waybetter-for-x/apps/desktop/tests/mutationGate.test.ts

import assert from 'node:assert/strict';
import { test } from 'node:test';
import { createLanes, type LaneRequest, type Settled } from '../src/fixes/mutationGate/lanes.ts';
import { classifyResponse, matchMutation, synthesizedBody, type MutationMatch } from '../src/fixes/mutationGate/matchers.ts';
import { installMutationGate } from '../src/fixes/mutationGate/index.ts';
import { X_FEATURES } from '../src/areas/table.ts';
import { FEATURE_DEFAULTS } from '../src/inject/features.ts';

const BASE = 'https://x.com/home';
const post = (body: BodyInit | null | undefined): RequestInit => ({ method: 'POST', body });
const likeBody = (id: unknown) => JSON.stringify({ variables: { tweet_id: id }, queryId: 'lI07N6Otwv1PhnEgXILM7A' });
const tick = () => new Promise(resolve => setImmediate(resolve));

// ---------- matchers ----------

test('matcher: like/unlike and follow/unfollow fixtures', () => {
  assert.deepEqual(matchMutation('/i/api/graphql/lI07N6Otwv1PhnEgXILM7A/FavoriteTweet', post(likeBody('1790000000000000001')), BASE),
    { kind: 'like', id: '1790000000000000001', key: 'tweet:1790000000000000001', want: true });
  assert.deepEqual(matchMutation(new URL('https://x.com/i/api/graphql/ZYKSe-w7KEslx3JhSIk5LA/UnfavoriteTweet'), post(likeBody('42')), BASE),
    { kind: 'like', id: '42', key: 'tweet:42', want: false });
  assert.deepEqual(matchMutation('https://x.com/i/api/1.1/friendships/create.json', post('include_profile_interstitial_type=1&user_id=783214&skip_status=1'), BASE),
    { kind: 'follow', id: '783214', key: 'user:783214', want: true });
  assert.deepEqual(matchMutation('/i/api/1.1/friendships/destroy.json', post(new URLSearchParams({ user_id: '783214' })), BASE),
    { kind: 'follow', id: '783214', key: 'user:783214', want: false });
  // Promoted like bodies carry extra variables and still match.
  assert.equal(matchMutation('/i/api/graphql/x/FavoriteTweet', post(JSON.stringify({ variables: { tweet_id: '7', promotedContent: { impressionId: 'a' } } })), BASE)?.key, 'tweet:7');
});

test('matcher: malformed, DM, read and other endpoints are untouched', () => {
  const none: [unknown, RequestInit | undefined][] = [
    ['/i/api/graphql/x/FavoriteTweet', post('{not json')],
    ['/i/api/graphql/x/FavoriteTweet', post(likeBody(42))],
    ['/i/api/graphql/x/FavoriteTweet', post(likeBody('12a'))],
    ['/i/api/graphql/x/FavoriteTweet', post(JSON.stringify({ variables: {} }))],
    ['/i/api/graphql/x/FavoriteTweet', post('null')],
    ['/i/api/graphql/x/FavoriteTweet', post(new Blob(['x']))],
    ['/i/api/graphql/x/FavoriteTweet', { body: likeBody('1') }],
    ['/i/api/graphql/x/FavoriteTweet', undefined],
    ['/i/api/graphql/x/FavoriteTweets', post(likeBody('1'))],
    ['/i/api/graphql/x/CreateRetweets', post(likeBody('1'))],
    ['/i/api/graphql/x/DeleteRetweet', post(likeBody('1'))],
    ['/i/api/graphql/x/CreateBookmark', post(likeBody(1))],
    ['/i/api/graphql/x/DeleteBookmark', post(new Blob(['x']))],
    ['/i/api/graphql/x/TweetDetail', post(likeBody('1'))],
    ['/i/api/graphql/x/useDMReactionMutationAddMutation', post(likeBody('1'))],
    ['/i/api/1.1/dm/new2.json', post('user_id=1')],
    ['/i/api/1.1/friendships/cancel.json', post('user_id=1')],
    ['/i/api/1.1/friendships/update.json', post('user_id=1')],
    ['/i/api/1.1/friendships/create.json', post('user_id=abc')],
    ['/i/api/1.1/friendships/create.json', post('screen_name=jack')],
    ['/i/api/1.1/friendships/create.json', post('user_id=1&user_id=2')],
    ['/i/api/1.1/friendships/create.json', post(new FormData())],
    ['https://api.x.com/1.1/friendships/create.json', post('user_id=1')],
    ['https://evil.example/i/api/1.1/friendships/create.json', post('user_id=1')],
    [new Request('https://x.com/i/api/1.1/friendships/create.json', { method: 'POST', body: 'user_id=1' }), undefined],
    ['http://[bad', post('user_id=1')],
    [42, post('user_id=1')],
  ];
  for (const [input, init] of none) assert.equal(matchMutation(input, init, BASE), null, `${String(input)} ${String(init?.body)}`);
});

