ui/e2e/quickmatch.spec.ts

@@ -76,3 +76,17 @@ test('quick game: a foreground resync recovers a join shed while the stream stay
   await expect(page.getByText('Robo')).toBeVisible();
   await expect(page.getByText(/Searching for opponent/)).toHaveCount(0);
 });
+
+// Regression: an opponent joining must not freeze the screen. The in-game live-event effect tracked
+// the `view` it also writes, so opponent_joined re-invalidated itself in a tight loop (opponent_moved
+// was spared only by its delta's move-count idempotency). The board must still respond afterwards.
+test('quick game: the board stays interactive after the opponent joins', async ({ page }) => {
+  await enterOpenGame(page);
+  await page.evaluate(() => (window as unknown as { __mock: { joinOpponent(): void } }).__mock.joinOpponent());
+  await expect(page.getByText('Robo')).toBeVisible();
+
+  // Place a rack tile on the centre star: a frozen screen renders no pending tile.
+  await page.locator('.rack .tile').first().click();
+  await page.locator('[data-cell]:not(.filled)').nth(112).click(); // row 7, col 7
+  await expect(page.locator('[data-cell].pending')).toHaveCount(1);
+});

ui/src/game/Game.svelte

@@ -1,5 +1,5 @@
 <script lang="ts">
-  import { onDestroy, onMount } from 'svelte';
+  import { onDestroy, onMount, untrack } from 'svelte';
   import Screen from '../components/Screen.svelte';
   import TabBar from '../components/TabBar.svelte';
   import TapConfirm from '../components/TapConfirm.svelte';
@@ -222,29 +222,38 @@
   $effect(() => {
     const e = app.lastEvent;
     if (!e) return;
-    if (e.kind === 'opponent_moved' && e.gameId === id) {
-      // While composing, reload so a draft overlapping the new move is reconciled; otherwise apply
-      // the move as a delta with no fetch.
-      if (placement.pending.length > 0) void load();
-      else applyDelta(applyMoveDelta(cacheSnapshot(), { move: e.move, game: e.game, bagLen: e.bagLen }));
-    } else if (e.kind === 'your_turn' && e.gameId === id) {
-      // The opponent_moved delta carries the new state; your_turn only confirms the turn. Refetch
-      // only if we missed the move (our cached count trails the event's).
-      if (view && e.moveCount > view.game.moveCount) void load();
-    } else if (e.kind === 'game_over' && e.gameId === id) {
-      applyDelta(applyGameOver(cacheSnapshot(), e.game));
-    } else if (e.kind === 'opponent_joined' && e.gameId === id && e.state) {
-      // The opponent took the empty seat: adopt the new participants and status in place,
-      // leaving the board, rack and any pending placement untouched (no refetch, no flicker).
-      const r = applyOpponentJoined(cacheSnapshot(), e.state);
-      if (r) {
-        view = r.view;
-        setCachedGame(id, r.view, r.moves);
+    // Depend only on app.lastEvent: process each event once. The branches below READ and WRITE
+    // view/moves/placement, so tracking those reads would re-run this effect from its own
+    // `view = …` write — with app.lastEvent unchanged it re-enters the same branch, a tight loop.
+    // opponent_moved self-limits via the delta's move-count idempotency, but opponent_joined (and
+    // game_over) do not, so an opponent joining froze the whole game screen. (Tracking placement
+    // likewise re-fired the handler on every tile a player placed.) untrack scopes the body's reads
+    // out of the effect's dependencies.
+    untrack(() => {
+      if (e.kind === 'opponent_moved' && e.gameId === id) {
+        // While composing, reload so a draft overlapping the new move is reconciled; otherwise apply
+        // the move as a delta with no fetch.
+        if (placement.pending.length > 0) void load();
+        else applyDelta(applyMoveDelta(cacheSnapshot(), { move: e.move, game: e.game, bagLen: e.bagLen }));
+      } else if (e.kind === 'your_turn' && e.gameId === id) {
+        // The opponent_moved delta carries the new state; your_turn only confirms the turn. Refetch
+        // only if we missed the move (our cached count trails the event's).
+        if (view && e.moveCount > view.game.moveCount) void load();
+      } else if (e.kind === 'game_over' && e.gameId === id) {
+        applyDelta(applyGameOver(cacheSnapshot(), e.game));
+      } else if (e.kind === 'opponent_joined' && e.gameId === id && e.state) {
+        // The opponent took the empty seat: adopt the new participants and status in place,
+        // leaving the board, rack and any pending placement untouched (no refetch, no flicker).
+        const r = applyOpponentJoined(cacheSnapshot(), e.state);
+        if (r) {
+          view = r.view;
+          setCachedGame(id, r.view, r.moves);
+        }
+      } else if (e.kind === 'notify' && (e.sub === 'friend_added' || e.sub === 'friend_declined')) {
+        // A request the player sent was answered: re-derive the in-game "add friend" state.
+        void loadFriends();
       }
-    } else if (e.kind === 'notify' && (e.sub === 'friend_added' || e.sub === 'friend_declined')) {
-      // A request the player sent was answered: re-derive the in-game "add friend" state.
-      void loadFriends();
-    }
+    });
   });
 
   // The live-event hub is best-effort and never replays (see lib/app.svelte.ts): an event dropped