Compare overridden cells with independent before-state and intent values,
while keeping copy child structure tied to the main. Remap child identities
across duplication, update-main, detach and frontend replay. Direction edits
track both changed groups. The former I4 reproduction stays unchanged.
Add grid actions and seven histories with exact undo/redo, plus controls
for corrupt values, membership, groups, child order and dropped main edits.
Keep random grid rollout pending track growth and switch carry coverage.
Validation: common JVM 2,009/32,967; JS 1,945/31,582; frontend
1,749/13,838; backend 1,793/9,007; exporter 16/40. All suites, lint and
format pass. Six properties run 40 programs at seed 712 in both runtimes.
AI-assisted-by: gpt-6
7d2c20b804