Clicking a History panel state ran Edit > Undo / Redo once per state. Each
step bumped the document revision, so the canvas could not tell what the
jump changed and recomposited the whole document (re-uploading every
changed layer on the GPU path).
history.selectState {state} returns the document to a state (numbered as
the panel lists them, redo states included) in one command: the history
moves by pointer swaps, the document becomes current once, with one
revision and the damage rect between start and target, and the targeted
layers restored as Undo restores them. The panel runs it once per click;
an open Free Transform refuses it (panel guard kept, and the transform
intercept greys and refuses it for every caller). A floating piece goes
back as with Undo instead of being dropped as a new step.
Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
