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-builder/busy.go

@@ -0,0 +1,101 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+)
+
+// **The build agent says whether it is busy, and being asked drains it** (novox/hq ADR 0335 §1, §5). Its
+// container declares `busy` as `mesh-builder busy`: the node-engine runs it inside the container before it
+// replaces it. It exits 0 while a build is in hand and 1 when none is; and from the first ask the agent takes
+// no new build request, so its answer ends once the build in hand ends — a replaced builder finishes the check
+// it runs, instead of the build queue handing it out again from the start (issue 594).
+//
+// Two marks in the container's own temporary directory, as the ready mark (ready.go): a new container starts
+// without them, and a restarted one removes them before it takes work again.
+//
+//   - in hand: written by the agent when it claims a request, before it reads whether it is drained; removed
+//     when the build ends.
+//   - drained: written by the ask, before it reads whether a build is in hand.
+//
+// Each side writes its own mark before it reads the other's, so an ask racing a fetch sees the build in hand,
+// or the agent sees the drain and hands the request back; never neither.
+
+func inHandMark() string { return filepath.Join(os.TempDir(), "mesh-builder.in-hand") }
+func drainMark() string  { return filepath.Join(os.TempDir(), "mesh-builder.drained") }
+
+// drained says the agent was asked whether it is busy: it takes no new build request.
+func drained() bool {
+	_, err := os.Stat(drainMark())
+	return err == nil
+}
+
+// claim marks a request in hand, unless the agent is drained: then nothing is in hand, and the request goes
+// back to the queue.
+func claim() bool {
+	// Made, never written over: one build at a time, and a mark already there is a build in hand.
+	f, err := os.OpenFile(inHandMark(), os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o644)
+	if err != nil {
+		// Unmarked, an ask would say idle while this build runs: the build is not taken.
+		fmt.Fprintf(os.Stderr, "cannot mark a build in hand (%s), so it is handed back: %v\n", inHandMark(), err)
+		return false
+	}
+	_, err = f.WriteString(time.Now().UTC().Format(time.RFC3339) + "\n")
+	if closeErr := f.Close(); err == nil {
+		err = closeErr
+	}
+	if err != nil {
+		_ = os.Remove(inHandMark())
+		fmt.Fprintf(os.Stderr, "cannot mark a build in hand (%s), so it is handed back: %v\n", inHandMark(), err)
+		return false
+	}
+	if drained() {
+		_ = os.Remove(inHandMark())
+		fmt.Fprintln(os.Stderr, "asked whether busy, so this agent takes no new build: handed back")
+		return false
+	}
+	return true
+}
+
+// holding says what is in hand, for the ask to print: written once the request is read.
+func holding(what string) {
+	_ = os.WriteFile(inHandMark(), []byte(time.Now().UTC().Format(time.RFC3339)+" "+what+"\n"), 0o644)
+}
+
+// released ends the build in hand.
+func released() {
+	if err := os.Remove(inHandMark()); err != nil && !errors.Is(err, os.ErrNotExist) {
+		fmt.Fprintf(os.Stderr, "cannot remove the mark of the build in hand (%s): %v\n", inHandMark(), err)
+	}
+}
+
+// undrained clears both marks at the start of a holder: a container started again is asked afresh.
+func undrained() error {
+	for _, mark := range []string{drainMark(), inHandMark()} {
+		if err := os.Remove(mark); err != nil && !errors.Is(err, os.ErrNotExist) {
+			return fmt.Errorf("cannot remove %s: %w", mark, err)
+		}
+	}
+	return nil
+}
+
+// busy is the ask: it drains the agent, then says whether a build is in hand. Nil — exit 0 — while one is.
+func busy() (string, error) {
+	if err := os.WriteFile(drainMark(), []byte(time.Now().UTC().Format(time.RFC3339)+"\n"), 0o644); err != nil {
+		// Not drained, it could take the next build: said, and answered busy only for what is in hand now.
+		fmt.Fprintf(os.Stderr, "cannot mark this agent drained (%s): %v\n", drainMark(), err)
+	}
+	held, err := os.ReadFile(inHandMark())
+	if err != nil {
+		return "", errors.New("idle: no build in hand, and this agent takes no new one")
+	}
+	since, what, _ := strings.Cut(strings.TrimSpace(string(held)), " ")
+	if what == "" {
+		what = "a build"
+	}
+	return fmt.Sprintf("busy: %s, in hand since %s; taking no new build", what, since), nil
+}

