Merge pull request 'node hand-over: the terminal hands a directory used as found to the mesh, asked of the node's engine (hq issue 356)' (#187) from fix/356-node-hand-over-at-the-terminal into main

The subject proved nothing: the bus lets any principal allowed to answer reply to a message it received on the reply subject that message named, so a tool server — the operator's account, every agent — could deliver a hand-over to an engine. The controller now signs the ask with the mesh's key over a fixed context (node, path, who asked, a minute's expiry, a fresh nonce), as declarations are signed, and the engine verifies it. The writers table gains the row for mesh.node.*.ask.hand-over; the subject's comment no longer claims who the engine hears. The line's known-node check and the refusal branch are tested; every check was removed in turn and a test failed.

cmd/mesh-controller/found_wait_test.go

@@ -18,7 +18,7 @@ func foundDirectory(module string, since time.Time) inventory.ResourceHealth {
 	return inventory.ResourceHealth{Module: module, Resource: module + ".data", Kind: link.KindDirectory,
 		Target: "/srv/" + module, State: link.StateUnhealthy, Since: since,
 		Reason: link.ReasonUsedAsFound + " owned by 1000:1000, mode 700, as found; root, mode 755 was declared and " +
-			"not given it — `mesh-host hand-over` at the machine hands it to the mesh"}
+			"not given it — `nox node hand-over laptop <directory>` on the control-node, with its path, hands it to the mesh"}
 }
 
 func TestADirectoryFoundBeforeTheSendIsAWaitForAPerson(t *testing.T) {

cmd/mesh-controller/handover_test.go

@@ -0,0 +1,134 @@
+package main
+
+import (
+	"bytes"
+	"errors"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/novox/mesh-controller/internal/conditions"
+	"github.com/novox/mesh-controller/internal/inventory"
+	"github.com/novox/mesh-controller/internal/link"
+)
+
+// A hand-over's line is judged before anything is asked (novox/hq issue 356): a node's name and the directory's
+// absolute path exactly as the engine states it — no `..`, no doubled or trailing separator, nothing relative.
+func TestAHandOverLineIsJudgedBeforeItIsAsked(t *testing.T) {
+	for _, args := range [][]string{
+		{},
+		{"laptop"},
+		{"laptop", "/srv/notes", "extra"},
+		{"", "/srv/notes"},
+		{"--node", "/srv/notes"},
+		{"laptop", "srv/notes"},
+		{"laptop", "/srv/../etc"},
+		{"laptop", "/srv//notes"},
+		{"laptop", "/srv/notes/"},
+		{"laptop", "/srv/notes/."},
+	} {
+		if _, _, err := handOverLine(args); err == nil {
+			t.Errorf("%q was taken", args)
+		}
+	}
+	node, path, err := handOverLine([]string{"laptop", "/srv/notes"})
+	if err != nil || node != "laptop" || path != "/srv/notes" {
+		t.Fatalf("read as %q %q %v", node, path, err)
+	}
+}
+
+// Who hands over is the line's caller in the words every verb's caller is recorded in — the operator through
+// mesh-cli — or the controller's terminal when nobody is named.
+func TestAHandOverNamesWhoAsked(t *testing.T) {
+	t.Setenv(link.CallerVar, " jo through mesh-cli on anchor ")
+	if by := handOverBy(); by != "jo through mesh-cli on anchor" {
+		t.Fatalf("by %q", by)
+	}
+	t.Setenv(link.CallerVar, "")
+	if by := handOverBy(); by != "the controller's terminal" {
+		t.Fatalf("by %q", by)
+	}
+}
+
+// **A hand-over is the controller's terminal's alone** (novox/hq issue 356, ADR 0266): through any verb, and
+// through mesh-cli outside the terminal, `node hand-over` is refused and nothing runs — at the next apply root
+// gives the directory to the account the module declares, and whoever may call a verb includes agents.
+func TestAHandOverIsRefusedThroughEveryVerb(t *testing.T) {
+	line := []string{"node", "hand-over", "laptop", "/srv/notes"}
+	if err := terminalOnly(line); err == nil {
+		t.Fatal("node hand-over passed as a verb's line")
+	}
+	if _, err := argvFor("command", map[string]any{"command": "node hand-over laptop /srv/notes"}); err == nil {
+		t.Fatal("the command verb composed node hand-over")
+	}
+	if _, err := ordinaryLine(line); err == nil {
+		t.Fatal("node hand-over composed as an ordinary mesh-cli line")
+	}
+	if _, err := argvFor("node", map[string]any{"node": "laptop", "hand-over": "/srv/notes"}); err == nil {
+		t.Fatal("the node verb composed a hand-over")
+	}
+}
+
+// The condition's words are plain and name no machine's binary; the operator's line, with the node and the path
+// (novox/hq ADR 0272), is in the summary the module's health gives (moduleHealthWord) and in the evidence.
+func TestTheUsedAsFoundConditionNamesTheOperatorsLine(t *testing.T) {
+	rs := []inventory.ResourceHealth{foundDirectory("notes", time.Now().Add(-24*time.Hour))}
+	o := usedAsFoundObservation("notes", "laptop", "notes on laptop uses notes.data as found", rs)
+	if strings.Contains(o.Needs, "mesh-host") || strings.Contains(o.Explanation, "mesh-host") ||
+		!strings.Contains(o.Needs, "control-node") {
+		t.Fatalf("the condition's words: %q %q", o.Needs, o.Explanation)
+	}
+	if why, ok := conditions.PlainWords(conditions.Words{Headline: o.Headline, Explanation: o.Explanation, Needs: o.Needs,
+		Resolved: o.Resolved}, "laptop"); !ok {
+		t.Fatalf("not plain: %s", why)
+	}
+	f := gateFacts{now: time.Now(), health: map[string]inventory.NodeHealth{"laptop": {Node: "laptop", HeardAt: time.Now(),
+		Resources: rs}}}
+	h, why := moduleHealthWord("notes", "laptop", time.Now().Add(-time.Hour), f)
+	if h != healthPerson || !strings.Contains(why, "`nox node hand-over laptop <directory>` on the control-node") ||
+		strings.Contains(why, "mesh-host") || strings.Contains(why, "/srv/") {
+		t.Fatalf("the module's health reads %v %q; want the operator's line", h, why)
+	}
+}
+
+// **Nothing is asked of a node the mesh does not know, and the engine's refusal is the command's failure**
+// (review of issue 356): a refused hand-over never exits as a success.
+func TestAHandOverAsksOnlyAKnownNodeAndFailsOnARefusal(t *testing.T) {
+	t.Setenv(link.CallerVar, "jo through mesh-cli on anchor")
+	asked := 0
+	ask := func(answer link.HandOverAnswer) func(node, path, by string) (link.HandOverAnswer, error) {
+		return func(node, path, by string) (link.HandOverAnswer, error) {
+			asked++
+			if node != "laptop" || path != "/srv/notes" || by != "jo through mesh-cli on anchor" {
+				t.Fatalf("asked %q %q %q", node, path, by)
+			}
+			return answer, nil
+		}
+	}
+	unknown := func(string) error { return errors.New("no node called laptop") }
+	known := func(string) error { return nil }
+	var out bytes.Buffer
+	err := handOverAsked([]string{"laptop", "/srv/notes"}, unknown, ask(link.HandOverAnswer{Said: "x"}), &out)
+	if err == nil || asked != 0 || !strings.Contains(err.Error(), "nothing was asked") {
+		t.Fatalf("an unknown node: %v, asked %d", err, asked)
+	}
+	err = handOverAsked([]string{"laptop", "/srv/../etc"}, known, ask(link.HandOverAnswer{Said: "x"}), &out)
+	if err == nil || asked != 0 {
+		t.Fatalf("a refused line was asked: %v, asked %d", err, asked)
+	}
+	err = handOverAsked([]string{"laptop", "/srv/notes"}, known,
+		ask(link.HandOverAnswer{Refused: "/srv/notes is not used as found; nothing was handed over"}), &out)
+	if err == nil || !strings.Contains(err.Error(), "laptop refused: /srv/notes is not used as found") || out.Len() != 0 {
+		t.Fatalf("a refusal: %v, printed %q", err, out.String())
+	}
+	err = handOverAsked([]string{"laptop", "/srv/notes"}, known, ask(link.HandOverAnswer{Said: "handed over"}), &out)
+	if err != nil || !strings.HasPrefix(out.String(), "handed over\n") || !strings.Contains(out.String(), "`nox push laptop`") {
+		t.Fatalf("a record: %v, printed %q", err, out.String())
+	}
+	failing := func(string, string, string) (link.HandOverAnswer, error) {
+		return link.HandOverAnswer{}, errors.New("no engine")
+	}
+	if err := handOverAsked([]string{"laptop", "/srv/notes"}, known, failing, &out); err == nil {
+		t.Fatal("an ask that failed was a success")
+	}
+}

cmd/mesh-controller/module_health.go

@@ -556,8 +556,8 @@ func moduleHealthWord(module, machine string, since time.Time, f gateFacts) (hea
 			said = append(said, wait)
 		}
 		if len(found) > 0 {
-			said = append(said, fmt.Sprintf("on %s, %s uses %s as found and waits for a person to hand it over "+
-				"(`mesh-host hand-over <directory>` at the machine)", machine, module, strings.Join(found, ", ")))
+			said = append(said, fmt.Sprintf("on %s, %s uses %s as found and waits for the operator to hand it over "+
+				"(`nox node hand-over %s <directory>` on the control-node)", machine, module, strings.Join(found, ", "), machine))
 		}
 		return healthPerson, strings.Join(said, "; ")
 	}
@@ -678,7 +678,9 @@ func usedAsFoundObservation(module, node, said string, rs []inventory.ResourceHe
 	o.Explanation = fmt.Sprintf("A directory of %s was already on %s, with another owner or mode than %s declares. "+
 		"The mesh left it as it was rather than hand it to an account, so %s may not be able to use it.",
 		module, node, module, module)
-	o.Needs = fmt.Sprintf("on %s, run mesh-host hand-over with the directory's path as root.", node)
+	// Plain words (ADR 0253): the line itself — `nox node hand-over <node> <path>` on the control-node (ADR 0272,
+	// issue 356) — is in the summary and the evidence, which name the directory; a path is never in these.
+	o.Needs = "hand the directory over from the control-node, as the operator; the details name it and the line to type."
 	o.Resolved = fmt.Sprintf("%s's directory on %s is the mesh's", module, node)
 	o.Actions = nil
 	return o

cmd/mesh-controller/network.go

@@ -426,10 +426,10 @@ func overlayShow(ctx context.Context, open *stores) error {
 				tunnel.Interface, tunnel.Range, tunnel.Port)
 		case n.Hub && hubName == n.Name && tunnel.Interface != "":
 			fmt.Printf("  hub — found a tunnel on %s and did NOT take it over: its key is not the tunnel's; "+
-				"`mesh-host overlay take --tunnel %s` on the machine takes it", tunnel.Interface, tunnel.Interface)
+				"`nox-mesh-host overlay take --tunnel %s` on the machine takes it", tunnel.Interface, tunnel.Interface)
 		case n.Hub:
 			fmt.Print("  hub — found no tunnel; if the machine runs the predecessor's, " +
-				"`mesh-host overlay take --tunnel <iface>` there adopts it (novox/hq ADR 0105)")
+				"`nox-mesh-host overlay take --tunnel <iface>` there adopts it (novox/hq ADR 0105)")
 		case !n.Reachable():
 			fmt.Print("  not dialable")
 		}

cmd/mesh-controller/nodes.go

@@ -10,6 +10,7 @@ import (
 	"io"
 	"net"
 	"os"
+	"path/filepath"
 	"strings"
 	"time"
 
@@ -17,6 +18,7 @@ import (
 	"github.com/novox/mesh-controller/internal/catalogue"
 	"github.com/novox/mesh-controller/internal/conditions"
 	"github.com/novox/mesh-controller/internal/inventory"
+	"github.com/novox/mesh-controller/internal/link"
 	"github.com/novox/mesh-controller/internal/token"
 )
 
@@ -28,7 +30,7 @@ import (
 
 func nodeCommand(ctx context.Context, args []string) error {
 	if len(args) == 0 {
-		return errors.New("node add <name>, node list, node show <name>, or " + publicDomainUsage)
+		return errors.New("node add <name>, node list, node show <name>, " + publicDomainUsage + ", or " + handOverUsage)
 	}
 	open, err := openStores(ctx)
 	if err != nil {
@@ -112,11 +114,102 @@ func nodeCommand(ctx context.Context, args []string) error {
 		// an optional second argument is the home when it is not /home/<account>.
 		return nodeAccount(ctx, inv, args[1:])
 
+	case "hand-over":
+		// A directory the node-engine uses as found, handed to the mesh (novox/hq issue 356, issue 339). Here, at
+		// the controller's terminal, and nowhere else: at the next apply root gives the directory to the account
+		// the module declares, and whoever may call a verb includes agents.
+		return nodeHandOver(ctx, open, args[1:])
+
 	default:
-		return fmt.Errorf("node has no %q; it has add, list, show, public-domain, account and agent-account", args[0])
+		return fmt.Errorf("node has no %q; it has add, list, show, public-domain, account, agent-account and hand-over", args[0])
 	}
 }
 
+const handOverUsage = "node hand-over <node> <directory> — hand a directory the node-engine on <node> uses as found " +
+	"to the mesh: its next apply gives it the declared owner and mode. The directory's absolute path, as the module's " +
+	"condition names it"
+
+// handOverLine reads a hand-over's line: the node and the directory's absolute path, exactly as the engine states
+// it. Judged before anything is asked, and judged again by the engine, which is the one that acts.
+func handOverLine(args []string) (node, path string, err error) {
+	if len(args) != 2 {
+		return "", "", errors.New(handOverUsage)
+	}
+	node, path = args[0], args[1]
+	if node == "" || strings.HasPrefix(node, "-") {
+		return "", "", fmt.Errorf("%q is not a node's name; %s", node, handOverUsage)
+	}
+	if !filepath.IsAbs(path) {
+		return "", "", fmt.Errorf("%q is not an absolute path; %s", path, handOverUsage)
+	}
+	if filepath.Clean(path) != path {
+		return "", "", fmt.Errorf("%q is not the directory's path as the engine states it (no `..`, no doubled or "+
+			"trailing separator); %s", path, handOverUsage)
+	}
+	return node, path, nil
+}
+
+// handOverBy is who hands the directory over, in the words a verb's caller is recorded in: the operator through
+// mesh-cli on the control-node, or whoever runs this controller's binary at its terminal.
+func handOverBy() string {
+	if by := strings.TrimSpace(os.Getenv(link.CallerVar)); by != "" {
+		return by
+	}
+	return "the controller's terminal"
+}
+
+// nodeHandOver asks the node's engine to take a directory it uses as found as the mesh's, and says what came of
+// it. The engine records the hand-over or refuses; nothing is recorded here, because the directory is the
+// machine's and the engine is the one that reads it. The ask is signed with the mesh's key (issue 356's review).
+func nodeHandOver(ctx context.Context, open *stores, args []string) error {
+	known := func(node string) error {
+		_, err := open.inventory.NodeByName(ctx, node)
+		return err
+	}
+	ask := func(node, path, by string) (link.HandOverAnswer, error) {
+		ident, err := open.Identity(ctx)
+		if err != nil {
+			return link.HandOverAnswer{}, fmt.Errorf("the mesh's signing key cannot be read, so nothing was asked of %s: %w",
+				node, err)
+		}
+		address, err := broker.BusAddress()
+		if err != nil {
+			return link.HandOverAnswer{}, err
+		}
+		js, err := broker.Dial(address)
+		if err != nil {
+			return link.HandOverAnswer{}, fmt.Errorf("cannot reach the bus, so nothing was asked of %s: %w", node, err)
+		}
+		defer js.Close()
+		return link.AskHandOver(ctx, js.Conn(), ident, node, path, by, link.HandOverWithin)
+	}
+	return handOverAsked(args, known, ask, os.Stdout)
+}
+
+// handOverAsked is the hand-over's line with its two acts given: whether the mesh knows the node, and the ask.
+// Nothing is asked of a line or a node that is refused, and the engine's refusal is this command's failure —
+// never a success with the refusal printed.
+func handOverAsked(args []string, known func(node string) error,
+	ask func(node, path, by string) (link.HandOverAnswer, error), out io.Writer) error {
+	node, path, err := handOverLine(args)
+	if err != nil {
+		return err
+	}
+	if err := known(node); err != nil {
+		return fmt.Errorf("nothing was asked: %w", err)
+	}
+	answer, err := ask(node, path, handOverBy())
+	if err != nil {
+		return err
+	}
+	if answer.Refused != "" {
+		return fmt.Errorf("%s refused: %s", node, answer.Refused)
+	}
+	fmt.Fprintln(out, answer.Said)
+	fmt.Fprintf(out, "  the module's condition clears once %s applies; `nox push %s` applies it now\n", node, node)
+	return nil
+}
+
 // addNode creates a node record, adopted when the operator says so (novox/hq ADR 0100).
 func addNode(ctx context.Context, inv *inventory.Inventory, args []string) error {
 	set := flag.NewFlagSet("node add", flag.ContinueOnError)

internal/broker/nats.go

@@ -289,6 +289,14 @@ func (p Principal) Username() string {
 // (novox/hq to-be 45 §6): its answer is an ordinary report, on its own report subject.
 func AskReportSubject(node string) string { return "mesh.node." + node + ".ask.report" }
 
+// AskHandOverSubject is where the controller's terminal asks one machine's node-engine to hand a directory it
+// uses as found to the mesh (novox/hq issue 356, issue 339): a request on core NATS, answered once on the reply
+// it carries. Only the controller is granted a publish here (the writers table holds it), but **that is not who
+// the engine hears**: the bus lets any principal allowed to answer reply to a message it received, on the reply
+// subject that message named, so a message can arrive here from any responder. The ask is therefore signed with
+// the mesh's key (link.SignedHandOver), and the engine verifies it before reading anything out of it.
+func AskHandOverSubject(node string) string { return "mesh.node." + node + ".ask.hand-over" }
+
 // inbox is a principal's own reply space. No user is ever granted a bare `_INBOX.>` (design 25
 // §4): with one account, inbox privacy is the permission list or it is nothing, so each user's
 // inbox is derived from its own identity and its permissions name that prefix and no other.
@@ -562,7 +570,10 @@ func PermissionsFor(p Principal) (Permissions, error) {
 			// And the mesh asking it to say again what it last applied (novox/hq to-be 45 §6, the
 			// `report` verb healer H1 asks): its own machine's, on core NATS and off any stream. It
 			// answers through its report, the one thing it already says — no reply to anybody's inbox.
-			AskReportSubject(p.Node)}
+			AskReportSubject(p.Node),
+			// And the controller's terminal asking it to hand a directory used as found to the mesh (novox/hq
+			// issue 356), which it answers on the request's reply: the one request a node is asked.
+			AskHandOverSubject(p.Node)}
 		// The node-engine witnesses the core builds it places (novox/hq to-be 45 §8, ADR 0236; the
 		// contract is lease/witness.go): it asks its own machine's node tools PING, and, where the
 		// machine runs the controller, reads the lease's one key — read, never written.
@@ -863,9 +874,12 @@ func PermissionsFor(p Principal) (Permissions, error) {
 		PublishDeny: deny,
 		Subscribe:   sub,
 		// A module answers what it was asked — a tool call reaches it on its own namespace, so the
-		// authority is bounded by having been asked — and so does the controller. A node and a
-		// person are never asked anything, and are granted nothing here.
-		AllowResponses: p.Kind == KindModule || p.Kind == KindController || p.Kind == KindNodeTools,
+		// authority is bounded by having been asked — and so does the controller. A node is asked one
+		// thing, a hand-over on its own subject (novox/hq issue 356), and answers that: the node is its
+		// machine's engine, root there already, and it is delivered only its own subjects. What it answers is
+		// never trusted for being an answer — the controller reads the engine's words and records nothing. A
+		// person is never asked anything, and is granted nothing here.
+		AllowResponses: p.Kind == KindModule || p.Kind == KindController || p.Kind == KindNodeTools || p.Kind == KindNode,
 	}, nil
 }
 

internal/broker/nats_test.go

@@ -103,7 +103,8 @@ func TestAnInboxIsScopedToItsOwner(t *testing.T) {
 
 // A responder answers on the caller's inbox, which it has no permission for. allow_responses is
 // what makes a scoped inbox workable at all — the authority is bounded by having been asked. A
-// module is asked on its own namespace and may answer; a node and a person are never asked.
+// module is asked on its own namespace and may answer; a node is asked one thing, a hand-over on its own
+// subject (novox/hq issue 356), and may answer that; a person is never asked.
 func TestOnlyWhatCanBeAskedMayAnswer(t *testing.T) {
 	module, _ := PermissionsFor(Principal{Kind: KindModule, Node: "one", Module: "audit",
 		Consumes: []string{"shop.order.placed"}, PasswordHash: "x"})
@@ -111,8 +112,12 @@ func TestOnlyWhatCanBeAskedMayAnswer(t *testing.T) {
 		t.Fatal("a module cannot answer a tool call on its own namespace")
 	}
 	node, _ := PermissionsFor(Principal{Kind: KindNode, Node: "one", PasswordHash: "x"})
-	if node.AllowResponses {
-		t.Fatal("a node was granted the right to answer, and nothing asks a node anything")
+	if !node.AllowResponses || !slices.Contains(node.Subscribe, AskHandOverSubject("one")) {
+		t.Fatalf("a node cannot answer the hand-over it is asked: %v %v", node.AllowResponses, node.Subscribe)
+	}
+	person, _ := PermissionsFor(Principal{Kind: KindPerson, Node: "one", Module: "jo", PasswordHash: "x"})
+	if person.AllowResponses {
+		t.Fatal("a person was granted the right to answer, and nothing asks a person anything")
 	}
 }
 

internal/broker/testdata/composed.conf

@@ -34,7 +34,8 @@ accounts {
       } }
       { user: "node.one", password: "$2a$11$nnnnnnnnnnnnnnnnnnnnnn", permissions: {
         publish: { allow: ["$JS.ACK.NODES.one.>", "$JS.API.CONSUMER.INFO.NODES.one", "$SRV.PING.node-tools.one", "mesh.control.one.>"] }
-        subscribe: { allow: ["_DELIVER.one", "_DELIVER.one.>", "_INBOX.node.one.>", "mesh.node.one.ask.report", "mesh.node.one.declare"] }
+        subscribe: { allow: ["_DELIVER.one", "_DELIVER.one.>", "_INBOX.node.one.>", "mesh.node.one.ask.hand-over", "mesh.node.one.ask.report", "mesh.node.one.declare"] }
+        allow_responses: { max: 1, ttl: "1m" }
       } }
       { user: "one.nats", password: "$2a$11$bbbbbbbbbbbbbbbbbbbbbb", permissions: {
         publish: { allow: ["$JS.API.STREAM.INFO.*", "$JS.API.STREAM.NAMES", "$JS.API.STREAM.SNAPSHOT.*", "$JS.SNAPSHOT.ACK.>"] }

internal/broker/writers.go

@@ -84,6 +84,13 @@ func kvOf(bucket string) []string { return []string{"$KV." + bucket + ".>"} }
 var WritersTable = []WriterRow{
 	{State: "a machine's declaration", Writer: "controller (lease holder)", KeptIn: "the bus, last per subject",
 		Others: "read", Subjects: []string{"mesh.node.*.declare"}, Writes: isController},
+	// The operator's hand-over of a directory used as found, asked of the machine's engine at the controller's
+	// terminal (novox/hq issue 356). One publisher; and because a responder can still reach the subject through a
+	// reply, the ask is signed with the mesh's key and the engine verifies it — the row bounds who is granted the
+	// publish, the signature who is believed.
+	{State: "a hand-over asked of a machine", Writer: "controller, at its terminal", KeptIn: "the machine, beside its state",
+		Others:   "the engine verifies the mesh's signature and records it, or refuses",
+		Subjects: []string{"mesh.node.*.ask.hand-over"}, Writes: isController},
 	{State: "a machine's applied state and its report", Writer: "the node-engine's apply queue",
 		KeptIn: "the machine; the report on the bus", Others: "the reconcile and a delivery enqueue, never apply",
 		// And its health statement between reports (novox/hq ADR 0240): the same writer stating the same

internal/broker/writers_test.go

@@ -15,6 +15,7 @@ import (
 // to the table; one dropped from either fails.
 var designRows = []string{
 	"a machine's declaration",
+	"a hand-over asked of a machine",
 	"a machine's applied state and its report",
 	"the controller lease",
 	"plans and their tiers",
@@ -150,3 +151,22 @@ func TestSubjectsOverlap(t *testing.T) {
 		}
 	}
 }
+
+// **A hand-over asked of a machine has one publisher, the controller** (novox/hq issue 356): a grant that lets any
+// other principal publish it — a node, the node tools, a module — is refused at composition, naming the state.
+// (Who the engine believes is the signature's; this bounds who is granted the publish.)
+func TestAHandOverAskHasOnePublisher(t *testing.T) {
+	for _, p := range []Principal{
+		{Kind: KindNode, Node: "laptop"},
+		{Kind: KindNodeTools, Node: "laptop", Module: RuntimeModule},
+		{Kind: KindModule, Node: "laptop", Module: "notes"},
+	} {
+		err := CheckWriters(p, []string{"mesh.node.laptop.ask.hand-over"})
+		if err == nil || !strings.Contains(err.Error(), "a hand-over asked of a machine") {
+			t.Errorf("%s may publish a hand-over: %v", p.Username(), err)
+		}
+	}
+	if err := CheckWriters(Principal{Kind: KindController}, []string{"mesh.node.>"}); err != nil {
+		t.Fatalf("the controller may not ask a hand-over: %v", err)
+	}
+}

