Each tilemap layer has its own Z: an offset added to the Z of the placed tilemap, like a child's Z to its parent, default 0 keeps the previous order (layers right after their map, in list order), a negative Z sorts a layer below the map, on a tie layers keep their list order and follow the hierarchy against other objects; editor scene and game use the same order through the new pure function drawSlots, a tilemap draws into one container per layer, and the tilemap panel gains a Z field for the selected layer with one undo step per change (#174)

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/editor/debugHook.ts

@@ -4,7 +4,7 @@ import { previewObjectId } from '../core/model/animationPreview';
 import { resolveObjects } from '../core/model/instance';
 import { findAsset, findAssetOf, findObjectHolder } from '../core/model/Project';
 import type { FrameRect } from '../core/model/texture';
-import { findLayer } from '../core/model/tilemap';
+import { findLayer, layerZ } from '../core/model/tilemap';
 import { effectiveScale, gameClock } from '../core/time';
 import { physicsStatus } from '../runtime/physics/engine';
 import {
@@ -554,6 +554,7 @@ export function installDebugHook(app: Application, state: EditorState, editor: E
           id: layer.id,
           name: layer.name,
           hidden: layer.hidden === true,
+          z: layerZ(layer),
           cells: Object.keys(layer.cells).length,
         })) ?? null,
       /** What the scene view drew: meshes (one draw call each), cells and visible layers. */
@@ -598,6 +599,11 @@ export function installDebugHook(app: Application, state: EditorState, editor: E
         const field = currentTilemapWidgets()?.layerName;
         return field ? { ...centreOf(field), value: field.value } : null;
       },
+      /** The Z field of the painted layer, with what it holds (#174). */
+      layerZAt: () => {
+        const field = currentTilemapWidgets()?.layerZ;
+        return field ? { ...centreOf(field), value: field.value } : null;
+      },
       focusAt: () => {
         const button = currentTilemapWidgets()?.focus;
         return button ? { ...centreOf(button), label: button.text } : null;