test(stammbaum): tidyTree centres a wide couple run and clears siblings (#724)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/lib/person/genealogy/layout/tidyTree.test.ts

@@ -116,3 +116,22 @@ describe('tidyTree — multi-root packing', () => {
 		expect(Math.min(...x.values())).toBe(0);
 	});
 });
+
+describe('tidyTree — variable-width run', () => {
+	it('centres a wide couple run over its children and clears its siblings', () => {
+		// A couple unit is one node whose width spans two cards + the gap. It
+		// must still centre over its own children and stay clear of siblings by
+		// the FULL run width, not a single card.
+		const COUPLE = 2 * W + GAP;
+		const couple = node('couple', [leaf('g1'), leaf('g2')], COUPLE);
+		const sibling = node('sib', [leaf('s1')]);
+		const roots = [sibling, couple];
+		const x = layoutForest(roots, GAP);
+
+		expectNoOverlap(x, roots, GAP);
+		// Couple centred over its two children.
+		expect(center(x, couple)).toBe((center(x, leaf('g1')) + center(x, leaf('g2'))) / 2);
+		// The sibling root clears the couple's full run width.
+		expect(x.get('couple')! - x.get('sib')!).toBeGreaterThanOrEqual(W + GAP);
+	});
+});