Merge commit 'ec821f6' into asm-l3/774-vault-mints

go/buscompose/buscompose_test.go

@@ -131,6 +131,8 @@ func grantsAsTheControllers(t *testing.T, got, want string) {
 	}
 }
 
+const SignersBucketName = "mesh-vault_signers"
+
 func TestTheCopiedComposerComposesAsTheControllers(t *testing.T) {
 	raw, err := os.ReadFile(filepath.Join("testdata", "controller-user-lists.json"))
 	if err != nil {
@@ -237,6 +239,21 @@ 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"}}}}})

go/buscompose/nats.go

@@ -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.
@@ -360,6 +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
@@ -953,6 +962,14 @@ 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, 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 {
@@ -1845,6 +1862,11 @@ 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"

go/buscompose/users.go

@@ -165,7 +165,7 @@ 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),
 			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.

go/catalogue/seats.go

@@ -228,6 +228,14 @@ var defaultSeats = append([]Seat{
 				"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).

go/compose/composed.go

@@ -8,6 +8,7 @@ import (
 	"sort"
 	"strings"
 
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
 	"git.novox.be/novox/mesh-sdk/go/declaration"
 	"git.novox.be/novox/mesh-sdk/go/delivery"
 	"git.novox.be/novox/mesh-sdk/go/overlay"
@@ -76,6 +77,42 @@ func compositions(in Input, node string, fps map[string]string, mode Mode, appli
 	if !found {
 		return nil, nil, nil, fmt.Errorf("compose: the mesh has no node %q", node)
 	}
+	// A folded module built by a build of the old form (Node.RunsOwn) is left to the node: composed as a stub, so what
+	// it provides and requires still shapes the rest, and its resources are then the ones the node runs.
+	carried := map[string]bool{}
+	var runsOwn *delivery.Composed
+	for i := range reading.Nodes {
+		n := &reading.Nodes[i]
+		if n.Name != node || n.RunsOwn == nil {
+			continue
+		}
+		runsOwn = n.RunsOwn
+		for m := range inOwn {
+			if !folds(m) {
+				continue
+			}
+			man, ok := n.Kept[m]
+			if !ok {
+				man, ok = reading.Catalogue[m]
+			}
+			if !ok || !NamesBuild(man) {
+				continue
+			}
+			carried[m] = true
+			kept := make(map[string]catalogue.Manifest, len(n.Kept)+1)
+			for k, v := range n.Kept {
+				kept[k] = v
+			}
+			kept[m] = Stub(man)
+			n.Kept = kept
+		}
+	}
+	isCarried := func(module, id string) bool {
+		if module == "" {
+			module, _ = declaration.ModuleGuess(id)
+		}
+		return carried[module]
+	}
 	d, problems, err := ComposeIn(reading, node, mode)
 	if err != nil {
 		return nil, nil, nil, err
@@ -118,6 +155,7 @@ func compositions(in Input, node string, fps map[string]string, mode Mode, appli
 	left := map[string]bool{}
 	for _, raw := range envelope.Resources {
 		var head struct {
+			ID     string `json:"id"`
 			Module string `json:"module"`
 			Type   string `json:"type"`
 			Path   string `json:"path"`
@@ -125,6 +163,9 @@ func compositions(in Input, node string, fps map[string]string, mode Mode, appli
 		if err := json.Unmarshal(raw, &head); err != nil {
 			return nil, nil, nil, err
 		}
+		if isCarried(head.Module, head.ID) {
+			continue // what the stub composed of it: the node's own carries what runs of it instead
+		}
 		if folds(head.Module) {
 			// Into the node's own, in its place among the node's resources, its module taken off (mesh-controller's
 			// compositionsOf): the node's own composition is then the controller's, byte for byte.
@@ -151,6 +192,18 @@ func compositions(in Input, node string, fps map[string]string, mode Mode, appli
 		}
 		kept = append(kept, raw)
 	}
+	// What runs of each carried module, in the node's own composition, each after the resource it runs after.