internal/link/handover.go

@@ -0,0 +1,140 @@
+package link
+
+import (
+	"context"
+	"crypto/rand"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/nats-io/nats.go"
+
+	"github.com/novox/mesh-controller/internal/broker"
+)
+
+// A hand-over asked of a machine's node-engine (novox/hq issue 356, issue 339).
+//
+// The operator hands a directory the node-engine uses as found to the mesh at the controller's terminal:
+// `nox node hand-over <node> <path>` on the control-node (ADR 0272). The controller asks that machine's
+// engine on its own subject, a request on core NATS the engine answers once; the engine judges every
+// value and records the hand-over, or refuses and records nothing. The engine holds the same two shapes
+// in its own link code (mesh-host internal/link HandOverAsk, HandOverAnswer); a test on each side holds
+// the field names.
+
+// HandOverAsk is what the controller asks: the node it is for, the directory's absolute path as the engine states
+// it, who asked in the controller's words, when the ask stops being good, and a nonce the engine takes once.
+type HandOverAsk struct {
+	Node    string    `json:"node"`
+	Path    string    `json:"path"`
+	By      string    `json:"by"`
+	Expires time.Time `json:"expires"`
+	Nonce   string    `json:"nonce"`
+}
+
+// SignedHandOver is the ask as it travels: its bytes exactly as signed, and the signature.
+//
+// **Signed, because the subject proves nothing** (review of issue 356). Only the controller may publish
+// `mesh.node.<node>.ask.hand-over`, but the bus lets any principal allowed to answer reply to a message it
+// received, on whatever reply subject that message named — so a tool server asked on its own subject with that
+// reply could hand the engine an ask the controller never made. The engine verifies this signature, with the
+// key it verifies declarations with, before it reads anything out of the ask.
+type SignedHandOver struct {
+	Ask       []byte `json:"ask"`
+	Signature []byte `json:"signature"`
+}
+
+// HandOverContext is prefixed to an ask's bytes before signing, so a hand-over's signature is never a
+// declaration's: the same key signs both, and a declaration is signed over its bytes alone.
+const HandOverContext = "novox-mesh hand-over v1\n"
+
+// HandOverGood is how long a signed ask is good for: the engine refuses one past it, and one further ahead.
+const HandOverGood = time.Minute
+
+// HandOverAnswer is the engine's answer: what it recorded, or why it refused.
+type HandOverAnswer struct {
+	Said    string `json:"said,omitempty"`
+	Refused string `json:"refused,omitempty"`
+}
+
+// HandOverWithin is how long the controller waits for the engine's answer: a file write, on a machine that is
+// up; a machine that is down is said as not answering.
+const HandOverWithin = 30 * time.Second
+
+// AskHandOver asks one machine's node-engine to hand a directory used as found to the mesh, and reads its
+// answer. An error is the ask not reaching an engine, or an answer that is not one; a refusal is the engine's
+// and comes back in the answer.
+func AskHandOver(ctx context.Context, conn *nats.Conn, signer Signer, node, path, by string,
+	timeout time.Duration) (HandOverAnswer, error) {
+	if conn == nil {
+		return HandOverAnswer{}, errors.New("this controller is not on the bus")
+	}
+	body, err := SignHandOver(ctx, signer, HandOverAsk{Node: node, Path: path, By: by})
+	if err != nil {
+		return HandOverAnswer{}, err
+	}
+	asking, cancel := context.WithTimeout(ctx, timeout)
+	defer cancel()
+	subject := broker.AskHandOverSubject(node)
+	refused, stop := refusalsOf(conn, subject)
+	defer stop()
+	type replied struct {
+		msg *nats.Msg
+		err error
+	}
+	done := make(chan replied, 1)
+	go func() {
+		msg, err := conn.RequestWithContext(asking, subject, body)
+		done <- replied{msg, err}
+	}()
+	var reply *nats.Msg
+	select {
+	case r := <-done:
+		reply, err = r.msg, r.err
+	case why := <-refused:
+		cancel()
+		return HandOverAnswer{}, fmt.Errorf("the bus refused the controller asking %s for a hand-over: %v", node, why)
+	}
+	switch {
+	case errors.Is(err, nats.ErrNoResponders):
+		return HandOverAnswer{}, fmt.Errorf("nothing on %s answers a hand-over: its node-engine is not running, is not "+
+			"on the bus, or is older than this ask (novox/hq issue 356); nothing was handed over", node)
+	case errors.Is(err, context.DeadlineExceeded), errors.Is(err, nats.ErrTimeout):
+		return HandOverAnswer{}, fmt.Errorf("%s did not answer the hand-over within %s; whether it was recorded is not "+
+			"known — the module's condition says whether the directory is still used as found", node, timeout)
+	case err != nil:
+		return HandOverAnswer{}, err
+	}
+	var answer HandOverAnswer
+	if err := json.Unmarshal(reply.Data, &answer); err != nil {
+		return HandOverAnswer{}, fmt.Errorf("%s answered the hand-over with something unreadable: %w", node, err)
+	}
+	if answer.Said == "" && answer.Refused == "" {
+		return HandOverAnswer{}, fmt.Errorf("%s answered the hand-over with neither a record nor a refusal", node)
+	}
+	return answer, nil
+}
+
+// SignHandOver fills the ask's expiry and nonce and signs it with the mesh's key, over HandOverContext and the
+// ask's bytes exactly as they travel.
+func SignHandOver(ctx context.Context, signer Signer, ask HandOverAsk) ([]byte, error) {
+	if signer == nil {
+		return nil, errors.New("no signing key, so no hand-over can be asked")
+	}
+	nonce := make([]byte, 16)
+	if _, err := rand.Read(nonce); err != nil {
+		return nil, err
+	}
+	ask.Nonce = hex.EncodeToString(nonce)
+	ask.Expires = time.Now().UTC().Add(HandOverGood)
+	raw, err := json.Marshal(ask)
+	if err != nil {
+		return nil, err
+	}
+	signature, err := signer.Sign(ctx, append([]byte(HandOverContext), raw...))
+	if err != nil {
+		return nil, fmt.Errorf("cannot sign the hand-over: %w", err)
+	}
+	return json.Marshal(SignedHandOver{Ask: raw, Signature: signature})
+}

