Session-harness tests for the cases Codex verified only statically:

- an edit a teammate partly reverted undoes and redoes only the fields
  they left alone (circle diameter and colour, colour reverted);
- a 0.001 move is still a move: undo puts it back and syncs a patch;
- a cone dropped on an agent, with the cone put back by a teammate, undoes
  only the conversion and leaves the step before in place;
- the same transaction fully reverted by a teammate is skipped, so undo
  undoes the step before.

No bug found. The partial-revert and fully-reverted cases fail on the undo
code before #202; the other two pass before and after it.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>