fix(ads): fire the hint interstitial on the confirmed move, not on the hint

Taking a hint fired the post-move interstitial immediately, when the hint's
preview tiles landed — interrupting the turn and reverting the board to the
rack on the ad's close while the hint stayed spent. Move the trigger to the
move confirmation: a hint applied this turn marks it (hintUsedThisTurn), and
the confirmed play fires the hint-kind interstitial (its own cooldown)
instead of the plain move one; the marker clears on any turn boundary
(applyMoveResult) so a hint-then-pass does not leak into the next move.

e2e: taking a hint fires no ad; confirming a move does.

ui/e2e/game.spec.ts

@@ -48,6 +48,33 @@ test('placing a tile and confirming via ✅ commits the move', async ({ page })
   await expect(page.locator('.make')).toBeHidden();
 });
 
+// Regression: taking a hint must NOT fire the post-move interstitial. Firing on the hint interrupted
+// placing the preview and reverted the board on the ad's close while the hint stayed spent (the
+// reported bug). In mock mode the ad stub shows an "ad fired" toast, standing in for a real VK ad.
+test('taking a hint does not fire the interstitial', async ({ page }) => {
+  await openGame(page);
+  // Take a hint (the control confirms on a second tap). It produces a legal preview, so the ✅
+  // control appears — proof the hint fired.
+  const hint = page.getByRole('button', { name: 'Hint' });
+  await hint.click();
+  await hint.click();
+  await expect(page.locator('.make')).toBeVisible();
+  // A spurious ad would have toasted by now; none may.
+  await page.waitForTimeout(400);
+  await expect(page.getByText('ad fired')).toHaveCount(0);
+});
+
+// The interstitial fires once the move is CONFIRMED (never on the hint / pass / exchange / resign).
+test('confirming a move fires the interstitial', 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();
+  await expect(page.getByText('ad fired')).toBeVisible();
+});
+
 test('a placed tile is saved as a draft and restored on reopening the game', async ({ page }) => {
   await openGame(page);
   await page.locator('.rack .tile').first().click();

ui/src/game/Game.svelte

@@ -94,6 +94,11 @@
   let exchangeOpen = $state(false);
   let exchangeSel = $state<number[]>([]);
   let resignOpen = $state(false);
+  // hintUsedThisTurn marks that a hint was applied on the current turn, so a confirmed play earns
+  // the hint-kind interstitial (its own 1-min cooldown) instead of the plain move one. Set in
+  // doHint when the hint's tiles land, read in commit, and cleared on any turn boundary
+  // (applyMoveResult) so a hint-then-pass does not leak into the next turn's move.
+  let hintUsedThisTurn = $state(false);
   let drag = $state<{ letter: string; blank: boolean; x: number; y: number; touch: boolean } | null>(null);
   // Landscape (wide) layout: when the viewport is wider than tall the game switches to a
   // two-column layout — the board fills the right side as a square fitted to the height (no
@@ -820,6 +825,9 @@
   // applyMoveResult renders the actor's own just-committed move from the response — the move, the
   // post-move game and the refilled rack — without a follow-up game.state + game.history.
   function applyMoveResult(r: MoveResult) {
+    // A turn boundary (play / pass / exchange / resign): clear the hint marker so it never leaks
+    // into the next turn. commit captures it before this runs.
+    hintUsedThisTurn = false;
     view = {
       game: r.game,
       seat: r.move.player,
@@ -942,6 +950,9 @@
     const sub = toSubmit(placement);
     if (!sub) return;
     busy = true;
+    // Capture the hint marker before applyMoveResult clears it: a move played off a hint earns the
+    // hint-kind interstitial (own cooldown), a plain move the move-kind one.
+    const usedHint = hintUsedThisTurn;
     try {
       applyMoveResult(await source.submitPlay(id, sub.tiles, variant));
       if (view?.game.hotseat) await advanceHotseat();
@@ -949,7 +960,7 @@
       zoomed = false;
       // A confirmed move may trigger a post-move interstitial (VK, frequency-gated, client-mirrored).
       // Only submitPlay earns one — never a pass / exchange / resign. Fire-and-forget.
-      void maybeShowInterstitial(app.profile?.ads, 'move', {
+      void maybeShowInterstitial(app.profile?.ads, usedHint ? 'hint' : 'move', {
         vsAi: !!view?.game.vsAi,
         online: connection.online && !offlineMode.active,
       });
@@ -1014,13 +1025,11 @@
     }
     try {
       const h = await source.hint(id);
-      // Applying a hint triggers its own post-move interstitial, independent of the move cooldown.
-      void maybeShowInterstitial(app.profile?.ads, 'hint', {
-        vsAi: !!view?.game.vsAi,
-        online: connection.online && !offlineMode.active,
-      });
       if (h.move.tiles.length && view) {
         placement = placementFromHint(h.move.tiles, view.rack);
+        // Mark the turn as hinted: the interstitial fires when the player CONFIRMS the move (commit),
+        // not now — showing it here would interrupt placing the preview and revert the board on close.
+        hintUsedThisTurn = true;
         // Scroll the (zoomed) board to the hint's placement rather than the top-left:
         // focus the centre of the laid tiles' bounding box.
         const p = placement.pending;