test('classifier: confirmed, requested and unknown outcomes', () => {
  const like: MutationMatch = { kind: 'like', id: '1', key: 'tweet:1', want: true };
  const unlike: MutationMatch = { ...like, want: false };
  const follow: MutationMatch = { kind: 'follow', id: '9', key: 'user:9', want: true };
  const unfollow: MutationMatch = { ...follow, want: false };
  assert.deepEqual(classifyResponse(like, 200, '{"data":{"favorite_tweet":"Done"}}'), { outcome: 'confirmed', state: true });
  assert.deepEqual(classifyResponse(unlike, 200, '{"data":{"unfavorite_tweet":"Done"}}'), { outcome: 'confirmed', state: false });
  assert.deepEqual(classifyResponse(like, 200, '{"errors":[{"code":139}],"data":{}}'), { outcome: 'confirmed', state: true });
  assert.deepEqual(classifyResponse(unlike, 200, '{"errors":[{"code":139}]}'), { outcome: 'unknown' });
  assert.deepEqual(classifyResponse(like, 429, '{"errors":[{"code":88}]}'), { outcome: 'unknown' });
  assert.deepEqual(classifyResponse(like, 500, 'oops'), { outcome: 'unknown' });
  assert.deepEqual(classifyResponse(like, 200, '{"data":{"favorite_tweet":"Nope"}}'), { outcome: 'unknown' });
  assert.deepEqual(classifyResponse(follow, 200, '{"id_str":"9","following":false}'), { outcome: 'confirmed', state: true });
  assert.deepEqual(classifyResponse(follow, 200, '{"id_str":"9","protected":true}'), { outcome: 'requested' });
  assert.deepEqual(classifyResponse(follow, 200, '{"id_str":"9","follow_request_sent":true}'), { outcome: 'requested' });
  assert.deepEqual(classifyResponse(unfollow, 200, '{"id_str":"9"}'), { outcome: 'confirmed', state: false });
  assert.deepEqual(classifyResponse(follow, 403, '{"errors":[{"code":161}]}'), { outcome: 'unknown' });
  assert.deepEqual(classifyResponse(follow, 200, '[]'), { outcome: 'unknown' });
});

test('synthesized bodies: like Done, follow clones the last user object', () => {
  assert.equal(synthesizedBody({ kind: 'like', id: '1', key: 'tweet:1', want: true }, undefined), '{"data":{"favorite_tweet":"Done"}}');
  assert.equal(synthesizedBody({ kind: 'like', id: '1', key: 'tweet:1', want: false }, undefined), '{"data":{"unfavorite_tweet":"Done"}}');
  const follow: MutationMatch = { kind: 'follow', id: '9', key: 'user:9', want: false };
  assert.deepEqual(JSON.parse(synthesizedBody(follow, '{"id_str":"9","screen_name":"a","following":true}')), { id_str: '9', screen_name: 'a', following: false });
  assert.deepEqual(JSON.parse(synthesizedBody(follow, '{"id_str":"8"}')), { id: 9, id_str: '9', following: false });
  assert.deepEqual(JSON.parse(synthesizedBody(follow, 'garbage')), { id: 9, id_str: '9', following: false });
});

// ---------- lane FSM ----------

type Result = { kind: 'wire' | 'synthetic'; want: boolean; n?: number };
type Wire = { n: number; key: string; want: boolean; resolve(outcome: 'ok' | 'unknown' | 'reject'): void };

function harness() {
  const lanes = createLanes<Result>();
  const wire: Wire[] = [];
  const open = new Map<string, number>();
  let maxConcurrent = 0;
  let n = 0;
  const click = (key: string, want: boolean, signal?: AbortSignal) => {
    const id = n++;
    const req: LaneRequest<Result> = {
      want,
      signal,
      send: () => new Promise<Result>((resolve, reject) => {
        open.set(key, (open.get(key) ?? 0) + 1);
        maxConcurrent = Math.max(maxConcurrent, open.get(key)!);
        wire.push({ n: id, key, want, resolve: outcome => {
          open.set(key, open.get(key)! - 1);
          if (outcome === 'reject') reject(new TypeError('Failed to fetch'));
          else resolve({ kind: 'wire', want, n: outcome === 'ok' ? id : -1 });
        } });
      }),
      classify: (result): Promise<Settled> => Promise.resolve(result.n === -1 ? { outcome: 'unknown' } : { outcome: 'confirmed', state: result.want }),
      synthesize: () => ({ kind: 'synthetic', want }),
    };
    return lanes.submit(key, req);
  };
  return { lanes, wire, click, get maxConcurrent() { return maxConcurrent; } };
}

