test: markdown parser subsystem (58) + custom-emoji readers (32)

Via subagents, probe-verified against real output, no bugs:
- markdown: internal/utils (11), inline/runner (7), inline/parser (21 — bold/
  italic/underline/strike/code/spoiler/link, nesting, precedence, URL lookbehind),
  block/parser (19 — headings/code-fences/quotes/lists/<br>/escapes). Closes the
  biggest coverage hole (core message rendering).
- custom-emoji: PackMetaReader (6), PackImageReader (7), PackImagesReader (4),
  utils equality+makeImagePacks (5), recent-emoji promote/increment/100-cap (10).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/plugins/recent-emoji.test.ts

@@ -0,0 +1,114 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { MatrixClient, MatrixEvent } from 'matrix-js-sdk';
+import { addRecentEmoji, getRecentEmojis, IRecentEmojiContent } from './recent-emoji';
+import { AccountDataEvent } from '../../types/matrix/accountData';
+import { emojis } from './emoji';
+
+// A Map-backed MatrixClient stub supporting get/setAccountData.
+const createMx = () => {
+  const store = new Map<string, unknown>();
+  const mx = {
+    getAccountData: (type: string): MatrixEvent | undefined => {
+      if (!store.has(type)) return undefined;
+      const content = store.get(type);
+      return { getContent: () => content } as unknown as MatrixEvent;
+    },
+    setAccountData: (type: string, content: unknown) => {
+      store.set(type, content);
+      return Promise.resolve({});
+    },
+  };
+  return { mx: mx as unknown as MatrixClient, store };
+};
+
+const getStored = (store: Map<string, unknown>): IRecentEmojiContent['recent_emoji'] =>
+  (store.get(AccountDataEvent.ElementRecentEmoji) as IRecentEmojiContent | undefined)?.recent_emoji;
+
+// Pick two real unicode emojis to drive add->get round trips.
+const u1 = emojis[0].unicode;
+const u2 = emojis[1].unicode;
+
+test('getRecentEmojis returns [] when there is no account data', () => {
+  const { mx } = createMx();
+  assert.deepEqual(getRecentEmojis(mx), []);
+});
+
+test('getRecentEmojis returns [] when content is not an array', () => {
+  const { mx, store } = createMx();
+  store.set(AccountDataEvent.ElementRecentEmoji, { recent_emoji: 'nope' });
+  assert.deepEqual(getRecentEmojis(mx), []);
+});
+
+test('addRecentEmoji creates an entry with count 1', () => {
+  const { mx, store } = createMx();
+  addRecentEmoji(mx, u1);
+  assert.deepEqual(getStored(store), [[u1, 1]]);
+});
+
+test('adding the same emoji again increments its count and keeps it at front', () => {
+  const { mx, store } = createMx();
+  addRecentEmoji(mx, u1);
+  addRecentEmoji(mx, u1);
+  assert.deepEqual(getStored(store), [[u1, 2]]);
+});
+
+test('a newly added emoji is promoted to the front', () => {
+  const { mx, store } = createMx();
+  addRecentEmoji(mx, u1);
+  addRecentEmoji(mx, u2);
+  assert.deepEqual(getStored(store), [
+    [u2, 1],
+    [u1, 1],
+  ]);
+});
+
+test('re-adding an existing emoji promotes it to front and increments', () => {
+  const { mx, store } = createMx();
+  addRecentEmoji(mx, u1);
+  addRecentEmoji(mx, u2);
+  addRecentEmoji(mx, u1);
+  assert.deepEqual(getStored(store), [
+    [u1, 2],
+    [u2, 1],
+  ]);
+});
+
+test('list is capped at 100 entries', () => {
+  const { mx, store } = createMx();
+  for (let i = 0; i < 120; i += 1) {
+    addRecentEmoji(mx, `:emoji-${i}:`);
+  }
+  const stored = getStored(store)!;
+  assert.equal(stored.length, 100);
+  // most recently added is at the front
+  assert.equal(stored[0][0], ':emoji-119:');
+});
+
+test('getRecentEmojis resolves stored unicodes to known emoji objects', () => {
+  const { mx } = createMx();
+  addRecentEmoji(mx, u1);
+  addRecentEmoji(mx, u2);
+  const recent = getRecentEmojis(mx);
+  assert.equal(recent.length, 2);
+  assert.equal(recent[0].unicode, u2);
+  assert.equal(recent[1].unicode, u1);
+});
+
+test('getRecentEmojis skips unicodes with no matching emoji definition', () => {
+  const { mx } = createMx();
+  addRecentEmoji(mx, ':not-a-real-emoji:');
+  addRecentEmoji(mx, u1);
+  const recent = getRecentEmojis(mx);
+  assert.equal(recent.length, 1);
+  assert.equal(recent[0].unicode, u1);
+});
+
+test('getRecentEmojis respects the limit argument (slice before resolve)', () => {
+  const { mx } = createMx();
+  addRecentEmoji(mx, u1);
+  addRecentEmoji(mx, u2);
+  const recent = getRecentEmojis(mx, 1);
+  assert.equal(recent.length, 1);
+  assert.equal(recent[0].unicode, u2);
+});