Merge pull request 'L3: the vault mints bus accounts, the grants part and the node seat node-engine (issue 774, ADR 0561), rebased onto L2' (#126) from feat/774-vault-mints-sdk into main

2026-10-28 22:27:36 +00:00
parent f9afe32888 8eafc0c5ce
commit d747c1128e
31 changed files with 2079 additions and 21 deletions
@@ -571,3 +571,8 @@ type ProofAnswer struct {
 	Accepted bool   `json:"accepted"`
 	Words    string `json:"words"`
 }
+
+// EngineAsker is the asker name a node's engine asks the operator under (novox/hq ADR 0563 §3, which changes ADR 0259
+// §2 to admit a node's engine as an asker): `node-engine-<node>`, the last token of the by-caller subjects granted to that
+// node's engine account alone, so no engine acts on another node's warrant.
+func EngineAsker(node string) string { return "node-engine-" + node }
@@ -0,0 +1,244 @@
+package buscompose
+
+import (
+	"encoding/json"
+	"fmt"
+	"slices"
+	"strings"
+	"time"
+)
+
+// **The accounts the grants part wants, and the one shape a held account takes** (novox/hq ADR 0561 §1, §2; issue 774).
+//
+// The bus composer derives every user from placement, the manifests and the wants. For each account the mesh mints (a
+// module's, a module's process's, a machine's provisioner client's), the grants part writes one key of its state
+// `accounts`, keyed by the bus user, holding the account's fields that are not secret: what the controller's credential
+// carries today beside the password. The vault watches that state, mints the user it holds no value for, and keeps the
+// value as the module's own secret on that node, built by HeldCredential, which gives byte for byte the controller's
+// shape, so a runtime reads it unchanged. The state is read by the vault alone (NamedReaders), as `bus-accounts` is read
+// by the grants part alone.
+//
+// The node accounts, the controller's own, an enrolment user and a person are never wanted here: the vault mints none
+// of them (ADR 0561 §4, §5).
+
+// AccountsState is the grants part's state of wanted accounts, by bus user.
+const AccountsState = "accounts"
+
+// GrantsAccounts is that state as a reader names it (`<owner>.<name>`).
+const GrantsAccounts = GrantsModule + "." + AccountsState
+
+// AccountsBucket is the bucket the state lives in.
+var AccountsBucket = BucketName(GrantsModule, AccountsState)
+
+// AccountsSubject is the subject of one wanted account's key: `$KV.mesh-grants_accounts.<user>`.
+func AccountsSubject(user string) string { return "$KV." + AccountsBucket + "." + user }
+
+// AccountIssuedEvent is what the vault says when it minted an account: AccountIssued, never a value or a hash.
+const AccountIssuedEvent = "account-issued"
+
+// AccountIssuedSubject is where it says it, as the runtime addresses mesh-vault's events.
+const AccountIssuedSubject = "mesh.mod." + VaultSeat + ".event." + AccountIssuedEvent
+
+// ClaimedSeat is one seat a module claims, as its runtime needs it (the controller's seatClaimed): the name, the scope (a
+// node-scoped seat's verb carries the machine) and the verbs the runtime serves for it.
+type ClaimedSeat struct {
+	Seat   string   `json:"seat"`
+	Scope  string   `json:"scope"`
+	Serves []string `json:"serves,omitempty"`
+}
+
+// WantedAccount is one key of the grants part's state `accounts`: an account the mesh needs, without its password.
+type WantedAccount struct {
+	User string `json:"user"`
+	// Kind is KindModule (KindNodeTools for the runtime, named as a module is), KindProcess or KindProvisioner.
+	Kind   Kind   `json:"kind"`
+	Node   string `json:"node"`
+	Module string `json:"module"`
+	// Process is a KindProcess account's process id.
+	Process string `json:"process,omitempty"`
+	// URL is the bus's address as that node reaches it, `nats://<host>:<port>`; Fingerprint the bus certificate's.
+	URL         string `json:"url"`
+	Fingerprint string `json:"fingerprint,omitempty"`
+	// Claims are a module's claims with the verbs each seat promises: none for a process or a provisioner client.
+	Claims []ClaimedSeat `json:"claims,omitempty"`
+	// At is when the grants part wrote the key: not compared (Same).
+	At time.Time `json:"at"`
+}
+
+// mintedKinds are the kinds of account the vault mints (ADR 0561 §1).
+var mintedKinds = []Kind{KindModule, KindNodeTools, KindProcess, KindProvisioner}
+
+// principal is the account as the composer names it.
+func (w WantedAccount) principal() Principal {
+	return Principal{Kind: w.Kind, Node: w.Node, Module: w.Module, Process: w.Process}
+}
+
+// Valid says why w is not an account the vault may mint, or nil: a kind it mints, every name a subject token, the user
+// the one the composer derives from them, and an address to reach the bus at.
+func (w WantedAccount) Valid() error {
+	if !slices.Contains(mintedKinds, w.Kind) {
+		return fmt.Errorf("%s is a %s account, which the vault never mints (ADR 0561 §4)", w.User, w.Kind)
+	}
+	for what, v := range map[string]string{"node": w.Node, "module": w.Module} {
+		if !safeSubject.MatchString(v) {
+			return fmt.Errorf("%s: the %s %q is not a name the mesh writes", w.User, what, v)
+		}
+	}
+	if w.Kind == KindProcess && !safeSubject.MatchString(w.Process) {
+		return fmt.Errorf("%s: the process %q is not a name the mesh writes", w.User, w.Process)
+	}
+	if w.Kind != KindProcess && w.Process != "" {
+		return fmt.Errorf("%s: only a process's account names a process", w.User)
+	}
+	if want := w.principal().Username(); w.User != want {
+		return fmt.Errorf("%s is not the user of a %s account of %s on %s (that is %s)", w.User, w.Kind, w.Module, w.Node, want)
+	}
+	if !strings.HasPrefix(w.URL, "nats://") || len(w.URL) == len("nats://") {
+		return fmt.Errorf("%s names no bus address (url, nats://<host>:<port>)", w.User)
+	}
+	if len(w.Claims) > 0 && w.Kind != KindModule && w.Kind != KindNodeTools {
+		return fmt.Errorf("%s: a %s account holds no seat, so it carries no claims", w.User, w.Kind)
+	}
+	return nil
+}
+
+// Same says whether two wanted accounts want the same account: every field but when it was written.
+func (w WantedAccount) Same(o WantedAccount) bool {
+	a, b := w, o
+	a.At, b.At = time.Time{}, time.Time{}
+	ra, _ := json.Marshal(a)
+	rb, _ := json.Marshal(b)
+	return string(ra) == string(rb)
+}
+
+// OwnSecret is the module's own secret the account is held in: `broker`, `broker-<process id>` or `provisioner-broker`
+// (the controller's names, ADR 0436 §2, ADR 0349 §11).
+func (w WantedAccount) OwnSecret() string {
+	switch w.Kind {
+	case KindProcess:
+		return "broker-" + w.Process
+	case KindProvisioner:
+		return "provisioner-broker"
+	}
+	return "broker"
+}
+
+// ReadWantedAccount reads the key user of the state: refused when it is not a valid wanted account of that user.
+func ReadWantedAccount(user string, raw []byte) (WantedAccount, error) {
+	var w WantedAccount
+	if err := json.Unmarshal(raw, &w); err != nil {
+		return WantedAccount{}, fmt.Errorf("%s %s is not a wanted account: %w", GrantsAccounts, user, err)
+	}
+	if w.User != user {
+		return WantedAccount{}, fmt.Errorf("%s %s names the user %q", GrantsAccounts, user, w.User)
+	}
+	return w, w.Valid()
+}
+
+// AccountIssued is the vault's account-issued: which account it minted, and its generation. Never a value or a hash.
+type AccountIssued struct {
+	User       string    `json:"user"`
+	Kind       Kind      `json:"kind"`
+	Node       string    `json:"node"`
+	Module     string    `json:"module"`
+	Process    string    `json:"process,omitempty"`
+	Generation int       `json:"generation"`
+	At         time.Time `json:"at"`
+}
+
+// HeldCredential is the value the account's holder reads, exactly as the controller builds it today (issueWith,
+// sealProcess and sealProvisionerClient): a module's `{url, fingerprint, node, module, user, password, claims}`, a
+// process's without claims, a provisioner client's without module or claims; an empty fingerprint or claims left out.
+func HeldCredential(w WantedAccount, password string) ([]byte, error) {
+	if err := w.Valid(); err != nil {
+		return nil, err
+	}
+	if password == "" {
+		return nil, fmt.Errorf("%s: an account is held with its password", w.User)
+	}
+	switch w.Kind {
+	case KindProcess:
+		return json.Marshal(struct {
+			URL         string `json:"url"`
+			Fingerprint string `json:"fingerprint,omitempty"`
+			Node        string `json:"node"`
+			Module      string `json:"module"`
+			User        string `json:"user"`
+			Password    string `json:"password"`
+		}{URL: w.URL, Fingerprint: w.Fingerprint, Node: w.Node, Module: w.Module, User: w.User, Password: password})
+	case KindProvisioner:
+		return json.Marshal(struct {
+			URL         string `json:"url"`
+			Fingerprint string `json:"fingerprint,omitempty"`
+			Node        string `json:"node"`
+			User        string `json:"user"`
+			Password    string `json:"password"`
+		}{URL: w.URL, Fingerprint: w.Fingerprint, Node: w.Node, User: w.User, Password: password})
+	}
+	return json.Marshal(struct {
+		URL         string        `json:"url"`
+		Fingerprint string        `json:"fingerprint,omitempty"`
+		Node        string        `json:"node"`
+		Module      string        `json:"module"`
+		User        string        `json:"user"`
+		Password    string        `json:"password"`
+		Claims      []ClaimedSeat `json:"claims,omitempty"`
+	}{URL: w.URL, Fingerprint: w.Fingerprint, Node: w.Node, Module: w.Module, User: w.User, Password: password,
+		Claims: w.Claims})
+}
+
+// **One issuer at every moment: minting turns on at the lease write** (novox/hq ADR 0561 §3, §6). The controller's lease
+// is the one key `holder` of its bucket (LeaseBucket). The operator's credential hands it away by writing a value that
+// names its new holder in `handed-to`; while the key holds that, the vault mints and the grants part creates the durable
+// consumers an account needs. A controller's value, a key deleted or expired, or one that cannot be read or parsed, turn
+// both off: when in doubt nothing is minted, so the controller and the vault never both mint one account. No clock and
+// no setting turns it.
+
+// ControllerLease is the lease's bucket as a reader names it; the vault and the grants part alone read it
+// (NamedReaders), the controller's announcement marking it readable by nobody.
+const ControllerLease = ControllerSeat + ".lease"
+
+// ControllerLeaseKey is the lease's one key.
+const ControllerLeaseKey = leaseKey
+
+// LeaseHolder is the lease key's value: a controller instance's (mesh-controller internal/lease Holder), or, once handed
+// away, one naming its holder in HandedTo.
+type LeaseHolder struct {
+	Instance string    `json:"instance,omitempty"`
+	Host     string    `json:"host,omitempty"`
+	Epoch    uint64    `json:"epoch,omitempty"`
+	Taken    time.Time `json:"taken,omitzero"`
+	Renewed  time.Time `json:"renewed,omitzero"`
+	// HandedTo is who holds the lease once the controller handed it away: never a controller instance.
+	HandedTo string `json:"handed-to,omitempty"`
+	// HandedBy is the credential that wrote it (the operator's), and Why its reason.
+	HandedBy string `json:"handed-by,omitempty"`
+	Why      string `json:"why,omitempty"`
+}
+
+// LeaseHandedAway reads the lease key as a getter answered it (its value, whether it was there, the read's error) and
+// says whether it is handed to a holder that is no controller, with why either way.
+func LeaseHandedAway(raw []byte, found bool, readErr error) (bool, string) {
+	switch {
+	case readErr != nil:
+		return false, "the controller's lease cannot be read (" + readErr.Error() + "), so nothing is minted"
+	case !found || len(raw) == 0 || string(raw) == "null":
+		return false, "no lease is written (expired, deleted, or never taken): a controller may take it, so nothing is minted"
+	}
+	var h LeaseHolder
+	if err := json.Unmarshal(raw, &h); err != nil {
+		return false, "the controller's lease is not readable as a holder (" + err.Error() + "), so nothing is minted"
+	}
+	if strings.TrimSpace(h.HandedTo) == "" {
+		who := h.Instance
+		if who == "" {
+			who = "an instance that names itself not"
+		}
+		return false, "the controller holds the lease (" + who + "): it mints, so the vault mints nothing (ADR 0561 §3)"
+	}
+	if h.Instance != "" {
+		return false, "the lease names both a controller instance (" + h.Instance + ") and a holder it is handed to (" +
+			h.HandedTo + "), so nothing is minted"
+	}
+	return true, "the lease is handed to " + h.HandedTo + ": the vault mints every new account (ADR 0561 §1, §3)"
+}
@@ -1,6 +1,7 @@
 package buscompose

 import (
+	"slices"
 	"sort"
 	"strings"

@@ -58,6 +59,10 @@ func ReadsAnnouncedBy(reader string, reads []string, announced map[string]announ
 		switch {
 		case reader != "" && !ReaderMay(reader, r):
 			refused = append(refused, r)
+		case reader != "" && namedReader(reader, r):
+			// A state the composer names its readers for is theirs whatever its owner announced (ADR 0561 §3: the
+			// controller's lease, which its announcement marks readable by nobody).
+			granted = append(granted, r)
 		case reader != "" && ok && said && s.Keeps(name):
 			if s.ReadableBy(name, reader) {
 				granted = append(granted, r)
@@ -95,3 +100,8 @@ func NotAnnounced(r Records) []string {
 	sort.Strings(out)
 	return out
 }
+
+// namedReader says the composer names module among the readers of read (NamedReaders).
+func namedReader(module, read string) bool {
+	return slices.Contains(NamedReaders[strings.TrimSpace(read)], module)
+}
@@ -2,6 +2,7 @@ package buscompose

 import (
 	"encoding/json"
+	"errors"
 	"os"
 	"path/filepath"
 	"reflect"
@@ -9,8 +10,11 @@ import (
 	"slices"
 	"strings"
 	"testing"
+	"time"

+	"git.novox.be/novox/mesh-sdk/go/announce"
 	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"github.com/nats-io/nats.go/jetstream"
 )

 // Defends issue 1377 and novox/hq ADR 0547 §5: this is the controller's bus composer copied, and it composes byte for
@@ -51,6 +55,26 @@ func mayBeyondTheControllers(user string) map[string]bool {
 		VaultSecretChanged: true}
 }

+// engineBeyond is a node's engine holding its node seat and asking the operator in its own name (novox/hq ADR 0563 §1,
+// §3), beyond the controller's on purpose: its own node's verbs, events and discovery, the bus's discovery asked, and
+// the router's seat traffic under node-engine-<node>.
+func engineBeyond(user, g string) bool {
+	node, ok := strings.CutPrefix(user, "node.")
+	if !ok {
+		return false
+	}
+	return strings.HasPrefix(g, "mesh.seat."+EngineSeat+".") && strings.Contains(g, "."+node) ||
+		strings.HasPrefix(g, "$SRV.") || strings.Contains(g, ".node-engine-"+node) ||
+		strings.Contains(g, "KV_"+EngineActsBucket) || strings.HasPrefix(g, "$KV."+EngineActsBucket+"."+node+".")
+}
+
+// createsAnAccountsConsumer is the grants part's create and read of a durable consumer an account needs, by its stream
+// and name (novox/hq ADR 0561 §6): beyond the controller's on purpose, since the controller made them alone.
+func createsAnAccountsConsumer(user, g string) bool {
+	return strings.HasSuffix(user, "."+GrantsModule) &&
+		(strings.HasPrefix(g, "$JS.API.CONSUMER.CREATE.") || strings.HasPrefix(g, "$JS.API.CONSUMER.INFO."))
+}
+
 // quotedToken is a quoted token of a composed list.
 var quotedToken = regexp.MustCompile(`"[^"]*"`)