test('lane table: idle sends; busy holds; same direction shares; opposite pair-cancels', async () => {
  const h = harness();
  const a = h.click('t', true);                     // idle -> wire
  const b = h.click('t', false);                    // busy -> held
  const c = h.click('t', true);                     // opposite of held -> pair cancel b+c
  assert.equal(h.wire.length, 1);
  const d = h.click('t', false);                    // busy -> held again
  const e = h.click('t', false);                    // same as held -> shares
  assert.deepEqual(h.lanes.stats, { sent: 1, held: 2, shared: 1, paired: 1, synthesized: 0, cancelled: 0 });
  h.wire[0]!.resolve('ok');
  assert.deepEqual(await a, { kind: 'wire', want: true, n: 0 });
  assert.deepEqual(await b, { kind: 'synthetic', want: false });
  assert.deepEqual(await c, { kind: 'synthetic', want: true });
  await tick();
  assert.equal(h.wire.length, 2);                   // d released exactly once; e waits behind it
  assert.equal(h.wire[1]!.n, 3);
  h.wire[1]!.resolve('ok');
  assert.deepEqual(await d, { kind: 'wire', want: false, n: 3 });
  assert.deepEqual(await e, { kind: 'synthetic', want: false });
  assert.equal(h.lanes.size(), 0);
  assert.equal(h.maxConcurrent, 1);
});

test('lane table: pending matching confirmed state is satisfied without a request', async () => {
  const h = harness();
  const a = h.click('t', true);
  const b = h.click('t', true);                     // stale duplicate like
  h.wire[0]!.resolve('ok');
  await a;
  assert.deepEqual(await b, { kind: 'synthetic', want: true });
  assert.equal(h.wire.length, 1);
});

test('lane table: unknown outcome and rejection release the held request as-is', async () => {
  const h = harness();
  const a = h.click('t', true);
  const b = h.click('t', true);
  h.wire[0]!.resolve('unknown');
  assert.deepEqual(await a, { kind: 'wire', want: true, n: -1 });
  await tick();
  assert.equal(h.wire.length, 2);                   // not synthesized: X's own behavior stands
  const c = h.click('t', false);
  h.wire[1]!.resolve('reject');
  await assert.rejects(b, TypeError);               // rejection reaches X unchanged
  await tick();
  assert.equal(h.wire.length, 3);
  h.wire[2]!.resolve('ok');
  assert.deepEqual(await c, { kind: 'wire', want: false, n: 2 });
});

test('lane table: aborting a held request rejects it and it never reaches the wire', async () => {
  const h = harness();
  const a = h.click('t', true);
  const controller = new AbortController();
  const b = h.click('t', false, controller.signal);
  controller.abort();
  await assert.rejects(b, (error: unknown) => (error as Error).name === 'AbortError');
  h.wire[0]!.resolve('ok');
  await a;
  await tick();
  assert.equal(h.wire.length, 1);
  assert.equal(h.lanes.size(), 0);
});

test('lane table: separate targets never block each other', () => {
  const h = harness();
  void h.click('t1', true);
  void h.click('t2', true);
  void h.click('u1', false);
  assert.equal(h.wire.length, 3);
});

function rng(seed: number) {
  return () => { seed = (seed * 1_103_515_245 + 12_345) & 0x7fffffff; return seed / 0x7fffffff; };
}

