feat(sdk): implement support for custom skills (#19031)

packages/sdk/src/skills.ts

@@ -0,0 +1,16 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+export type SkillReference = { type: 'dir'; path: string };
+
+/**
+ * Reference a directory containing skills.
+ *
+ * @param path Path to the skill directory
+ */
+export function skillDir(path: string): SkillReference {
+  return { type: 'dir', path };
+}