Compose a node's two logins from the vault's node-logins, so a rotation can switch with both loaded

ADR 0583 §1: a node's account rotates between node.<n> and node.<n>--b, each with the node's permissions and its
inbox _INBOX.node.<n>. Records gains NodeLogins (each node's key of node-logins; the context file's NodeRotating,
renamed because a node that rotated and rotates no more logs in as its second login alone), and Users composes one
node user per login: the one in use and, while it rotates, the other. Each login calls in its own name, which is how
the vault tells the login that confirms (§3). While the vault serves rotate-node, each node reads its own node's key
of node-logins alone and may call node-account-confirm in its own name (§1 insight); the grants part is the state's
one named reader. With no rotation every list is the controller's golden one, unchanged. Tested as a subtest of
TestTheCopiedComposerComposesAsTheControllers, no new test function.

(issue 774, 774/S39)

Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL

go/buscompose/buscompose_test.go

@@ -3,6 +3,7 @@ package buscompose
 import (
 	"encoding/json"
 	"errors"
+	"maps"
 	"os"
 	"path/filepath"
 	"reflect"
@@ -419,6 +420,76 @@ func TestTheCopiedComposerComposesAsTheControllers(t *testing.T) {
 			}
 		}
 	})
+	// 774/S39 (ADR 0583 §1): while a node rotates, both its logins are users with the node's permissions and its one
+	// inbox, each calling in its own name; every node reads its own node-logins key alone; with no rotation the list
+	// is the one above (AC2: the controller's golden lists, unchanged).
+	t.Run("a node rotating has two logins of one node", func(t *testing.T) {
+		vault := Seat{Name: VaultSeat, Serves: []string{"rotate-node", "node-account-confirm", "sign", "own"}}
+		since := time.Date(2026, 11, 2, 1, 0, 0, 0, time.UTC)
+		users, err := Users(Records{Nodes: []string{"ace", "g14"},
+			Assigned: map[string][]Declared{"ace": {{Module: "mesh-vault", Holds: []Seat{vault}}}},
+			NodeLogins: map[string]delivery.NodeLogin{
+				"g14": {Node: "g14", Login: "node.g14", Rotating: "node.g14--b", Stage: delivery.RotationBegun, Since: since},
+				// A node that rotated before and rotates no more logs in as its second login alone.
+				"ace": {Node: "ace", Login: "node.ace--b", Since: since}}})
+		if err != nil {
+			t.Fatal(err)
+		}
+		perms := map[string]Permissions{}
+		for _, u := range users {
+			if u.Kind == KindNode {
+				p, err := PermissionsFor(u)
+				if err != nil {
+					t.Fatal(err)
+				}
+				perms[u.Username()] = p
+			}
+		}
+		if len(perms) != 3 || perms["node.g14"].Publish == nil || perms["node.g14--b"].Publish == nil || perms["node.ace--b"].Publish == nil {
+			t.Fatalf("the node users are %v", slices.Sorted(maps.Keys(perms)))
+		}
+		// Equal, but for the caller each names in its calls (the bus's proof of which login called, ADR 0583 §3).
+		own := func(p Permissions, login string) Permissions {
+			swap := func(in []string) []string {
+				out := make([]string, len(in))
+				for i, s := range in {
+					out[i] = strings.ReplaceAll(s, CallerToken(login), "<caller>")
+				}
+				return out
+			}
+			return Permissions{Publish: swap(p.Publish), PublishDeny: swap(p.PublishDeny), Subscribe: swap(p.Subscribe),
+				AllowResponses: p.AllowResponses}
+		}
+		if a, b := own(perms["node.g14"], "node.g14"), own(perms["node.g14--b"], "node.g14--b"); !reflect.DeepEqual(a, b) {
+			t.Errorf("the two logins' permissions differ:\n%v\n%v", a, b)
+		}
+		for login, p := range perms {
+			node, _ := delivery.LoginNode(login)
+			if !slices.Contains(p.Subscribe, "_INBOX.node."+node+".>") || slices.Contains(p.Subscribe, "_INBOX."+login+".>") && login != "node."+node {
+				t.Errorf("%s's inbox: %v", login, p.Subscribe)
+			}
+		}
+		// AC3: g14 reads node-logins key g14 and not ace, and writes neither; it confirms in its own login's name.
+		get := func(key string) string {
+			return "$JS.API.DIRECT.GET.KV_" + delivery.NodeLoginsBucket + ".$KV." + delivery.NodeLoginsBucket + "." + key
+		}
+		confirm := func(login string) string {
+			return "mesh.seat.mesh-vault.call.node-account-confirm." + CallerToken(login)
+		}
+		for subject, want := range map[string]bool{get("g14"): true, get("ace"): false, "$KV." + delivery.NodeLoginsBucket + ".g14": false,
+			confirm("node.g14--b"): true, confirm("node.g14"): false} {
+			if MayPublish(perms["node.g14--b"], subject) != want {
+				t.Errorf("node.g14--b may publish %s: %v, want %v", subject, !want, want)
+			}
+		}
+		if plain, _ := PermissionsFor(Principal{Kind: KindNode, Node: "g14"}); MayPublish(plain, get("g14")) {
+			t.Error("a node reads node-logins while the vault does not rotate")
+		}
+		// And nothing but the grants part names node-logins among its reads.
+		if !ReaderMay(GrantsModule, delivery.NodeLoginsRead) || ReaderMay("shop", delivery.NodeLoginsRead) {
+			t.Error("node-logins' named readers")
+		}
+	})
 	t.Run("the controller's golden server configuration", func(t *testing.T) {
 		seat := Seat{Name: "telegram-sender", Accepts: []string{"send"}, Emits: []string{"delivered", "failed"}}
 		got, err := Compose(