cmd/mesh-builder/busy_test.go

@@ -0,0 +1,77 @@
+package main
+
+import (
+	"strings"
+	"sync"
+	"testing"
+)
+
+// `mesh-builder busy` answers 0 while a build is in hand and non-zero when idle, and after its first ask the
+// agent takes no new build request (novox/hq ADR 0335 §5).
+func TestBusyAnswersWhileABuildIsInHandAndDrainsTheAgent(t *testing.T) {
+	t.Setenv("TMPDIR", t.TempDir())
+	if err := undrained(); err != nil {
+		t.Fatal(err)
+	}
+	if drained() {
+		t.Fatal("an agent never asked is drained")
+	}
+	// A build is claimed and runs.
+	if !claim() {
+		t.Fatal("an agent never asked refused a build")
+	}
+	holding("novox/mesh-controller (check-280)")
+	said, err := busy()
+	if err != nil || !strings.Contains(said, "novox/mesh-controller (check-280)") {
+		t.Fatalf("an agent with a build in hand did not answer busy with what it holds: %q %v", said, err)
+	}
+	// From that ask on it takes nothing new: the fetch is not made, and one fetched is handed back.
+	if !drained() {
+		t.Fatal("the ask did not drain the agent")
+	}
+	if claim() {
+		t.Fatal("a drained agent took a new build")
+	}
+	// The build in hand is still in hand after the refused claim, and busy goes on saying so.
+	if _, err := busy(); err != nil {
+		t.Fatalf("a refused claim ended the build in hand: %v", err)
+	}
+	// It ends: idle, and still drained.
+	released()
+	if _, err := busy(); err == nil {
+		t.Fatal("an agent with nothing in hand answered busy")
+	}
+	if claim() {
+		t.Fatal("a drained agent took a build after its last one ended")
+	}
+	// Started again, it is asked afresh.
+	if err := undrained(); err != nil {
+		t.Fatal(err)
+	}
+	if drained() || !claim() {
+		t.Fatal("a holder started again is still drained")
+	}
+	released()
+}
+
+// An ask racing a fetch sees the build in hand, or the agent sees the drain and hands the request back: never
+// neither, which would replace the container under a build just taken.
+func TestAnAskRacingAFetchNeverMissesTheBuild(t *testing.T) {
+	t.Setenv("TMPDIR", t.TempDir())
+	for i := 0; i < 200; i++ {
+		if err := undrained(); err != nil {
+			t.Fatal(err)
+		}
+		var claimed bool
+		var askErr error
+		var wg sync.WaitGroup
+		wg.Add(2)
+		go func() { defer wg.Done(); claimed = claim() }()
+		go func() { defer wg.Done(); _, askErr = busy() }()
+		wg.Wait()
+		if claimed && askErr != nil {
+			t.Fatalf("round %d: the agent took a build and the ask said idle", i)
+		}
+		released()
+	}
+}

cmd/mesh-builder/main.go

@@ -71,6 +71,12 @@ digest of their own configuration. The result is printed as JSON.
 
