Shaping a successor as its change from the predecessor dropped the
predecessor's fields, so Keep mine after the predecessor was refused sent
only the later change. A successor now names its own fields and every
field the predecessor names, with the user's current values: a field set
back in flight is still written, Keep mine carries the whole change, and
nothing depends on whether a restart came between. Work the canvas never
drew is still left out.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>