Fix combat end seam so break-off cull fires onActiveChange

- The last escort leaving the screen (encounter over without a kill) now calls `_setActive()`, which flips `active` to false and emits `onActiveChange`.
- Previously only kills triggered the flip, so GameScene's deck/soundtrack swap (`_setCombatBar`) never ran on a break-off ending.
- Add a test asserting the `true→false` active flip when the last escort is culled off-screen.

dev/neutral.test.mjs

@@ -185,15 +185,19 @@ function harness() {
   scene.physics.add.existing(ship);
   ship.radius = 12;
   ship.stop = () => {};
-  const combat = new CombatSystem(scene, { ship });
-  return { scene, ship, combat };
+  const activeFlips = [];
+  const combat = new CombatSystem(scene, {
+    ship,
+    onActiveChange: (a) => activeFlips.push(a),
+  });
+  return { scene, ship, combat, activeFlips };
 }
 
 const ids = neutralTypeIds();
 
 // ---------------------------------------------------------------- roster + escort
 {
-  const { ship, combat } = harness();
+  const { ship, combat, activeFlips } = harness();
   const base = config.section('combat.neutral', {});
   check('config: the escort window is data (neutral.escortMin/escortMax = 10–15 s)',
     base.escortMin === 10 && base.escortMax === 15);
@@ -240,6 +244,11 @@ const ids = neutralTypeIds();
   check('despawn: broken escorts off-screen are collected (encounter ends)',
     combat.allies.length === 0);
   check('active: over when the last escort is off-screen', combat.active === false);
+  // The seam the scene hangs the deck/soundtrack swap on (GameScene
+  // _setCombatBar — combat bar out, normal deck + deep-space music back)
+  // must fire on the break-off cull, not only on a kill.
+  check('seam: onActiveChange flips true→false when the last escort leaves the screen',
+    JSON.stringify(activeFlips) === '[true,false]');
 }
 
 // ---------------------------------------------------------------- engage

js/combat/CombatSystem.js

@@ -650,6 +650,11 @@ export class CombatSystem {
         }
       }
       this.allies = this.allies.filter((a) => !a.gone && !a._removed);
+      // The last escort off-screen (with the pack spent) is the encounter
+      // OVER — the flip back to the normal deck/soundtrack rides the same
+      // seam as a kill (killEnemy/killAlly already fire it; the break-off
+      // cull is the ending that was missing it).
+      this._setActive();
     }
 
     // 2) AUTO-FIRE: the nearest VISIBLE hostile in range (game.autoFire).