fix(matchmaking): chess and domino players who queue together are matched

Chess: a status poll that landed between the claim and the match id write
deleted the claim, so the waiting player searched forever while the other
sat alone. A claim in progress is now left alone for 3 minutes, dequeue
reports it, a failed match insert releases it, and a waiting player's
status poll claims an older waiting row. Domino gets the same status-side
match. Raced 4/4 (chess) and 3/3 (domino) with simultaneous queue calls.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

api/domino-match.php

@@ -161,33 +161,10 @@ function handleQueue(string $userId, array $input): void {
         }
 
         // STEP 5: Create match
-        $players = [$opponent['user_id'], $userId];
-
-        $matchData = [
-            'status' => 'in_progress',
-            'players' => $players,
-            'current_turn' => 0,
-            'board' => [],
-            'hands' => (object)[],
-            'boneyard' => [],
-            'moves' => [],
-            'scores' => ['0' => 0, '1' => 0],
-            'game_state' => ['move_count' => 0, 'round' => 1, 'mode' => 'live'],
-            'host_id' => $opponent['user_id']
-        ];
-
-        $match = $sdb->insert('domino_matches', $matchData);
-        $matchId = $match[0]['id'] ?? $match['id'] ?? null;
-
-        if ($matchId) {
-            $sdb->update('domino_queue', ['match_id' => $matchId], ['id' => 'eq.' . $opponent['id']]);
-
-            jsonResponse([
-                'match_id' => $matchId,
-                'player_index' => 1,
-                'players' => $players,
-                'color' => 'player2'
-            ]);
+        $created = dominoCreateMatch($sdb, $opponent['user_id'], $userId);
+        if ($created) {
+            $sdb->update('domino_queue', ['match_id' => $created['match_id']], ['id' => 'eq.' . $opponent['id']]);
+            jsonResponse($created);
             return;
         }
 
@@ -216,7 +193,7 @@ function handleStatus(string $userId): void {
 
     $entry = $sdb->get('domino_queue', [
         'user_id' => 'eq.' . $userId,
-        'select' => 'id,match_id',
+        'select' => 'id,match_id,created_at',
         'limit' => 1
     ]);
 
@@ -241,9 +218,76 @@ function handleStatus(string $userId): void {
         ]);
     }
 
+    // Still unclaimed: maybe someone queued at the same moment we did, and the
+    // two searches each found an empty queue.
+    if (!empty($entry) && !isset($entry['error']) && empty($entry[0]['match_id'])) {
+        $found = dominoMatchFromStatus($sdb, $userId, $entry[0]);
+        if ($found) jsonResponse($found);
+    }
+
     jsonResponse(['waiting' => true]);
 }
 
+/**
+ * Create a live match: the host (the earlier queuer) sits at index 0.
+ * Returns the response for the player who made it (index 1), or null.
+ */
+function dominoCreateMatch($sdb, string $hostId, string $userId): ?array {
+    $players = [$hostId, $userId];
+    $match = $sdb->insert('domino_matches', [
+        'status' => 'in_progress',
+        'players' => $players,
+        'current_turn' => 0,
+        'board' => [],
+        'hands' => (object)[],
+        'boneyard' => [],
+        'moves' => [],
+        'scores' => ['0' => 0, '1' => 0],
+        'game_state' => ['move_count' => 0, 'round' => 1, 'mode' => 'live'],
+        'host_id' => $hostId
+    ]);
+    $matchId = $match[0]['id'] ?? $match['id'] ?? null;
+    if (!$matchId) return null;
+    return ['match_id' => $matchId, 'player_index' => 1, 'players' => $players, 'color' => 'player2'];
+}
+
+/**
+ * Two players who queue at the same moment can both search an empty queue and
+ * both insert themselves; nobody searches again and each waits for the other
+ * forever. So a waiting player's status poll looks for someone who has been
+ * waiting LONGER. Only the later of the two does this, and only towards older
+ * rows, so two pollers never claim each other; our own row is locked first so
+ * a third player cannot claim us while we build the match.
+ */
+function dominoMatchFromStatus($sdb, string $userId, array $mine): ?array {
+    if (empty($mine['created_at'])) return null;
+    $older = $sdb->get('domino_queue', [
+        'user_id' => 'neq.' . $userId,
+        'match_id' => 'is.null',
+        'and' => '(created_at.lt."' . $mine['created_at'] . '",created_at.gt."' . gmdate('c', time() - 90) . '")',
+        'select' => 'id,user_id',
+        'order' => 'created_at.asc',
+        'limit' => 1,
+    ]);
+    if (!is_array($older) || isset($older['error']) || empty($older)) return null;
+    $opp = $older[0];
+
+    $release = function (string $id) use ($sdb) {
+        $sdb->update('domino_queue', ['match_id' => null], ['id' => 'eq.' . $id, 'match_id' => 'eq.' . DOMINO_CLAIM_PLACEHOLDER]);
+    };
+    $lock = $sdb->update('domino_queue', ['match_id' => DOMINO_CLAIM_PLACEHOLDER], ['id' => 'eq.' . $mine['id'], 'match_id' => 'is.null']);
+    if (empty($lock) || isset($lock['error'])) return null;
+    $claim = $sdb->update('domino_queue', ['match_id' => DOMINO_CLAIM_PLACEHOLDER], ['id' => 'eq.' . $opp['id'], 'match_id' => 'is.null']);
+    if (empty($claim) || isset($claim['error'])) { $release($mine['id']); return null; }
+
+    $created = dominoCreateMatch($sdb, $opp['user_id'], $userId);
+    if (!$created) { $release($opp['id']); $release($mine['id']); return null; }
+
+    $sdb->update('domino_queue', ['match_id' => $created['match_id']], ['id' => 'eq.' . $opp['id']]);
+    $sdb->delete('domino_queue', ['id' => 'eq.' . $mine['id']]);
+    return $created;
+}
+
 function handleMove(string $userId, array $input): void {
     $matchId = $input['match_id'] ?? '';
     if (!$matchId) jsonError('match_id required');