refactor: unify skill source model

skiff/sources.py

@@ -9,7 +9,7 @@ from typing import Any
 from skiff import yaml_io
 from skiff.paths import CONFIG_FILE, SOURCES_DIR
 
-RESERVED_SOURCES = {"owned", "registry"}
+RESERVED_SOURCES = {"builtin", "catalog", "owned", "registry"}
 
 
 def validate_source_name(name: str) -> None:
@@ -68,15 +68,23 @@ def source_skills_root(name: str, entry: dict[str, Any]) -> Path:
     return root
 
 
-def list_source_skills(name: str, entry: dict[str, Any]) -> list[str]:
+def discover_source_skills(name: str, entry: dict[str, Any]) -> dict[str, Path]:
     root = source_skills_root(name, entry)
+    if (root / "SKILL.md").is_file():
+        return {name: root}
     if not root.is_dir():
-        return []
-    return [
-        item.name
+        return {}
+    return {
+        item.name: item
         for item in sorted(root.iterdir())
-        if item.is_dir() and not item.name.startswith("_") and (item / "SKILL.md").is_file()
-    ]
+        if item.is_dir()
+        and not item.name.startswith("_")
+        and (item / "SKILL.md").is_file()
+    }
+
+
+def list_source_skills(name: str, entry: dict[str, Any]) -> list[str]:
+    return list(discover_source_skills(name, entry))
 
 
 def fetch_source(name: str, entry: dict[str, Any]) -> Path: