MIGRATE — taking over a setup already here

Raised by lemonfiber migrate replace, which stands in place of a setup already on this machine. It names an offer first, and the offer is answered by that name with --offer.

Code	Severity	Exit	What it means	What to do
MIGRATE-1	warning	1	What you agreed to is not what standing in place of this setup would stop now. A fresh look offers something else — something started, stopped or changed since you read it — so nothing was stopped. The message names what replacing would stop now.	Ask what replacing would stop again, and read what it says now.

What each severity and each exit means is on every error by code, beside every other family.