feat: add shallow fetch and grouped skill selection

tests/test_custom_sources.py

@@ -6,7 +6,9 @@ import sys
 import tempfile
 import unittest
 from pathlib import Path
+from unittest.mock import patch
 
+from skiff.sources import fetch_source
 
 REPO_ROOT = Path(__file__).resolve().parents[1]
 
@@ -228,6 +230,32 @@ class CustomSourceTests(unittest.TestCase):
         self.assertTrue((checkout / ".git").is_dir())
         self.assertTrue((checkout / "skills" / "release-check" / "SKILL.md").is_file())
 
+    def test_git_source_clone_is_shallow(self) -> None:
+        checkout = self.home / "checkout"
+        entry = {
+            "repo": "https://example.test/company-skills.git",
+            "ref": "main",
+            "checkout": str(checkout),
+        }
+
+        with patch("skiff.sources.subprocess.run") as run:
+            fetch_source("company", entry)
+
+        run.assert_called_once_with(
+            [
+                "git",
+                "clone",
+                "--depth",
+                "1",
+                "--branch",
+                "main",
+                "--",
+                "https://example.test/company-skills.git",
+                str(checkout),
+            ],
+            check=True,
+        )
+
 
 if __name__ == "__main__":
     unittest.main()