+	if len(carried) > 0 {
+		var err error
+		if kept, foldedPaths, err = carry(kept, foldedPaths, runsOwn, isCarried); err != nil {
+			return nil, nil, nil, err
+		}
+		for _, p := range runsOwn.Filled {
+			if foldedPaths[p] && !slices.Contains(envelope.Filled, p) {
+				envelope.Filled = append(envelope.Filled, p)
+			}
+		}
+	}
 	// A filled file of a module's own composition goes with that module (SplitComposed); one of a folded module goes with
 	// the node's own, after them, in the declaration's order; one of a module left out is dropped.
 	var filled, ownFilled []string
@@ -188,3 +241,83 @@ func compositions(in Input, node string, fps map[string]string, mode Mode, appli
 	sort.Strings(skipped)
 	return out, skipped, stood, nil
 }
+
+// NamesBuild says a manifest names what a build makes: its build, or a resource naming an artifact. A node cannot
+// compose such a module folded into its own composition: the build of the old form it runs is held by the controller
+// alone (issue 1126).
+func NamesBuild(m catalogue.Manifest) bool {
+	if m.Build != nil {
+		return true
+	}
+	for _, r := range m.Resources {
+		if _, ok := r["artifact"]; ok {
+			return true
+		}
+	}
+	return false
+}
+
+// Stub is m with nothing to build and no resource but its directories: what it provides, requires, serves and grants
+// still shape the rest of the composition, the places its own secrets, data and grants name (${dir:…}) still resolve,
+// and nothing else of its own is composed (issue 1126: nats's ${dir:mesh-state} on novox).
+func Stub(m catalogue.Manifest) catalogue.Manifest {
+	m.Build = nil
+	var dirs []map[string]any
+	for _, r := range m.Resources {
+		if r["type"] == "directory" {
+			dirs = append(dirs, r)
+		}
+	}
+	m.Resources = dirs
+	return m
+}
+
+// carry puts into the node's resources (kept, in the declaration's order) the resources of the node's own composition as
+// it runs (runs) that belong to a carried module, each after the resource it runs after, or first when that one is
+// not among them; a file among them is a folded path.
+func carry(kept []json.RawMessage, foldedPaths map[string]bool, runs *delivery.Composed, carried func(module, id string) bool) ([]json.RawMessage, map[string]bool, error) {
+	idOf := func(raw json.RawMessage) (string, string, string, string, error) {
+		var head struct {
+			ID     string `json:"id"`
+			Module string `json:"module"`
+			Type   string `json:"type"`
+			Path   string `json:"path"`
+		}
+		err := json.Unmarshal(raw, &head)
+		return head.ID, head.Module, head.Type, head.Path, err
+	}
+	present := map[string]bool{}
+	for _, raw := range kept {
+		if id, module, _, _, err := idOf(raw); err == nil && module == "" {
+			present[id] = true
+		}
+	}
+	// By the id of the resource of the node's own it runs after, "" for first: the last one before it that is composed.
+	after := map[string][]json.RawMessage{}
+	anchor := ""
+	for _, raw := range runs.Resources {
+		id, module, typ, path, err := idOf(raw)
+		if err != nil {
+			return nil, nil, fmt.Errorf("compose: a resource the node runs in its own composition: %w", err)
+		}
+		if !carried(module, id) {
+			if module == "" && present[id] {
+				anchor = id
+			}
+			continue
+		}
+		after[anchor] = append(after[anchor], raw)
+		if typ == string(declaration.TypeFile) {
+			foldedPaths[path] = true
+		}
+	}
+	out := make([]json.RawMessage, 0, len(kept)+len(runs.Resources))
+	out = append(out, after[""]...)
+	for _, raw := range kept {
+		out = append(out, raw)
+		if id, module, _, _, err := idOf(raw); err == nil && module == "" {
+			out = append(out, after[id]...)
+		}
+	}
+	return out, foldedPaths, nil
+}

go/compose/frombus/answer.go

@@ -4,9 +4,11 @@ import (
 	"context"
 	"fmt"
 	"regexp"
+	"slices"
 	"sort"
 	"strings"
 
