Stage 7: regression tests for the polished UI (logic + behaviour)

Lock the polish branch's behaviour so a future UI edit surfaces as a failing
assertion to re-agree or fix.

Unit (vitest, node env):
- placement: recallIndex, cellOccupied/isBlankSlot, non-linear direction, the
  single-tile submit default, and placementFromHint blank-fallback / rack-exhausted.
- banner: the marquee scroll-cycle repeat-then-advance, stop(), root-relative and
  multiple links.
- client.GatewayError. Extract the check-word constraints out of Game.svelte into a
  pure lib/checkword.ts (sanitize + canCheck) and cover them.

E2E (playwright mock, Chromium + WebKit):
- commit via the 🏁 control, history slide-down + close, the exchange dialog,
  check-word input sanitising + verdict, resign-to-finished, and the Settings
  board-label mode changing the on-board labels.

ui/e2e/game.spec.ts

@@ -0,0 +1,86 @@
+import { expect, test, type Page } from '@playwright/test';
+
+// Behaviour/display coverage for the polished game screen, driven entirely by the mock
+// transport (no backend). These lock the round-1..4 interactions so future UI edits
+// surface as a failing assertion — to be re-agreed or fixed. The pure logic behind them
+// (placement, check-word, board labels, result badges) is unit-tested separately.
+
+async function openGame(page: Page): Promise<void> {
+  await page.goto('/');
+  await page.getByRole('button', { name: /guest/i }).click();
+  await page.getByRole('button', { name: /Ann/ }).click(); // the seeded active game vs Ann
+  await expect(page.locator('[data-cell]').first()).toBeVisible();
+}
+
+test('placing a tile and confirming via 🏁 commits the move', async ({ page }) => {
+  await openGame(page);
+  await page.locator('.rack .tile').first().click();
+  await page.locator('[data-cell]:not(.filled)').nth(30).click();
+  await expect(page.locator('[data-cell].pending')).toHaveCount(1);
+
+  await page.locator('.make').click(); // open the MakeMove popover (short tap)
+  await page.locator('.pop.go').click(); // "Make move ✅"
+
+  // After the commit the placement is cleared: no pending tile, no 🏁 control.
+  await expect(page.locator('[data-cell].pending')).toHaveCount(0);
+  await expect(page.locator('.make')).toBeHidden();
+});
+
+test('history slides the board down and closes on a board tap', async ({ page }) => {
+  await openGame(page);
+  await page.locator('.burger').click();
+  await page.locator('.dropdown button').nth(0).click(); // History
+  await expect(page.locator('.history')).toBeVisible();
+  await expect(page.locator('.boardwrap.slid')).toBeVisible();
+
+  await page.locator('.boardwrap').click(); // tapping the board closes it
+  await expect(page.locator('.history')).toBeHidden();
+});
+
+test('Draw opens the exchange dialog and confirms a selection', async ({ page }) => {
+  await openGame(page);
+  await page.locator('button:has-text("🔄")').click(); // Draw tab
+  await expect(page.locator('.exch')).toBeVisible();
+
+  await page.locator('.etile').first().click();
+  await expect(page.locator('.etile.sel')).toHaveCount(1);
+  await page.locator('button.confirm').click();
+  await expect(page.locator('.exch')).toBeHidden();
+});
+
+test('check-word sanitises input and shows a verdict', async ({ page }) => {
+  await openGame(page);
+  await page.locator('.burger').click();
+  await page.locator('.dropdown button').nth(2).click(); // Check word
+
+  const input = page.locator('.check input');
+  await input.fill('qz9!a'); // digits/punctuation dropped, letters upper-cased
+  await expect(input).toHaveValue('QZA');
+
+  await page.locator('.check button').click(); // Check (enabled: length 3)
+  await expect(page.locator('.ok, .bad')).toBeVisible();
+});
+
+test('dropping the game ends it and shows the result', async ({ page }) => {
+  await openGame(page);
+  await page.locator('.burger').click();
+  await page.locator('.dropdown button').nth(3).click(); // Drop game
+  await page.locator('button.danger').click(); // confirm in the modal
+  await expect(page.locator('.status .over')).toBeVisible();
+});
+
+test('the board-label mode in Settings changes the on-board labels', async ({ page }) => {
+  await openGame(page);
+  // beginner (default) renders split "3× / word" labels.
+  await expect(page.locator('.bsplit').first()).toBeVisible();
+  await expect(page.locator('.b1')).toHaveCount(0);
+
+  // Switch to "classic" in Settings (in-SPA hash nav keeps the guest session).
+  await page.evaluate(() => (location.hash = '/settings'));
+  await page.locator('.seg').nth(2).locator('.opt').nth(1).click(); // board labels -> classic
+  await page.evaluate(() => (location.hash = '/game/g1'));
+
+  // classic renders single "3W"/"2L" labels and no split labels.
+  await expect(page.locator('.b1').first()).toBeVisible();
+  await expect(page.locator('.bsplit')).toHaveCount(0);
+});