#1983 Guard Library mirrors against post-Save aliasing in version handlers

[LarryThiessen]

Fixes #1983

Standalone resubmit of the second commit from closed PR #1982 — this part is independent of the content-version storage discussion there and addresses the still-open crash family in #1983.

Problem

After a Save, GSE.ReplaceSequence stores the editor's own sequence object into GSE.Library, so editframe.Sequence and the Library entry are the same table. The editor's per-version handlers also "mirror" their change into the Library display cache, which post-Save runs twice on one Versions array:

• Delete Version removes two versions per click (2 → 0; the tree shows no version rows).
• New Version inserts two copies, then Editor.lua:5889: attempt to index field '?' (a nil value) in GUIDrawMacroEditor.
• Drag-reorder applies the move twice, scrambling order.

All three work before the first Save of the session (separate copies) — that's the tell.

Fix

Guard the three mirror sites with libSeq ~= sequence so the mirror only runs when the Library holds a distinct copy. Also: Delete Version decremented MetaData.Default unconditionally; it now only shifts when the deleted index is at/before the Default (same rule the content-type keys already use).

Verified

In-game: delete keeps the remaining versions; New Version creates exactly one with no error. luac -p clean. 2 files, +22/−5, cherry-picked onto current master (34b29a5).

🤖 Generated with Claude Code

[TimothyLuke]

This fixes some of the bugs and introduces other. After applying this I can’t create a new version from the right hand menu. That’s why I am working on the whole of the problem not just this part.