Add support for message history pagination, preserve scroll in rendering, and improve draft/message workflows.

test/workspaceTransferUi.test.js

@@ -0,0 +1,17 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import {createWorkspaceTransfer} from "../public/js/workspaceTransfer.js";
+
+test("export cancellation makes no request and failed downloads report structured server errors", async t => {
+    let requests = 0, format = null;
+    t.mock.method(globalThis, "fetch", async () => { requests++; return Response.json({error: "Session expired", code: "LOGIN_REQUIRED"}, {status: 403}); });
+    const notices = [];
+    const transfer = createWorkspaceTransfer({conversation: {activeChatId: 1, currentMessages: [{}]}, getChatById: () => ({id: 1, title: "Chat"}),
+        setNotice: (text, kind) => notices.push({text, kind}), promptPopup: async () => format});
+    await transfer.exportCurrentChat(); assert.equal(requests, 0);
+    format = "md";
+    await transfer.exportCurrentChat();
+    await transfer.backupWorkspace();
+    assert.equal(requests, 2);
+    assert.deepEqual(notices, [{text: "Session expired", kind: "error"}, {text: "Session expired", kind: "error"}]);
+});