diff --git a/src/config.js b/src/config.js
index 7305e5f..9477555 100644
--- a/src/config.js
+++ b/src/config.js
@@ -9,6 +9,12 @@ export const GAME_HEIGHT = 540 * WORLD_SCALE;
 // Set true to show live g-force / debug readouts during PlayScene.
 export const DEBUG = false;
 
+// Set true to render the invisible kid compartment (floor + left/right
+// walls) as simple colored rectangles that track the chassis, plus a live
+// per-kid local-position/state readout in the PlayScene HUD. Troubleshooting
+// aid for ejection behavior - off during normal play.
+export const COMPARTMENT_DEBUG = true;
+
 export const STORAGE_KEY = 'monsterplex.progress.v1';
 
 // Matter runs Phaser's default fixed 60Hz step.
diff --git a/src/scenes/PlayScene.js b/src/scenes/PlayScene.js
index c9fd76b..be86fa1 100644
--- a/src/scenes/PlayScene.js
+++ b/src/scenes/PlayScene.js
@@ -1,5 +1,5 @@
 import Phaser from 'phaser';
-import { GAME_WIDTH, GAME_HEIGHT, DEBUG, WORLD_SCALE } from '../config.js';
+import { GAME_WIDTH, GAME_HEIGHT, DEBUG, WORLD_SCALE, COMPARTMENT_DEBUG } from '../config.js';
 import { getLevelById } from '../data/levels/index.js';
 import Bus from '../entities/Bus.js';
 import Terrain from '../entities/Terrain.js';
@@ -13,6 +13,7 @@ import { stopMenuMusic } from '../util/music.js';
 import { playLevelVoiceLine } from '../util/voiceLine.js';
 import { formatTime } from '../util/formatTime.js';
 import { createPill } from '../util/pill.js';
+import buildCompartmentDebug from '../util/compartmentDebug.js';
 
 export default class PlayScene extends Phaser.Scene {
   constructor() {
@@ -41,6 +42,11 @@ export default class PlayScene extends Phaser.Scene {
 
     this.kidManager = new KidManager(this, this.bus, this.level.kidsAboard);
 
+    // Troubleshooting overlay: renders the invisible compartment fixtures
+    // (floor + walls) as simple rectangles tracking the bus, plus per-kid
+    // state readout. Off by default - toggle COMPARTMENT_DEBUG in config.js.
+    this.compartmentDebug = COMPARTMENT_DEBUG ? buildCompartmentDebug(this, this.bus, this.kidManager) : null;
+
     this.inputController = new InputController(this);
 
