fix: parse multi-line YAML block scalars in frontmatter

_parse_frontmatter used manual line splitting which only handled
simple key: value pairs. Multi-line block scalars (|) returned
only '|' as the value, dropping all subsequent indented lines.

Replace with yaml.safe_load() to correctly parse all YAML syntax.
Add pyyaml>=6.0 to requirements.txt.

agents/s05_skill_loading.py

@@ -38,6 +38,7 @@ Key insight: "Don't put everything in the system prompt. Load on demand."
 import os
 import re
 import subprocess
+import yaml
 from pathlib import Path
 
 from anthropic import Anthropic
@@ -75,11 +76,10 @@ class SkillLoader:
         match = re.match(r"^---\n(.*?)\n---\n(.*)", text, re.DOTALL)
         if not match:
             return {}, text
-        meta = {}
-        for line in match.group(1).strip().splitlines():
-            if ":" in line:
-                key, val = line.split(":", 1)
-                meta[key.strip()] = val.strip()
+        try:
+            meta = yaml.safe_load(match.group(1)) or {}
+        except yaml.YAMLError:
+            meta = {}
         return meta, match.group(2).strip()
 
     def get_descriptions(self) -> str:

requirements.txt

@@ -1,2 +1,3 @@
 anthropic>=0.25.0
 python-dotenv>=1.0.0
+pyyaml>=6.0