@@ -102,7 +126,8 @@ func grantsAsTheControllers(t *testing.T, got, want string) {
 			}
 		}
 		for g := range now {
-			if !was[g] && !intended[g] && !mayBeyondTheControllers(user)[g] && !createdAdvisory.MatchString(`"`+g+`", `) {
+			if !was[g] && !intended[g] && !mayBeyondTheControllers(user)[g] && !createdAdvisory.MatchString(`"`+g+`", `) &&
+				!createsAnAccountsConsumer(user, g) && !engineBeyond(user, g) {
 				t.Errorf("%s: the copy grants %s beyond the controller's, and no decision names it", user, g)
 			}
 		}
@@ -119,6 +144,8 @@ func grantsAsTheControllers(t *testing.T, got, want string) {
 	}
 }

+const SignersBucketName = "mesh-vault_signers"
+
 func TestTheCopiedComposerComposesAsTheControllers(t *testing.T) {
 	// ADR 0567 §3, §9: a node reads every key of the seat's placement and its candidates (it composes with the whole
 	// proposal laid over), and none of its open proposals; it writes neither.
@@ -221,6 +248,55 @@ func TestTheCopiedComposerComposesAsTheControllers(t *testing.T) {
 			t.Error("a user of a seat not pulled by kind reads DEAD_LETTERS")
 		}
 	})
+	// ADR 0563 §1, §3, §6: each node's engine alone answers its own node's node-engine verbs and says its events, any
+	// runtime may call them, and it asks the operator under node-engine-<node> alone.
+	t.Run("a node's engine holds its node seat and asks in its own name", func(t *testing.T) {
+		router := Seat{Name: AsksSeat, Accepts: []string{"ask", "cancel"}, Emits: []string{"decided"},
+			ByCaller: []string{"ask", "cancel", "decided"}, Records: []string{"messenger_asks"}}
+		users, err := Users(Records{Nodes: []string{"one", "two"}, Assigned: map[string][]Declared{
+			"one": {{Module: "messenger", Holds: []Seat{router}, Invokes: []string{"seat:" + EngineSeat + ".root-free"}}},
+			"two": {{Module: RuntimeModule}, {Module: "shop", Invokes: []string{"*"}}}}})
+		if err != nil {
+			t.Fatal(err)
+		}
+		for _, u := range users {
+			perms, err := PermissionsFor(u)
+			if err != nil {
+				t.Fatal(err)
+			}
+			answers := MaySubscribe(perms, "mesh.seat."+EngineSeat+".tool.root-free.one") ||
+				MaySubscribe(perms, "mesh.seat."+EngineSeat+".call.root-free.one.messenger~one")
+			if engineOne := u.Kind == KindNode && u.Node == "one"; answers != engineOne {
+				t.Errorf("%s answers one's root-free: %v", u.Username(), answers)
+			}
+			switch {
+			case u.Kind == KindNode && u.Node == "one":
+				for subject, want := range map[string]bool{
+					"mesh.seat.operator-channel.accept.ask.node-engine-one":                               true,
+					"mesh.seat.operator-channel.accept.cancel.node-engine-one":                            true,
+					"mesh.seat.operator-channel.accept.ask.node-engine-two":                               false,
+					"$JS.API.DIRECT.GET.KV_messenger_asks.$KV.messenger_asks.node-engine-one.hand-over-1": true,
+					"$JS.API.DIRECT.GET.KV_messenger_asks.$KV.messenger_asks.node-engine-two.hand-over-1": false,
+					"mesh.seat." + EngineSeat + ".event.done.one":                                         true,
+					"mesh.seat." + EngineSeat + ".event.done.two":                                         false,
+					"$SRV.INFO": true,
+				} {
+					if got := MayPublish(perms, subject); got != want {
+						t.Errorf("node one may publish %s: %v, want %v", subject, got, want)
+					}
+				}
+				if !MaySubscribe(perms, "mesh.seat.operator-channel.event.decided.node-engine-one") ||
+					MaySubscribe(perms, "mesh.seat.operator-channel.event.decided.node-engine-two") ||
+					!MaySubscribe(perms, "$SRV.INFO."+EngineSeat) || MaySubscribe(perms, "mesh.seat."+EngineSeat+".tool.hand-over.two") {
+					t.Errorf("node one hears %v", perms.Subscribe)
+				}
+			case u.Kind == KindNodeTools || u.Module == "messenger":
+				if !MayPublish(perms, "mesh.seat."+EngineSeat+".tool.root-free.one") {
+					t.Errorf("%s cannot call one's root-free", u.Username())
+				}
+			}
+		}
+	})
 	// Issue 1126 (ADR 0550 §5): a node's engine asks the vault's `own` in its own name while the vault serves it, and no
 	// other node's.
 	t.Run("a node asks the vault its own secrets", func(t *testing.T) {
@@ -239,6 +315,21 @@ func TestTheCopiedComposerComposesAsTheControllers(t *testing.T) {
 		if !slices.Contains(perms.Subscribe, VaultSecretChanged) {
 			t.Errorf("node one does not hear the vault's secret-changed: %v", perms.Subscribe)
 		}
+		// L3 s6 (ADR 0550 §2): while the vault serves `sign`, a node asks it in its own name alone, and reads the vault's
+		// `signers` and the lease key, never writing either.
+		signs, _ := PermissionsFor(Principal{Kind: KindNode, Node: "one", AsksTheVaultToSign: true})
+		signersGet := "$JS.API.DIRECT.GET.KV_" + SignersBucketName + ".$KV." + SignersBucketName + ".key"
+		leaseGet := "$JS.API.DIRECT.GET.KV_" + LeaseBucket + ".$KV." + LeaseBucket + ".holder"
+		for subject, want := range map[string]bool{VaultSignCall(one): true, signersGet: true, leaseGet: true,
+			VaultSignCall(Principal{Kind: KindNode, Node: "two"}): false, "$KV." + SignersBucketName + ".key": false,
+			"$KV." + LeaseBucket + ".holder": false} {
+			if MayPublish(signs, subject) != want {
+				t.Errorf("a node asking sign may publish %s: %v, want %v", subject, !want, want)
+			}
+		}
+		if MayPublish(perms, VaultSignCall(one)) || MayPublish(perms, signersGet) {
+			t.Error("a node asks sign or reads signers while the vault does not serve sign")
+		}
 		// And what a module on another node serves from its settings, that key alone (mailu's smtp domain, issue 1126).
 		users, err := Users(Records{Nodes: []string{"one", "two"}, Assigned: map[string][]Declared{
 			"two": {{Module: "mailer", Served: []string{"domain", "not.a.token"}}}}})
@@ -293,4 +384,174 @@ func TestTheCopiedComposerComposesAsTheControllers(t *testing.T) {
 		}
 		grantsAsTheControllers(t, got, string(want))
 	})
+	// 774/AC2 (novox/hq ADR 0561 §2): a wanted account round-trips through the grants part's state `accounts`, keyed by
+	// its user, at the subject `$KV.mesh-grants_accounts.<user>`, read by the vault alone; and the vault's account-issued
+	// names the account, never a value.
+	t.Run("a wanted account is kept by its user and read by the vault alone", func(t *testing.T) {
+		for _, w := range []WantedAccount{
+			{User: "ace.mesh-build-go", Kind: KindModule, Node: "ace", Module: "mesh-build-go", URL: "nats://novox.mesh:4222",
+				Fingerprint: "ab", Claims: []ClaimedSeat{{Seat: "node-build-go", Scope: "node", Serves: []string{"build"}}}},
+			{User: "novox.mesh-mail.send", Kind: KindProcess, Node: "novox", Module: "mesh-mail", Process: "send",
+				URL: "nats://novox.mesh:4222"},
+			{User: "provisioner.g14", Kind: KindProvisioner, Node: "g14", Module: "mesh-provisioner-client",
+				URL: "nats://novox.mesh:4222", Fingerprint: "ab"},
+		} {
+			if err := w.Valid(); err != nil {
+				t.Fatalf("%s: %v", w.User, err)
+			}
+			raw, err := json.Marshal(w)
+			if err != nil {
+				t.Fatal(err)
+			}
+			back, err := ReadWantedAccount(w.User, raw)
+			if err != nil || !back.Same(w) {
+				t.Errorf("%s does not round-trip: %+v, %v", w.User, back, err)
+			}
+			if got := AccountsSubject(w.User); got != "$KV.mesh-grants_accounts."+w.User {
+				t.Errorf("%s is kept at %s", w.User, got)
+			}
+			if _, err := ReadWantedAccount("someone.else", raw); err == nil {
+				t.Errorf("%s was read under another user's key", w.User)
+			}
+		}
+		for _, bad := range []WantedAccount{
+			{User: "ace.x", Kind: KindModule, Node: "ace", Module: "y", URL: "nats://a:1"},
+			{User: "ace.x.p", Kind: KindProcess, Node: "ace", Module: "x", URL: "nats://a:1"},
+			{User: "node.ace", Kind: KindNode, Node: "ace", URL: "nats://a:1"},
+			{User: "controller", Kind: KindController, URL: "nats://a:1"},
+			{User: "ace.x", Kind: KindModule, Node: "ace", Module: "x"},
+		} {
+			if bad.Valid() == nil {
+				t.Errorf("%+v is taken as a wanted account", bad)
+			}
+		}
+		if ReaderMay("mesh-delivery-assigner", GrantsAccounts) || !ReaderMay(VaultSeat, GrantsAccounts) {
+			t.Errorf("%s is read by %v alone, want the vault's", GrantsAccounts, NamedReaders[GrantsAccounts])
+		}
+		e := AccountIssued{User: "ace.x", Kind: KindModule, Node: "ace", Module: "x", Generation: 1}
+		raw, _ := json.Marshal(e)
+		if strings.Contains(string(raw), "password") || strings.Contains(string(raw), "hash") ||
+			AccountIssuedSubject != "mesh.mod.mesh-vault.event.account-issued" {
+			t.Errorf("account-issued says %s at %s", raw, AccountIssuedSubject)
+		}
+	})
+	// 774/AC3 (novox/hq ADR 0561 §2): the account the vault seals is, byte for byte, what the controller hands for each of
+	// its three kinds: testdata/controller-credentials.json was written by the controller's own code (its "how").
+	t.Run("a held account is the controller's shape byte for byte", func(t *testing.T) {
+		raw, err := os.ReadFile(filepath.Join("testdata", "controller-credentials.json"))
+		if err != nil {
+			t.Fatal(err)
+		}
+		var captured struct {
+			Rows []struct{ Name, Held string }
+		}
+		if err := json.Unmarshal(raw, &captured); err != nil {
+			t.Fatal(err)
+		}
+		vault := ClaimedSeat{Seat: "mesh-vault", Scope: "mesh", Serves: []string{"get", "accept", "secret-ask", "issued",
+			"rotate", "move-in", "node-key", "own", "move-asks"}}
+		controller := ClaimedSeat{Seat: "mesh-controller", Scope: "mesh", Serves: strings.Split("tools,calls,status,nodes,"+
+			"node,placement-export,modules,seats,builds,plans,delivery-plan,delivery-order,delivery-check,deliver,"+
+			"delivery-stop,delivery-backups-again,delivery-walks,plan,assign,unassign,pin,unpin,push,rotate,give,issued,"+
+			"secret-move,secret-ask,issue,token,settings,command,queue,cancel,clear,replay,try,kill,pause,resume,hand-act,"+
+			"drill,warranted,hand-acts,durations,conditions,healers,doctor,upgrade,bus,retire,cleanup,judge-directories,"+
+			"root-free,dead-letters,data,build,artifacts,held,collect,move-placement,move-config,mirrors,images", ",")}
+		at := "nats://10.0.0.1:4222"
+		wanted := map[string]struct {
+			w        WantedAccount
+			password string
+		}{
+			"module": {WantedAccount{User: "laptop.cap-bot", Kind: KindModule, Node: "laptop", Module: "cap-bot", URL: at,
+				Fingerprint: "ab:cd", Claims: []ClaimedSeat{vault, {Seat: "node-service-manager", Scope: "node",
+					Serves: []string{"status"}}, controller, {Seat: "no-such-seat", Scope: "node"}}}, "pw-module"},
+			"module-no-claims-no-fingerprint": {WantedAccount{User: "laptop.cap-plain", Kind: KindModule, Node: "laptop",
+				Module: "cap-plain", URL: at}, "pw-plain"},
+			"provisioner": {WantedAccount{User: "provisioner.laptop", Kind: KindProvisioner, Node: "laptop", Module: "nats",
+				URL: at, Fingerprint: "ab:cd"}, "pw-prov"},
+			"process": {WantedAccount{User: "laptop.mesh-mail.send", Kind: KindProcess, Node: "laptop", Module: "mesh-mail",
+				Process: "send", URL: at, Fingerprint: "ab:cd"}, "pw-proc"},
+		}
+		if len(captured.Rows) != len(wanted) {
+			t.Fatalf("%d rows captured, %d wanted", len(captured.Rows), len(wanted))
+		}
+		for _, row := range captured.Rows {
+			c, ok := wanted[row.Name]
+			if !ok {
+				t.Fatalf("no wanted account for the captured %s", row.Name)
+			}
+			got, err := HeldCredential(c.w, c.password)
+			if err != nil || string(got) != row.Held {
+				t.Errorf("%s:\n got %s (%v)\nwant %s", row.Name, got, err, row.Held)
+			}
+		}
+		if _, err := HeldCredential(wanted["module"].w, ""); err == nil {
+			t.Error("an account was held with no password")
+		}
+	})
+	// 774 subtasks 6 and 8 (novox/hq ADR 0561 §3, §6): minting and the grants part's consumers turn on only while the
+	// lease is handed to a holder that is no controller; the vault and the grants part alone read the lease, whatever the
+	// controller announced; a module's consumer is created as the controller's EnsureConsumer creates it.
+	t.Run("the lease turns minting on only when handed away; a consumer is created as the controller's", func(t *testing.T) {
+		for _, row := range []struct {
+			name  string
+			raw   string
+			found bool
+			err   error
+			on    bool
+		}{
+			{"a controller holds it", `{"instance":"novox/1234/2026-10-27T20:00:00Z","epoch":57}`, true, nil, false},
+			{"handed away", `{"handed-to":"the operator's hand-over","handed-by":"person.jochen"}`, true, nil, true},
+			{"expired or deleted", ``, false, nil, false},
+			{"unreadable", ``, false, errors.New("refused"), false},
+			{"not a holder", `[1]`, true, nil, false},
+			{"both a controller and a handed holder", `{"instance":"novox/1","handed-to":"x"}`, true, nil, false},
+		} {
+			if on, why := LeaseHandedAway([]byte(row.raw), row.found, row.err); on != row.on || why == "" {
+				t.Errorf("%s: on %v (%s), want %v", row.name, on, why, row.on)
+			}
+			// The assigner's grants source follows it: the grants part's bucket only for a handed-away lease (issue 774).
+			on, _ := LeaseHandedAway([]byte(row.raw), row.found, row.err)
+			if bucket, _ := delivery.GrantSource(on); (bucket == delivery.PartGrantsBucket) != row.on {
+				t.Errorf("%s: the grants source is %s", row.name, bucket)
+			}
+		}
+		announced := map[string]announce.States{ControllerSeat: ControllerAnnouncement("novox")}
+		for reader, want := range map[string]bool{VaultSeat: true, GrantsModule: true, "mesh-delivery-assigner": true, "mesh-delivery-view": false} {
+			granted, _ := ReadsAnnouncedBy(reader, []string{ControllerLease}, announced)
+			if (len(granted) == 1) != want {
+				t.Errorf("%s reads the lease: %v, want %v", reader, granted, want)
+			}
+		}
+		c, _ := ConsumerFor(Principal{Kind: KindModule, Node: "a", Module: "m", Consumes: []string{"x.happened"}})
+		cfg := ConsumerConfig(c)
+		if cfg.Durable != "a_m" || cfg.AckPolicy != jetstream.AckExplicitPolicy || cfg.AckWait != 30*time.Second ||
+			cfg.MaxDeliver != 5 || cfg.DeliverPolicy != jetstream.DeliverNewPolicy || len(cfg.FilterSubjects) != 2 ||
+			cfg.Description == "" {
+			t.Errorf("a module's consumer is created as %+v", cfg)
+		}
+		// The grants part is granted the create of each account's consumer by its stream and name, and no other.
+		users, err := Users(Records{Nodes: []string{"a"}, Assigned: map[string][]Declared{"a": {
+			{Module: GrantsModule}, {Module: "m", Consumes: []string{"x.happened"}}, {Module: "quiet"}}}})
+		if err != nil {
+			t.Fatal(err)
+		}
+		for _, u := range users {
+			if u.Module != GrantsModule || u.Kind != KindModule {
+				continue
+			}
+			perms, err := PermissionsFor(u)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if !MayPublish(perms, "$JS.API.CONSUMER.CREATE.EVENTS.a_m") || MayPublish(perms, "$JS.API.CONSUMER.CREATE.EVENTS.a_quiet") ||
+				MayPublish(perms, "$JS.API.CONSUMER.DELETE.EVENTS.a_m") || MayPublish(perms, "$JS.API.CONSUMER.CREATE.EVENTS.a_m.mesh.mod.x.event.happened") {
+				t.Errorf("the grants part creates consumers as %v", u.CreatesConsumers)
+			}
+		}
+		q := ConsumerConfig(QueueConsumer(Principal{Kind: KindProcess, Node: "a", Module: "m", Process: "p"},
+			QueueOwner{Process: "p", Stream: "M_WORK", MaxDeliver: 3}))
+		if q.Durable != "a_m_p" || q.FilterSubject != "" || q.MaxDeliver != 3 || q.DeliverPolicy != jetstream.DeliverAllPolicy {
+			t.Errorf("a process's queue consumer is created as %+v", q)
+		}
+	})
 }
@@ -86,3 +86,30 @@ func ModuleStreamConfig(m ModuleStream) jetstream.StreamConfig {
 	}
 	return cfg
 }
+
+// ConsumerConfig is a pull consumer as the controller's EnsureConsumer creates it (mesh-controller internal/broker
+// JetStream.EnsureConsumer, a consumer not there yet): its durable name, explicit acks, its ack wait, max deliver and max
+// ack pending, its description, one filter or several, and from the stream's end when it is made FromNow. The grants part
+// creates a module's and a process's consumers with it from the lease write (novox/hq ADR 0561 §6): a create alone,
+// never an update of one the bus holds. A push consumer or a queue group is the controller's own and never made here.
+func ConsumerConfig(c Consumer) jetstream.ConsumerConfig {
+	cfg := jetstream.ConsumerConfig{
+		Durable:       c.Name,
+		AckPolicy:     jetstream.AckExplicitPolicy,
+		AckWait:       time.Duration(c.AckWaitSeconds) * time.Second,
+		MaxDeliver:    c.MaxDeliver,
+		MaxAckPending: c.MaxAckPending,
+		Description:   c.Why,
+	}
+	switch len(c.Filters) {
+	case 0:
+	case 1:
+		cfg.FilterSubject = c.Filters[0]
+	default:
+		cfg.FilterSubjects = c.Filters
+	}
+	if c.FromNow {
+		cfg.DeliverPolicy = jetstream.DeliverNewPolicy
+	}
+	return cfg
+}
@@ -23,6 +23,8 @@ func TestTheGrantsPartCreatesOnlyDeclaredStreams(t *testing.T) {
 			{Module: GrantsModule, State: []Bucket{{Module: GrantsModule, Name: "assertions"}}, Reads: []string{VaultBusAccounts}},
 			{Module: RuntimeModule},
 		}},
+		// The node-engine's own manifest, placed on every node though no node is assigned it (novox/hq ADR 0563 §2, §3).
+		Engine: &Declared{Module: EngineModule, State: []Bucket{{Module: EngineModule, Name: EngineActsState}}},
 	}
 	users, err := Users(records)
 	if err != nil {
@@ -64,6 +66,15 @@ func TestTheGrantsPartCreatesOnlyDeclaredStreams(t *testing.T) {
 		{GrantsModule, "$JS.API.STREAM.CREATE.ASSIGNMENTS", false},
 		{GrantsModule, "$JS.API.STREAM.INFO.EVENTS", false},
 		{"mesh-delivery-builder", "$JS.API.STREAM.CREATE.KV_mesh-delivery-builder_steps", false},
+		// The node-engine's acts: created by the grants part, written by each node's engine under its own keys alone.
+		{GrantsModule, "$JS.API.STREAM.CREATE.KV_mesh-host_acts", true},
+		{"node.ace", "$JS.API.STREAM.CREATE.KV_mesh-host_acts", false},
+		{"node.ace", "$KV.mesh-host_acts.ace.act.hand-over-1", true},
+		{"node.ace", "$KV.mesh-host_acts.ace.open.hand-over.abc", true},
+		{"node.ace", "$KV.mesh-host_acts.novox.act.hand-over-1", false},
+		{"node.ace", "$JS.API.DIRECT.GET.KV_mesh-host_acts.$KV.mesh-host_acts.ace.ask.hand-over-1", true},
+		{"node.ace", "$JS.API.DIRECT.GET.KV_mesh-host_acts.$KV.mesh-host_acts.novox.ask.hand-over-1", false},
+		{"novox.node-tools", "$KV.mesh-host_acts.novox.act.hand-over-1", false},
 		// The sealed user list (ADR 0547 clause 7): the grants part writes its own bucket and no other.
 		{GrantsModule, "$JS.API.STREAM.CREATE.OBJ_mesh-grants-user-list", true},
 		{GrantsModule, "$O.mesh-grants-user-list.C.abc", true},
@@ -247,6 +247,30 @@ func ConsumersOf(users []Principal) []ModuleConsumer {
 	return out
 }

