feat(dmg): add a guided macOS installer layout

apps/desktop/electron-builder.config.mjs

@@ -186,6 +186,16 @@ export default {
     },
   },
   dmg: {
+    title: 'Maka Installer',
+    // Relative to electron-builder's default buildResources directory (build/).
+    background: 'background.png',
+    window: { width: 540, height: 380 },
+    iconSize: 112,
+    iconTextSize: 16,
+    contents: [
+      { x: 130, y: 190, type: 'file' },
+      { x: 410, y: 190, type: 'link', path: '/Applications' },
+    ],
     sign: true,
     // Stapling the notarization ticket after electron-builder exits changes the
     // DMG bytes. macOS updates use the ZIP, so do not publish a stale DMG hash

scripts/product-release.test.mjs

@@ -194,6 +194,19 @@ test('Desktop packaging does not distribute the retired bundled Git runtime', ()
   );
 });
 
+test('macOS DMG ships correctly sized background assets', async () => {
+  const backgroundDirectory = join(repoRoot, 'apps', 'desktop', 'build');
+  const pngSignature = Buffer.from([137, 80, 78, 71, 13, 10, 26, 10]);
+  for (const [name, dimensions] of [
+    ['background.png', { width: 540, height: 380 }],
+    ['background@2x.png', { width: 1080, height: 760 }],
+  ]) {
+    const data = await readFile(join(backgroundDirectory, name));
+    assert.deepEqual(data.subarray(0, pngSignature.length), pngSignature, `${name} must be a PNG`);
+    assert.deepEqual({ width: data.readUInt32BE(16), height: data.readUInt32BE(20) }, dimensions);
+  }
+});
+
 test('a successful Windows upgrade invalidates stale backup authority before best-effort cleanup', async () => {
   const source = await readFile(
     join(repoRoot, 'apps', 'desktop', 'build', 'installer.nsh'),