Two operations set the touched groups of a shape: a :set of :touched,
which assigns the value as given, and :set-touched, which keeps them
only on a copy and drops an empty set. update-shapes and the undo of
add-component wrote the first while their own undo and sync wrote the
second. The contract prefers :set-touched; both builders now write it,
and an update with only its touched groups changed still records their
undo. A :set of :touched is still applied, for changes already stored.
Case AE leaves no empty touched set on the shape a detach turned plain;
both golden masters record the state again for it.
comp-touched-test: an update that sets the touched groups of a copy
shape writes one :set-touched operation, and its undo restores them.
Benchmark (lower quantile, ms; baseline / now / ratio):
deepest-edit-through-three-levels 35.2 / 16.6 / 0.47
edit-through-a-chain-of-dependents 68.9 / 32.8 / 0.48
library-update-into-copies 83.1 / 42.8 / 0.51
main-edit-among-many-shapes 4.8 / 2.3 / 0.48
main-edit-into-10-copies 1.8 / 1.0 / 0.54
main-edit-into-100-copies 15.4 / 8.9 / 0.58
main-edit-into-1000-copies 153.1 / 82.0 / 0.54
variant-switch-into-copies 32.1 / 17.7 / 0.55
AI-assisted-by: claude-opus-5-5
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