+// AccountConsumers are the durable consumers an account needs (novox/hq ADR 0561 §6): of ConsumersOf, each module's on
+// EVENTS and each process's on its own work queue, never one on a module stream it hears (those the controller makes with
+// the stream's grant). The grants part creates them from the lease write, with these configurations.
+func AccountConsumers(users []Principal) []ModuleConsumer {
+	queues := map[string]bool{}
+	for _, p := range users {
+		for _, q := range p.Queues {
+			queues[q.Stream] = true
+		}
+		for _, d := range p.Carries {
+			for _, q := range d.Queues {
+				queues[q.Stream] = true
+			}
+		}
+	}
+	var out []ModuleConsumer
+	for _, mc := range ConsumersOf(users) {
+		if mc.Consumer.Stream == consumerStream(Principal{Kind: KindModule}) || queues[mc.Consumer.Stream] {
+			out = append(out, mc)
+		}
+	}
+	return out
+}
+
 // HolderConsumerFor is the worker a seat's holders share on that seat's work queue.
 //
 // **One worker for every holder, and each holder pulls one ask when it is idle** (novox/hq ADR
@@ -0,0 +1,45 @@
+package buscompose
+
+import (
+	"git.novox.be/novox/mesh-sdk/go/asks"
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+)
+
+// The node seat node-engine (novox/hq ADR 0563 §1): every node's engine holds it on its own bus account, and no module
+// claims it. Its verbs and events are the catalogue's (catalogue.EngineVerbs), read here rather than copied.
+
+// EngineSeat is the seat.
+const EngineSeat = catalogue.EngineSeat
+
+// EngineModule is the node-engine's manifest's module name, and EngineActsState its state the acts asked through the
+// node seat and its own asks are kept in (ADR 0563 §2, §3: "the engine's own state"): the bucket mesh-host_acts, keys
+// `<node>.act.<id>`, `<node>.open.<act>.<digest>` and `<node>.ask.<id>`, each written by that node's engine alone.
+const (
+	EngineModule    = "mesh-host"
+	EngineActsState = "acts"
+)
+
+// EngineActsBucket is that state's bucket.
+var EngineActsBucket = BucketName(EngineModule, EngineActsState)
+
+// engineGrants is what a node's engine is granted to hold its node seat and to ask the operator (ADR 0563 §1, §3): it
+// answers its own node's verbs (the caller-named subjects are added beside them with every principal's), says the
+// seat's events about its node, answers discovery for the seat, asks who answers what (the login shell's execute, ADR
+// 0563 §6), and asks the operator under asks.EngineAsker(node) on the router's seat as its holder declares it, as any
+// user of that seat is granted.
+func engineGrants(p Principal) (pub, sub []string) {
+	for _, v := range catalogue.EngineVerbs() {
+		sub = append(sub, "mesh.seat."+EngineSeat+".tool."+v.Name+"."+p.Node)
+	}
+	for _, e := range catalogue.EngineEvents {
+		pub = append(pub, "mesh.seat."+EngineSeat+".event."+e+"."+p.Node)
+	}
+	sub = append(sub, announcing(EngineSeat)...)
+	pub = append(pub, discovering()...)
+	tp, ts := seatTrafficGrants(SeatTrafficOf(asks.EngineAsker(p.Node), nil, p.Uses, nil))
+	// And its acts and asks, under its own node's keys alone; never the bucket's creation, which is the grants part's.
+	if own, err := NodeKeysGrants(EngineActsBucket, p.Node); err == nil {
+		pub = append(pub, own...)
+	}
+	return append(pub, tp...), append(sub, ts...)
+}
@@ -217,6 +217,11 @@ type Principal struct {
 	// ADR 0547 §2, ADR 0550 §5, issue 1126): its modules' own secrets sealed to its key, for the compositions it makes
 	// itself. Set while the vault's holder serves it.
 	AsksItsOwnSecrets bool
+	// AsksTheVaultToSign is a machine principal whose node-engine may ask the vault's `sign` in its own name, read the
+	// vault's public signing halves (`signers`) and the controller's lease key (novox/hq ADR 0550 §2): its own node's
+	// certificate, the keys it trusts, and the lease write that drops the controller's key. Set while the vault's holder
+	// serves `sign`.
+	AsksTheVaultToSign bool
 	// ServedReads are, for a machine principal, the keys of mesh-config's resolved values that other nodes' modules serve
 	// from (`<node>.<module>.<key>`, catalogue.ServedSettings): what every consumer is told, and so what a node composing
 	// its own modules reads of a provider elsewhere (issue 1126), each key alone. Sorted, none twice.
@@ -232,6 +237,10 @@ type Principal struct {
 	// by name. Created only, never updated or deleted: a new module state is on the bus when the grants part hears its
 	// manifest, not at the controller's next start (issue 1790).
 	CreatesStreams []string
+	// CreatesConsumers are the durable consumers the grants part's principal alone may create beside the controller
+	// (novox/hq ADR 0561 §6): each placed module's on EVENTS and each process's on its work queue (AccountConsumers), by
+	// stream and name. Created only, never updated or deleted.
+	CreatesConsumers []ModuleConsumer

 	// 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
@@ -356,6 +365,10 @@ var VaultNodeKey = SeatVerb{Seat: "mesh-vault", Verb: "node-key"}
 // key (issue 1126, ADR 0550 §5); granted as Principal.AsksItsOwnSecrets says.
 var VaultOwn = SeatVerb{Seat: "mesh-vault", Verb: "own"}

+// VaultSign is the vault's verb a machine's node-engine asks in its own name for its own node's certificate (novox/hq
+// ADR 0550 §2); granted as Principal.AsksTheVaultToSign says.
+var VaultSign = SeatVerb{Seat: "mesh-vault", Verb: delivery.SignVerb}
+
 // 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
@@ -952,6 +965,18 @@ func PermissionsFor(p Principal) (Permissions, error) {
 			// on it rather than at the next unrelated change (ADR 0547 §2).
 			sub = append(sub, VaultSecretChanged)
 		}
+		// And, while the vault serves `sign`, its own node's certificate in its own name, the vault's public signing
+		// halves, read and watched, and the controller's lease key, read and watched, which says when the controller's key
+		// is no longer trusted (ADR 0550 §2). Read only.
+		if p.AsksTheVaultToSign {
+			pub = append(pub, VaultSignCall(p))
+			pub = append(pub, readGrants(delivery.SignersBucket, "")...)
+			pub = append(pub, readGrants(LeaseBucket, leaseKey)...)
+		}
+		// 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...)
+		sub = append(sub, es...)
 		// And, on the node holding mesh-broker, the grants part's sealed user list it follows from take-over (novox/hq ADR
 		// 0547 clause 7): one key, and an object by its name.
 		if p.FollowsGrantsUserList {
@@ -972,6 +997,8 @@ func PermissionsFor(p Principal) (Permissions, error) {
 			// And creating each stream a manifest declares, by its own name (the operator, 2026-10-26 08:54; issue
 			// 1790): the create and the read of that one stream, never an update, a delete or a stream not declared.
 			pub = append(pub, CreateStreamGrants(p.CreatesStreams)...)
+			// And creating each durable consumer an account needs, by its stream and name (ADR 0561 §6).
+			pub = append(pub, CreateConsumerGrants(p.CreatesConsumers)...)
 			// And its own object bucket, where it writes the user list sealed to the bus node (ADR 0547 clause 7).
 			pub = append(pub, GrantsUserListWrites()...)
 		}
@@ -1659,6 +1686,21 @@ func CreateStreamGrants(streams []string) []string {
 	return out
 }

+// CreateConsumerGrants are the subjects that create each consumer by its stream and name, and read its info back: the
+// create of the client library's CreateConsumer for a consumer with no filter or several, never one filter's form (a
+// wildcard in a filter would widen the grant), an update or a delete.
+func CreateConsumerGrants(consumers []ModuleConsumer) []string {
+	var out []string
+	for _, mc := range consumers {
+		c := mc.Consumer
+		if !safeSubject.MatchString(c.Stream) || !safeSubject.MatchString(c.Name) || len(c.Filters) == 1 {
+			continue
+		}
+		out = append(out, "$JS.API.CONSUMER.CREATE."+c.Stream+"."+c.Name, "$JS.API.CONSUMER.INFO."+c.Stream+"."+c.Name)
+	}
+	return out
+}
+
 // GrantsModule is the one module whose principal publishes the modules' memberships (novox/hq ADR 0547 §5): the grants
 // part, which composes them from the manifests and placement. It defines no stream and is granted no other subject here.
 const GrantsModule = "mesh-grants"
@@ -1827,6 +1869,11 @@ func VaultOwnCall(p Principal) string {
 	return "mesh.seat." + VaultOwn.Seat + "." + CallKind + "." + VaultOwn.Verb + "." + CallerToken(p.Username())
 }

+// VaultSignCall is the subject a machine principal's node-engine asks the vault's `sign` on, in its own name.
+func VaultSignCall(p Principal) string {
+	return "mesh.seat." + VaultSign.Seat + "." + CallKind + "." + VaultSign.Verb + "." + CallerToken(p.Username())
+}
+
 // VaultSecretChanged is the vault's event that a secret changed (a name and its generation, never a value), which a
 // node composing its own hears to compose again (issue 1126, ADR 0547 §2).
 var VaultSecretChanged = "mesh.mod." + VaultOwn.Seat + ".event.secret-changed"
@@ -0,0 +1,21 @@
+{
+ "how": "Written by mesh-controller 0fbb5ef's own issueWith, sealProvisionerClient and heldProcessAccount (cmd/mesh-controller), run unchanged in a scratch integration test against a local store with the default seats seeded, on 2026-10-27 (issue 774): each row is the exact value the controller handed the vault. Never edit a row by hand: capture it again.",
+ "rows": [
+  {
+   "name": "module",
+   "held": "{\"url\":\"nats://10.0.0.1:4222\",\"fingerprint\":\"ab:cd\",\"node\":\"laptop\",\"module\":\"cap-bot\",\"user\":\"laptop.cap-bot\",\"password\":\"pw-module\",\"claims\":[{\"seat\":\"mesh-vault\",\"scope\":\"mesh\",\"serves\":[\"get\",\"accept\",\"secret-ask\",\"issued\",\"rotate\",\"move-in\",\"node-key\",\"own\",\"move-asks\"]},{\"seat\":\"node-service-manager\",\"scope\":\"node\",\"serves\":[\"status\"]},{\"seat\":\"mesh-controller\",\"scope\":\"mesh\",\"serves\":[\"tools\",\"calls\",\"status\",\"nodes\",\"node\",\"placement-export\",\"modules\",\"seats\",\"builds\",\"plans\",\"delivery-plan\",\"delivery-order\",\"delivery-check\",\"deliver\",\"delivery-stop\",\"delivery-backups-again\",\"delivery-walks\",\"plan\",\"assign\",\"unassign\",\"pin\",\"unpin\",\"push\",\"rotate\",\"give\",\"issued\",\"secret-move\",\"secret-ask\",\"issue\",\"token\",\"settings\",\"command\",\"queue\",\"cancel\",\"clear\",\"replay\",\"try\",\"kill\",\"pause\",\"resume\",\"hand-act\",\"drill\",\"warranted\",\"hand-acts\",\"durations\",\"conditions\",\"healers\",\"doctor\",\"upgrade\",\"bus\",\"retire\",\"cleanup\",\"judge-directories\",\"root-free\",\"dead-letters\",\"data\",\"build\",\"artifacts\",\"held\",\"collect\",\"move-placement\",\"move-config\",\"mirrors\",\"images\"]},{\"seat\":\"no-such-seat\",\"scope\":\"node\"}]}"
+  },
+  {
+   "name": "module-no-claims-no-fingerprint",
+   "held": "{\"url\":\"nats://10.0.0.1:4222\",\"node\":\"laptop\",\"module\":\"cap-plain\",\"user\":\"laptop.cap-plain\",\"password\":\"pw-plain\"}"
+  },
+  {
+   "name": "provisioner",
+   "held": "{\"url\":\"nats://10.0.0.1:4222\",\"fingerprint\":\"ab:cd\",\"node\":\"laptop\",\"user\":\"provisioner.laptop\",\"password\":\"pw-prov\"}"
+  },
+  {
+   "name": "process",
+   "held": "{\"url\":\"nats://10.0.0.1:4222\",\"fingerprint\":\"ab:cd\",\"node\":\"laptop\",\"module\":\"mesh-mail\",\"user\":\"laptop.mesh-mail.send\",\"password\":\"pw-proc\"}"
+  }
+ ]
+}
@@ -77,8 +77,12 @@ func grantsOwnObjects(p Principal, pattern string) bool {
 // readers too (announce.State.Readers); both are honoured.
 const VaultBusAccounts = "mesh-vault.bus-accounts"