go/buscompose/nats.go

@@ -253,6 +253,16 @@ type Principal struct {
 	// stream and name. Created only, never updated or deleted.
 	CreatesConsumers []ModuleConsumer
 
+	// Login is a node principal's login when it is not `node.<n>`: its second login, `node.<n>--b`, composed beside or
+	// in place of the first as the vault's node-logins says (novox/hq ADR 0583 §1, issue 774). Each login is granted
+	// the node's permissions and the node's inbox `_INBOX.node.<n>`; what it calls, it calls in its own name, so the
+	// vault tells the login that confirms a rotation from the one it replaces (§3).
+	Login string
+	// RotatesItsLogin is a machine principal whose node-engine reads its own node's key of the vault's node-logins,
+	// and no other key, and confirms a switch with node-account-confirm in its own name (novox/hq ADR 0583 §1 insight,
+	// §3). Set while the vault's holder serves rotate-node.
+	RotatesItsLogin bool
+
 	// PasswordHash is the bcrypt hash the mesh minted. The plaintext is sealed to the principal
 	// and never appears here: this file is written to a node's disk and read by a server, and a
 	// secret that can be read from a configuration file is a secret with a wider blast radius
@@ -380,6 +390,23 @@ var VaultOwn = SeatVerb{Seat: "mesh-vault", Verb: "own"}
 // ADR 0550 §2); granted as Principal.AsksTheVaultToSign says.
 var VaultSign = SeatVerb{Seat: "mesh-vault", Verb: delivery.SignVerb}
 
