The state of a collapsed stack (expanded/collapsed) should be saved in the project json file and restored when reloading the project.

probably something like;

[0, ['start', false], 100, 100, [1]]

or

[0, ['action', true], 100, 100, [1, 2]]

When restoring, the old format should also work, defaulting to expanded.

[0, 'start', 100, 100, [1]]

or

[0, [action', 100, 100, [1, 2]]