test('property: wire ⊆ naive in click order, never concurrent, final state == last intent', async () => {
  for (let seed = 1; seed <= 300; seed++) {
    const random = rng(seed);
    const h = harness();
    const keys = ['a', 'b', 'c'];
    const intent = new Map<string, boolean>();       // X's optimistic view: each click toggles
    const server = new Map<string, boolean>();
    const naive: { n: number; key: string; want: boolean }[] = [];
    const failures = random() < 0.3;
    const results: Promise<unknown>[] = [];
    const done = new Set<Wire>();
    const settleOne = () => {
      const openWire = h.wire.filter(w => !done.has(w));
      if (!openWire.length) return;
      const w = openWire[Math.floor(random() * openWire.length)]!;
      done.add(w);
      const roll = random();
      const outcome = failures && roll < 0.2 ? 'unknown' : failures && roll < 0.3 ? 'reject' : 'ok';
      if (outcome === 'ok') server.set(w.key, w.want);
      w.resolve(outcome);
    };
    for (let step = 0; step < 40; step++) {
      if (random() < 0.6) {
        const key = keys[Math.floor(random() * keys.length)]!;
        const want = !(intent.get(key) ?? false);
        intent.set(key, want);
        naive.push({ n: naive.length, key, want });
        results.push(h.click(key, want).catch(() => {}));
      } else settleOne();
      await tick();
    }
    while (h.wire.length > done.size) { settleOne(); await tick(); }
    await Promise.all(results);
    assert.equal(h.maxConcurrent <= 1, true, `seed ${seed}: concurrent`);
    // Every wire request is one of X's own, sent in click order per target.
    for (const key of keys) {
      const sent = h.wire.filter(w => w.key === key).map(w => w.n);
      assert.deepEqual(sent, [...sent].sort((x, y) => x - y), `seed ${seed}: order`);
      for (const n of sent) assert.equal(naive[n]!.key, key);
      for (const w of h.wire) assert.equal(naive[w.n]!.want, w.want);
      if (!failures && intent.has(key) && naive.some(c => c.key === key)) {
        // With no failures the confirmed server state equals the last click intent.
        assert.equal(server.get(key) ?? false, intent.get(key), `seed ${seed}: final ${key}`);
      }
    }
    assert.equal(new Set(h.wire.map(w => w.n)).size, h.wire.length, `seed ${seed}: sent twice`);
    assert.ok(h.wire.length <= naive.length);
    assert.equal(h.lanes.size(), 0, `seed ${seed}: lanes drained`);
  }
});

// ---------- fetch gate ----------

function fakeWindow(respond: (input: unknown, init?: RequestInit) => Promise<Response>) {
  const calls: { input: unknown; init?: RequestInit }[] = [];
  const original = function (input: unknown, init?: RequestInit) { calls.push({ input, init }); return respond(input, init); } as typeof fetch;
  return { win: { fetch: original, location: { href: BASE } }, original, calls };
}
const json = (body: unknown, status = 200) => new Response(JSON.stringify(body), { status, headers: { 'content-type': 'application/json' } });

test('gate: unmatched requests return the original promise; rejections pass through', async () => {
  const failure = Promise.reject(new TypeError('Failed to fetch'));
  failure.catch(() => {});
  const { win, calls } = fakeWindow((input, init) => String(input).includes('fail') || String(init?.body).includes('666') ? failure : Promise.resolve(json({})));
  const gate = installMutationGate(win);
  assert.equal(gate.installed, true);
  assert.equal(win.fetch('/i/api/fail'), failure);
  await assert.rejects(win.fetch('/i/api/graphql/x/FavoriteTweet', post(likeBody('666'))));
  assert.equal(calls.length, 2);
  gate.dispose();
});

test('gate: burst like/unlike/like on one tweet sends one request and resolves every caller', async () => {
  let release!: () => void;
  const gateOpen = new Promise<void>(resolve => { release = resolve; });
  const { win, calls, original } = fakeWindow(async () => { await gateOpen; return json({ data: { favorite_tweet: 'Done' } }); });
  const gate = installMutationGate(win);
  const url = '/i/api/graphql/lI07N6Otwv1PhnEgXILM7A/FavoriteTweet';
  const unurl = '/i/api/graphql/ZYKSe-w7KEslx3JhSIk5LA/UnfavoriteTweet';
  const a = win.fetch(url, post(likeBody('5')));
  const b = win.fetch(unurl, post(likeBody('5')));
  const c = win.fetch(url, post(likeBody('5')));
  assert.equal(calls.length, 1);
  release();
  assert.deepEqual(await (await a).json(), { data: { favorite_tweet: 'Done' } });
  assert.deepEqual(await (await b).json(), { data: { unfavorite_tweet: 'Done' } });
  assert.deepEqual(await (await c).json(), { data: { favorite_tweet: 'Done' } });
  assert.equal(calls.length, 1);
  gate.dispose();
  assert.equal(win.fetch, original);
});