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
 	"git.novox.be/novox/mesh-sdk/go/compose"
 	"git.novox.be/novox/mesh-sdk/go/delivery"
 )
@@ -32,7 +34,13 @@ func Answer(ctx context.Context, r Reader, mesh Mesh, s Scope, fps map[string]st
 	if err != nil {
 		return refuse(fmt.Errorf("frombus: placement: %w", err))
 	}
-	in, err := Input(ctx, r, mesh, s)
+	if s.Running == nil {
+		s.Running = running
+	}
+	// Every module it cannot compose is named, not the first only (issue 1126): a build it cannot read or take in, and
+	// below, a module the composition refuses, each composed as a stub so the rest is composed and compared.
+	failed := map[string]string{}
+	in, err := input(ctx, r, mesh, s, func(module string, err error) { failed[module] = err.Error() })
 	if err != nil {
 		return refuse(err)
 	}
@@ -63,8 +71,20 @@ func Answer(ctx context.Context, r Reader, mesh Mesh, s Scope, fps map[string]st
 		}
 	}
 	composed, skipped, stood, err := compose.CompositionsShadow(in, s.Node, fps)
-	if err != nil {
-		return refuse(err)
+	for err != nil {
+		module := culprit(in, s.Node, fps, failed, err)
+		if module == "" {
+			// Not one module's: the node's own (a value served elsewhere, the mesh's network), said once as the node's.
+			if len(failed) == 0 {
+				return refuse(err)
+			}
+			failed[delivery.HaveNodeWord] = err.Error()
+			composed, skipped, stood = nil, nil, nil
+			break
+		}
+		failed[module] = err.Error()
+		in = stubbed(in, s.Node, module)
+		composed, skipped, stood, err = compose.CompositionsShadow(in, s.Node, fps)
 	}
 	// The node's own composition is judged only where the node runs one: one that runs none applies it only once a want
 	// names it (the node agent's own composer hands it on that want alone), so a candidate does not add it.
@@ -79,8 +99,49 @@ func Answer(ctx context.Context, r Reader, mesh Mesh, s Scope, fps map[string]st
 			}
 		}
 	}
-	cmp := delivery.CompareComposed(composed, running)
-	a.Same, a.Differs, a.Removed = cmp.Same, cmp.Differs, cmp.Removed
+	if _, whole := failed[delivery.HaveNodeWord]; whole {
+		// Nothing composed to compare: every refusal is said, and nothing else.
+		for _, m := range sortedKeys(failed) {
+			a.Refusals = append(a.Refusals, delivery.ModuleRefused{Module: m, Why: failed[m]})
+		}
+		a.Verdict = delivery.VerdictOf(a)
+		return a
+	}
+	// A module the composition folds inside the node's own is judged there: the agent also says it runs by module, from
+	// the declaration it kept before the switch (agent.Everything), which is no removal (issue 1126, seed #531).
+	if len(s.InOwn) > 0 {
+		var judged []delivery.Composed
+		for _, c := range running {
+			if c.Module == "" || !slices.Contains(s.InOwn, c.Module) {
+				judged = append(judged, c)
+			}
+		}
+		running = judged
+	}
+	cmp := delivery.CompareComposedWith(composed, running, s.SameValue)
+	// The answer rides in the node's have key: its shown bodies are bounded, the rest named only.
+	budget := MaxShown
+	for i := range cmp.Differs {
+		kept := cmp.Differs[i].Bodies[:0]
+		for _, b := range cmp.Differs[i].Bodies {
+			if n := len(b.Composed) + len(b.Running); n <= budget {
+				budget -= n
+				kept = append(kept, b)
+			} else {
+				kept = append(kept, delivery.ResourceBodies{ID: b.ID, Why: b.Why})
+				a.Note = "some differing resources are named without their bodies: the answer holds at most " +
+					fmt.Sprint(MaxShown) + " bytes of them"
+			}
+		}
+		cmp.Differs[i].Bodies = kept
+	}
+	// A refused module was composed as a stub: what it composed is no difference; its refusal is said.
+	notFailed := func(m string) bool { _, ok := failed[m]; return !ok }
+	a.Same = slices.DeleteFunc(cmp.Same, func(m string) bool { return !notFailed(m) })
+	a.Removed = slices.DeleteFunc(cmp.Removed, func(m string) bool { return !notFailed(m) })
+	a.Differs = slices.DeleteFunc(cmp.Differs, func(d delivery.ModuleDiffers) bool { return !notFailed(d.Module) })
+	cmp.Added = slices.DeleteFunc(cmp.Added, func(d delivery.ModuleAdded) bool { return !notFailed(d.Module) })
+	skipped = slices.DeleteFunc(skipped, func(m string) bool { return !notFailed(m) })
 
