Entries dropped because at least one of their ops lacked a name
and therefore couldn't round-trip through the op-factory registry.
Always present (zero when nothing was dropped) so callers can detect
loss without parsing the debug log.
Stored newest-first, mirroring the in-memory stack so a deserialized
history matches the original's entries().redo ordering.
Snapshot of an entire
Historyinstance. Designed to live alongside the scene snapshot in IDB so a reload restores the undo / redo stacks to exactly where they were.