test('gate: kill switch leaves a captured wrapper as pure pass-through', async () => {
  const { win, calls } = fakeWindow(() => new Promise(() => {}));
  const gate = installMutationGate(win);
  const captured = win.fetch;
  const wrapped = { fetch: captured };               // e.g. another wrapper installed on top
  gate.dispose();
  void wrapped.fetch('/i/api/graphql/x/FavoriteTweet', post(likeBody('1')));
  void wrapped.fetch('/i/api/graphql/x/FavoriteTweet', post(likeBody('1')));
  assert.equal(calls.length, 2);
});

test('gate: composes with an earlier fetch wrapper instead of replacing it', async () => {
  const { win, original } = fakeWindow(() => Promise.resolve(json({ data: { favorite_tweet: 'Done' } })));
  const seen: unknown[] = [];
  const observer = function (this: unknown, ...args: Parameters<typeof fetch>) { seen.push(args[0]); return Reflect.apply(original, this, args); } as typeof fetch;
  win.fetch = observer;
  const gate = installMutationGate(win);
  await win.fetch('/i/api/graphql/x/FavoriteTweet', post(likeBody('1')));
  assert.equal(seen.length, 1);
  gate.dispose();
  assert.equal(win.fetch, observer);
});

// ---------- click guard: see tests/clickGuard.test.ts (held clicks are delivered, never dropped) ----------

// ---------- XHR transport (X's logged-in client sends these mutations with XMLHttpRequest) ----------

type XhrWire = { name: string; id: string };
function xhrEnv(liked: boolean) {
  const server = { liked, wire: [] as XhrWire[], inflight: new Map<string, number>(), concurrent: false };
  const replies: (() => void)[] = [];
  class FakeXHR extends EventTarget {
    #s = { readyState: 0, status: 0, text: '', method: '', url: '' };
    responseType: XMLHttpRequestResponseType = '';
    get readyState() { return this.#s.readyState; }
    get status() { return this.#s.status; }
    get responseText() { return this.#s.text; }
    get response() { return this.#s.text; }
    get responseURL() { return this.#s.readyState === 4 ? `https://x.com${this.#s.url}` : ''; }
    getResponseHeader() { return 'application/json'; }
    getAllResponseHeaders() { return 'content-type: application/json\r\n'; }
    open(method: string, url: string) { Object.assign(this.#s, { method, url, readyState: 1, status: 0, text: '' }); }
    send(body: string) {
      const name = this.#s.url.split('/').pop()!;
      const id = String(JSON.parse(body).variables.tweet_id);
      const n = (server.inflight.get(id) ?? 0) + 1;
      server.inflight.set(id, n);
      if (n > 1) server.concurrent = true;
      server.wire.push({ name, id });
      replies.push(() => {
        server.inflight.set(id, server.inflight.get(id)! - 1);
        const want = name === 'FavoriteTweet';
        let text: string;
        if (want && server.liked) text = '{"data":{},"errors":[{"code":139,"message":"already favorited"}]}';
        else { server.liked = want; text = want ? '{"data":{"favorite_tweet":"Done"}}' : '{"data":{"unfavorite_tweet":"Done"}}'; }
        Object.assign(this.#s, { readyState: 4, status: 200, text });
        for (const type of ['readystatechange', 'load', 'loadend']) this.dispatchEvent(new Event(type));
      });
    }
    abort() {
      Object.assign(this.#s, { readyState: 4, status: 0 });
      for (const type of ['readystatechange', 'abort', 'loadend']) this.dispatchEvent(new Event(type));
      this.#s.readyState = 0;
    }
  }
  const win = { fetch: (async () => json({})) as typeof fetch, location: { href: BASE }, XMLHttpRequest: FakeXHR as unknown as typeof XMLHttpRequest };
  // X's click handler: sends the opposite of the current UI state and flips the UI optimistically.
  let ui = liked;
  const results: { xhr: XMLHttpRequest; events: string[] }[] = [];
  const click = (id = '5') => {
    const xhr = new win.XMLHttpRequest();
    const events: string[] = [];
    for (const type of ['readystatechange', 'load', 'abort', 'loadend']) xhr.addEventListener(type, () => events.push(type === 'readystatechange' ? `rs${xhr.readyState}` : type));
    xhr.open('POST', `/i/api/graphql/q/${ui ? 'UnfavoriteTweet' : 'FavoriteTweet'}`);
    xhr.send(likeBody(id));
    ui = !ui;
    results.push({ xhr, events });
    return xhr;
  };
  return { win, server, replies, click, results, get ui() { return ui; } };
}

