter_field_reads_block_scalar_description():
+    src = "---\nname: x\ndescription: |\n  line1\n  line2\n---\nbody\n"
+    assert get_frontmatter_field(src, "description") == "line1\nline2"
+
+
+def test_get_frontmatter_field_missing_returns_none():
+    src = "---\nname: x\n---\n"
+    assert get_frontmatter_field(src, "description") is None