 	// What the group adds, by node and module: placed by a candidate and not by the trunk on that node.
 	added := map[string]bool{}
@@ -138,13 +199,25 @@ func Answer(ctx context.Context, r Reader, mesh Mesh, s Scope, fps map[string]st
 		if _, isAdded := addedHere[m]; isAdded {
 			continue // a module the candidate adds here: what it lacks is said under Added
 		}
+		if _, isFailed := failed[m]; isFailed {
+			continue // said below, as why it could not be composed
+		}
 		a.Refusals = append(a.Refusals, delivery.ModuleRefused{Module: m, Why: "stands in for " + strings.Join(refusals[m], ", ")})
 	}
+	for _, m := range sortedKeys(failed) {
+		a.Refusals = append(a.Refusals, delivery.ModuleRefused{Module: m, Why: failed[m]})
+	}
 	sort.Slice(a.Refusals, func(i, j int) bool { return a.Refusals[i].Module < a.Refusals[j].Module })
 	a.Verdict = delivery.VerdictOf(a)
 	return a
 }
 
+// maxCulprits bounds the modules one refusal is tried on, each a whole composition.
+const maxCulprits = 8
+
+// MaxShown bounds the bytes of shown resource bodies in one answer (delivery.ModuleDiffers.Bodies).
+const MaxShown = 256 << 10
+
 var (
 	grantStandIn = regexp.MustCompile(`^the grant of \S+ for (\S+) on (\S+)$`)
 	needsStandIn = regexp.MustCompile(`^(\S+) on (\S+) needs `)
@@ -170,3 +243,57 @@ func standsInFor(x, node string) (string, string) {
 	}
 	return node, ""
 }
+
+// culprit is the module placed on node whose composition the error is of: the first, in placement order, whose stub
+// (compose.Stub) makes the composition succeed or fail otherwise; empty when none does (the error is not one module's).
+// Modules already refused are passed over.
+func culprit(in compose.Input, node string, fps map[string]string, failed map[string]string, err error) string {
+	var assigned []string
+	for _, n := range in.Nodes {
+		if n.Name == node {
+			assigned = n.Assigned
+		}
+	}
+	// Only the modules the error names: the words of a module's refusal name it. Each try is a whole composition, so a
+	// refusal naming none is no module's, answered at once rather than after a composition per module (issue 1126: ace's
+	// answer took 7m46s).
+	var order []string
+	for _, m := range assigned {
+		if strings.Contains(err.Error(), m) && len(order) < maxCulprits {
+			order = append(order, m)
+		}
+	}
+	for _, m := range order {
+		if _, done := failed[m]; done {
+			continue
+		}
+		if _, _, _, again := compose.CompositionsShadow(stubbed(in, node, m), node, fps); again == nil || again.Error() != err.Error() {
+			return m
+		}
+	}
+	return ""
+}
+
+// stubbed is in with module composed as a stub on node alone (compose.Stub, as node's Kept).
+func stubbed(in compose.Input, node, module string) compose.Input {
+	out := in
+	out.Nodes = append([]compose.Node(nil), in.Nodes...)
+	for i := range out.Nodes {
+		if out.Nodes[i].Name != node {
+			continue
+		}
+		man, ok := out.Nodes[i].Kept[module]
+		if !ok {
+			if man, ok = in.Catalogue[module]; !ok {
+				return in
+			}
+		}
+		kept := make(map[string]catalogue.Manifest, len(out.Nodes[i].Kept)+1)
+		for k, v := range out.Nodes[i].Kept {
+			kept[k] = v
+		}
+		kept[module] = compose.Stub(man)
+		out.Nodes[i].Kept = kept
+	}
+	return out
+}

