Undo left others' changes alone

Per-participant undo reverts only your own change. Fields someone else changed after you keep their value; the undo result lists them under skipped with who changed them.

#Common causes

• Another participant edited the same field after your change.

#Fixes

• Nothing, if their change should stand; otherwise set the field yourself.

• Code: ARA2509

• Constant: collab::UNDO_PARTIAL

• Reported by: ara-collab