test('gate (XHR): 7 like/unlike clicks with out-of-order completion: wire ⊆ naive, final server == last intent', async () => {
  const env = xhrEnv(true);
  const gate = installMutationGate(env.win);
  for (let i = 0; i < 7; i++) { env.click(); await tick(); }
  // Naive X sends 7 concurrent requests; the lane sends the first and pairs the rest away.
  assert.deepEqual(env.server.wire.map(w => w.name), ['UnfavoriteTweet']);
  // Complete whatever is on the wire, newest first (out of order).
  while (env.replies.length) { env.replies.pop()!(); await tick(); }
  await tick();
  assert.equal(env.server.liked, env.ui, 'server state equals the last click intent');
  assert.equal(env.server.concurrent, false);
  for (const { xhr, events } of env.results) {
    assert.equal(xhr.readyState, 4);
    assert.equal(xhr.status, 200);
    assert.equal(events.filter(e => e === 'loadend').length, 1, 'every X request completes exactly once');
    assert.ok(JSON.parse(xhr.responseText).data, 'with a success body of its own shape');
  }
  const held = env.results[1]!;
  assert.deepEqual(held.events, ['rs2', 'rs3', 'rs4', 'load', 'loadend'], 'browser event order for a synthesized completion');
  assert.deepEqual(JSON.parse(held.xhr.responseText), { data: { favorite_tweet: 'Done' } });
  assert.equal(held.xhr.getResponseHeader('Content-Type'), 'application/json; charset=utf-8');
  assert.equal(gate.lanes.size(), 0);
  gate.dispose();
});

test('gate (XHR): randomized bursts keep wire ⊆ naive, never concurrent, final == last intent', async () => {
  for (let seed = 1; seed <= 40; seed++) {
    const random = rng(seed);
    const env = xhrEnv(random() < 0.5);
    const gate = installMutationGate(env.win);
    const clicks = 1 + Math.floor(random() * 8);
    for (let i = 0; i < clicks; i++) {
      env.click();
      await tick();
      // Sometimes the server answers an in-flight request before the next click, in any order.
      while (env.replies.length && random() < 0.4) { env.replies.splice(Math.floor(random() * env.replies.length), 1)[0]!(); await tick(); }
    }
    while (env.replies.length) { env.replies.splice(Math.floor(random() * env.replies.length), 1)[0]!(); await tick(); }
    await tick();
    assert.equal(env.server.concurrent, false, `seed ${seed}: concurrent`);
    assert.ok(env.server.wire.length <= clicks, `seed ${seed}: wire ⊆ naive`);
    assert.equal(env.server.liked, env.ui, `seed ${seed}: final state`);
    for (const { events } of env.results) assert.equal(events.filter(e => e === 'loadend').length, 1, `seed ${seed}: one loadend each`);
    assert.equal(gate.lanes.size(), 0, `seed ${seed}: lanes drained`);
    gate.dispose();
  }
});

test('gate (XHR): abort of a held request never reaches the wire; unmatched XHRs are untouched', async () => {
  const env = xhrEnv(false);
  const nativeSend = env.win.XMLHttpRequest.prototype.send;
  const gate = installMutationGate(env.win);
  env.click();                                   // Favorite: on the wire
  const held = env.click();                      // Unfavorite: held behind it
  held.abort();
  await tick();
  assert.deepEqual(env.results[1]!.events, ['rs4', 'abort', 'loadend']);
  assert.equal(held.readyState, 0);
  env.replies.shift()!();
  await tick();
  assert.deepEqual(env.server.wire.map(w => w.name), ['FavoriteTweet']);
  // Reuse after abort: the object behaves natively again.
  held.open('POST', '/i/api/graphql/q/UnfavoriteTweet');
  assert.equal(held.readyState, 1);
  // A non-mutation XHR goes straight to the native send (the fake parses its body and throws on null).
  const plain = new env.win.XMLHttpRequest();
  plain.open('GET', '/i/api/2/badge_count/badge_count.json');
  assert.throws(() => plain.send(null));
  assert.notEqual(env.win.XMLHttpRequest.prototype.send, nativeSend, 'hooked while installed');
  gate.dispose();
  assert.equal(env.win.XMLHttpRequest.prototype.send, nativeSend, 'dispose restores the native send');
});

test('feature flag: fixLikeFollow defaults on and is one of the Fixes', () => {
  assert.equal(FEATURE_DEFAULTS.fixLikeFollow, true);
  // A core flag: owned by no plugin, so no plugin switch can turn it off (src/areas/table.ts).
  assert.deepEqual(X_FEATURES.filter(feature => feature.area === null && feature.group === 'fixes').map(feature => feature.id),
    ['fixLikeFollow', 'fixScrollRestore', 'fixTimelineJump', 'fixHomeTab', 'fixNotificationBadge', 'fixNewPostsPill', 'fixMediaUpload', 'followingChronological', 'fixChatButton', 'composerRestorePrompt']);
  for (const key of ['fixScrollRestore', 'fixTimelineJump', 'fixHomeTab', 'fixNotificationBadge', 'fixNewPostsPill', 'fixMediaUpload', 'followingChronological', 'fixChatButton', 'composerRestorePrompt'] as const) {
    assert.equal(FEATURE_DEFAULTS[key], true, key);
  }
});