go/compose/frombus/answer_rows_test.go

@@ -0,0 +1,209 @@
+package frombus
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"reflect"
+	"slices"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/compose"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/overlay"
+)
+
+// Issue 1126 (the seed's shadow, round 2): a node's answer names every module it cannot compose, not the first only;
+// and a module folded into its own composition that names a build of the old form (de-spiegel on novox, nats, photos,
+// systemd-resolved: their haves name a build-... id and no fingerprint) is left to the node, carried as it runs.
+func answerNamesEveryRefusalAndLeavesAnOldBuildToTheNode(t *testing.T) {
+	ctx := context.Background()
+	image := "alpine@sha256:" + strings.Repeat("a", 64)
+	manifest := func(module string) []byte {
+		// Its data names its directory, as nats's names ${dir:mesh-state} (issue 1126: novox's own composition refused
+		// "nats says ${dir:mesh-state}, and nats declares no directory mesh-state" when its stub held no directory).
+		return []byte(`{"module":"` + module + `","version":"1","capabilities":["container-runtime"],` +
+			`"own-secrets":{"token":"${dir:state}/token"},` +
+			`"resources":[{"id":"state","type":"directory","path":"/var/lib/` + module + `","mode":"0700"},` +
+			`{"id":"server","type":"container","name":"` + module + `","artifact":"site"}],` +
+			`"build":{"artifacts":[{"name":"site","kind":"upstream","from":"` + image + `"}]}}`)
+	}
+	lemurs := []byte(`{"module":"lemurs","version":"1","resources":[{"id":"service","type":"service","unit":"lemurs.service","state":"running","boot":"enabled"}]}`)
+	fp := func(c string) string { return "src2:" + strings.Repeat(c, 64) }
+	mk := func(placed ...string) *bus {
+		p := delivery.Placement{Node: "n1", Decided: delivery.NodeDecided{Hub: true, Address: "10.77.0.1"}}
+		for _, m := range placed {
+			p.Modules = append(p.Modules, delivery.PlacedModule{Module: m})
+		}
+		b := &bus{placements: map[string]delivery.Placement{"n1": p},
+			records:   map[string]delivery.NodeRecord{"n1": {Node: "n1", TunnelKey: publicKey(t), SealingKey: "sk", Capabilities: []string{"systemd", "container-runtime"}}},
+			modules:   map[string]delivery.Module{"lemurs": {Manifest: delivery.ManifestDigest(lemurs)}},
+			manifests: map[string][]byte{delivery.ManifestDigest(lemurs): lemurs},
+			builds:    map[string]*delivery.BuilderBuild{}}
+		for _, m := range []string{"web", "api", "spiegel"} {
+			b.own = append(b.own, compose.OwnSecretRow{Node: "n1", Module: m, Name: "token", Origin: "made", SealedTo: "sk", Sealed: `"box"`})
+		}
+		for _, m := range []string{"web", "api", "spiegel"} {
+			raw := manifest(m)
+			b.manifests[delivery.ManifestDigest(raw)] = raw
+			b.modules[m] = delivery.Module{Manifest: delivery.ManifestDigest(raw)}
+		}
+		// web and api are built, their keys done and waiting for the reference of their image; spiegel has no build of
+		// the new form at all.
+		for i, m := range []string{"web", "api"} {
+			mod := b.modules[m]
+			mod.FP2 = fp(string(rune('1' + i)))
+			b.modules[m] = mod
+			b.builds[m+" "+mod.FP2] = &delivery.BuilderBuild{State: delivery.BuildDone, Manifest: mod.Manifest,
+				Artifacts: []delivery.BuiltArtifact{{Name: "site", Kind: "image", Digest: "sha256:" + strings.Repeat("b", 64)}}}
+		}
+		return b
+	}
+	given := func(b *bus) map[string]*delivery.Placement {
+		p := b.placements["n1"]
