Route non-stacked derived commits to their applied group when a later
edit or transaction intervenes. Copy remeasurement must undo with the
font action rather than becoming a separate step after an unrelated edit.
Keep adjacent non-stacked entries and exclude the redo tail from routing.
Extend the font-boundary regression to component mains and copies, and
cover both stacking modes during a later transaction. The regression
fails before the fix; all 1,563 frontend tests and 10,880 assertions pass.
Live WASM history passes exact undo/redo and full-sync consistency.
The sync core is unchanged by this undo fix. Its preceding benchmark
ratios remain 0.48-0.76 of the unchanged baseline, with no regression flag.
AI-assisted-by: gpt-6
a62a15206d