If anyone else is wondering what the difference is between a peacekeeping force and a “reassurance” force:

Peacekeeping forces - under the aegis of either the United Nations or Nato - traditionally are impartial, operate with the consent of both parties and use force only to defend themselves. The multinational force being discussed would very much be on Ukraine’s side, there to help deter future Russian aggression.

It sounds to me it’s more of a tripwire force if anything.