-// NamedReaders are the states only the modules named may read, by `<owner>.<name>`.
-var NamedReaders = map[string][]string{VaultBusAccounts: {GrantsModule}}
+// NamedReaders are the states only the modules named may read, by `<owner>.<name>`: the grants part's wanted accounts
+// are read by the vault alone (novox/hq ADR 0561 §2).
+// The controller's lease is read by the parts that turn on at its write (ADR 0561 §3, §6), and by the assigner, which
+// reads the catalogue's placement alone from then (ADR 0549 §5, issue 774).
+var NamedReaders = map[string][]string{VaultBusAccounts: {GrantsModule}, GrantsAccounts: {VaultSeat},
+	ControllerLease: {VaultSeat, GrantsModule, delivery.AssignerModule}}

 // ReaderMay says whether module may read the state read (`<owner>.<name>`) by the named readers: always, for a state
 // that names none.
@@ -134,6 +134,11 @@ type Records struct {
 	// account agents run as, judged unable to become root by its node-engine, and serves no login shell
 	// execute. A machine absent is not free: no record of a pass is no pass.
 	RootFree map[string]bool
+	// Engine is the node-engine's own declaration, from its manifest (EngineModule): placed on every node though no node is
+	// assigned it, since every node runs it (novox/hq ADR 0563 §2, §3). Its state, logs and streams are created by the
+	// 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
 	// 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
@@ -149,6 +154,7 @@ func Users(r Records) ([]Principal, error) {
 		AsksTheConfig: servedOf(r, VerbsTheControllerAsksTheConfig), FilesFor: sortedCopy(r.Nodes)}}

 	served := servedReadsOf(r)
+	grants := -1
 	for _, node := range sortedCopy(r.Nodes) {
 		witness := false
 		var checks []string
@@ -164,7 +170,7 @@ func Users(r Records) ([]Principal, error) {
 		}
 		out = append(out, Principal{Kind: KindNode, Node: node, WitnessesController: witness, Checks: checks,
 			MovesIntoTheVault: servesMoveIn(r), StatesItsKeyToTheVault: servesVerb(r, VaultNodeKey),
-			AsksItsOwnSecrets:     servesVerb(r, VaultOwn),
+			AsksItsOwnSecrets: servesVerb(r, VaultOwn), AsksTheVaultToSign: servesVerb(r, VaultSign), Uses: asksSeatOf(r),
 			FollowsGrantsUserList: bus, ServedReads: servedOn(served, node)})
 		// **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.
@@ -225,6 +231,7 @@ func Users(r Records) ([]Principal, error) {
 			// 08:54): every placed module's buckets, logs and streams, each by its stream's name.
 			if d.Module == GrantsModule {
 				out[len(out)-1].CreatesStreams = declaredStreamsOf(r)
+				grants = len(out) - 1
 			}
 			// **The vault's holder asks the desks and the issuing providers itself** (issue 723), under the
 			// account its own runtime runs on (ADR 0259 §8's runs-as): the one module granted it.
@@ -258,6 +265,11 @@ func Users(r Records) ([]Principal, error) {
 		out = append(out, p)
 	}

+	// The grants part creates the durable consumers the accounts need (novox/hq ADR 0561 §6), by stream and name.
+	if grants >= 0 {
+		out[grants].CreatesConsumers = AccountConsumers(out)
+	}
+
 	// Refused here rather than discovered by the server. Two users with one name is a file the
 	// server reads as one of them, and which one depends on the order — so a module assigned to a
 	// node twice, or a person named after nothing, is a composition that must not be written.
@@ -444,7 +456,15 @@ func runnerServes(d Declared) bool {
 // name. What the grants part may create, and nothing beside.
 func declaredStreamsOf(r Records) []string {
 	seen := map[string]bool{}
+	placed := [][]Declared{}
 	for _, mods := range r.Assigned {
+		placed = append(placed, mods)
+	}
+	// The node-engine's manifest is placed on every node (ADR 0563): its declared state is created as a placed module's.
+	if r.Engine != nil {
+		placed = append(placed, []Declared{*r.Engine})
+	}
+	for _, mods := range placed {
 		for _, d := range mods {
 			for _, b := range d.State {
 				seen["KV_"+b.Bucket()] = true
@@ -245,6 +245,11 @@ var WritersTable = []WriterRow{
 	{State: "a machine's have", Writer: "the node-engine of the machine, under its own keys `<node>.>`",
 		KeptIn: "key-value " + delivery.HaveBucket + ", twenty revisions of each key",
 		Others: "read through `reads` as node-engine.have", Subjects: kvOf(delivery.HaveBucket), Writes: ownNodeKeys},
+	// The acts a node's engine was asked through its node seat, and its own asks (novox/hq ADR 0563 §2, §3): the
+	// node-engine's declared state, created by the grants part, written by each node's engine under its own keys.
+	{State: "a machine's hand acts", Writer: "the node-engine of the machine, under its own keys `<node>.>`, compare-and-set",
+		KeptIn: "key-value " + EngineActsBucket + ", the node-engine's declared state acts",
+		Others: "read through the node seat's verb acts", Subjects: kvOf(EngineActsBucket), Writes: ownNodeKeys},
 	// The contents of a declaration's files over 64 KiB (novox/hq ADR 0486 §2): the controller alone writes the bucket, each
 	// object under the digest of its content; a node-engine reads one by its name, with no list and no write.
 	{State: "a declaration's large files", Writer: "controller, each object under the sha256 digest of its content; the " +
@@ -75,6 +75,21 @@ func TestACallerInTheArgumentsIsNeverTheCaller(t *testing.T) {
 	if got != "shanks.node-tools" {
 		t.Fatalf("with a caller in the arguments the tool read %q, want the runtime's", got)
 	}
+	// A module's trusted list of callers (issue 774, ADR 0563 §8) grants the callers it names as the runtime proved them:
+	// a module on any machine, <machine>.<module> exactly, person.<name> exactly; no wildcard, never one unproven.
+	callers, err := ParseCallers([]byte(`{"callers":["node-tools","ace.claude-code","person.jo","*"]}`))
+	if err != nil {
+		t.Fatal(err)
+	}
+	for caller, want := range map[string]bool{"shanks.node-tools": true, "ace.claude-code": true, "g14.claude-code": false,
+		"person.jo": true, "person.node-tools": false, Unproven: false, "": false, "novox.mesh-vault": false} {
+		if callers.Allows(caller) != want {
+			t.Errorf("%q allowed: %v, want %v", caller, !want, want)
+		}
+	}
+	if _, err := ParseCallers([]byte(`{"callers":["x"],"more":1}`)); err == nil {
+		t.Error("a list with a field it does not know was read")
+	}
 }

 // A runtime that names no caller — one from before issue 365, or a call on the subject that names none — is
@@ -0,0 +1,48 @@
+package stdio
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"strings"
+)
+
+// Callers is a module's trusted list of who may call a verb of its (novox/hq ADR 0459 §2, ADR 0563 §8), as the mesh
+// writes a list setting into a file the module reads: `{"callers": [...]}`. An entry is a module's name (that module on
+// any machine), exactly <machine>.<module>, or exactly person.<name>. Each caller is the runtime's proof (CallerOf), never
+// an argument; nobody beyond the list is granted, a wildcard is no entry, and an unproven caller never matches.
+type Callers []string
+
+// ParseCallers reads a callers file: the list under `callers`, and nothing else.
+func ParseCallers(raw []byte) (Callers, error) {
+	var f struct {
+		Callers Callers `json:"callers"`
+	}
+	dec := json.NewDecoder(bytes.NewReader(raw))
+	dec.DisallowUnknownFields()
+	if err := dec.Decode(&f); err != nil {
+		return nil, fmt.Errorf("the callers setting is not a list of callers: %v", err)
+	}
+	return f.Callers, nil
+}
+
+// Allows says whether caller, as the runtime proved it, is one the list names.
+func (c Callers) Allows(caller string) bool {
+	if caller == "" || caller == Unproven {
+		return false
+	}
+	for _, entry := range c {
+		if entry == "" || strings.ContainsAny(entry, "*> ") {
+			continue
+		}
+		if entry == caller {
+			return true
+		}
+		if !strings.Contains(entry, ".") {
+			if _, module, ok := strings.Cut(caller, "."); ok && module == entry && !strings.HasPrefix(caller, "person.") {
+				return true
+			}
+		}
+	}
+	return false
+}
@@ -0,0 +1,37 @@
+package catalogue
+
+// The delivery's checker (novox/hq ADR 0547 §10, issue 774): one holder for the mesh, the module
+// mesh-delivery-checker, which judges a pull request's head and a pushed head the same way. The try the
+// controller forwarded to it is a verb of this seat, answered by the checker with the verdict it gives a pull
+// request, so the try outlives the controller.
+
+// CheckerSeat is the seat mesh-delivery-checker holds.
+const CheckerSeat = "mesh-delivery-checker"
+
+// checkerVerbs are the checker seat's verbs: ask a try, read one, end one by hand. Optional until the checker serves them
+// everywhere.
+func checkerVerbs() []Verb {
+	return []Verb{
+		{Name: "try", Optional: true, Description: "Try a pushed head before its pull request is opened: the checker " +
+			"judges it as it judges a pull request's head, merged onto its trunk's head, its unit and integration " +
+			"levels through the build modules, and owes the forge nothing. Answers the try's id at once; try-read " +
+			"reads where it stands. A try of the same head that waits or runs is the answer to a second ask; at most " +
+			"4 wait or run at once, mesh-wide.",
+			Input: schema(map[string]string{"repository": "<owner>/<name>",
+				"head":  "the full commit to try, 40 or 64 hex digits",
+				"trunk": "the trunk commit to merge it onto, or the trunk's branch for its head now; the trunk's head when absent",
+				"tests": "a go test -run pattern: only those tests run, and nothing is kept",
+				"level": "unit or integration: only this level; both when absent"},
+				[]string{"repository", "head"}),
+			Replaces: []string{"sh merge-check.sh", "docker run postgres"}},
+		{Name: "try-read", Optional: true, Description: "Where a try stands, as stored: queued, running, or its end " +
+			"(pass, fail, or error when it could not run), with what was said of it, the head and the trunk commit " +
+			"it was merged onto, the time it took and what failed first. Read-only.",
+			Input: schema(map[string]string{"id": "the try's id, try-<digits>"}, []string{"id"})},
+		{Name: "try-end", Optional: true, Description: "End a try that waits or runs, as error, by hand: say why (kept in " +
+			"what it says). Its place among the tries is free at once and the next try of its head asks anew with a new " +
+			"id. A try that ended already is refused.",
+			Input: schema(map[string]string{"id": "the try's id, try-<digits>", "why": "why it is ended, in words"},
+				[]string{"id", "why"})},
+	}
+}
@@ -0,0 +1,57 @@
+package catalogue
+
+// The node seat node-engine (novox/hq ADR 0563 §1): held on every node by that node's engine (mesh-host), which serves
+// its verbs on its own bus account. No module claims it and no assignment holds it: what the mesh knows of its holder
+// is the node's record and the engine's haves (ADR 0563 §1 changes ADR 0110 §6 and §7 for this one seat).
+//
+// Its verbs carry no signature (§7): the runtime proves the caller, which matters only for the record. The read-only
+// ones change nothing or are bounded in the engine's own state (§2); hand-over and access-act perform nothing on the
+// call, and act only on the operator's warrant to the engine's own ask (§3).
+
+// EngineSeat is the node seat every node's engine holds.
+const EngineSeat = "node-engine"
+
+// EngineVerbs are the node-engine seat's verbs, in the order ADR 0563 §1 names them.
+func EngineVerbs() []Verb {
+	return []Verb{
+		{Name: "hand-over", Description: "Hand a directory this machine uses as found to the mesh (novox/hq ADR 0563 §3, " +
+			"§5): the engine judges the path as it does every hand-over (absolute, as it states it, used as found, " +
+			"reached through no link) and refuses in words, or asks the operator on their channel at the level approve, " +
+			"binding the owner, group and mode it will set. Nothing changes on the call: only the operator's yes hands " +
+			"it over. One ask is open per path; acts shows where it stands.",
+			Input: schema(map[string]string{"path": "the directory's absolute path, as the engine states it",
+				"why": "why it is asked, in words the operator reads"}, []string{"path"})},
+		{Name: "access-act", Description: "Ask the operator for the take act on a library whose root holds data outside its " +
+			"group (novox/hq ADR 0328 §7, ADR 0563 §3, §4), on the library's home engine: the access as declared and its " +
+			"root as last declared, judged and refused in words or asked at the level approve. Only the operator's yes " +
+			"sets the library's group, group write and setgid under its root. One ask is open per access.",
+			Input: schema(map[string]string{"act": "the act: take", "access": "the access, library:<name>",
+				"why": "why it is asked, in words the operator reads"}, []string{"act", "access"})},
+		{Name: "judge-directories", Description: "Which of this machine's declared directories the engine would refuse to " +
+			"make or keep, one line each (novox/hq ADR 0563 §2). Read-only: changes no owner or mode.",
+			Input: schema(map[string]string{}, nil)},
+		{Name: "setuid-search", Description: "Throw away the engine's last search for setuid programs and start a full one " +
+			"(novox/hq ADR 0563 §2); until it completes root-free answers that the machine is not judged yet. Refused while " +
+			"one runs, and when one was started within the hour, naming when the next may start.",
+			Input: schema(map[string]string{"why": "why it is asked, in words"}, nil)},
+		{Name: "root-free", Description: "Whether this machine is root-free (novox/hq ADR 0259 §8, ADR 0563 §6): free only " +
+			"on the engine's own verdict, at most fifteen minutes old, that the account agents run as cannot become root " +
+			"without a person, and the login shell's execute not served here. Anything else is no pass, and says why. " +
+			"Answered by this machine's engine alone.",
+			Input: schema(map[string]string{}, nil)},
+		{Name: "acts", Description: "Every act this machine's engine was asked through this seat (novox/hq ADR 0563 §9): " +
+			"each hand-over, access act and setuid search, open, done or refused, with who asked, the ask and the " +
+			"operator's warrant. Read-only.",
+			Input: schema(map[string]string{"limit": "at most this many, newest", "id": "one act, by its id"}, nil)},
+	}
+}
+
+// EngineEvents are what the seat says of an act, each naming the act, the path or access, the caller as the runtime
+// proved it and the ask (ADR 0563 §1).
+var EngineEvents = []string{"asked", "done", "refused"}
+
+// engineSeat is the seat's row in the closed set.
+func engineSeat() Seat {
+	return Seat{Name: EngineSeat, Scope: ScopeNode, Serves: EngineVerbs(), Emits: append([]string(nil), EngineEvents...),
+		HeldByTheEngine: true, Decision: "novox/hq ADR 0563"}
+}
@@ -67,6 +67,10 @@ type Seat struct {
 	// names paths. Compiled, never stored, like Receives: adding or taking away a path is a decision,
 	// recorded, and the store's rows carry no column for it.
 	Paths []SeatPath
+	// HeldByTheEngine says the seat is held on every node by that node's engine, which serves its verbs on its own bus
+	// account (novox/hq ADR 0563 §1): no module claims it and no assignment holds it. Compiled, never stored, like
+	// Receives.
+	HeldByTheEngine bool
 	// Decision is the record that made it a seat.
 	Decision string
 }
@@ -171,7 +175,8 @@ var defaultSeats = append([]Seat{
 					"origin": "issued for a bus account the controller minted for a core or moved module and hands " +
 						"at once (ADR 0374, issue 787); left out for a value given at the terminal"}), nil)},
 			{Name: "secret-ask", Optional: true, Description: "Ask the operator for a module's own secret at a desk, " +
-				"from the controller alone: the ask is recorded in the vault's store and bounded before the prompt " +
+				"from the controller or a caller the vault's manifest names, named as the bus proved it (novox/hq ADR " +
+				"0563 §8): the ask is recorded in the vault's store and bounded before the prompt " +
 				"opens, and what is typed is sealed to a key the vault made for the call and opens there alone.",
 				Input: schema(vaultIntake(map[string]string{"node": "the machine the secret is for",
 					"module": "the module", "name": "the secret's name in the module",
@@ -224,6 +229,18 @@ var defaultSeats = append([]Seat{
 				Input: map[string]any{"type": "object", "properties": map[string]any{"asks": map[string]any{
 					"type": "array", "items": map[string]any{"type": "object"},
 					"description": "the controller's rows: id, node, module, name, desk, asked_by, opened_at, ended_at, outcome"}}}},
+			{Name: "issue-account", Optional: true, Description: "Mint one bus account the grants part wants, now (novox/hq " +
+				"ADR 0561 §9): only while the controller's lease is handed away, never a node's account or the " +
+				"controller's, never anew for one the vault holds a value or an adopted hash for. Never the value.",
+				Input: schema(map[string]string{"user": "the bus user, e.g. ace.mesh-build-go"}, []string{"user"})},
+			{Name: "sign", Optional: true, Description: "Sign with the vault's key or authority (novox/hq ADR 0550 §2): " +
+				"kind node-certificate signs the certificate of the calling machine's internal name for the serving key " +
+				"its record states, built from bus state alone and asked by that machine's node-engine only; kind " +
+				"enrolment signs an enrolment reply under its own context, for a caller the adoption record names. " +
+				"Answers the certificate or the signature and the signer's fingerprint, and says signed; never a key.",
+				Input: schema(map[string]string{"kind": "node-certificate or enrolment",
+					"node":  "the machine, for a node certificate: the caller's own",
+					"reply": "the enrolment reply's bytes in base64, for an enrolment"}, []string{"kind"})},
 		}},
 	// The owner of every config value (novox/hq ADR 0348 §9, design 57 K3): its holder alone writes the buckets
 	// mesh-config_values, _resolved, _predefined and _proposals, and serves the one verb `config` (§1, §10).
@@ -261,6 +278,8 @@ var defaultSeats = append([]Seat{
 	// Placement (novox/hq ADR 0567): which module runs on which node, state on the bus held by the assigner, changed only by
 	// a proposal the nodes answer and the operator approves. Its states and events are the holder module's.
 	{Name: PlacementSeat, Scope: ScopeMesh, Serves: placementVerbs(), Decision: "novox/hq ADR 0567"},
+	// The delivery's checker (novox/hq ADR 0547 §10, issue 774): the try is its verb, not the controller's.
+	{Name: CheckerSeat, Scope: ScopeMesh, Serves: checkerVerbs(), Decision: "novox/hq ADR 0547"},
 	// Deferred renames (novox/hq ADR 0121): these deliver a provision, so renaming them is a
 	// delivering-seat migration with a mesh-wide cascade if a holder stops resolving mid-flight.
 	// They keep their names until that migration is done deliberately, apart from the node-* pass.
@@ -442,6 +461,8 @@ var defaultSeats = append([]Seat{
 	// A node's files, read and managed (novox/hq ADR 0394, files.go): beside node-reads until mesh-files is assigned
 	// on every node, then node-reads goes (ADR 0394 §9).
 	{Name: FilesSeat, Scope: ScopeNode, Decision: "novox/hq ADR 0394", Serves: filesVerbs()},
+	// The node's engine's own verbs and asks (novox/hq ADR 0563 §1): held by the engine on every node, by no module.
+	engineSeat(),
 },
 	// The graphical session's roles (novox/hq ADR 0208), last because they are a workstation's.
 	graphicalSessionSeats()...)
@@ -515,7 +536,8 @@ func UseSeats(s []Seat) {
 			row.Paths = d.Paths
 			row.Replicated = d.Replicated
 			row.PulledByKind = d.PulledByKind
-			row.Yields = d.Yields // never stored (ADR 0553)
+			row.Yields = d.Yields                   // never stored (ADR 0553)
+			row.HeldByTheEngine = d.HeldByTheEngine // never stored (ADR 0563)
 			row.Serves = optionalAsCompiled(row.Serves, d.Serves)
 		}
 		merged = append(merged, row)
@@ -628,6 +650,13 @@ func claimProblems(m Manifest) []string {
 	}

