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

cmd/mesh-controller/release_plan.go

@@ -27,6 +27,10 @@ import (
 // alone cannot (a tier waiting for machines to report); a controller replaced mid-plan finds the
 // plan where it left it.
 
+// gateFirstMachine sends a module that rolls out to one machine first and judges it there (ADR 0236). Off since
+// novox/hq ADR 0360: the gate's code is kept for the walks a controller before it started, and its tests turn it on.
+var gateFirstMachine = false
+
 // planWaitBound is how long a plan may wait on one thing before `status` names it red.
 const planWaitBound = 30 * time.Minute
 
@@ -846,8 +850,11 @@ func advanceOnce(ctx context.Context, open *stores, p *inventory.Plan,
 			return false, err
 		}
 		// **Every machine at once** (novox/hq ADR 0360 §1, §2): a module that rolls out is sent to every machine
-		// running it in one step, with no first machine and no gate, whatever module it is.
-		policy.Together = true
+		// running it in one step, with no first machine and no gate, whatever module it is. A module a controller
+		// before ADR 0360 already sent to its first machine finishes under its gate.
+		if !gateFirstMachine && state.FirstAt == nil {
+			policy.Together = true
+		}
 		var reports []inventory.Reported
 		if !policy.Together {
 			// Read for the choice of the first machine as well as for its report.