Gate a release plan's first machine and roll a failed build back there (hq ADR 0236)

A build that reported applied was sent everywhere; one that then did nothing, served
no tools or broke its machine's word reached every machine. Now the first machine is
judged by the component's health (the core's definitions, as doctor probes H-*, or a
module's own) three times over two minutes within ten; a failing gate puts the previous
build back there once, marks the build, and says it as a condition and an event.
Upgrades roll out by default; the bus is a planned step; a module deleted at its
source is not built (the public-acme plan failure).

cmd/mesh-controller/held_back_test.go

@@ -193,6 +193,10 @@ func TestANamedPushLeavesAMachineAPolicyHoldsBack(t *testing.T) {
 			t.Fatal(err)
 		}
 	}
+	// Recorded by a person's choice: the default rolls out since novox/hq ADR 0235.
+	if err := inv.SetUpgradeOf(ctx, "resolver", inventory.Upgrade{Why: "each machine checked by hand"}); err != nil {
+		t.Fatal(err)
+	}
 	gens, err := generators(ctx, open)
 	if err != nil {
 		t.Fatal(err)
@@ -214,7 +218,7 @@ func TestANamedPushLeavesAMachineAPolicyHoldsBack(t *testing.T) {
 	}
 	before := digestOfLaptop()
 
-	// The change merges; the policy is the default, record. `push anchor` sends the anchor...
+	// The change merges; the policy is record. `push anchor` sends the anchor...
 	aResolver(t, open, "c2c2c2c2c2", asked.Add(time.Minute))
 	d.declared = nil
 	if _, err := sendRound(ctx, open, []string{"anchor"}, compose, d, ""); err != nil {