internal/link/handover_test.go

@@ -0,0 +1,177 @@
+package link
+
+import (
+	"context"
+	"crypto/ed25519"
+	"encoding/json"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/nats-io/nats.go"
+
+	"github.com/novox/mesh-controller/internal/broker"
+	"github.com/novox/mesh-controller/internal/testbus"
+)
+
+// The hand-over's ask and answer hold these field names; the engine's side holds the same list (mesh-host
+// internal/link, TestTheHandOverAskAndAnswerKeepTheirFieldNames).
+func TestTheHandOverAskAndAnswerKeepTheirFieldNames(t *testing.T) {
+	body, _ := json.Marshal(HandOverAsk{Node: "laptop", Path: "/srv/notes", By: "jo through mesh-cli on anchor",
+		Expires: time.Now(), Nonce: "n"})
+	if got := keysIn(t, body); got != "by expires node nonce path" {
+		t.Fatalf("the ask's fields are %q", got)
+	}
+	body, _ = json.Marshal(SignedHandOver{Ask: []byte("{}"), Signature: []byte("s")})
+	if got := keysIn(t, body); got != "ask signature" {
+		t.Fatalf("the signed ask's fields are %q", got)
+	}
+	body, _ = json.Marshal(HandOverAnswer{Said: "s", Refused: "r"})
+	if got := keysIn(t, body); got != "refused said" {
+		t.Fatalf("the answer's fields are %q", got)
+	}
+	if broker.AskHandOverSubject("laptop") != "mesh.node.laptop.ask.hand-over" {
+		t.Fatalf("the subject is %q", broker.AskHandOverSubject("laptop"))
+	}
+	if HandOverContext != "novox-mesh hand-over v1\n" {
+		t.Fatalf("the signing context is %q; the engine holds the same words", HandOverContext)
+	}
+}
+
+// keySigner signs with one key, as the controller's identity does.
+type keySigner struct{ key ed25519.PrivateKey }
+
+func (k keySigner) Sign(_ context.Context, message []byte) ([]byte, error) {
+	return ed25519.Sign(k.key, message), nil
+}
+
+func testSigner(t *testing.T) (keySigner, ed25519.PublicKey) {
+	t.Helper()
+	public, private, err := ed25519.GenerateKey(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return keySigner{private}, public
+}
+
+// **The ask is signed over the context and its bytes, with a fresh nonce and a short expiry** (review of issue
+// 356): the signature verifies over HandOverContext and the ask's bytes, and not over the bytes alone — so it is
+// never a declaration's — and two asks never share a nonce.
+func TestAHandOverIsSignedWithAContextANonceAndAnExpiry(t *testing.T) {
+	signer, public := testSigner(t)
+	body, err := SignHandOver(context.Background(), signer, HandOverAsk{Node: "laptop", Path: "/srv/notes", By: "jo"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	var signed SignedHandOver
+	if err := json.Unmarshal(body, &signed); err != nil {
+		t.Fatal(err)
+	}
+	if !ed25519.Verify(public, append([]byte(HandOverContext), signed.Ask...), signed.Signature) {
+		t.Fatal("the signature does not verify over the context and the ask")
+	}
+	if ed25519.Verify(public, signed.Ask, signed.Signature) {
+		t.Fatal("the signature verifies over the ask's bytes alone, as a declaration's would")
+	}
+	var ask HandOverAsk
+	if err := json.Unmarshal(signed.Ask, &ask); err != nil {
+		t.Fatal(err)
+	}
+	if ask.Node != "laptop" || ask.Path != "/srv/notes" || ask.By != "jo" || len(ask.Nonce) != 32 {
+		t.Fatalf("signed %+v", ask)
+	}
+	if left := time.Until(ask.Expires); left <= 0 || left > HandOverGood {
+		t.Fatalf("the ask is good for %s", left)
+	}
+	again, _ := SignHandOver(context.Background(), signer, HandOverAsk{Node: "laptop", Path: "/srv/notes", By: "jo"})
+	var other SignedHandOver
+	_ = json.Unmarshal(again, &other)
+	var second HandOverAsk
+	_ = json.Unmarshal(other.Ask, &second)
+	if second.Nonce == ask.Nonce {
+		t.Fatal("two asks share a nonce")
+	}
+	if _, err := SignHandOver(context.Background(), nil, HandOverAsk{}); err == nil {
+		t.Fatal("an ask was made with no key")
+	}
+}
+
+// The ask reaches the machine's engine on its own subject and its answer comes back whole: what it recorded, or
+// its refusal as the engine worded it. A machine with no engine listening is said as not answering, and an
+// answer that is neither is refused rather than read as a record.
+func TestAHandOverIsAskedOfTheMachineAndItsAnswerComesBack(t *testing.T) {
+	url := testbus.URL(t)
+	conn, err := nats.Connect(url)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(conn.Close)
+
+	signer, public := testSigner(t)
+	var heard HandOverAsk
+	engine, err := conn.Subscribe(broker.AskHandOverSubject("laptop"), func(msg *nats.Msg) {
+		var signed SignedHandOver
+		_ = json.Unmarshal(msg.Data, &signed)
+		if !ed25519.Verify(public, append([]byte(HandOverContext), signed.Ask...), signed.Signature) {
+			_ = msg.Respond([]byte(`{"refused":"not the mesh's signature"}`))
+			return
+		}
+		_ = json.Unmarshal(signed.Ask, &heard)
+		switch heard.Path {
+		case "/srv/notes":
+			body, _ := json.Marshal(HandOverAnswer{Said: "/srv/notes (notes.data) is handed to the mesh by " + heard.By})
+			_ = msg.Respond(body)
+		case "/srv/empty":
+			_ = msg.Respond([]byte(`{}`))
+		default:
+			body, _ := json.Marshal(HandOverAnswer{Refused: heard.Path + " is not a directory this machine uses as found; nothing was handed over"})
+			_ = msg.Respond(body)
+		}
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = engine.Unsubscribe() })
+
+	ctx := context.Background()
+	a, err := AskHandOver(ctx, conn, signer, "laptop", "/srv/notes", "jo through mesh-cli on anchor", 5*time.Second)
+	if err != nil || a.Refused != "" || !strings.Contains(a.Said, "handed to the mesh by jo through mesh-cli on anchor") {
+		t.Fatalf("answered %+v, %v", a, err)
+	}
+	if heard.Node != "laptop" || heard.Path != "/srv/notes" || heard.By != "jo through mesh-cli on anchor" {
+		t.Fatalf("the engine heard %+v", heard)
+	}
+	a, err = AskHandOver(ctx, conn, signer, "laptop", "/srv/other", "jo", 5*time.Second)
+	if err != nil || a.Said != "" || !strings.Contains(a.Refused, "nothing was handed over") {
+		t.Fatalf("a refusal came back as %+v, %v", a, err)
+	}
+	if _, err := AskHandOver(ctx, conn, signer, "laptop", "/srv/empty", "jo", 5*time.Second); err == nil ||
+		!strings.Contains(err.Error(), "neither") {
+		t.Fatalf("an empty answer was taken: %v", err)
+	}
+	if _, err := AskHandOver(ctx, conn, signer, "anchor", "/srv/notes", "jo", 5*time.Second); err == nil ||
+		!strings.Contains(err.Error(), "node-engine") {
+		t.Fatalf("a machine with no engine listening: %v", err)
+	}
+	if _, err := AskHandOver(ctx, nil, signer, "anchor", "/srv/notes", "jo", time.Second); err == nil {
+		t.Fatal("asked with no bus")
+	}
+}
+
+// A machine's grant hears its own hand-over ask and nobody else's, and may answer it: the one request a node is
+// asked (novox/hq issue 356).
+func TestAMachineHearsItsOwnHandOverAskAndMayAnswerIt(t *testing.T) {
+	perms, err := broker.PermissionsFor(broker.Principal{Kind: broker.KindNode, Node: "laptop", PasswordHash: "x"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	var hears, other bool
+	for _, s := range perms.Subscribe {
+		hears = hears || s == "mesh.node.laptop.ask.hand-over"
+		other = other || s == "mesh.node.anchor.ask.hand-over"
+	}
+	if !hears || other || !perms.AllowResponses {
+		t.Fatalf("a machine's grant: hears its own %v, another's %v, answers %v (%v)", hears, other, perms.AllowResponses,
+			perms.Subscribe)
+	}
+}

