Tell the operator at once when sends wait for the bus's planned step, and say it before the merge (hq issue 336)

For 28 minutes on 2026-10-08 every send to the control-node was refused for a new bus build that only a
person's bus upgrade moves, and no condition said so: the refusal lived only in each walk's note, and S3
would have called it lateness after half an hour, in words that named neither the bus nor the verb.

- Row S17, bus.<module>.step-waiting: raised on the first watchdog tick after a walk's send is refused for
  the bus, for the operator, naming the machines, what waits, the bus build from and to, since when and
  mesh-controller.bus upgrade. It clears once the bus's machine runs the build the mesh holds.
- S3 leaves out a walk held only by the bus's step.
- A change that builds the bus says in its delivery plan and summary (which mesh/merge-gate carries) that
  merging it needs a person's bus upgrade, and that nothing else reaches its machine until then.
- TestReplay336 fails on the commit before and passes on this one.

cmd/mesh-controller/changeplan_test.go

@@ -45,7 +45,7 @@ func TestAChangePlanSaysWhatEachMachineReceives(t *testing.T) {
 	}
 
 	p = plan("modules/nats/Dockerfile", "modules/photos/x.js")
-	if !strings.Contains(p.Summary, "a bus step") || !strings.Contains(p.Summary, "2 wait(s) for a person") ||
+	if !strings.Contains(p.Summary, "needs a person's bus upgrade") || !strings.Contains(p.Summary, "2 wait(s) for a person") ||
 		!strings.Contains(p.Summary, "(+1 dependent(s))") {
 		t.Errorf("the bus and a held module read %q", p.Summary)
 	}
@@ -58,7 +58,11 @@ func TestAChangePlanSaysWhatEachMachineReceives(t *testing.T) {
 		t.Errorf("the deploy plan reads %v", got)
 	}
 	text := strings.Join(p.Steps, "\n")
-	for _, want := range []string{"a planned bus step", "photos waits for a person", "nats provides mesh-bus"} {
+	// Said before the merge (novox/hq issue 336): merging it holds every send to the bus's machine until a
+	// person runs the bus's step, and the verb that does.
+	for _, want := range []string{"merging this needs a person's bus upgrade", "nothing else is sent to anchor",
+		"`mesh-controller.bus upgrade --why … --reversible|--irreversible`", "photos waits for a person",
+		"nats provides mesh-bus"} {
 		if !strings.Contains(text, want) {
 			t.Errorf("the steps do not say %q:\n%s", want, text)
 		}