Send the rest at once after the first passes, and resume a stored gate (hq ADR 0353)

A release now sends every other machine in one step once its first machine
passed, each judged by its own gate; a failing one is put back without
stopping the others, a silent one is left. A send is kept before it is made,
and a machine already sent what a gate is for is not sent again: the gate
counts from that send and takes over another walk's readings of the same
build there.

cmd/mesh-controller/upgrades.go

@@ -79,7 +79,7 @@ func (f following) Upgraded(ctx context.Context, u link.Upgraded) error {
 	// `rebuild`, a `replay` registered — was sent here one machine after another without any judging; it
 	// now waits for a gate like any other build, and the release plan walks it through the machines, one
 	// at a time, each judged.
-	fmt.Printf("%s moved to %s outside a plan; a release plan sends it to %s, one machine at a time, each judged "+
+	fmt.Printf("%s moved to %s outside a plan; a release plan sends it to %s, one machine first and then the rest at once, each judged "+
 		"(`upgrade backlog` lists what waits)\n", u.Module, shortCommit(u.Commit), readableList(on))
 	return nil
 }