// ---------- failed in-flight request: nothing unconfirmed is ever answered with a success ----------

type XResult = { kind: 'wire' | 'synthetic'; ok: boolean; n: number };
/**
 * Lane harness with X's view of each caller: a wire result with ok=false (429, 5xx) or a rejection
 * (network, abort) makes X revert that click's optimistic change; a success commits it. X's UI ends
 * on the intent of the last committed click (redux-optimist replay of absolute `following`/`favorited`).
 */
function failHarness(initial = false) {
  const lanes = createLanes<XResult>();
  const wire: { n: number; want: boolean; settle(outcome: 'ok' | 'fail' | 'odd' | 'reject' | 'abort'): void }[] = [];
  const clicks: { want: boolean; status: 'pending' | 'committed' | 'reverted'; how?: string }[] = [];
  let server = initial;
  let open = 0, maxOpen = 0;
  const click = (want: boolean) => {
    const n = clicks.length;
    const entry: { want: boolean; status: 'pending' | 'committed' | 'reverted'; how?: string } = { want, status: 'pending' };
    clicks.push(entry);
    const promise = lanes.submit('user:9', {
      want,
      send: () => new Promise<XResult>((resolve, reject) => {
        open++; maxOpen = Math.max(maxOpen, open);
        wire.push({ n, want, settle: outcome => {
          open--;
          if (outcome === 'ok') { server = want; resolve({ kind: 'wire', ok: true, n }); }
          else if (outcome === 'odd') resolve({ kind: 'wire', ok: true, n: -1 }); // a 200 the lane cannot read
          else if (outcome === 'fail') resolve({ kind: 'wire', ok: false, n });
          else reject(outcome === 'abort' ? new DOMException('The operation was aborted.', 'AbortError') : new TypeError('Failed to fetch'));
        } });
      }),
      classify: (result): Promise<Settled> => Promise.resolve(result.ok && result.n >= 0 ? { outcome: 'confirmed', state: want } : { outcome: 'unknown' }),
      synthesize: () => ({ kind: 'synthetic', ok: true, n }),
    });
    promise.then(result => { entry.status = result.ok ? 'committed' : 'reverted'; entry.how = result.kind; },
      error => { entry.status = 'reverted'; entry.how = (error as Error).name; });
    return promise.catch(() => undefined);
  };
  const ui = () => [...clicks].reverse().find(c => c.status === 'committed')?.want ?? initial;
  return { lanes, wire, clicks, click, ui, get server() { return server; }, get maxOpen() { return maxOpen; } };
}

test('lanes: follow (429) + unfollow + follow while it is in flight: no synthesized success, the last follow is sent', async () => {
  const h = failHarness(false);
  const a = h.click(true);
  const b = h.click(false); // held (after the confirm sheet)
  const c = h.click(true); // pairs with the held unfollow
  h.wire[0]!.settle('fail'); // HTTP 429
  await Promise.all([a, b]);
  await tick();
  assert.equal(h.clicks[1]!.how, 'AbortError', 'the unfollow fails like an aborted request: X reverts it');
  assert.equal(h.wire.length, 2, 'the latest intent goes out once, as X made it');
  assert.deepEqual([h.wire[1]!.n, h.wire[1]!.want], [2, true]);
  assert.equal(h.lanes.stats.synthesized, 0);
  h.wire[1]!.settle('ok');
  await c;
  assert.equal(h.clicks[2]!.how, 'wire');
  assert.equal(h.server, true);
  assert.equal(h.ui(), h.server);
  await tick();
  assert.equal(h.lanes.size(), 0);
});

test('lanes: follow (429) + unfollow + follow, and the released follow is rate-limited too', async () => {
  const h = failHarness(false);
  const all = [h.click(true), h.click(false), h.click(true)];
  h.wire[0]!.settle('fail');
  await tick(); await tick();
  h.wire[1]!.settle('fail');
  await Promise.all(all);
  assert.equal(h.server, false);
  assert.equal(h.ui(), false, 'every optimistic change reverted: X shows the real state');
  assert.equal(h.lanes.stats.synthesized, 0);
});

