feat(overlay): split secondary subtitles into dedicated top window

src/core/services/overlay-window.test.ts

@@ -0,0 +1,37 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { splitOverlayGeometryForSecondaryBar } from './overlay-window-geometry';
+
+test('splitOverlayGeometryForSecondaryBar returns 20/80 top-bottom regions', () => {
+  const regions = splitOverlayGeometryForSecondaryBar({
+    x: 100,
+    y: 50,
+    width: 1200,
+    height: 900,
+  });
+
+  assert.deepEqual(regions.secondary, {
+    x: 100,
+    y: 50,
+    width: 1200,
+    height: 180,
+  });
+  assert.deepEqual(regions.primary, {
+    x: 100,
+    y: 230,
+    width: 1200,
+    height: 720,
+  });
+});
+
+test('splitOverlayGeometryForSecondaryBar keeps positive sizes for tiny heights', () => {
+  const regions = splitOverlayGeometryForSecondaryBar({
+    x: 0,
+    y: 0,
+    width: 300,
+    height: 1,
+  });
+
+  assert.ok(regions.secondary.height >= 1);
+  assert.ok(regions.primary.height >= 1);
+});