+// VaultRotateNode is the vault's verb that begins a node's account rotation; while its holder serves it, every node
+// principal reads its own node's key of node-logins (novox/hq ADR 0583 §1, §2). VaultNodeAccountConfirm is the verb a
+// node-engine confirms a switch with, in its new login's name (§3).
+var (
+	VaultRotateNode         = SeatVerb{Seat: "mesh-vault", Verb: delivery.RotateNodeVerb}
+	VaultNodeAccountConfirm = SeatVerb{Seat: "mesh-vault", Verb: delivery.NodeAccountConfirmVerb}
+)
+
+// NodeLoginsReads is what a node's engine is granted of the vault's node-logins: its own node's key, read and watched,
+// and no other (novox/hq ADR 0583 §1 insight).
+func NodeLoginsReads(node string) []string {
+	if !safeSubject.MatchString(node) {
+		return nil
+	}
+	return readGrants(delivery.NodeLoginsBucket, node)
+}
+
 // VerbsTheControllerActsOnAWarrant are the other seat verbs the controller calls when the operator's warrant
 // chooses them (novox/hq ADR 0259): a machine's service restarted, and a walk started or stopped through the
 // controller's own `plans`, a machine's held builds sent by its own `push` and the builds held after a failed release
@@ -528,6 +555,9 @@ func (p Principal) Username() string {
 		// never the module's own name alone, which is a different account with a different secret.
 		return p.Node + "." + p.Module + "." + p.Process
 	case KindNode:
+		if p.Login != "" {
+			return p.Login
+		}
 		return "node." + p.Node
 	case KindController:
 		return "controller"
@@ -587,7 +617,14 @@ func AskAccessActSubject(node string) string { return "mesh.node." + node + ".as
 // 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.
-func (p Principal) inbox() string { return "_INBOX." + p.Username() + ".>" }
+//
+// A node's two logins share the node's inbox (novox/hq ADR 0583 §1): its answers reach it whichever login it dials as.
+func (p Principal) inbox() string {
+	if p.Kind == KindNode {
+		return "_INBOX.node." + p.Node + ".>"
+	}
+	return "_INBOX." + p.Username() + ".>"
+}
 
 // Permissions is what a principal may publish and subscribe, and whether it may answer.
 type Permissions struct {
@@ -1003,6 +1040,13 @@ func PermissionsFor(p Principal) (Permissions, error) {
 			pub = append(pub, readGrants(delivery.SignersBucket, "")...)
 			pub = append(pub, readGrants(LeaseBucket, leaseKey)...)
 		}
+		// And, while the vault rotates node accounts, its own node's key of node-logins, read and watched, and no other
+		// key (novox/hq ADR 0583 §1 insight): the login it dials as; and the confirmation of a switch in its own name (§3).
+		if p.RotatesItsLogin {
+			pub = append(pub, NodeLoginsReads(p.Node)...)
+			pub = append(pub, "mesh.seat."+VaultNodeAccountConfirm.Seat+"."+CallKind+"."+VaultNodeAccountConfirm.Verb+"."+
+				CallerToken(p.Username()))
+		}
 		// And its node seat, node-engine, and its asks to the operator in its own name (novox/hq ADR 0563 §1, §3).
 		ep, es := engineGrants(p)
 		pub = append(pub, ep...)

go/buscompose/userlist_switch.go

@@ -104,7 +104,10 @@ var NamedReaders = map[string][]string{VaultBusAccounts: {GrantsModule}, GrantsA
 	ControllerConditions: {health.KeeperModule}, ControllerHandActs: {health.HealersModule, handacts.Module}, HealersWould: {},
 	// ADR 0577 clause 1: the node-engine's data items are read by disk-load alone, each node's its own node's keys
 	// (NodeKeyedReads); the engine announces nothing of its own, so its readers are named here.
-	delivery.EngineDataRead: {health.DiskLoadModule}}
+	delivery.EngineDataRead: {health.DiskLoadModule},
+	// ADR 0583 §1 insight: every node's login is read by the grants part alone, each engine its own node's key through its
+	// machine principal (NodeLoginsReads), never through `reads`.
+	delivery.NodeLoginsRead: {GrantsModule}}
 
 // ReaderMay says whether module may read the state read (`<owner>.<name>`) by the named readers: always, for a state
 // that names none.

