fix(ui): an undo in the same tick as a rebase steps back to a rebased snapshot

rebase updated the state only, so the mirror the callbacks read still held the removed
row and an undo right after it wrote that row back for a moment.

frontend/src/lib/useUndoable.dom.test.ts

@@ -26,4 +26,15 @@ describe("useUndoable", () => {
     act(() => result.current.undo());
     expect(result.current.value).toEqual([2]);
   });
+
+  it("undoes to a rebased snapshot when the undo comes in the same tick as the rebase", () => {
+    const { result } = renderHook(() => useUndoable<number[]>([1, 2]));
+    act(() => result.current.set([2, 1]));
+    act(() => {
+      result.current.rebase((xs) => xs.filter((x) => x !== 2)); // a row removed
+      result.current.undo();
+    });
+    expect(result.current.value).toEqual([1]);
+    expect(result.current.canRedo).toBe(true);
+  });
 });