 	for _, c := range m.Claims {
+		if s, known := SeatNamed(c.Name); known && s.HeldByTheEngine {
+			// The node's engine holds it on every node, and no module may (novox/hq ADR 0563 §1): a module answering
+			// root-free or a hand-over would be an agent answering it.
+			problems = append(problems, fmt.Sprintf("%s claims %s, which every node's engine holds itself and no "+
+				"module may (novox/hq ADR 0563 §1)", m.Module, c.Name))
+			continue
+		}
 		if _, known := SeatNamed(c.Name); known {
 			// **A seat's scope and what it delivers are not judged here** (novox/hq ADR 0122).
 			// This function runs wherever a manifest is parsed, and one of those places is the
@@ -49,6 +49,43 @@ func TestTheSeatsAreAClosedSetAndEachNamesItsDecision(t *testing.T) {
 		[]string{"placement", "proposals", "propose", "withdraw", "again", "adopt", "hand-back"}) {
 		t.Errorf("the placement seat is %v, %v", ok, s)
 	}
+	// The checker's seat serves the try, which replaces the shell's merge check (ADR 0547 §10, ADR 0245).
+	var checkerVerbs []string
+	for _, s := range Seats() {
+		if s.Name == CheckerSeat {
+			for _, v := range s.Serves {
+				checkerVerbs = append(checkerVerbs, v.Name)
+				if v.Name == "try" && strings.Join(v.Replaces, "|") != "sh merge-check.sh|docker run postgres" {
+					t.Errorf("try replaces %v", v.Replaces)
+				}
+			}
+		}
+	}
+	if strings.Join(checkerVerbs, ",") != "try,try-read,try-end" {
+		t.Errorf("the checker seat serves %v", checkerVerbs)
+	}
+	// The node seat node-engine is the node's engine's (novox/hq ADR 0563 §1): at node scope, delivering nothing, its six
+	// verbs and three events, held by no assignment, and a module's claim of it refused.
+	if engine, ok := SeatNamed(EngineSeat); !ok || engine.Scope != ScopeNode || engine.Delivers != "" || !engine.HeldByTheEngine {
+		t.Errorf("node-engine is %+v, not a node seat delivering nothing that the engine holds", engine)
+	} else {
+		var verbs []string
+		for _, v := range engine.Serves {
+			verbs = append(verbs, v.Name)
+		}
+		// acts reads one act by its id too (ADR 0563 §9: the seat's tools are its command line).
+		if props, _ := engine.Serves[len(engine.Serves)-1].Input["properties"].(map[string]any); props["id"] == nil {
+			t.Errorf("acts takes no id: %v", engine.Serves[len(engine.Serves)-1].Input)
+		}
+		if strings.Join(verbs, ",") != "hand-over,access-act,judge-directories,setuid-search,root-free,acts" ||
+			strings.Join(engine.Emits, ",") != "asked,done,refused" {
+			t.Errorf("node-engine serves %v and emits %v", verbs, engine.Emits)
+		}
+	}
+	if _, err := ParseManifest([]byte(`{"module":"thing","version":"1","claims":[{"name":"node-engine","scope":"node"}]}`)); err == nil ||
+		!strings.Contains(err.Error(), "node-engine") {
+		t.Errorf("a module's claim of node-engine was not refused: %v", err)
+	}
 	// Forty-six with the three build seats replacing node-build-agent and the retired mesh-build-machine (novox/hq
 	// ADR 0525 §2, §10); forty-five with node-files (novox/hq ADR 0394); forty-four again once node-reads goes.
 	// Forty-four with node-provisioner (novox/hq ADR 0349 clause 3); forty-three with mesh-provisioner (novox/hq ADR 0349 clause 3); forty-two with mesh-config (novox/hq ADR 0348 §9); forty-one with node-reads (novox/hq ADR 0310); forty with node-nfs-server and node-mounts (novox/hq ADR 0263); thirty-eight with node-resolver (novox/hq ADR 0247); thirty-seven with mesh-delivery (novox/hq ADR 0239); thirty-six since node-resolver-config retired
@@ -62,8 +99,9 @@ func TestTheSeatsAreAClosedSetAndEachNamesItsDecision(t *testing.T) {
 	// node-container-runtime (ADR 0207); nineteen with node-environment and node-login-shell (ADR 0203,
 	// ADR 0204); seventeen with node-build-agent (ADR 0190). One fewer once the retired
 	// mesh-build-machine row goes, when no registered manifest claims it.
-	if len(Seats()) != 47 {
-		t.Errorf("the mesh defines %d seats rather than 47; the set is closed, so a change here is "+
+	// Forty-eight with mesh-delivery-checker (novox/hq ADR 0547 §10, issue 774); forty-nine with node-engine (novox/hq ADR 0563 §1).
+	if len(Seats()) != 49 {
+		t.Errorf("the mesh defines %d seats rather than 49; the set is closed, so a change here is "+
 			"a decision (novox/hq ADR 0110): %s", len(Seats()), seatNames())
 	}
 }
@@ -83,6 +83,16 @@ type Reader interface {
 	Served(ctx context.Context, node, module string, keys []string) (map[string]any, error)
 }

+// SignersReader is a Reader that also reads the vault's public authority from its state `signers` (delivery.SignersBucket,
+// key delivery.SignersAuthorityKey; ADR 0550 §2). A Reader that has it composes the mesh's authority as a bundle, the
+// controller's and the vault's; one that has not, or that answers none, composes the controller's alone, as before.
+type SignersReader interface {
+	// VaultAuthority is the vault's authority certificate as PEM, checked (delivery.DecodeSignerAuthority); empty when the
+	// vault has published none. A read that fails is said by the reader and answered empty: a node that may not read the
+	// state yet composes as before rather than not at all.
+	VaultAuthority(ctx context.Context) string
+}
+
 // Mesh is what is true of the whole mesh and is no part's state on the bus yet: the private network's range and the
 // internal names' suffix as genesis was told them, and the mesh's authority certificate (public). Empty fields take
 // compose's defaults.
@@ -223,6 +233,13 @@ func input(ctx context.Context, r Reader, mesh Mesh, s Scope, refuse func(module
 			}
 		}
 	}
+	// And the vault's authority beside it, once the vault publishes one (ADR 0550 §2): a certificate either signed checks
+	// against the bundle. The controller's stays while a certificate it issued is in a node's record.
+	if sr, ok := r.(SignersReader); ok {
+		if vault := sr.VaultAuthority(ctx); vault != "" {
+			in.Authority = delivery.AuthorityBundle(in.Authority, vault)
+		}
+	}
 	parse := func(raw []byte) (catalogue.Manifest, error) {
 		if mesh.Predefined != nil {
 			return catalogue.ParseManifestWith(raw, mesh.Predefined)
@@ -25,14 +25,15 @@ import (