go/buscompose/users.go

@@ -2,10 +2,12 @@ package buscompose
 
 import (
 	"fmt"
-	"git.novox.be/novox/mesh-sdk/go/announce"
 	"slices"
 	"sort"
 	"strings"
+
+	"git.novox.be/novox/mesh-sdk/go/announce"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
 )
 
 // Every user the composed file should contain, derived from what the mesh knows.
@@ -145,6 +147,9 @@ type Records struct {
 	// grants part as a placed module's are; it adds no principal, since each node's engine speaks as the node's account.
 	// Nil where its manifest was not read.
 	Engine *Declared
+	// NodeLogins is each node's key of the vault's node-logins (novox/hq ADR 0583 §1): the login in use and the one
+	// rotating, each composed as a user of the node's permissions. A node absent logs in as `node.<n>` alone.
+	NodeLogins map[string]delivery.NodeLogin
 	// Announced is each module's last announcement of the states it keeps (novox/hq ADR 0495, issue 1790), as the
 	// controller keeps it; a module absent has announced nothing yet. Nil where none was read.
 	Announced map[string]announce.States
@@ -180,10 +185,14 @@ func Users(r Records) ([]Principal, error) {
 			}
 			checks = append(checks, d.Checks...)
 		}
-		out = append(out, Principal{Kind: KindNode, Node: node, WitnessesController: witness, Checks: checks,
-			MovesIntoTheVault: servesMoveIn(r), StatesItsKeyToTheVault: servesVerb(r, VaultNodeKey),
-			AsksItsOwnSecrets: servesVerb(r, VaultOwn), AsksTheVaultToSign: servesVerb(r, VaultSign), Uses: asksSeatOf(r),
-			FollowsGrantsUserList: bus, ServedReads: servedOn(served, node)})
+		// **One user per login the node has** (novox/hq ADR 0583 §1): the one in use, and while it rotates the other too,
+		// each with the node's permissions.
+		for _, login := range nodeLoginsOf(r, node) {
+			out = append(out, Principal{Kind: KindNode, Node: node, Login: login, WitnessesController: witness, Checks: checks,
+				MovesIntoTheVault: servesMoveIn(r), StatesItsKeyToTheVault: servesVerb(r, VaultNodeKey),
+				AsksItsOwnSecrets: servesVerb(r, VaultOwn), AsksTheVaultToSign: servesVerb(r, VaultSign), Uses: asksSeatOf(r),
+				FollowsGrantsUserList: bus, ServedReads: servedOn(served, node), RotatesItsLogin: servesVerb(r, VaultRotateNode)})
+		}
 		// **And the machine's provisioner client, on an account of its own** (novox/hq ADR 0349 clause 11): one
 		// per machine that runs it, delivered to the module running it.
 		for _, d := range r.Assigned[node] {
@@ -385,6 +394,27 @@ func asksSeatOf(r Records) []Seat {
 	return nil
 }
 
+// nodeLoginsOf are the logins composed for node, as Principal.Login names them ("" for `node.<n>`): the one its
+// node-logins key says is in use and the one rotating, in that order; `node.<n>` alone when the key is absent or does
+// not hold (a key naming another node's login is no login of this node's).
+func nodeLoginsOf(r Records, node string) []string {
+	l, ok := r.NodeLogins[node]
+	if !ok || l.Node != node || (l.Login != delivery.FirstLogin(node) && l.Login != delivery.SecondLogin(node)) {
+		return []string{""}
+	}
+	login := func(name string) string {
+		if name == delivery.FirstLogin(node) {
+			return ""
+		}
+		return name
+	}
+	out := []string{login(l.Login)}
+	if l.Rotates() && l.Rotating == delivery.OtherLogin(node, l.Login) {
+		out = append(out, login(l.Rotating))
+	}
+	return out
+}
+
 // VaultSeat is the vault's seat: its holder alone asks the desks and the issuing providers in its own name.
 const VaultSeat = "mesh-vault"