Admit Mirror and Stone in Basic native E3 battles

Reuse original copied-weapon and typed coalition accounting for bare Basic
Ecaz/Moritani and selected Ix. Preserve optional-module guards and physical
card identity, actual force-owner commitments and native continuations.

tests/fixture-battle-outcome-window.ts

@@ -0,0 +1,21 @@
+import assert from 'node:assert/strict';
+import { applyAction, viewGame, type Game } from '../game/engine';
+
+/** Close only the actual final-priority controls. Do not bypass a response,
+ * pending native decision, Stone count, casualty choice or cleanup. */
+export function finishBattleOutcomeWindow(source: Game): Game {
+  let game = source;
+  for (let count = 0; count < 2; count++) {
+    const window = game.battle?.outcomeWindow;
+    if (!window || window.closed) return game;
+    assert.ok(!game.response && !game.decision && !game.phaseOpening,
+      'Finish the actual native control before final battle priority');
+    const actor = [window.attacker, window.defender].find(id => !window.ready.includes(id));
+    assert.ok(actor);
+    const own = viewGame(game, actor).battle!.outcomeWindow;
+    assert.ok(own && !own.closed);
+    game = applyAction(game, actor, { type: 'battleOutcomeReady', event: own.event });
+  }
+  assert.ok(!game.battle?.outcomeWindow || game.battle.outcomeWindow.closed);
+  return game;
+}