The previous dispose() was documented as "equivalent to cancel()" and
fired onCancel. That breaks React StrictMode's mount → cleanup → mount
cycle for useDragAction consumers: the first cleanup's onCancel resets
the parent state machine (e.g. setCurvingFence(null)), which unmounts
the component before the second mount runs. Net result: the tool blinks
in and out instantly.
dispose() now restores scene state + resumes history but skips onCancel.
Explicit cancel() still fires onCancel (Esc / external aborts). New
test locks this in.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
