I wish filesystems had a first-in, first-out "garbage heap" model.

The problem with snapshots is that they take up space. The trash has the same issue, with the added drawback that you have to think about emptying it, and if you empty it before realizing you made a mistake, it won't help you.

With a "garbage heap" model, all deleted files would automatically end up on the "heap" when deleted. The heap would be exactly as large as the amount of free space you have left, and shrink when necessary by deleting the oldest files, perhaps with a minimum size (expressed in days) that would require manual action to shrink beyond.