test('lanes: like (500) + held unlike: the unlike is sent for real, never answered by the lane', async () => {
  const h = failHarness(false);
  const a = h.click(true);
  const b = h.click(false);
  h.wire[0]!.settle('fail'); // HTTP 500
  await a;
  await tick();
  assert.equal(h.wire.length, 2);
  assert.deepEqual([h.wire[1]!.n, h.wire[1]!.want], [1, false]);
  h.wire[1]!.settle('ok');
  await b;
  assert.equal(h.clicks[1]!.how, 'wire');
  assert.equal(h.ui(), h.server);
  assert.equal(h.lanes.stats.synthesized, 0);
});

test('lanes: X aborts the in-flight request: held pair fails, the latest intent is released', async () => {
  const h = failHarness(true);
  const all = [h.click(false), h.click(true), h.click(false)];
  h.wire[0]!.settle('abort');
  await tick(); await tick();
  assert.equal(h.clicks[1]!.how, 'AbortError');
  assert.equal(h.wire.length, 2);
  assert.equal(h.wire[1]!.n, 2);
  h.wire[1]!.settle('ok');
  await Promise.all(all);
  assert.equal(h.server, false);
  assert.equal(h.ui(), false);
  assert.equal(h.lanes.stats.synthesized, 0);
});

test('lanes: unknown outcome (a 200 the lane cannot read) confirms nothing', async () => {
  const h = failHarness(false);
  const all = [h.click(true), h.click(false), h.click(true), h.click(true)];
  h.wire[0]!.settle('odd');
  await tick(); await tick();
  assert.equal(h.clicks[1]!.how, 'AbortError');
  assert.equal(h.wire.length, 2, 'one follow of the trailing run is released, the other waits behind it');
  assert.equal(h.wire[1]!.n, 2);
  h.wire[1]!.settle('ok');
  await Promise.all(all);
  assert.equal(h.clicks[3]!.how, 'synthetic', 'the stale duplicate is satisfied by the confirmed follow');
  assert.equal(h.wire.length, 2);
  assert.equal(h.ui(), true);
  assert.equal(h.server, true);
});

test('lanes: a held click in the same direction as the in-flight one no longer swallows a later reversal', async () => {
  const h = failHarness(false);
  const all = [h.click(true), h.click(true), h.click(false)]; // stale double follow, then unfollow
  h.wire[0]!.settle('ok');
  await tick(); await tick();
  assert.equal(h.clicks[1]!.how, 'synthetic', 'already satisfied by the confirmed follow');
  assert.equal(h.wire.length, 2, 'the unfollow is sent');
  h.wire[1]!.settle('ok');
  await Promise.all(all);
  assert.equal(h.server, false);
  assert.equal(h.ui(), false);
});

test('property: with failures the final UI equals the server; each request sent once, in click order, never concurrent', async () => {
  for (let seed = 1; seed <= 400; seed++) {
    const random = rng(seed);
    const h = failHarness(random() < 0.5);
    const results: Promise<unknown>[] = [];
    let intent = h.ui();
    const settled = new Set<number>();
    const settleOne = () => {
      const index = h.wire.findIndex((_, i) => !settled.has(i));
      if (index < 0) return;
      settled.add(index);
      const roll = random();
      h.wire[index]!.settle(roll < 0.2 ? 'fail' : roll < 0.3 ? 'reject' : roll < 0.35 ? 'abort' : 'ok');
    };
    for (let step = 0; step < 30; step++) {
      if (random() < 0.6) { intent = !intent; results.push(h.click(intent)); }
      else settleOne();
      await tick();
    }
    while (h.wire.length > settled.size) { settleOne(); await tick(); }
    await Promise.all(results);
    assert.equal(h.ui(), h.server, `seed ${seed}: UI differs from the server`);
    assert.ok(h.maxOpen <= 1, `seed ${seed}: concurrent`);
    const ns = h.wire.map(w => w.n);
    assert.deepEqual(ns, [...ns].sort((x, y) => x - y), `seed ${seed}: order`);
    assert.equal(new Set(ns).size, ns.length, `seed ${seed}: sent twice`);
    for (const w of h.wire) assert.equal(h.clicks[w.n]!.want, w.want);
    assert.equal(h.lanes.size(), 0, `seed ${seed}: drained`);
  }
});