 // bus is a Reader over values held in memory, counting whose config values were read.
 type bus struct {
-	placements map[string]delivery.Placement
-	records    map[string]delivery.NodeRecord
-	modules    map[string]delivery.Module
-	manifests  map[string][]byte
-	values     map[string]map[string]any // by node.module
-	valuesRead []string
-	own        []compose.OwnSecretRow
-	ownErr     error
+	vaultAuthority string
+	placements     map[string]delivery.Placement
+	records        map[string]delivery.NodeRecord
+	modules        map[string]delivery.Module
+	manifests      map[string][]byte
+	values         map[string]map[string]any // by node.module
+	valuesRead     []string
+	own            []compose.OwnSecretRow
+	ownErr         error
 	// asked is every consumer credential asked; the fake refuses the whole ask, as the vault's own does, for a consuming
 	// module its placement does not put on the node.
 	asked []compose.CredentialKey
@@ -74,6 +75,7 @@ func (b *bus) Served(_ context.Context, node, module string, keys []string) (map
 func (b *bus) Placements(context.Context) (map[string]delivery.Placement, error) {
 	return b.placements, nil
 }
+func (b *bus) VaultAuthority(context.Context) string                           { return b.vaultAuthority }
 func (b *bus) Records(context.Context) (map[string]delivery.NodeRecord, error) { return b.records, nil }
 func (b *bus) Modules(context.Context) (map[string]delivery.Module, error)     { return b.modules, nil }
 func (b *bus) Manifest(_ context.Context, digest string) ([]byte, error) {
@@ -216,6 +218,14 @@ func TestInput(t *testing.T) {
 		wj, _ := json.MarshalIndent(want, "", " ")
 		t.Fatalf("Input from the bus differs from the store's:\n got %s\nwant %s", gj, wj)
 	}
+	// L3 s8 (ADR 0550 §2): with the vault's authority published, the mesh's authority is the bundle of the controller's
+	// and the vault's; with none, the controller's alone, as above.
+	signing := mk()
+	signing.vaultAuthority = "the vault's certificate"
+	if bundled, err := Input(ctx, signing, Mesh{}, Scope{Node: "laptop"}); err != nil ||
+		bundled.Authority != "the mesh's certificate\nthe vault's certificate\n" {
+		t.Errorf("the authority with the vault's published: %q, %v", bundled.Authority, err)
+	}
 	if !reflect.DeepEqual(b.valuesRead, []string{"laptop." + overlay.Name, "laptop.xterm", "laptop.media"}) {
 		t.Errorf("laptop read config values %v; a node reads its own slice alone", b.valuesRead)
 	}
@@ -298,6 +298,25 @@ func TestControllerGrant(t *testing.T) {
 	if _, err := EncodeControllerGrant(ControllerGrant{Accounts: []string{""}}); err == nil {
 		t.Errorf("a grant naming an empty account was accepted")
 	}
+	// The grants part's keys are the controller's: the same key round-trips; the source is the part's bucket only for a
+	// handed-away lease (issue 774).
+	if pk, err := PartGrantKey("mesh-delivery-assigner", fp); err != nil || pk != key {
+		t.Errorf("PartGrantKey = %q, %v, want the controller's %q", pk, err, key)
+	}
+	if m, f, err := ParsePartGrantKey(key); err != nil || m != "mesh-delivery-assigner" || f != fp {
+		t.Errorf("ParsePartGrantKey = %q, %q, %v", m, f, err)
+	}
+	for _, c := range []struct {
+		away         bool
+		bucket, read string
+	}{
+		{false, "mesh-controller_grants", "mesh-controller.grants"},
+		{true, "mesh-grants_grants", "mesh-grants.grants"},
+	} {
+		if b, r := GrantSource(c.away); b != c.bucket || r != c.read {
+			t.Errorf("GrantSource(%v) = %q, %q, want %q, %q", c.away, b, r, c.bucket, c.read)
+		}
+	}
 	g := ControllerGrant{Accounts: []string{"ace.mesh-build-go", "shanks.mesh-mail.reader"}}
 	for _, c := range []struct {
 		g            ControllerGrant
@@ -0,0 +1,225 @@
+package buildrun
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"maps"
+	"slices"
+	"sync"
+	"time"
+
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/process"
+)
+
+// A build module writes <node>.<language> of its toolchains state on every node it runs on, and nothing deletes the key
+// when the module leaves a node: no part writes another module's state, and the module is gone. A report of a node the
+// build module no longer runs on is therefore no builder's (issue 1940: mesh-build-node taken off ace on 2026-10-23 left
+// ace.typescript at v26.12.0, and every Node fingerprint said "builders disagree").
+//
+// ToolchainGate stands between the toolchains buckets and what takes their entries in (the indexer's PutToolchain, a
+// ToolchainSet): an entry is passed on only while the placement (the seat mesh-placement's state `placement`, held by
+// the assigner, delivery.PlacementBucket, read by delivery.Placed; ADR 0567, ADR 0549 §3) places its build module on
+// its node, and only once it was written since that placement; it is passed on as deleted otherwise, said once, and
+// passed on when its node writes it again. A report written before the placement is one an earlier run of the module
+// left (issue 1940, 2026-10-25 20:56: mesh-build-node put on ace again brought ace.typescript v26.12.0 of 2026-10-23
+// back into the agreement before the module ran there). Until the placement is settled, and while no node's placement
+// is held (before the assigner's adopt writes the first one, or where the state cannot be read), every entry is passed
+// on. Builders that run and report different versions still disagree: that refusal is the guard of novox/hq ADR 0465,
+// and it stays.
+//
+// This replaces the copies of the gate the indexer, the builder and the checker each kept over the controller's
+// assignments (issue 1940's subtask, issue 774: those go with the controller's lease, ADR 0549 §6).
+type ToolchainGate struct {
+	mu      sync.Mutex
+	modules map[string]bool                                           // the build modules whose toolchains pass the gate
+	forward func(module, key string, value []byte, deleted bool) bool // answers whether it changed what it holds
+	logf    func(format string, a ...any)
+	placed  *delivery.Placed
+	known   bool                         // the placement is settled
+	raw     map[string]map[string][]byte // module -> toolchains key -> value, as the bucket holds it
+	left    map[string]string            // <module>/<key> -> why it was said left out, so each reason is said once
+}
+
+// NewToolchainGate is a gate over the toolchains of modules, passing what stands on to forward and saying with logf what
+// it leaves out.
+func NewToolchainGate(modules []string, forward func(module, key string, value []byte, deleted bool) bool, logf func(string, ...any)) *ToolchainGate {
+	g := &ToolchainGate{modules: map[string]bool{}, forward: forward, logf: logf, placed: delivery.NewPlaced(),
+		raw: map[string]map[string][]byte{}, left: map[string]string{}}
+	for _, m := range modules {
+		g.modules[m] = true
+	}
+	return g
+}
+
+// Toolchain takes one change of a build module's toolchains bucket in and answers whether what it passed on changed.
+func (g *ToolchainGate) Toolchain(module, key string, value []byte, deleted bool) bool {
+	g.mu.Lock()
+	defer g.mu.Unlock()
+	if g.raw[module] == nil {
+		g.raw[module] = map[string][]byte{}
+	}
+	if deleted {
+		delete(g.raw[module], key)
+	} else {
+		g.raw[module][key] = value
+	}
+	return g.pass(module, key)
+}
+
+// Placement takes one revision of the seat mesh-placement's placement in (at is when the bus wrote it) and answers whether what it
+// passed on changed. A value that does not read is said, and places nothing on its node.
+func (g *ToolchainGate) Placement(key string, value []byte, deleted bool, at time.Time) bool {
+	g.mu.Lock()
+	defer g.mu.Unlock()
+	was := g.placed.Seeded()
+	node, changed, err := g.placed.Put(key, value, deleted, at)
+	if err != nil {
+		g.logf("%s: %v (issue 1940)", delivery.PlacementBucket, err)
+	}
+	if !g.known {
+		return false
+	}
+	if was != g.placed.Seeded() {
+		// The first placement came, or the last went: every report's standing changed.
+		return g.all()
+	}
+	return g.again(node, changed)
+}
+
+// Settled says the placement's history is read: from now on only the reports of placed nodes pass, once a node's
+// placement is held. It answers whether what it passed on changed.
+func (g *ToolchainGate) Settled() bool {
+	g.mu.Lock()
+	defer g.mu.Unlock()
+	g.known = true
+	return g.all()
+}
+
+// all passes on every report again. The caller holds mu.
+func (g *ToolchainGate) all() bool {
+	changed := false
+	for _, module := range slices.Sorted(maps.Keys(g.raw)) {
+		for _, k := range slices.Sorted(maps.Keys(g.raw[module])) {
+			changed = g.pass(module, k) || changed
+		}
+	}
+	return changed
+}
+
+// again passes on every report of node by a build module among modules. The caller holds mu.
+func (g *ToolchainGate) again(node string, modules []string) bool {
+	changed := false
+	for _, module := range modules {
+		if !g.modules[module] {
+			continue
+		}
+		for _, k := range slices.Sorted(maps.Keys(g.raw[module])) {
+			if n, _, err := delivery.ParseToolchainKey(k); err == nil && n == node {
+				changed = g.pass(module, k) || changed
+			}
+		}
+	}
+	return changed
+}
+
+// pass hands one key on as it stands: its value when its node is placed and wrote it since (or the placement is not
+// known), deleted otherwise. The caller holds mu.
+func (g *ToolchainGate) pass(module, key string) bool {
+	value, held := g.raw[module][key]
+	if !held {
+		return g.forward(module, key, nil, true)
+	}
+	node, _, err := delivery.ParseToolchainKey(key)
+	why := ""
+	if err == nil && g.known && g.placed.Seeded() {
+		why = g.leftOut(module, node, value)
+	}
+	if why == "" {
+		delete(g.left, module+"/"+key)
+		return g.forward(module, key, value, false)
+	}
+	if g.left[module+"/"+key] != why {
+		g.left[module+"/"+key] = why
+		g.logf("%s.%s is left out of the agreed toolchain: %s (issue 1940)", delivery.ToolchainsBucket(module), key, why)
+	}
+	return g.forward(module, key, nil, true)
+}
+
+// leftOut is why a node's report is no builder's, or empty when it counts: the catalogue does not place the module on its
+// node, or the report was written before it did. A value that is no toolchain is passed on for its reader to refuse.
+// The caller holds mu.
+func (g *ToolchainGate) leftOut(module, node string, value []byte) string {
+	since, placed := g.placed.Since(node, module)
+	if !placed {
+		return fmt.Sprintf("the catalogue does not place %s on %s, so it is no builder", module, node)
+	}
+	tc, err := delivery.DecodeToolchain(value)
+	if err == nil && tc.At.Before(since) {
+		return fmt.Sprintf("it was written at %s, before %s was placed on %s at %s: it counts once %s writes it again",
+			tc.At.UTC().Format(time.RFC3339), module, node, since.UTC().Format(time.RFC3339), node)
+	}
+	return ""
+}
+
+// FollowPlacement reads the seat mesh-placement's placement with its history into gate, says it settled, and follows it; changed
+// is told whenever what the gate passes on changed. Where the state cannot be read or watched (not there, or this part
+// may not read it) it says so and the gate passes every report on: not fatal, since an indexer, builder or checker that
+// stops for it stops every delivery (issue 1945). An error of the watch after that ends on the channel.
+func FollowPlacement(ctx context.Context, js process.BucketOpener, gate *ToolchainGate, changed func(context.Context), logf func(string, ...any)) (<-chan error, error) {
+	errs := make(chan error, 1)
+	kv, err := js.KeyValue(ctx, delivery.PlacementBucket)
+	if err != nil {
+		logf("the state %s cannot be read, so every node's toolchain report counts, a build node's the catalogue does not place too (issue 1940): %v", delivery.PlacementBucket, err)
+		return errs, nil
+	}
+	w, err := kv.WatchAll(ctx, jetstream.IncludeHistory())
+	if err != nil {
+		logf("the state %s cannot be watched, so every node's toolchain report counts, a build node's the catalogue does not place too (issue 1940): %v", delivery.PlacementBucket, err)
+		return errs, nil
+	}
+	put := func(e jetstream.KeyValueEntry) bool {
+		return gate.Placement(e.Key(), e.Value(), e.Operation() != jetstream.KeyValuePut, e.Created())
+	}
+	for settled := false; !settled; {
+		select {
+		case <-ctx.Done():
+			_ = w.Stop()
+			return errs, ctx.Err()
+		case e, ok := <-w.Updates():
+			if !ok {
+				return errs, errors.New("the watch of " + delivery.PlacementBucket + " ended before it settled")
+			}
+			if e == nil {
+				settled = true
+				continue
+			}
+			put(e)
+		}
+	}
+	if gate.Settled() {
+		changed(ctx)
+	}
+	go func() {
+		defer func() { _ = w.Stop() }()
+		for {
+			select {
+			case <-ctx.Done():
+				errs <- ctx.Err()
+				return
+			case e, ok := <-w.Updates():
+				if !ok {
+					errs <- errors.New("the watch of " + delivery.PlacementBucket + " ended")
+					return
+				}
+				if e != nil && put(e) {
+					changed(ctx)
+				}
+			}
+		}
+	}()
+	return errs, nil
+}
@@ -0,0 +1,238 @@
+package buildrun
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"fmt"
+	"log"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+func gateReport(t *testing.T, node, version string, at time.Time) (string, []byte) {
+	t.Helper()
+	key, err := delivery.ToolchainKey(node, "typescript")
+	if err != nil {
+		t.Fatal(err)
+	}
+	value, err := delivery.EncodeToolchain(delivery.Toolchain{Language: "typescript", Version: version, Recipe: "f59571cf4be75adf", At: at})
+	if err != nil {
+		t.Fatal(err)
+	}
+	return key, value
+}
+
+// placing is a value of the state `placement` placing modules on node.
+func placing(t *testing.T, node string, modules ...string) (string, []byte) {
+	t.Helper()
+	p := delivery.Placement{Node: node}
+	for _, m := range modules {
+		p.Modules = append(p.Modules, delivery.PlacedModule{Module: m})
+	}
+	key, err := delivery.PlacementKey(node)
+	if err != nil {
+		t.Fatal(err)
+	}
+	value, err := delivery.EncodePlacement(p)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return key, value
+}
+
+func agreedOf(set *ToolchainSet) (string, string) {
+	tc, none := delivery.AgreedToolchain(set.Entries("typescript"))
+	return tc.Version, none
+}
+
+// Issue 1940, the gate over the catalogue's placement (issue 774, ADR 0549 §3): a build node's report counts only while
+// the placement places its build module on its node, and only once written since; before the placement is settled, and
+// while no node's placement is held, every report counts. The live cases: mesh-build-node taken off ace left
+// ace.typescript at v26.12.0 against v26.12.1 on the three others; put on ace again, its report of 2026-10-23 06:29 came
+// back before the module ran there.
+func TestToolchainGate(t *testing.T) {
+	old := time.Date(2026, 10, 23, 6, 29, 18, 0, time.UTC)     // ace's report from its earlier run
+	placed := time.Date(2026, 10, 25, 19, 56, 45, 0, time.UTC) // mesh-build-node placed on ace again
+	three := []string{"g14", "novox", "shanks"}
+	start := func(t *testing.T, seeded bool) (*ToolchainGate, *ToolchainSet, *[]string) {
+		set := &ToolchainSet{}
+		said := &[]string{}
+		gate := NewToolchainGate([]string{GoBuildModule, NodeBuildModule}, set.Put, func(f string, a ...any) { *said = append(*said, fmt.Sprintf(f, a...)) })
+		for _, node := range three {
+			if seeded {
+				key, value := placing(t, node, NodeBuildModule)
+				gate.Placement(key, value, false, old.Add(-time.Hour))
+			}
+			key, value := gateReport(t, node, "v26.12.1", placed.Add(time.Minute))
+			gate.Toolchain(NodeBuildModule, key, value, false)
+		}
+		return gate, set, said
+	}
+
+	t.Run("not placed on ace: its report is no builder's", func(t *testing.T) {
+		gate, set, said := start(t, true)
+		key, value := gateReport(t, "ace", "v26.12.0", old)
+		gate.Toolchain(NodeBuildModule, key, value, false)
+		if _, none := agreedOf(set); !strings.HasPrefix(none, "builders disagree") {
+			t.Fatalf("before the placement is settled every report counts; got %q", none)
+		}
+		k, v := placing(t, "ace", GoBuildModule) // another build module on ace: no matter
+		gate.Placement(k, v, false, old)
+		if !gate.Settled() {
+			t.Fatal("settling left ace's report out, so what was passed on changed")
+		}
+		if v, none := agreedOf(set); v != "v26.12.1" || none != "" {
+			t.Fatalf("the placed nodes agree on v26.12.1; got %q, %q", v, none)
+		}
+		if len(*said) != 1 || !strings.Contains((*said)[0], "does not place mesh-build-node on ace") {
+			t.Fatalf("ace's report is said left out once; said %q", *said)
+		}
+		if gate.Toolchain(NodeBuildModule, key, value, false) {
+			t.Fatal("a report of a node not placed changed what was passed on")
+		}
+		// Placed on ace with a report written since: it counts, and the builders really disagree.
+		k, v = placing(t, "ace", GoBuildModule, NodeBuildModule)
+		gate.Placement(k, v, false, old.Add(-time.Minute))
+		if _, none := agreedOf(set); !strings.HasPrefix(none, "builders disagree: v26.12.0 recipe f59571cf4be75adf on ace") {
+			t.Fatalf("builders that run different versions still disagree; got %q", none)
+		}
+		// Taken off ace again (its key deleted): its report goes again.
+		if !gate.Placement(k, nil, true, placed) {
+			t.Fatal("taking ace's placement away passed nothing on")
+		}
+		if v, none := agreedOf(set); v != "v26.12.1" || none != "" {
+			t.Fatalf("got %q, %q", v, none)
+		}
+		// A report deleted from the bucket goes whether its node is placed or not.
+		key, _ = gateReport(t, "g14", "v26.12.1", placed)
+		if !gate.Toolchain(NodeBuildModule, key, nil, true) || len(set.Entries("typescript")) != 2 {
+			t.Fatalf("deleting g14's report: %d entries left, want novox and shanks", len(set.Entries("typescript")))
+		}
+	})
+
+	for _, c := range []struct {
+		name   string
+		at     time.Time // when ace wrote its report
+		counts bool
+	}{
+		{"a report left before the placement", old, false},
+		{"a report written since the placement", placed.Add(30 * time.Second), true},
+	} {
+		t.Run(c.name, func(t *testing.T) {
+			gate, set, said := start(t, true)
+			k, v := placing(t, "ace") // ace's key, first heard placing nothing
+			gate.Placement(k, v, false, old.Add(-time.Hour))
+			gate.Settled()
+			k, v = placing(t, "ace", NodeBuildModule)
+			if gate.Placement(k, v, false, placed) {
+				t.Fatal("a placement with no report passed something on")
+			}
+			key, value := gateReport(t, "ace", "v26.12.0", c.at)
+			if got := gate.Toolchain(NodeBuildModule, key, value, false); got != c.counts {
+				t.Fatalf("ace's report passed on: %v, want %v", got, c.counts)
+			}
+			// ace's placement written again with another module beside: its standing does not move, nothing is said again.
+			k, v = placing(t, "ace", GoBuildModule, NodeBuildModule)
+			if gate.Placement(k, v, false, placed.Add(time.Minute)) {
+				t.Fatal("the same placement of mesh-build-node changed what was passed on")
+			}
+			if c.counts {
+				return
+			}
+			if v, none := agreedOf(set); v != "v26.12.1" || none != "" {
+				t.Fatalf("ace's left report is no builder's; got %q, %q", v, none)
+			}
+			if len(*said) != 1 || !strings.Contains((*said)[0], "before mesh-build-node was placed on ace at 2026-10-25T19:56:45Z") {
+				t.Fatalf("said %q, want once why ace's report is left out", *said)
+			}
+			key, value = gateReport(t, "ace", "v26.12.1", placed.Add(time.Minute))
+			if !gate.Toolchain(NodeBuildModule, key, value, false) || len(set.Entries("typescript")) != 4 {
+				t.Fatal("ace's new report was not passed on")
+			}
+		})
+	}
+
+	t.Run("no placement held: every report counts", func(t *testing.T) {
+		gate, set, _ := start(t, false)
+		key, value := gateReport(t, "ace", "v26.12.0", old)
+		gate.Toolchain(NodeBuildModule, key, value, false)
+		gate.Settled()
+		if n := len(set.Entries("typescript")); n != 4 {
+			t.Fatalf("before the first placement file every report counts; got %d", n)
+		}
+		k, v := placing(t, "g14", NodeBuildModule)
+		if !gate.Placement(k, v, false, old.Add(-time.Hour)) || len(set.Entries("typescript")) != 1 {
+			t.Fatalf("the first placement leaves every node it does not place out; got %d", len(set.Entries("typescript")))
+		}
+		if !gate.Placement(k, nil, true, placed) || len(set.Entries("typescript")) != 4 {
+			t.Fatal("the last placement gone: every report counts again")
+		}
+	})
+
+	t.Run("the history: a module in the first revision heard of a key stands since before it", func(t *testing.T) {
+		p := delivery.NewPlaced()
+		k, v := placing(t, "ace", NodeBuildModule)
+		p.Put(k, v, false, old)
+		k2, v2 := placing(t, "g14")
+		p.Put(k2, v2, false, old)
+		k2, v2 = placing(t, "g14", NodeBuildModule)
+		if _, changed, _ := p.Put(k2, v2, false, placed); strings.Join(changed, ",") != NodeBuildModule {
+			t.Errorf("a module placed says changed %v", changed)
+		}
+		if _, _, err := p.Put("placement.novox", []byte("not json"), false, old); err == nil {
+			t.Error("a value that does not read was not said")
+		}
+		if s, ok := p.Since("ace", NodeBuildModule); !ok || !s.IsZero() {
+			t.Errorf("ace's module stands since %v, %v; want the zero time", s, ok)
+		}
+		if s, ok := p.Since("g14", NodeBuildModule); !ok || !s.Equal(placed) {
+			t.Errorf("g14's module stands since %v, %v; want the revision that placed it", s, ok)
+		}
+		if got := p.PlacedNodes(NodeBuildModule); strings.Join(got, ",") != "ace,g14" || len(p.ByNode()) != 2 || !p.Seeded() {
+			t.Errorf("PlacedNodes = %v, ByNode = %v", got, p.ByNode())
+		}
+	})
+
+	t.Run("a placement the bus refuses is said, and the part goes on", func(t *testing.T) {
+		var logs bytes.Buffer
+		logger := log.New(&logs, "", 0)
+		refused := errors.New("nats: permissions violation for publish to $JS.API.CONSUMER.CREATE.KV_mesh-delivery-assigner_placement")
+		gate, _, _ := start(t, false)
+		for _, bus := range []refusingBus{{err: refused}, {refuseOpen: true, err: refused}} {
+			if _, err := FollowPlacement(context.Background(), bus, gate, func(context.Context) {}, logger.Printf); err != nil {
+				t.Errorf("a refused placement stopped the start: %v", err)
+			}
+		}
+		if !strings.Contains(logs.String(), "cannot be watched") || !strings.Contains(logs.String(), "cannot be read") {
+			t.Errorf("the refusals were not said: %q", logs.String())
+		}
+	})
+}
+
+// refusingBus is a bus that refuses: every open (refuseOpen), or every watch of a bucket it opens, with err.
+type refusingBus struct {
+	refuseOpen bool
+	err        error
+}
+
+func (r refusingBus) KeyValue(context.Context, string) (jetstream.KeyValue, error) {
+	if r.refuseOpen {
+		return nil, r.err
+	}
+	return refusedWatch{err: r.err}, nil
+}
+
+type refusedWatch struct {
+	jetstream.KeyValue
+	err error
+}
+
+func (r refusedWatch) WatchAll(context.Context, ...jetstream.WatchOpt) (jetstream.KeyWatcher, error) {
+	return nil, r.err
+}
@@ -35,10 +35,8 @@ func TestToolchainSetKeepsEachNodesEntryByLanguageAndSaysWhenOneChanged(t *testi
 	if !s.Put(GoBuildModule, "ace.go", nil, true) || len(s.Entries("go")) != 1 {
 		t.Error("a delete did not remove the node's entry")
 	}
-}
-
-func TestToolchainSetLeavesOutWhatIsNotAToolchainOfTheModulesLanguage(t *testing.T) { // 1607/AC6
-	var s ToolchainSet
+	// What is not a toolchain of the module's language is left out.
+	s = ToolchainSet{}
 	if s.Put(GoBuildModule, "novox.typescript", tcValue(t, "typescript", "x"), false) {
 		t.Error("a typescript toolchain in the go build module's bucket counted")
 	}
@@ -3,9 +3,12 @@ package delivery
 import (
 	"crypto/ed25519"
 	"crypto/rand"
+	"crypto/x509"
 	"encoding/json"
+	"encoding/pem"
 	"strings"
 	"testing"
+	"time"
 )

