Hold a walk's first-machine gate while its busy container finishes its build

A merge into mesh-controller replaced every build agent and threw away the
checks in flight (issue 594). The manifest's container busy is checked and
sent only to an engine that reads it; a report's busy waits are kept, the
gate starts at the report that says the container replaced, and the wait is
a phase of the delivery time. mesh-builder busy drains the agent and answers
while a build is in hand (novox/hq ADR 0335).

cmd/mesh-controller/gate.go

@@ -544,6 +544,11 @@ func judgeMoves(ctx context.Context, open *stores, g *inventory.PlanGate, pairs
 			facts.sentBuilds[j.node] = builds
 		}
 	}
+	// **A busy container on a judged machine holds the judging before it starts** (novox/hq ADR 0335 §4): the
+	// walk says it waits there, and its gate starts at the report that says the container replaced.
+	if busyWait(g, pairs, facts, now) {
+		return "", nil
+	}
 	// **What is wrong with a machine itself is the machine's** (novox/hq issue 281): read once for each
 	// machine judged, apart from what is wrong with a module there, and never pinned on the module the
 	// gate happens to be kept on.
@@ -568,6 +573,9 @@ func judgeMoves(ctx context.Context, open *stores, g *inventory.PlanGate, pairs
 	for _, j := range pairs {
 		w := words[j.node]
 		h, said := judgeHealth(j.module, coreComponent(j.module), shelf[j.module], j.node, *g.Since, w.facts)
+		if why, still := busyStill(j, facts); still && (h == healthGood || h == healthPerson) {
+			h, said = healthNotYet, why
+		}
 		if h == healthGood || h == healthPerson {
 			if on, named := w.on[j.module]; named {
 				h, said = healthNotYet, on
@@ -1372,6 +1380,9 @@ func gateLine(g *inventory.PlanGate) string {
 	case inventory.GateFailed:
 		what = "FAILED"
 	}
+	if g.Verdict == "" && g.Waiting() {
+		what = "waits for a busy container on " + g.Busy.Machine
+	}
 	line := fmt.Sprintf("gate on %s: %s", strings.Join(g.Machines, ", "), what)
 	if g.Component != "" {
 		line += " (core: " + g.Component + ")"