A raise's level compaction counted and packed every level any frame of the stratum held, hidden or shown, so a frame given a high level while hidden was pulled down and later showed under a dialog it should cover.
In the reference, each stratum keeps a level bound that grows only when a visible frame links into a level, and the compaction examines and moves only the levels below it, then sets the bound to its count, which the raised frame takes. A frame above the bound keeps its level.
The arena now keeps that bound per stratum, grown on every visible link and set by the compaction, which packs only below it.
Tests cover the hidden frame above the bound and a high show raising the bound for the next raise.
Fixes#885
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