 exits 0 once the agent running in this container is bound to its build work and pulls it, and
 1 before: its container's health check.
+
+  mesh-builder busy
+
+exits 0 while the agent running in this container has a build in hand, and 1 when it has none;
+from the first ask the agent takes no new build: its container's busy command, asked before the
+container is replaced (novox/hq ADR 0335).
 `
 
 func run() error {
@@ -84,6 +90,15 @@ func run() error {
 		case "ready":
 			// The container's health check (novox/hq issue 544): exits non-zero until the agent takes work.
 			return ready()
+		case "busy":
+			// The container's busy command (novox/hq ADR 0335): drains the agent, and exits non-zero once
+			// nothing is in hand.
+			said, err := busy()
+			if err != nil {
+				return err
+			}
+			fmt.Println(said)
+			return nil
 		default:
 			fmt.Print(usage)
 			return nil
@@ -93,6 +108,9 @@ func run() error {
 	if err := notReady(); err != nil {
 		return err
 	}
+	if err := undrained(); err != nil {
+		return err
+	}
 	credential, err := brokerFrom()
 	if err != nil {
 		return err
@@ -145,8 +163,13 @@ func run() error {
 	// **What an earlier holder here left goes before anything is taken** (novox/hq issue 306): a holder
 	// recreated mid-check left the check's store and bus running, and the ask went to another machine.
 	h.removeLeftBehind()
-	machine := link.MachineOverNATSWith(js, on, seat, link.MachineOptions{Paused: h.Paused,
-		Taking: func() { taking(seat) }})
+	// Paused or drained, it takes nothing new (novox/hq ADR 0219, ADR 0335): a drained agent finishes the build
+	// in hand and then says idle, and its container is replaced between builds.
+	machine := link.MachineOverNATSWith(js, on, seat, link.MachineOptions{
+		Paused: func() bool { return h.Paused() || drained() },
+		Taking: func() { taking(seat) },
+		Claim:  claim,
+	})
 	defer machine.Close()
 
 	// The seat's verbs, on this machine's subjects. Only the seat that declares them: the retired
@@ -172,6 +195,8 @@ func run() error {
 	publisher := builder.Registry{Address: registry, Run: builder.Command}
 
 	return machine.Take(ctx, func(ctx context.Context, work link.Build) {
+		defer released()
+		holding(work.Request().Repository + " (" + work.Request().ID + ")")
 		answer(ctx, publisher, on, workspace, work, h)
 	})
 }

cmd/mesh-builder/stdout_test.go

@@ -16,6 +16,7 @@ func TestBuilderDiagnosticsStayOffStdout(t *testing.T) {
 		"version)":     true, // --version
 		`"stopping")`:  true, // the loop.s shutdown line
 		"usage)":       true, // --help text, for a human
+		"said)":        true, // busy: the answer its node-engine reads (novox/hq ADR 0335)
 	}
 	for _, file := range []string{"once.go", "main.go"} {
 		src, err := os.ReadFile(file)

