feat(offline): hotseat record schema + source (locks, host actions)

Extend the local game to offline pass-and-play (hotseat):
- serialize.ts: Seat.pin, record hotseat + hostPin (all optional; old
  vs_ai records read hotseat as false).
- source.ts: create() takes hotseat/hostPin + per-seat pins; stateView
  reveals the seat-to-move's rack and withholds it (locked) when that
  seat is PIN-locked, until unlockSeat; ephemeral per-turn unlock
  re-locks on advance; new unlockSeat / verifyHostPin / hostAction
  (skip/resign/terminate); gameView sets vsAi=!hotseat + the hotseat flag.
- model.ts: GameView.hotseat, StateView.locked (offline-only, optional).

Tests: source.hotseat (lock/unlock/re-lock, host skip/resign/terminate,
master-PIN gate, natural-end persistence) + serialize hotseat shape.

ui/src/lib/localgame/source.hotseat.test.ts

@@ -0,0 +1,132 @@
+import { describe, it, expect, vi } from 'vitest';
+import type { StateView } from '../model';
+
+// getDawg is mocked to the committed sample dictionary (the store's IndexedDB is absent under node,
+// so games live in the source's in-memory cache — created once, then driven without reload).
+vi.mock('../dict', () => ({
+  getDawg: async () => {
+    const { Dawg } = await import('../dict/dawg');
+    const { readFileSync } = await import('node:fs');
+    return new Dawg(new Uint8Array(readFileSync(new URL('../dict/testdata/sample_en.dawg', import.meta.url))));
+  },
+}));
+
+import { LocalSource } from './source';
+import type { Seat } from './serialize';
+import { newLock } from '../pin';
+
+async function hotseat(id: string, seats: Seat[], hostDigits = '9999'): Promise<LocalSource> {
+  const src = new LocalSource();
+  await src.create({
+    id,
+    variant: 'scrabble_en',
+    dictVersion: 'sample',
+    seed: 3n,
+    multipleWords: true,
+    seats,
+    hotseat: true,
+    hostPin: await newLock(hostDigits),
+  });
+  return src;
+}
+
+describe('LocalSource hotseat', () => {
+  it('creates a pass-and-play game: not vs_ai, board visible, first seat to move', async () => {
+    const src = await hotseat('local:h1', [
+      { kind: 'human', name: 'Ann' },
+      { kind: 'human', name: 'Bob' },
+    ]);
+    const st = await src.gameState('local:h1');
+    expect(st.game.vsAi).toBe(false);
+    expect(st.game.hotseat).toBe(true);
+    expect(st.game.toMove).toBe(0);
+    expect(st.locked).toBeFalsy(); // seat 0 has no PIN
+    expect(st.rack.length).toBe(7);
+    expect(st.game.seats.map((s) => s.displayName)).toEqual(['Ann', 'Bob']);
+  });
+
+  it('hides the rack of a PIN-locked seat until the right PIN unlocks it', async () => {
+    const src = await hotseat('local:h2', [
+      { kind: 'human', name: 'Ann', pin: await newLock('1234') },
+      { kind: 'human', name: 'Bob' },
+    ]);
+    const st = await src.gameState('local:h2');
+    expect(st.locked).toBe(true);
+    expect(st.rack).toEqual([]);
+
+    await expect(src.unlockSeat('local:h2', '0000')).rejects.toMatchObject({ code: 'wrong_pin' });
+
+    const opened = await src.unlockSeat('local:h2', '1234');
+    expect(opened.locked).toBe(false);
+    expect(opened.rack.length).toBe(7);
+  });
+
+  it('re-locks the seat when the turn advances and again when it comes back', async () => {
+    const src = await hotseat('local:h3', [
+      { kind: 'human', name: 'A', pin: await newLock('1111') },
+      { kind: 'human', name: 'B' },
+      { kind: 'human', name: 'C' },
+    ]);
+    await src.unlockSeat('local:h3', '1111');
+    await src.pass('local:h3'); // seat 0 -> 1
+    let st = await src.gameState('local:h3');
+    expect(st.game.toMove).toBe(1);
+    expect(st.locked).toBeFalsy(); // seat 1 has no PIN
+
+    await src.pass('local:h3'); // 1 -> 2
+    await src.pass('local:h3'); // 2 -> 0
+    st = await src.gameState('local:h3');
+    expect(st.game.toMove).toBe(0);
+    expect(st.locked).toBe(true); // seat 0 needs re-unlocking
+  });
+
+  it('lets the host skip the current turn, gated by the master PIN', async () => {
+    const src = await hotseat('local:h4', [
+      { kind: 'human', name: 'A' },
+      { kind: 'human', name: 'B' },
+    ], '4321');
+    expect((await src.gameState('local:h4')).game.toMove).toBe(0);
+    await expect(src.hostAction('local:h4', '0000', 'skip')).rejects.toMatchObject({ code: 'wrong_pin' });
+    const st = await src.hostAction('local:h4', '4321', 'skip');
+    expect(st).not.toBeNull();
+    expect((st as StateView).game.toMove).toBe(1);
+  });
+
+  it('lets the host resign a seat (ending a two-player game)', async () => {
+    const src = await hotseat('local:h5', [
+      { kind: 'human', name: 'A' },
+      { kind: 'human', name: 'B' },
+    ], '4321');
+    const st = await src.hostAction('local:h5', '4321', 'resign', 1);
+    expect((st as StateView).game.status).toBe('finished');
+  });
+
+  it('lets the host terminate the game, deleting it', async () => {
+    const src = await hotseat('local:h6', [
+      { kind: 'human', name: 'A' },
+      { kind: 'human', name: 'B' },
+    ], '4321');
+    const r = await src.hostAction('local:h6', '4321', 'terminate');
+    expect(r).toBeNull();
+    await expect(src.gameState('local:h6')).rejects.toMatchObject({ code: 'game_not_found' });
+  });
+
+  it('verifies the master PIN', async () => {
+    const src = await hotseat('local:h7', [
+      { kind: 'human', name: 'A' },
+      { kind: 'human', name: 'B' },
+    ], '4321');
+    expect(await src.verifyHostPin('local:h7', '4321')).toBe(true);
+    expect(await src.verifyHostPin('local:h7', '0000')).toBe(false);
+  });
+
+  it('persists a naturally finished game (scoreless run) as finished', async () => {
+    const src = await hotseat('local:h8', [
+      { kind: 'human', name: 'A' },
+      { kind: 'human', name: 'B' },
+    ]);
+    for (let i = 0; i < 6; i++) await src.pass('local:h8');
+    const st = await src.gameState('local:h8');
+    expect(st.game.status).toBe('finished');
+  });
+});