feat(cli): implement compact tool output (#20974)

packages/cli/src/ui/utils/fileUtils.ts

@@ -0,0 +1,19 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import * as path from 'node:path';
+
+/**
+ * Gets the file extension from a filename or path, excluding the leading dot.
+ * Returns null if no extension is found.
+ */
+export function getFileExtension(
+  filename: string | null | undefined,
+): string | null {
+  if (!filename) return null;
+  const ext = path.extname(filename);
+  return ext ? ext.slice(1) : null;
+}