cmd/mesh-controller/busy.go

@@ -0,0 +1,84 @@
+package main
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/novox/mesh-controller/internal/inventory"
+)
+
+// A first-node gate waits for a busy container (novox/hq ADR 0335 §4).
+//
+// When a machine reports, on what the gate sent it, that a container of a judged module was left running
+// because it said busy, the judging has not started: the build is not yet what runs there. The walk says it
+// waits for a busy container on that machine, counts no pass and no bound, and starts the judging — its
+// Since — at the report that no longer lists the container waiting. The wait is the node-engine's, bounded
+// at 15 minutes; the controller's own bound (busyGateBound past the engine's) is for an engine that stopped
+// reporting while it waited, so no walk waits for ever. An engine older than the field never lists one, and
+// its gate starts as before.
+
+// busyGateSlack is how long past the engine's bound the controller still waits for the report that says the
+// container replaced: a pass of the engine (its asks every 20 seconds) and the report's way here.
+var busyGateSlack = 5 * time.Minute
+
+// busyWait decides, before a judging, whether the gate waits for a busy container on a machine it judges:
+// true while it waits, the gate saying so. False when nothing waits, or no longer: a wait that ended moves the
+// gate's Since to its end. Pure but for the gate it is handed.
+func busyWait(g *inventory.PlanGate, pairs []judged, f gateFacts, now time.Time) bool {
+	if g.Busy != nil && g.Busy.Ended != nil {
+		return false
+	}
+	for _, j := range pairs {
+		b, waits := busyOn(j, f)
+		if !waits {
+			continue
+		}
+		if g.Busy == nil {
+			g.Busy = &inventory.GateBusy{Machine: j.node, Module: j.module, Container: b.Container, Since: b.Since}
+		}
+		g.Busy.Until, g.Busy.Said = b.Until, b.Said
+		if now.After(g.Busy.Until.Add(busyGateSlack)) {
+			// The engine said it would have replaced it by now: the judging starts, and finds the module not
+			// yet healthy while the machine still lists it waiting (busyStill), until the gate's own bound.
+			end := now
+			g.Busy.Ended, g.Busy.PastBound = &end, true
+			g.Since, g.Passes, g.LastPass, g.Healthy, g.HealthyAt = &end, 0, nil, nil, nil
+			return false
+		}
+		g.Passes, g.LastPass, g.Last, g.Failing = 0, nil, g.Busy.Words(), nil
+		g.Read(now, false, g.Busy.Words())
+		return true
+	}
+	if g.Busy == nil {
+		return false
+	}
+	// Replaced: the judging starts at the report that said so.
+	end := now
+	if r, said := f.reports[g.Busy.Machine]; said && r.At != nil && r.At.After(g.Busy.Since) && r.At.Before(now) {
+		end = r.At.UTC()
+	}
+	g.Busy.Ended = &end
+	g.Since, g.Passes, g.LastPass, g.Last, g.Healthy, g.HealthyAt = &end, 0, nil, "", nil, nil
+	return false
+}
+
+// busyOn is the container of a judged module its machine last reported, on what the gate sent it, as left
+// running because it said busy.
+func busyOn(j judged, f gateFacts) (inventory.BusyWait, bool) {
+	r, said := f.reports[j.node]
+	if !said || r.At == nil || !f.reportedOn(j.node, r) {
+		return inventory.BusyWait{}, false
+	}
+	return inventory.WaitingFor(r.Busy, j.module)
+}
+
+// busyStill is a judged module whose container its machine still lists waiting once the gate stopped waiting
+// for it: not yet what was sent, so not healthy, whatever its health says of the container still running.
+func busyStill(j judged, f gateFacts) (string, bool) {
+	b, waits := busyOn(j, f)
+	if !waits {
+		return "", false
+	}
+	return fmt.Sprintf("%s still runs its busy container %s, past its node-engine's bound of %s",
+		j.node, b.Container, b.Until.UTC().Format(time.RFC3339)), true
+}