 func aSigningKey(t *testing.T) (ed25519.PublicKey, ed25519.PrivateKey) {
@@ -100,4 +103,88 @@ func TestACompositionIsSignedByAKeptKey(t *testing.T) {
 	if _, err := SignComposedBy(c, pub, func(m []byte) ([]byte, error) { return ed25519.Sign(other, m), nil }); err == nil {
 		t.Errorf("a signature by another key than the one named was accepted")
 	}
+
+	// L3 s1 (ADR 0550 §2): a message the vault or the controller signed under a kind's context verifies against the
+	// signers a node trusts and names which; an unknown key and another kind's context are refused.
+	vaultPub, vault := aSigningKey(t)
+	controllerPub, controller := aSigningKey(t)
+	trusted := []Signer{{Name: SignerController, Key: controllerPub}, {Name: SignerVault, Key: vaultPub}}
+	enrol, _ := SignContext(KindEnrolment)
+	certCtx, _ := SignContext(KindNodeCertificate)
+	msg := []byte("the reply")
+	for _, row := range []struct {
+		name    string
+		key     ed25519.PrivateKey
+		signed  string
+		checked string
+		want    string
+	}{
+		{"the vault's key verifies", vault, enrol, enrol, SignerVault},
+		{"the controller's key verifies", controller, enrol, enrol, SignerController},
+		{"an unknown key is refused", other, enrol, enrol, ""},
+		{"the wrong context is refused", vault, certCtx, enrol, ""},
+	} {
+		got, err := VerifyBy(trusted, row.checked, msg, SignMessage(row.key, row.signed, msg))
+		if row.want == "" && err == nil {
+			t.Errorf("%s: verified as %s", row.name, got.Name)
+		}
+		if row.want != "" && (err != nil || got.Name != row.want) {
+			t.Errorf("%s: %+v, %v", row.name, got.Name, err)
+		}
+	}
+	if _, err := SignContext("hand-over"); err == nil {
+		t.Error("a kind the vault does not sign has a context")
+	}
+	// The signers' key reads back only when its fingerprint is its key's, and what a node trusts names both holders.
+	k := NewSignerKey(vaultPub, time.Unix(0, 0))
+	raw, _ := json.Marshal(k)
+	if back, err := DecodeSignerKey(raw); err != nil || back.Fingerprint != SignerFingerprint(vaultPub) {
+		t.Errorf("the signers' key: %+v, %v", back, err)
+	}
+	k.Fingerprint = SignerFingerprint(controllerPub)
+	if raw, _ := json.Marshal(k); true {
+		if _, err := DecodeSignerKey(raw); err == nil {
+			t.Error("a signers' key naming another fingerprint was taken")
+		}
+	}
+	if got := Trusts(trusted, nil); len(got) != 2 || !TrustsKey(got, SignerVault, SignerFingerprint(vaultPub)) ||
+		!TrustsKey(got, SignerController, SignerFingerprint(controllerPub)) {
+		t.Errorf("trusts: %v", got)
+	}
+	// A certificate the vault's authority signs for a node's name and serving key checks against a bundle holding that
+	// authority, and not for another name, another key, or against the controller's alone; a bundle given again adds no
+	// certificate twice.
+	authority := func(pub ed25519.PublicKey, priv ed25519.PrivateKey) string {
+		tpl := AuthorityTemplate(pub, time.Now().Add(-time.Hour))
+		der, err := x509.CreateCertificate(nil, tpl, tpl, pub, priv)
+		if err != nil {
+			t.Fatal(err)
+		}
+		return string(pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: der}))
+	}
+	vaultCA, controllerCA := authority(vaultPub, vault), authority(controllerPub, controller)
+	parent, _ := ParseCertificate(vaultCA)
+	serving, _ := aSigningKey(t)
+	der, err := x509.CreateCertificate(nil, NodeCertificateTemplate("ace.internal", serving, time.Now().Add(-time.Hour)), parent, serving, vault)
+	if err != nil {
+		t.Fatal(err)
+	}
+	leaf := string(pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: der}))
+	bundle := AuthorityBundle(controllerCA, AuthorityBundle(controllerCA, vaultCA))
+	if n := strings.Count(bundle, "BEGIN CERTIFICATE"); n != 2 {
+		t.Errorf("the bundle holds %d certificates, want 2", n)
+	}
+	now := time.Now()
+	if err := CheckNodeCertificate(leaf, []string{bundle}, "ace.internal", serving, now); err != nil {
+		t.Errorf("the vault's certificate does not check: %v", err)
+	}
+	for name, err := range map[string]error{
+		"another name":           CheckNodeCertificate(leaf, []string{vaultCA}, "g14.internal", serving, now),
+		"another key":            CheckNodeCertificate(leaf, []string{vaultCA}, "ace.internal", controllerPub, now),
+		"the controller's alone": CheckNodeCertificate(leaf, []string{controllerCA}, "ace.internal", serving, now),
+	} {
+		if err == nil {
+			t.Errorf("%s: checked", name)
+		}
+	}
 }
@@ -90,3 +90,39 @@ func (g ControllerGrant) NamesNode(node, module string) bool {
 	}
 	return false
 }
+
+// **The grants part's grants** (novox/hq ADR 0547 §4, §5, ADR 0561 §2, §6; issue 774). The grants part writes the same
+// keys, with the same value, into its own state `grants` (the bucket PartGrantsBucket), beside the controller's: first in
+// shadow, which nobody reads, so a tool can compare the two before anything switches. The assigner reads the part's keys
+// only once the controller's lease is handed away (GrantSource), and the controller's until then.
+const (
+	// PartGrantsState is the grants part's state of issued credentials by fingerprint, as its manifest names it.
+	PartGrantsState = "grants"
+	// PartGrantsBucket is that state's bucket, `<owner module>_<name>`.
+	PartGrantsBucket = "mesh-grants_" + PartGrantsState
+	// PartGrantsRead is that state as a reader names it in `reads`.
+	PartGrantsRead = "mesh-grants." + PartGrantsState
+	// PartGrantsHistory is the revisions the bucket keeps per key.
+	PartGrantsHistory = ControllerGrantsHistory
+)
+
+// PartGrantKey is the key, in PartGrantsBucket, of a module's credential issued for a fingerprint: the layout of the
+// controller's key (ControllerGrantKey), so a key of one is the key of the other and a compare is by key.
+func PartGrantKey(module, fingerprint string) (string, error) {
+	return ControllerGrantKey(module, fingerprint)
+}
+
+// ParsePartGrantKey is the inverse of PartGrantKey.
+func ParsePartGrantKey(key string) (module, fingerprint string, err error) {
+	return ParseControllerGrantKey(key)
+}
+
+// GrantSource names the bucket the assigner reads grants from, and the `reads` name that grants it: the grants part's
+// once the controller's lease is handed away (buscompose.LeaseHandedAway, which refuses every other value of the lease,
+// an unreadable one included), the controller's in every other case.
+func GrantSource(leaseHandedAway bool) (bucket, read string) {
+	if leaseHandedAway {
+		return PartGrantsBucket, PartGrantsRead
+	}
+	return ControllerGrantsBucket, "mesh-controller.grants"
+}
@@ -55,6 +55,10 @@ type NodeRecord struct {
 	// Authority is the mesh's own certificate as this machine holds it (public): the one its declaration last wrote where
 	// a module asked for it. A node composing its own composes a certificate with it (compose.Input.Authority).
 	Authority string `json:"authority,omitempty"`
+	// Trusts is what this machine trusts a mesh signature from now (Trusts in signers.go, ADR 0550 §2): the controller's
+	// key until the lease is handed away, and the vault's key and authority once it reads them from `signers`. The gate
+	// before the lease write reads every node's from the bus.
+	Trusts []string `json:"trusts,omitempty"`
 }