+		return map[string]*delivery.Placement{"n1": &p}
+	}
+
+	// Every refusal: two builds taken in, and a module the composition refuses (its image never built), each named.
+	b := mk("lemurs", "web", "api", "spiegel")
+	a := Answer(ctx, b, Mesh{}, Scope{Node: "n1", Placements: given(b)},
+		map[string]string{"lemurs": fp("e"), "web": fp("1"), "api": fp("2"), "spiegel": fp("3")}, nil, "h1", 3)
+	var refused []string
+	for _, r := range a.Refusals {
+		refused = append(refused, r.Module)
+	}
+	if a.Verdict != delivery.CandidateRefused || a.Refused != "" || !reflect.DeepEqual(refused, []string{"api", "spiegel", "web"}) {
+		t.Errorf("every refusal: %+v, want api, spiegel and web refused, each named", a)
+	}
+	for _, r := range a.Refusals {
+		want := map[string]string{"api": "waits for the reference of site", "web": "waits for the reference of site",
+			"spiegel": "spiegel has not been built for this mesh"}[r.Module]
+		if !strings.Contains(r.Why, want) {
+			t.Errorf("%s refused as %q, want %q", r.Module, r.Why, want)
+		}
+	}
+	if raw, err := delivery.EncodeHaveNode(delivery.HaveNode{Candidates: map[string]delivery.CandidateAnswer{"g": a}}); err != nil {
+		t.Errorf("the answer is not one a have holds: %v (%s)", err, raw)
+	}
+	if lemursOK := slices.ContainsFunc(a.Added, func(m delivery.ModuleAdded) bool { return m.Module == "lemurs" }); !lemursOK {
+		t.Errorf("lemurs, which composes, is not answered beside the refusals: %+v", a)
+	}
+
+	// The fold: spiegel runs inside the node's own composition at a build of the old form. Its resources are carried as
+	// they run, each after the one it runs after: the node's own is the one it runs, and the node composes itself.
+	b = mk("lemurs", overlay.Name, "spiegel")
+	p := b.placements["n1"]
+	p.Decided.Endpoint = "n1.example:51820"
+	b.placements["n1"] = p
+	fps := map[string]string{"lemurs": fp("e")}
+	stub := Scope{Node: "n1"}
+	in, err := Input(ctx, b, Mesh{}, stub)
+	if err != nil {
+		t.Fatal(err)
+	}
+	in.Nodes[0].Kept = map[string]catalogue.Manifest{"spiegel": compose.Stub(in.Catalogue["spiegel"])}
+	base, _, err := compose.Compositions(in, "n1", fps, compose.Reading)
+	if err != nil {
+		t.Fatal(err)
+	}
+	// A refusal naming no module placed here is no module's: no compose is spent stubbing each in turn (issue 1126: ace's
+	// answer took 7m46s, one compose per module), though here a stub would compose.
+	if m := culprit(in, "n1", fps, map[string]string{}, fmt.Errorf("nothing in this mesh provides \"artifact-store\"")); m != "" {
+		t.Errorf("a refusal naming no placed module was laid on %s", m)
+	}
+	ownKey, _ := delivery.ComposedNodeKey("n1")
+	own := base[ownKey]
+	carriedRes := []json.RawMessage{
+		json.RawMessage(`{"id":"spiegel.state","type":"directory","path":"/var/lib/spiegel","mode":"0700"}`),
+		json.RawMessage(`{"id":"spiegel.server","type":"container","name":"spiegel","image":"registry.example/spiegel@sha256:` + strings.Repeat("c", 64) + `"}`)}
+	// They run after the node's first own resource.
+	own.Resources = append(append(append([]json.RawMessage{}, own.Resources[:1]...), carriedRes...), own.Resources[1:]...)
+	var running []delivery.Composed
+	for k, c := range base {
+		if k == ownKey {
+			c = own
+		}
+		running = append(running, c)
+	}
+	scope := Scope{Node: "n1", InOwn: []string{"spiegel"}, Running: running}
+	got, _, err := Compose(ctx, b, Mesh{}, scope, fps)
+	if err != nil {
+		t.Fatalf("the node does not compose itself with spiegel folded at a build of the old form: %v", err)
