Keep the first-machine gate behind a switch for walks begun before hq ADR 0360, and test both paths

cmd/mesh-controller/release_test.go

@@ -169,6 +169,7 @@ func (b *backlogMesh) release(t *testing.T) inventory.Plan {
 // The backlog goes out one machine at a time: the first judged before the second is sent, each build's
 // pass kept; a rebuild with the same bytes is no move at all; and a send outside a gate is refused.
 func TestTheBacklogIsReleasedOneMachineAtATimeEachJudged(t *testing.T) {
+	withTheGate(t) // the first-machine gate's own path (novox/hq ADR 0360 keeps it for earlier walks)
 	judgeLeavesAsTheCore(t)
 	b := aBacklog(t)
 	ctx := t.Context()
@@ -224,6 +225,7 @@ func TestTheBacklogIsReleasedOneMachineAtATimeEachJudged(t *testing.T) {
 // A release that fails on its first machine puts back what it carried there, goes no further, and the
 // next one waits for a person, said as a condition; a person releases it with why.
 func TestAFailedReleaseIsPutBackAndTheNextWaitsForAPerson(t *testing.T) {
+	withTheGate(t) // the first-machine gate's own path (novox/hq ADR 0360 keeps it for earlier walks)
 	b := aBacklog(t)
 	ctx := t.Context()
 	inv := b.open.inventory