internal/link/protocol.go

@@ -471,8 +471,9 @@ const KindUnit = "unit"
 const KindAccount = "account"
 
 // KindDirectory is a directory of a module that the node-engine uses as found (novox/hq issue 339): there before
-// the mesh, with another owner or mode than declared, and left so until a person hands it over at the machine
-// (`mesh-host hand-over`). Stated unhealthy with a reason that starts ReasonUsedAsFound.
+// the mesh, with another owner or mode than declared, and left so until the operator hands it over at the
+// controller's terminal (`nox node hand-over <node> <path>`, issue 356). Stated unhealthy with a reason that starts
+// ReasonUsedAsFound.
 const KindDirectory = "directory"
 
 // ReasonUsedAsFound starts the reason of a directory used as found.

lab/adopt-the-tunnel/README.md

@@ -46,7 +46,7 @@ bed asserts genesis **says** it found and took the tunnel.
 **Review changes (2026-09-24).** A spoke's `wg0.conf` names one peer — the hub — routed the
 whole range; the controller skips range-routed peers, so T2's enrolment carries no peer from the
 spoke. A hub that enrolled *before* this feature (a generated key) takes the tunnel over without
-re-enrolling: `mesh-host overlay take --tunnel wg0` on the machine rekeys the overlay key only and
+re-enrolling: `nox-mesh-host overlay take --tunnel wg0` on the machine rekeys the overlay key only and
 sends a signed rekey; the bed adds **R0** for it below. A takeover is composed only for a hub
 placed at the tunnel's address on the tunnel's port, and the host stops nothing until the declared
 interface matches the found one and the key file holds the found key; a mesh interface that fails
@@ -58,7 +58,7 @@ to start gives the found unit back. The host's account has three states: `not-ta
 - **R0 — a hub enrolled with its own key takes the tunnel over by rekeying.** Genesis is run
   adopted *without* the tunnel being found (the bed stops `wg-quick@wg0` for the run, so the
   installer sees no tunnel, then starts it again — the pre-feature shape). Then on the anchor:
-  `mesh-host overlay take --tunnel wg0`; `node show anchor` says "tunnel found wg0 …"; `overlay
+  `nox-mesh-host overlay take --tunnel wg0`; `node show anchor` says "tunnel found wg0 …"; `overlay
   place anchor --hub --endpoint 192.0.2.10:51900 --site hosting` (with `:51820` first, which must
   be refused naming 51900); `plan anchor --json` names `Address = 10.10.0.1/32`, `ListenPort =
   51900`, two `/32` peers, `takes-over` wg0 and nothing in 10.42.0.0/16; then `push anchor --wait
@@ -82,7 +82,7 @@ to start gives the found unit back. The host's account has three states: `not-ta
   - `overlay show` lists `anchor` as the hub over the tunnel it took over, and both peers under
     "peers of the tunnel … not nodes of the mesh", not yet enrolled.
 - **T2 — a peer enrols and keeps its address.** On `peer-a`: `node add peer-a --adopted`,
-  token issued, `mesh-host enrol --token …` **with the broker reached over the tunnel** (the
+  token issued, `nox-mesh-host enrol --token …` **with the broker reached over the tunnel** (the
   broker address in the token is `10.10.0.1:<bus>`, which only the tunnel routes); then `overlay
   place peer-a --site house` and a push. Assert: `node show peer-a` says a tunnel `wg0` was
   found and `overlay show` puts `peer-a` at **10.10.0.2**; the carried-peers list now says