test: add edge case tests

src/kanban/buildKanbanBoard.test.ts

@@ -117,4 +117,31 @@ describe("buildKanbanBoard", () => {
 			expect(col.tasks).toEqual([]);
 		}
 	});
+
+	it("preserves input order for tasks with same updated timestamp (stable sort)", () => {
+		const sameUpdated = "2026-01-01T00:00:00.000Z";
+		const tasks: Task[] = [
+			task({
+				id: "a",
+				title: "A",
+				status: TaskStatus.TODO,
+				updated: sameUpdated,
+			}),
+			task({
+				id: "b",
+				title: "B",
+				status: TaskStatus.TODO,
+				updated: sameUpdated,
+			}),
+			task({
+				id: "c",
+				title: "C",
+				status: TaskStatus.TODO,
+				updated: sameUpdated,
+			}),
+		];
+		const board = buildKanbanBoard(tasks);
+		const todo = board.columns.find((col) => col.status === TaskStatus.TODO);
+		expect(todo?.tasks.map((t) => t.id)).toEqual(["a", "b", "c"]);
+	});
 });