Allow explicit publication stores in Git metadata

internal/git/source.go

@@ -56,6 +56,23 @@ func normalizeRepositoryRoot(root string) (string, error) {
 	return resolved, nil
 }
 
+// MetadataDirectories returns the checkout's private and shared Git directories.
+func MetadataDirectories(ctx context.Context, directory string) ([]string, error) {
+	var directories []string
+	for _, flag := range []string{"--absolute-git-dir", "--git-common-dir"} {
+		output, err := run(ctx, directory, nil, "rev-parse", "--path-format=absolute", flag)
+		if err != nil {
+			return nil, fmt.Errorf("resolve Git metadata directory: %w", err)
+		}
+		resolved, err := normalizeRepositoryRoot(output)
+		if err != nil {
+			return nil, err
+		}
+		directories = append(directories, resolved)
+	}
+	return directories, nil
+}
+
 // DiscoverRepositoryRoot finds a containing checkout or confirms standalone use.
 func DiscoverRepositoryRoot(ctx context.Context, directory string) (string, bool, error) {
 	if directory == "" {