test(search): add applyOffsets coverage for negative start offsets

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/search.spec.ts

@@ -92,4 +92,19 @@ describe('applyOffsets', () => {
 			{ text: 'Brief', highlight: true }
 		]);
 	});
+
+	it('clamps negative start to 0 and highlights from the beginning', () => {
+		// start = -2, length = 5 → effective range [-2, 3) → clamped to [0, 3)
+		expect(applyOffsets('Hello', [{ start: -2, length: 5 }])).toEqual([
+			{ text: 'Hel', highlight: true },
+			{ text: 'lo', highlight: false }
+		]);
+	});
+
+	it('ignores offset whose end is also negative', () => {
+		// start = -5, length = 2 → end = -3, completely before text
+		expect(applyOffsets('Hi', [{ start: -5, length: 2 }])).toEqual([
+			{ text: 'Hi', highlight: false }
+		]);
+	});
 });