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

test/api.test.js

@@ -1,6 +1,30 @@
 import test from "node:test";
 import assert from "node:assert/strict";
-import {ApiError, get, post, stream} from "../public/js/api.js";
+import {ApiError, get, post, stream, multipart, download} from "../public/js/api.js";
+
+test("multipart and downloads share HTTP checks, cancellation and body deadlines", async t => {
+    const form = new FormData(); form.append("image", new Blob(["image"]), "image.png");
+    t.mock.method(globalThis, "fetch", async (_url, options) => {
+        assert.equal(options.body, form);
+        assert.equal(options.headers["Content-Type"], undefined);
+        return Response.json({id: "uploaded"});
+    });
+    assert.deepEqual(await multipart("/uploads", form), {id: "uploaded"});
+    t.mock.method(globalThis, "fetch", async () => Response.json({error: "Please log in", code: "LOGIN_REQUIRED"}, {status: 403}));
+    const failed = await download("/export");
+    assert.equal(failed.code, "LOGIN_REQUIRED");
+    assert.equal(failed.blob, undefined);
+    t.mock.method(globalThis, "fetch", async () => new Response("download content"));
+    assert.equal(await (await download("/export")).blob.text(), "download content");
+    t.mock.method(globalThis, "fetch", async () => new Response(new ReadableStream()));
+    assert.equal((await download("/stalled", {timeoutMs: 10})).code, "TIMEOUT");
+    t.mock.method(globalThis, "fetch", async () => new Promise(() => {}));
+    const controller = new AbortController();
+    const pending = multipart("/upload", form, {signal: controller.signal});
+    controller.abort();
+    assert.equal((await pending).code, "ABORTED");
+    assert.equal((await multipart("/upload", form, {timeoutMs: 10})).code, "TIMEOUT");
+});
 
 test("JSON requests retain HTTP metadata, handle empty success, and distinguish bad bodies from network errors", async t => {
     let response;