fix: guard invalid turn transitions

src/Domain/CombatEngine.php

@@ -93,8 +93,25 @@ final class CombatEngine
             throw new CombatException('Matches require alpha and bravo teams.');
         }
 
+        $livingTeams = ['alpha' => false, 'bravo' => false];
+
+        foreach ($match->units as $unit) {
+            if (!$unit->isDefeated()) {
+                $livingTeams[$unit->teamId] = true;
+            }
+        }
+
+        if (!$livingTeams['alpha'] || !$livingTeams['bravo']) {
+            throw new CombatException('Cannot end turn while a team is eliminated.');
+        }
+
         $endingTeamId = $match->activeTeamId;
         $nextTeamId = $endingTeamId === 'alpha' ? 'bravo' : 'alpha';
+
+        if ($nextTeamId === 'alpha' && $match->round === PHP_INT_MAX) {
+            throw new CombatException('Match round limit reached.');
+        }
+
         $units = [];
 
         foreach ($match->units as $unit) {