 func (r NodeRecord) check() error {
@@ -18,7 +18,7 @@ var secretNamed = regexp.MustCompile(`(?i)(secret|passw|token|api[-_]?key|privat
 func TestNodeRecord(t *testing.T) {
 	hub := NodeRecord{Node: "novox", TunnelKey: "k", Capabilities: []string{"docker"}, SealingKey: "age1x", ServingKey: "pub",
 		Certificate: "cert", OutwardLinks: []string{"eth0"}, Networks: []catalogue.AttachedNetwork{{Link: "eth0", Network: "192.0.2.0/24"}},
-		NetworksSaid: true, Contract: 3}
+		NetworksSaid: true, Contract: 3, Trusts: []string{"controller key sha256:aa", "vault key sha256:bb"}}
 	raw, err := EncodeNodeRecord(hub)
 	if err != nil {
 		t.Fatal(err)
@@ -0,0 +1,126 @@
+package delivery
+
+import (
+	"fmt"
+	"maps"
+	"slices"
+	"sync"
+	"time"
+)
+
+// Placed is where the placement (the seat mesh-placement's state `placement`, held by the assigner; ADR 0567, ADR 0549 §3) places each module, and since when:
+// the one reader of that state for every part that asks "does module stand on node" (issue 774, design 47's third
+// milestone), in place of each part reading the controller's assignments (`mesh-controller_assignments`, which goes
+// with the controller's lease, ADR 0549 §6).
+//
+// Its input is the state's revisions in the order the bus wrote them, as a watch with the history (jetstream's
+// IncludeHistory) hands them: Put takes each. A module stands since the revision of its node's key that first named it
+// in an unbroken run. A module in the first revision heard of a key stands since the zero time: that revision is the
+// key's first (the seed of ADR 0549 §4 placed what already ran there) or the oldest the bus still keeps
+// (PlacementHistory), and either way the module may have run there before it. A key's value that does not read places
+// nothing on its node, and Put says why.
+//
+// Safe for use from a watch and from a reader at once.
+type Placed struct {
+	mu    sync.Mutex
+	since map[string]map[string]time.Time // node -> module -> since when it stands
+	heard map[string]bool                 // the nodes whose key was heard at all
+}
+
+// NewPlaced is a Placed that holds no placement yet.
+func NewPlaced() *Placed {
+	return &Placed{since: map[string]map[string]time.Time{}, heard: map[string]bool{}}
+}
+
+// Put takes one revision of a key of the state `placement` (its value, whether it is a delete, and when the bus wrote
+// it). It answers the node the key is of and the modules whose standing on it changed (placed or removed), in name
+// order, and an error for a key or a value that does not read (the node then places nothing).
+func (p *Placed) Put(key string, value []byte, deleted bool, at time.Time) (node string, changed []string, err error) {
+	node, err = ParsePlacementKey(key)
+	if err != nil {
+		return "", nil, err
+	}
+	now := map[string]bool{}
+	if !deleted {
+		pl, derr := DecodePlacement(value)
+		switch {
+		case derr != nil:
+			err = fmt.Errorf("the placement of %s does not read, so it places nothing there: %w", node, derr)
+		case pl.Node != node:
+			err = fmt.Errorf("the placement under %s names the node %q, so it places nothing there", key, pl.Node)
+		default:
+			for _, m := range pl.Assigned() {
+				now[m] = true
+			}
+		}
+	}
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	if !p.heard[node] {
+		p.heard[node] = true
+		at = time.Time{}
+	}
+	was := p.since[node]
+	next := map[string]time.Time{}
+	for m := range now {
+		if s, ok := was[m]; ok {
+			next[m] = s
+		} else {
+			next[m] = at
+			changed = append(changed, m)
+		}
+	}
+	for m := range was {
+		if !now[m] {
+			changed = append(changed, m)
+		}
+	}
+	if len(next) == 0 {
+		delete(p.since, node)
+	} else {
+		p.since[node] = next
+	}
+	slices.Sort(changed)
+	return node, changed, err
+}
+
+// Seeded says some node's placement is held: before the assigner's adopt writes the first placement nothing is placed,
+// and a reader keeps what it did before (ADR 0549 §5).
+func (p *Placed) Seeded() bool {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	return len(p.since) > 0
+}
+
+// Since says whether module stands on node, and since when (the zero time: since before the revisions kept).
+func (p *Placed) Since(node, module string) (time.Time, bool) {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	s, ok := p.since[node][module]
+	return s, ok
+}
+
+// PlacedNodes is every node module is placed on, in name order.
+func (p *Placed) PlacedNodes(module string) []string {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	var out []string
+	for node, mods := range p.since {
+		if _, ok := mods[module]; ok {
+			out = append(out, node)
+		}
+	}
+	slices.Sort(out)
+	return out
+}
+
+// ByNode is, by node, the modules placed on it in name order.
+func (p *Placed) ByNode() map[string][]string {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	out := make(map[string][]string, len(p.since))
+	for node, mods := range p.since {
+		out[node] = slices.Sorted(maps.Keys(mods))
+	}
+	return out
+}
@@ -0,0 +1,350 @@
+package delivery
+
+import (
+	"crypto/ed25519"
+	"crypto/sha256"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/base64"
+	"encoding/hex"
+	"encoding/json"
+	"encoding/pem"
+	"errors"
+	"fmt"
+	"math/big"
+	"slices"
+	"strings"
+	"time"
+)
+
+// **The vault signs** (novox/hq ADR 0550 §2; design 47's L3 item d). The vault makes an ed25519 signing key and an x509
+// authority once, keeps both as its own secrets with their operator copies, and publishes their public halves in its
+// state `signers`, which only the vault writes and every node principal and composing part reads. Its verb `sign` signs a
+// node's certificate for that node's own node-engine, from bus state alone (the name from the node's placement, the
+// serving key from its record), and says `signed` naming the caller, the kind, the node and the digest, never the key.
+//
+// A node trusts the vault's key through the bus grants alone (the lead's design limit, 2026-10-28): only the vault may
+// write `signers`, the same trust the wants and the placement rest on. Until the controller's lease is handed away the
+// node trusts the controller's key beside it; from then on the vault's alone (LeaseHandedAway). What a node trusts now
+// it states in its record, NodeRecord.Trusts, so the gate before the lease write reads it from the bus.
+
+const (
+	// VaultModule is the module holding the seat mesh-vault, whose state `signers` is.
+	VaultModule = "mesh-vault"
+	// SignersState is the vault's state of its public signing halves, and SignersBucket its bucket.
+	SignersState  = "signers"
+	SignersBucket = VaultModule + "_" + SignersState
+	// SignersRead is the state as a manifest's `reads` names it.
+	SignersRead = VaultModule + "." + SignersState
+	// SignersKeyKey holds the signing key's public half (SignerKey); SignersAuthorityKey the authority (SignerAuthority).
+	SignersKeyKey       = "key"
+	SignersAuthorityKey = "authority"
+
+	// SignVerb is the vault's verb that signs.
+	SignVerb = "sign"
+	// SignedEvent is what the vault says when it signed (Signed), on SignedSubject.
+	SignedEvent   = "signed"
+	SignedSubject = "mesh.mod." + VaultModule + ".event." + SignedEvent
+
+	// KindNodeCertificate is a node's certificate for its internal name, asked by that node's node-engine alone.
+	KindNodeCertificate = "node-certificate"
+	// KindEnrolment is an enrolment reply, signed under its own context; no caller is named until adoption's record
+	// (ADR 0561 §5).
+	KindEnrolment = "enrolment"
+	// KindAuthority is the vault's own authority certificate, which the vault signs for itself.
+	KindAuthority = "authority"
+
+	// SignerController and SignerVault name the two signers a node may trust.
+	SignerController = "controller"
+	SignerVault      = "vault"
+
+	// CertificateLife is how long a certificate the vault signs for a node lasts: the controller's ten years
+	// (identity.forever), renewed by asking again, never by a clock running out unseen.
+	CertificateLife = 10 * 365 * 24 * time.Hour
+)
+
+// SignKinds are the kinds `sign` knows.
+var SignKinds = []string{KindNodeCertificate, KindEnrolment, KindAuthority}
+
+// SignContext is the line a message of kind is signed after, so a signature made for one kind never verifies as
+// another's (as the composition's and the asks' contexts are kept apart).
+func SignContext(kind string) (string, error) {
+	if !slices.Contains(SignKinds, kind) {
+		return "", fmt.Errorf("delivery: %q is not a kind the vault signs (%s)", kind, strings.Join(SignKinds, ", "))
+	}
+	return "novox " + kind + " v1\n", nil
+}
+
+// SignerKey is the key `key` of `signers`: the vault's signing key's public half in standard base64, its fingerprint,
+// and when it was made.
+type SignerKey struct {
+	Key         string    `json:"key"`
+	Fingerprint string    `json:"fingerprint"`
+	Made        time.Time `json:"made"`
+}
+
+// SignerAuthority is the key `authority` of `signers`: the vault's authority certificate as PEM, its fingerprint, and
+// when it was made.
+type SignerAuthority struct {
+	Certificate string    `json:"certificate"`
+	Fingerprint string    `json:"fingerprint"`
+	Made        time.Time `json:"made"`
+}
+
+// SignerFingerprint is an ed25519 public key's fingerprint, `sha256:<hex>` of its 32 bytes.
+func SignerFingerprint(key ed25519.PublicKey) string {
+	sum := sha256.Sum256(key)
+	return "sha256:" + hex.EncodeToString(sum[:])
+}
+
+// AuthorityFingerprint is an authority certificate's fingerprint, `sha256:<hex>` of its DER; refused when certificate is
+// not one PEM certificate.
+func AuthorityFingerprint(certificate string) (string, error) {
+	c, err := ParseCertificate(certificate)
+	if err != nil {
+		return "", err
+	}
+	sum := sha256.Sum256(c.Raw)
+	return "sha256:" + hex.EncodeToString(sum[:]), nil
+}
+
+// ParseCertificate is the first certificate of a PEM text.
+func ParseCertificate(text string) (*x509.Certificate, error) {
+	block, _ := pem.Decode([]byte(strings.TrimSpace(text)))
+	if block == nil || block.Type != "CERTIFICATE" {
+		return nil, errors.New("delivery: not a PEM certificate")
+	}
+	return x509.ParseCertificate(block.Bytes)
+}
+
+// NewSignerKey is the value of `key` for pub.
+func NewSignerKey(pub ed25519.PublicKey, made time.Time) SignerKey {
+	return SignerKey{Key: base64.StdEncoding.EncodeToString(pub), Fingerprint: SignerFingerprint(pub), Made: made.UTC()}
+}
+
+// PublicKey is k's key, checked: an ed25519 public key whose fingerprint is the one k names.
+func (k SignerKey) PublicKey() (ed25519.PublicKey, error) {
+	raw, err := base64.StdEncoding.DecodeString(k.Key)
+	if err != nil || len(raw) != ed25519.PublicKeySize {
+		return nil, errors.New("delivery: the signers' key is not an ed25519 public key in base64")
+	}
+	if fp := SignerFingerprint(raw); fp != k.Fingerprint {
+		return nil, fmt.Errorf("delivery: the signers' key has the fingerprint %s, and names %s", fp, k.Fingerprint)
+	}
+	return ed25519.PublicKey(raw), nil
+}
+
+// DecodeSignerKey reads the key `key` of `signers`, refused when it does not check.
+func DecodeSignerKey(raw []byte) (SignerKey, error) {
+	var k SignerKey
+	if err := json.Unmarshal(raw, &k); err != nil {
+		return SignerKey{}, fmt.Errorf("delivery: %s %s: %w", SignersRead, SignersKeyKey, err)
+	}
+	if _, err := k.PublicKey(); err != nil {
+		return SignerKey{}, err
+	}
+	return k, nil
+}
+
+// DecodeSignerAuthority reads the key `authority` of `signers`: one authority certificate (a CA that signs leaves
+// alone) whose fingerprint is the one named.
+func DecodeSignerAuthority(raw []byte) (SignerAuthority, error) {
+	var a SignerAuthority
+	if err := json.Unmarshal(raw, &a); err != nil {
+		return SignerAuthority{}, fmt.Errorf("delivery: %s %s: %w", SignersRead, SignersAuthorityKey, err)
+	}
+	c, err := ParseCertificate(a.Certificate)
+	if err != nil {
+		return SignerAuthority{}, err
+	}
+	if !c.IsCA {
+		return SignerAuthority{}, errors.New("delivery: the signers' authority is not an authority certificate")
+	}
+	if fp, _ := AuthorityFingerprint(a.Certificate); fp != a.Fingerprint {
+		return SignerAuthority{}, fmt.Errorf("delivery: the signers' authority has the fingerprint %s, and names %s", fp, a.Fingerprint)
+	}
+	return a, nil
+}
+
+// Signer is one key a node trusts, by who holds it (SignerController, SignerVault, or the operator's).
+type Signer struct {
+	Name string
+	Key  ed25519.PublicKey
+}
+
+// Fingerprint is the signer's key's fingerprint.
+func (s Signer) Fingerprint() string { return SignerFingerprint(s.Key) }
+
+// VerifyBy is the trusted signer whose key verifies sig over context and msg: refused when no trusted key does, saying
+// so, and when a key is not an ed25519 key. A signature made under another context never verifies.
+func VerifyBy(trusted []Signer, context string, msg, sig []byte) (Signer, error) {
+	if len(sig) != ed25519.SignatureSize {
+		return Signer{}, errors.New("delivery: not an ed25519 signature")
+	}
+	message := append([]byte(context), msg...)
+	for _, s := range trusted {
+		if len(s.Key) != ed25519.PublicKeySize {
+			continue
+		}
+		if ed25519.Verify(s.Key, message, sig) {
+			return s, nil
+		}
+	}
+	names := make([]string, 0, len(trusted))
+	for _, s := range trusted {
+		names = append(names, s.Name)
+	}
+	return Signer{}, fmt.Errorf("delivery: the signature verifies against no trusted key (%s)", strings.Join(names, ", "))
+}
+
+// SignMessage is sig over context and msg by key: what the vault's `sign` does for a kind whose bytes are given.
+func SignMessage(key ed25519.PrivateKey, context string, msg []byte) []byte {
+	return ed25519.Sign(key, append([]byte(context), msg...))
+}
+
+// Signed is the vault's `signed`: who asked, the kind, the node, and the sha256 digest of what was signed. Never a key.
+type Signed struct {
+	Caller string    `json:"caller"`
+	Kind   string    `json:"kind"`
+	Node   string    `json:"node,omitempty"`
+	Digest string    `json:"digest"`
+	Signer string    `json:"signer"`
+	At     time.Time `json:"at"`
+}
+
+// SignAnswer is what `sign` answers: for a node certificate the certificate as PEM and the authority that signed it,
+// for an enrolment the signature in base64; always the signer's fingerprint and the digest. Never a key's private half.
+type SignAnswer struct {
+	Kind        string `json:"kind"`
+	Node        string `json:"node,omitempty"`
+	Certificate string `json:"certificate,omitempty"`
+	Authority   string `json:"authority,omitempty"`
+	Signature   string `json:"signature,omitempty"`
+	Signer      string `json:"signer"`
+	Digest      string `json:"digest"`
+}
+
+// DigestOf is the digest a `signed` names: `sha256:<hex>` of the bytes signed.
+func DigestOf(b []byte) string {
+	sum := sha256.Sum256(b)
+	return "sha256:" + hex.EncodeToString(sum[:])
+}
+
+// NodeCertificateTemplate is the certificate the vault signs for node's internal name, as the controller's authority
+// shaped it (identity.Certify): the name in the subject and the subject alternative names, server and client use, the
+// serial derived from the name and the key so the same ask gives the same certificate, and its life from notBefore.
+func NodeCertificateTemplate(name string, servingKey ed25519.PublicKey, notBefore time.Time) *x509.Certificate {
+	sum := sha256.Sum256(append([]byte(name+"\n"), servingKey...))
+	return &x509.Certificate{
+		SerialNumber: new(big.Int).SetBytes(sum[:16]),
+		Subject:      pkix.Name{CommonName: name},
+		DNSNames:     []string{name},
+		NotBefore:    notBefore.UTC().Truncate(time.Second),
+		NotAfter:     notBefore.UTC().Truncate(time.Second).Add(CertificateLife),
+		KeyUsage:     x509.KeyUsageDigitalSignature,
+		ExtKeyUsage:  []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth, x509.ExtKeyUsageClientAuth},
+	}
+}
+
+// AuthorityTemplate is the vault's authority certificate for its key, made once: an authority that signs leaves and no
+// other authority, as the controller's.
+func AuthorityTemplate(key ed25519.PublicKey, made time.Time) *x509.Certificate {
+	sum := sha256.Sum256(append([]byte("authority\n"), key...))
+	return &x509.Certificate{
+		SerialNumber:          new(big.Int).SetBytes(sum[:16]),
+		Subject:               pkix.Name{CommonName: "the mesh's vault"},
+		NotBefore:             made.UTC().Truncate(time.Second),
+		NotAfter:              made.UTC().Truncate(time.Second).Add(2 * CertificateLife),
+		IsCA:                  true,
+		KeyUsage:              x509.KeyUsageCertSign | x509.KeyUsageCRLSign,
+		BasicConstraintsValid: true,
+		MaxPathLen:            0,
+		MaxPathLenZero:        true,
+	}
+}
+
+// CheckNodeCertificate says why certificate is not a certificate of name for servingKey by one of the authorities, or
+// nil: a node uses it to tell whether its record holds a certificate from an authority it trusts, and another node to
+// check one the vault signed (ADR 0550 §2's live check).
+func CheckNodeCertificate(certificate string, authorities []string, name string, servingKey ed25519.PublicKey, at time.Time) error {
+	c, err := ParseCertificate(certificate)
+	if err != nil {
+		return err
+	}
+	pool := x509.NewCertPool()
+	for _, a := range authorities {
+		pool.AppendCertsFromPEM([]byte(a)) // a bundle is every certificate it holds
+	}
+	if _, err := c.Verify(x509.VerifyOptions{Roots: pool, DNSName: name, CurrentTime: at,
+		KeyUsages: []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth}}); err != nil {
+		return fmt.Errorf("delivery: the certificate of %s is not one a trusted authority signed for it: %w", name, err)
+	}
+	held, ok := c.PublicKey.(ed25519.PublicKey)
+	if !ok || !held.Equal(servingKey) {
+		return fmt.Errorf("delivery: the certificate of %s binds another key than the node serves with", name)
+	}
+	return nil
+}
+
+// AuthorityBundle is the authorities given as one PEM text, each certificate once, in the order given, blanks left out:
+// what a module asking for the mesh's authority is given once the vault signs beside the controller (ADR 0550 §2). An
+// authority given is split into its certificates, so a bundle given again (the one a node kept from its last
+// composition) adds nothing twice; a text that holds no PEM block is taken whole.
+func AuthorityBundle(authorities ...string) string {
+	var out []string
+	for _, a := range authorities {
+		for _, piece := range pemPieces(a) {
+			if !slices.Contains(out, piece) {
+				out = append(out, piece)
+			}
+		}
+	}
+	if len(out) == 0 {
+		return ""
+	}
+	return strings.Join(out, "\n") + "\n"
+}
+
+// pemPieces is each PEM block of text re-encoded, or the trimmed text whole when it holds none.
+func pemPieces(text string) []string {
+	text = strings.TrimSpace(text)
+	if text == "" {
+		return nil
+	}
+	var out []string
+	rest := []byte(text)
+	for {
+		block, more := pem.Decode(rest)
+		if block == nil {
+			break
+		}
+		out = append(out, strings.TrimSpace(string(pem.EncodeToMemory(block))))
+		rest = more
+	}
+	if len(out) == 0 {
+		return []string{text}
+	}
+	return out
+}
+
+// Trusts is what a node states it trusts now (NodeRecord.Trusts): `<who> key <fingerprint>` for each signer and
+// `<who> authority <fingerprint>` for each authority certificate, by who holds it, each once, sorted. The gate before the
+// lease write reads `vault key <fingerprint>` in every node's record.
+func Trusts(signers []Signer, authorities map[string]string) []string {
+	var out []string
+	for _, s := range signers {
+		if len(s.Key) == ed25519.PublicKeySize {
+			out = append(out, s.Name+" key "+s.Fingerprint())
+		}
+	}
+	for who, a := range authorities {
+		if fp, err := AuthorityFingerprint(a); err == nil {
+			out = append(out, who+" authority "+fp)
+		}
+	}
+	slices.Sort(out)
+	return slices.Compact(out)
+}
+
+// TrustsKey says whether trusts names the key with fingerprint fp held by who.
+func TrustsKey(trusts []string, who, fp string) bool { return slices.Contains(trusts, who+" key "+fp) }