cmd/mesh-controller/busy_test.go

@@ -0,0 +1,111 @@
+package main
+
+import (
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/novox/mesh-controller/internal/inventory"
+)
+
+// A walk whose module's container waits as busy on its first machine says so, and starts that machine's
+// first-machine gate only once the machine reports the container replaced (novox/hq ADR 0335 §4).
+func TestAGateWaitsForABusyContainerAndStartsWhenItIsReplaced(t *testing.T) {
+	sent := time.Date(2026, 10, 13, 1, 0, 0, 0, time.UTC)
+	g := &inventory.PlanGate{Machines: []string{"novox"}, Since: &sent,
+		Sent: map[string]inventory.SentDeclaration{"novox": {Digest: "d1", Sequence: 7}}}
+	pairs := []judged{{module: "build-agent", node: "novox"}, {module: "mesh-controller", node: "novox"}}
+	reported := sent.Add(20 * time.Second)
+	waiting := []inventory.BusyWait{{ID: "build-agent.server", Container: "mesh-build-agent",
+		State: inventory.BusyWaiting, Since: reported, Until: reported.Add(15 * time.Minute),
+		Said: "busy: novox/mesh-controller (check of #280), in hand since 00:58:00Z"}}
+	facts := func(at time.Time, busy []inventory.BusyWait) gateFacts {
+		// As judgeMoves hands it: the report held against the gate's own send.
+		return gateFacts{sent: g.Sent, reports: map[string]inventory.Reported{"novox": {Node: "novox",
+			Outcome: inventory.OutcomeApplied, At: &at, Declared: "d1", ReportedSequence: 7, Busy: busy}}}
+	}
+
+	now := reported.Add(time.Minute)
+	if !busyWait(g, pairs, facts(reported, waiting), now) {
+		t.Fatal("a gate whose module's container waits as busy judged it")
+	}
+	if !g.Since.Equal(sent) || g.Busy == nil || g.Busy.Machine != "novox" || g.Busy.Ended != nil {
+		t.Fatalf("the gate does not keep the wait: %+v %+v", g.Since, g.Busy)
+	}
+	for _, said := range []string{gateLine(g), g.Last} {
+		if !strings.Contains(said, "waits for a busy container on novox") {
+			t.Errorf("the walk does not say it waits for a busy container there: %s", said)
+		}
+	}
+	if !strings.Contains(g.Last, "check of #280") {
+		t.Errorf("the wait does not say what the container holds: %s", g.Last)
+	}
+
+	// Ten minutes on, still busy, within the engine's bound: still waiting, nothing judged, no bound run.
+	now = reported.Add(10 * time.Minute)
+	if !busyWait(g, pairs, facts(reported.Add(9*time.Minute), waiting), now) || g.Passes != 0 {
+		t.Fatalf("the gate stopped waiting within the bound: %+v", g)
+	}
+
+	// The machine reports it replaced: the judging starts at that report.
+	replacedAt := reported.Add(12 * time.Minute)
+	now = replacedAt.Add(5 * time.Second)
+	replaced := []inventory.BusyWait{{ID: "build-agent.server", Container: "mesh-build-agent",
+		State: "replaced-when-idle", Since: reported, Until: reported.Add(15 * time.Minute)}}
+	if busyWait(g, pairs, facts(replacedAt, replaced), now) {
+		t.Fatal("the gate still waits after the container was replaced")
+	}
+	if g.Since == nil || !g.Since.Equal(replacedAt) || g.Busy.Ended == nil || !g.Busy.Ended.Equal(replacedAt) {
+		t.Fatalf("the gate does not start at the report that said it replaced: since %v, %+v", g.Since, g.Busy)
+	}
+	if strings.Contains(gateLine(g), "waits for a busy container") {
+		t.Errorf("a gate judging still says it waits: %s", gateLine(g))
+	}
+	// And a later report listing it waiting again does not hold a gate that started.
+	if busyWait(g, pairs, facts(now, waiting), now.Add(time.Minute)) {
+		t.Error("a gate that started waits again")
+	}
+}
+
+// An engine that stops reporting while it waits holds no walk for ever: past the engine's bound and the slack,
+// the judging starts, and finds the module not yet healthy while its container is still listed waiting.
+func TestAGateWaitsNoLongerThanTheEnginesBound(t *testing.T) {
+	sent := time.Date(2026, 10, 13, 1, 0, 0, 0, time.UTC)
+	g := &inventory.PlanGate{Machines: []string{"novox"}, Since: &sent}
+	pairs := []judged{{module: "build-agent", node: "novox"}}
+	waiting := []inventory.BusyWait{{ID: "build-agent.server", Container: "mesh-build-agent",
+		State: inventory.BusyWaiting, Since: sent, Until: sent.Add(15 * time.Minute)}}
+	f := gateFacts{reports: map[string]inventory.Reported{"novox": {Node: "novox", Outcome: inventory.OutcomeApplied,
+		At: &sent, Current: true, Busy: waiting}}}
+	now := sent.Add(15*time.Minute + busyGateSlack + time.Second)
+	if busyWait(g, pairs, f, now) {
+		t.Fatal("a gate waited past the engine's bound and the slack")
+	}
+	if !g.Busy.PastBound || !g.Since.Equal(now) {
+		t.Fatalf("the gate does not start, said past the bound: %+v %v", g.Busy, g.Since)
+	}
+	if why, still := busyStill(pairs[0], f); !still || !strings.Contains(why, "past its node-engine's bound") {
+		t.Fatalf("a module still running its busy container reads as what was sent: %q", why)
+	}
+}
+
+// A report from an engine older than the field lists nothing: the gate starts at the send, as before; and a
+// report not about the gate's send says nothing of it.
+func TestAGateOfAnEngineThatNeverWaitsStartsAsBefore(t *testing.T) {
+	sent := time.Date(2026, 10, 13, 1, 0, 0, 0, time.UTC)
+	g := &inventory.PlanGate{Machines: []string{"ace"}, Since: &sent,
+		Sent: map[string]inventory.SentDeclaration{"ace": {Digest: "d2", Sequence: 9}}}
+	pairs := []judged{{module: "build-agent", node: "ace"}}
+	at := sent.Add(time.Minute)
+	older := gateFacts{sent: g.Sent, reports: map[string]inventory.Reported{"ace": {Node: "ace", Outcome: inventory.OutcomeApplied,
+		At: &at, Declared: "d2", ReportedSequence: 9}}}
+	if busyWait(g, pairs, older, at) || g.Busy != nil || !g.Since.Equal(sent) {
+		t.Fatalf("a gate on an engine that never waits did not start at the send: %+v %v", g.Busy, g.Since)
+	}
+	elsewhere := gateFacts{sent: g.Sent, reports: map[string]inventory.Reported{"ace": {Node: "ace", Outcome: inventory.OutcomeApplied,
+		At: &at, Declared: "d1", ReportedSequence: 8, Busy: []inventory.BusyWait{{ID: "build-agent.server",
+			State: inventory.BusyWaiting, Until: at.Add(time.Hour)}}}}}
+	if busyWait(g, pairs, elsewhere, at) {
+		t.Fatal("a wait reported about an earlier declaration held the gate")
+	}
+}