     this.engineSound = new EngineSound(this, this.bus);
@@ -320,6 +326,7 @@ export default class PlayScene extends Phaser.Scene {
     // Matter.World#shutdown() already calls removeAllListeners() on itself
     // internally (verified against the vendored source), so this was always
     // redundant, not just now-unsafe.
+    if (this.compartmentDebug) this.compartmentDebug.destroy();
     if (this.gForceMonitor) this.gForceMonitor.destroy();
     if (this.kidManager) this.kidManager.destroy();
     if (this.engineSound) this.engineSound.destroy();
diff --git a/src/util/compartmentDebug.js b/src/util/compartmentDebug.js
new file mode 100644
index 0000000..7d6501a
--- /dev/null
+++ b/src/util/compartmentDebug.js
@@ -0,0 +1,95 @@
+import Phaser from 'phaser';
+import { BUS, KID, WORLD_SCALE } from '../config.js';
+
+// Debug-only visualisation of the invisible kid compartment (see
+// Bus._buildCompartment): one simple colored rectangle per fixture
+// (floor + left wall + right wall) tracking the chassis every frame, plus
+// the open-top line and one marker per kid showing its state. Used for
+// troubleshooting ejection behavior (does the kid visually leave through
+// the open top before KidManager latches it? where does it sit relative to
+// the floor/walls while aboard?).
+//
+// Rectangles are plain Phaser.GameObjects.Rectangle (rendering only - they
+// are NOT physics bodies, deliberately, so they can't interfere with the
+// very collision behavior being observed).
+export default function buildCompartmentDebug(scene, bus, kidManager) {
+  const depth = 5;
+
+  const mkRect = (w, h, color, alpha) =>
+    scene.add.rectangle(0, 0, w, h, color, alpha).setOrigin(0.5).setDepth(depth);
+
+  const floor = mkRect(BUS.compartmentHalfWidth * 2, BUS.compartmentFloorThickness, 0x00e676, 0.75);
+  const leftWall = mkRect(BUS.compartmentWallThickness, (BUS.compartmentFloorY - BUS.compartmentTopY) + BUS.compartmentFloorThickness, 0x40c4ff, 0.75);
+  const rightWall = mkRect(BUS.compartmentWallThickness, (BUS.compartmentFloorY - BUS.compartmentTopY) + BUS.compartmentFloorThickness, 0xff5252, 0.75);
+
+  // The open-top boundary (BUS.compartmentTopY) is where the aboard/ejected
+  // transition happens - drawn as a thin dashed-style line so "crossing
+  // this line" is visible in gameplay.
+  const topLine = mkRect(BUS.compartmentHalfWidth * 2 + BUS.compartmentWallThickness * 2, 2 * WORLD_SCALE, 0xffeb3b, 0.9);
+
+  // One marker per kid: small rectangle at the kid's position, color-coded
+  // by state (green = aboard, red = ejected).
+  const kidMarkers = kidManager.kids.map((kid) => mkRect(KID.radius * 2 + 4 * WORLD_SCALE, KID.radius * 2 + 4 * WORLD_SCALE, 0xffffff, 0.0));
+
+  // HUD readout, same style as the other pills.
+  const label = scene.add.text(24 * WORLD_SCALE, 110 * WORLD_SCALE, '', {
+    fontFamily: 'monospace',
+    fontSize: `${13 * WORLD_SCALE}px`,
+    color: '#1a1f29',
+  }).setScrollFactor(0).setDepth(10);
+
+  const shapes = [floor, leftWall, rightWall, topLine];
+
+  function update() {
+    const chassis = bus.chassis;
+    const cos = Math.cos(chassis.rotation);
+    const sin = Math.sin(chassis.rotation);
+    const toWorld = (localX, localY) => ({
+      x: chassis.x + localX * cos - localY * sin,
+      y: chassis.y + localX * sin + localY * cos,
+    });
+
+    const f = toWorld(0, BUS.compartmentFloorY);
+    floor.setPosition(f.x, f.y);
+    floor.setAngle(chassis.rotation);
+
+    const wallHeight = (BUS.compartmentFloorY - BUS.compartmentTopY) + BUS.compartmentFloorThickness;
+    const wallCenterY = (BUS.compartmentFloorY + BUS.compartmentTopY) / 2;
+    const l = toWorld(-BUS.compartmentHalfWidth, wallCenterY);
+    leftWall.setPosition(l.x, l.y);
+    leftWall.setAngle(chassis.rotation);
+    const r = toWorld(BUS.compartmentHalfWidth, wallCenterY);
+    rightWall.setPosition(r.x, r.y);
+    rightWall.setAngle(chassis.rotation);
+
+    const t = toWorld(0, BUS.compartmentTopY);
+    topLine.setPosition(t.x, t.y);
+    topLine.setAngle(chassis.rotation);
+
+    let lines = [`floor: x${-BUS.compartmentHalfWidth}..${BUS.compartmentHalfWidth} y=${BUS.compartmentFloorY}`];
+    lines.push(`walls: x=${-BUS.compartmentHalfWidth} / x=${BUS.compartmentHalfWidth}  top(open): y=${BUS.compartmentTopY}`);
+    for (let i = 0; i < kidManager.kids.length; i++) {
+      const kid = kidManager.kids[i];
+      const dx = kid.image.x - chassis.x;
+      const dy = kid.image.y - chassis.y;
+      const localX = dx * cos + dy * sin;
+      const localY = -dx * sin + dy * cos;
+      const marker = kidMarkers[i];
+      marker.setPosition(kid.image.x, kid.image.y);
+      marker.setFillStyle(kid.state === 'aboard' ? 0x00e676 : 0xff5252, 0.9);
+      marker.setSize(KID.radius * 2 + 4 * WORLD_SCALE, KID.radius * 2 + 4 * WORLD_SCALE);
+      lines.push(`kid${i}: ${kid.state}  local=(${localX.toFixed(0)}, ${localY.toFixed(0)})${kid.state === 'ejected' && kid.ejectedAt !== null ? `  outFor=${((scene.time.now - kid.ejectedAt) / 1000).toFixed(1)}s` : ''}`);
+    }
+    label.setText(lines.join('\n'), { align: 'left' });
+  }
+
+  scene.events.on('update', update);
+  scene.events.once('shutdown', () => {
+    scene.events.off('update', update);
+    for (const s of shapes) s.destroy();
+    for (const m of kidMarkers) m.destroy();
+    label.destroy();
+  });
+
+  return { shapes, kidMarkers, label, destroy: () => { shapes.concat(kidMarkers).concat([label]).forEach((s) => s.destroy()); } };
+}