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/core/commands/tilemapCommands.ts

@@ -245,6 +245,34 @@ export class RenameTilemapLayerCommand implements Command {
   }
 }
 
+/** A layer's `z` above its tilemap's (#174); 0 is stored as nothing, the way a layer starts out. */
+export class SetTilemapLayerZCommand implements Command {
+  readonly label = 'Set layer z';
+  private previous: number | undefined;
+
+  constructor(
+    private readonly assetId: string,
+    private readonly layerId: string,
+    private readonly z: number,
+  ) {}
+
+  execute(project: Project): void {
+    if (!Number.isFinite(this.z)) throw new CommandError('A layer z is a number');
+    const layer = requireTilemapLayer(project, this.assetId, this.layerId);
+    this.previous = layer.z;
+    setLayerZ(layer, this.z);
+  }
+
+  undo(project: Project): void {
+    setLayerZ(requireTilemapLayer(project, this.assetId, this.layerId), this.previous ?? 0);
+  }
+}
+
+function setLayerZ(layer: TilemapLayer, z: number): void {
+  if (z === 0) delete layer.z;
+  else layer.z = z;
+}
+
 /** A hidden layer keeps its cells and is left out of the drawing, in the editor and in the game alike. */
 export class SetTilemapLayerHiddenCommand implements Command {
   readonly label: string;