Extract mention-aware link node helper and add tests

Co-Authored-By: Paperclip <noreply@paperclip.ing>

ui/src/lib/mention-aware-link-node.test.ts

@@ -0,0 +1,50 @@
+import { describe, expect, it } from "vitest";
+import { $createLinkNode } from "@lexical/link";
+import { createEditor } from "lexical";
+import {
+  MentionAwareLinkNode,
+  getMentionAwareLinkNodeInit,
+  mentionAwareLinkNodeReplacement,
+} from "./mention-aware-link-node";
+
+function createTestEditor() {
+  return createEditor({
+    namespace: "mention-aware-link-node-test",
+    nodes: [MentionAwareLinkNode, mentionAwareLinkNodeReplacement],
+    onError(error: Error) {
+      throw error;
+    },
+  });
+}
+
+describe("getMentionAwareLinkNodeInit", () => {
+  it("copies link attributes without carrying over a node key", () => {
+    const init = getMentionAwareLinkNodeInit({
+      getURL: () => "agent://agent-123",
+      getRel: () => "noreferrer",
+      getTarget: () => "_blank",
+      getTitle: () => "Agent mention",
+    });
+
+    expect(Object.keys(init)).toEqual(["url", "attributes"]);
+    expect(init).toEqual({
+      url: "agent://agent-123",
+      attributes: {
+        rel: "noreferrer",
+        target: "_blank",
+        title: "Agent mention",
+      },
+    });
+  });
+
+  it("replaces LinkNode creation with MentionAwareLinkNode without throwing", () => {
+    const editor = createTestEditor();
+    let created: unknown;
+
+    editor.update(() => {
+      created = $createLinkNode("agent://agent-123");
+    });
+
+    expect(created).toBeInstanceOf(MentionAwareLinkNode);
+  });
+});