const UNDO_DEPTH: usize = 50;Expand description
How many model states the undo (and redo) stack keeps; older entries are evicted.
ponytail: history is a bounded stack of FULL Model clones — one clone per
mutation, up to 50 resident copies. That is honest and obviously correct
(the model already round-trips and compares by value), but the ceiling is
memory: 50 × model size. If models get big enough for that to hurt, replace
the snapshots with a command/delta log (per-edit inverse operations) behind
the same undo/redo/record_history API — the call sites do not care
which it is.