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 + ")"

cmd/mesh-controller/plan.go

@@ -975,9 +975,14 @@ func renderingFor(ctx context.Context, open *stores, node string,
 	if err != nil {
 		return catalogue.Rendering{}, inventory.Node{}, err
 	}
+	readsBusy, err := engineReadsBusy(ctx, inv, node)
+	if err != nil {
+		return catalogue.Rendering{}, inventory.Node{}, err
+	}
 	return catalogue.Rendering{
 		ReadsHealth:   readsHealth,
 		JudgesRoot:    judgesRoot,
+		ReadsBusy:     readsBusy,
 		BusMembership: memberships[node],
 		Settings:      settings, Generators: gens, Grants: grants, Needed: needed, Foreseen: foreseen, Ports: ports,
 		Certificate: certificate, Authority: authority, Mesh: private, Names: names,
@@ -1010,6 +1015,16 @@ func engineJudgesRoot(ctx context.Context, inv *inventory.Inventory, node string
 	return had && stated.Contract >= link.RootContract, nil
 }
 
+// engineReadsBusy says whether a machine's node-engine reads a container's `busy` (novox/hq ADR 0335), by its
+// own newest statement, for the same reason as engineReadsHealth: an older engine parses strictly.
+func engineReadsBusy(ctx context.Context, inv *inventory.Inventory, node string) (bool, error) {
+	stated, had, err := inv.HealthOf(ctx, node)
+	if err != nil {
+		return false, err
+	}
+	return had && stated.Contract >= link.BusyContract, nil
+}
+
 // zonesInTheMesh is every zone a module in the mesh declares, where the mesh placed it (novox/hq ADR
 // 0199): the zone settled from that node's settings, the node's private address, the port the
 // answering listen is published on there.