fix: reuse cached config profile git mounts

- Reuse valid deterministic git mount clones on repeated starts
- Remove incomplete clone destinations before retrying
- Add regression coverage for cached and partial clones
- Document OpenSpec change fix-config-profile-git-mount-clone-reuse

Quality gates: pytest (13 passed), ruff, mypy

apps/api/tests/unit/test_instance_service.py

@@ -1,5 +1,6 @@
 """Unit tests for the tool instance service."""
 
+import hashlib
 import uuid
 from unittest.mock import MagicMock, AsyncMock
 
@@ -8,6 +9,7 @@ import pytest
 from src.services.tool.instance_service import (
     _get_repository_mount_name,
     _stack_profile_mounts_with_git_mounts,
+    clone_git_repo,
     modify_compose_file,
     prepare_manifest_instance,
 )
@@ -67,6 +69,61 @@ class TestGetRepositoryMountName:
         assert _get_repository_mount_name(project, repo) == "project-v2-0"
 
 
+@pytest.mark.unit
+class TestCloneGitRepo:
+    """Regression tests for reusable config-profile git mount clones."""
+
+    def test_reuses_existing_clone(self, monkeypatch, tmp_path) -> None:
+        from src.services.tool import instance_service
+
+        remote_url = "https://gitlab.com/example/dotfiles"
+        branch = None
+        clone_parent = str(tmp_path)
+        url_hash = hashlib.md5(f"{remote_url}:default".encode()).hexdigest()[:12]
+        repo_path = (
+            tmp_path
+            / "git-mounts"
+            / f"dotfiles-{url_hash}"
+            / "repo-clone"
+        )
+        (repo_path / ".git").mkdir(parents=True)
+
+        clone = MagicMock(side_effect=AssertionError("existing clone must be reused"))
+        pull = MagicMock()
+        monkeypatch.setattr(instance_service, "clone_repository", clone)
+        monkeypatch.setattr(instance_service, "pull_repository_updates", pull)
+
+        result = clone_git_repo(remote_url, branch, clone_parent)
+
+        assert result == str(repo_path)
+        clone.assert_not_called()
+        pull.assert_called_once_with(str(repo_path), remote_url)
+
+    def test_replaces_incomplete_clone_before_retry(self, monkeypatch, tmp_path) -> None:
+        from src.services.tool import instance_service
+
+        remote_url = "https://gitlab.com/example/dotfiles"
+        url_hash = hashlib.md5(f"{remote_url}:main".encode()).hexdigest()[:12]
+        clone_dir = tmp_path / "git-mounts" / f"dotfiles-{url_hash}"
+        repo_path = clone_dir / "repo-clone"
+        repo_path.mkdir(parents=True)
+        (repo_path / "partial-file").write_text("incomplete")
+
+        def clone(_url, _key, destination, _branch, project_name=None):
+            assert destination == str(clone_dir)
+            assert project_name is None
+            assert not repo_path.exists()
+            (repo_path / ".git").mkdir(parents=True)
+            return str(repo_path)
+
+        monkeypatch.setattr(instance_service, "clone_repository", clone)
+
+        result = clone_git_repo(remote_url, "main", str(tmp_path))
+
+        assert result == str(repo_path)
+        assert (repo_path / ".git").is_dir()
+
+
 @pytest.mark.unit
 class TestStackProfileMountsWithGitMounts:
     """Tests for _stack_profile_mounts_with_git_mounts."""