+	}
+	gotOwn, _ := json.Marshal(got[ownKey].Resources)
+	wantOwn, _ := json.Marshal(own.Resources)
+	if string(gotOwn) != string(wantOwn) {
+		t.Errorf("the node's own composition is\n%s\nwant what runs\n%s", gotOwn, wantOwn)
+	}
+	a = Answer(ctx, b, Mesh{}, Scope{Node: "n1", Placements: given(b), InOwn: []string{"spiegel"}}, fps, running, "h1", 3)
+	if a.Verdict != delivery.CandidateSame {
+		t.Errorf("the fold's answer: %+v, want the same", a)
+	}
+	// (A) The agent also says spiegel runs by module, from the declaration kept before the switch (agent.Everything): a
+	// module the composition folds is judged inside the node's own, not as removed (issue 1126, seed #531's answer).
+	keptToo := append(append([]delivery.Composed{}, running...), delivery.Composed{Node: "n1", Module: "spiegel", Resources: carriedRes})
+	if a = Answer(ctx, b, Mesh{}, Scope{Node: "n1", Placements: given(b), InOwn: []string{"spiegel"}}, fps, keptToo, "h1", 3); a.Verdict != delivery.CandidateSame || len(a.Removed) != 0 {
+		t.Errorf("a folded module running from the kept declaration is answered %+v, want the same", a)
+	}
+	// (B) The node's own composition carries its bus membership as it runs it (the controller's, from its store): composed
+	// the same, not 'in what runs, not composed' (seed #531, novox).
+	membership := json.RawMessage(`{"id":"bus-membership","type":"file","path":"` + catalogue.BusMembershipPath + `","sealed":"{\"box\":\"m\"}","mode":"0600"}`)
+	withMembership := make([]delivery.Composed, 0, len(running))
+	for _, c := range running {
+		if c.Module == "" {
+			c.Resources = append(append([]json.RawMessage{}, c.Resources...), membership)
+		}
+		withMembership = append(withMembership, c)
+	}
+	if a = Answer(ctx, b, Mesh{}, Scope{Node: "n1", Placements: given(b), InOwn: []string{"spiegel"}}, fps, withMembership, "h1", 3); a.Verdict != delivery.CandidateSame {
+		t.Errorf("the node's own with its bus membership is answered %+v, want the same", a)
+	}
+	// Without what runs, the fold composes spiegel from its manifest, as before, and the composition refuses it.
+	if _, _, err := Compose(ctx, b, Mesh{}, Scope{Node: "n1", InOwn: []string{"spiegel"}}, fps); err == nil ||
+		!strings.Contains(err.Error(), "spiegel has not been built for this mesh") {
+		t.Errorf("composed spiegel without what runs: %v", err)
+	}
+}
+
+// A module another node cannot run in this composition offers nothing in it: the refusal names it and why
+// (issue 1126, probe #532: ace and g14 answered "nothing in this mesh provides artifact-store … assign distribution to a
+// node" while novox runs it). And a refusal no module's stub changes is answered at once, not after a compose per module
+// (ace took 7m46s).
+func otherNodeNotResolvedIsNamed(t *testing.T) {
+	ctx := context.Background()
+	prov := []byte(`{"module":"prov","version":"1","capabilities":["container-runtime"],"provides":[{"name":"thing","scope":"mesh"}]}`)
+	cons := []byte(`{"module":"cons","version":"1","requires":["thing"]}`)
+	// n2 runs prov, which needs a container runtime n2's record does not say it has: n2's set does not resolve here.
+	b := &bus{placements: map[string]delivery.Placement{
+		"n1": {Node: "n1", Decided: delivery.NodeDecided{Hub: true, Address: "10.77.0.1", Endpoint: "n1.example:51820"}, Modules: []delivery.PlacedModule{{Module: "cons"}, {Module: overlay.Name}}},
+		"n2": {Node: "n2", Decided: delivery.NodeDecided{Address: "10.77.0.2"}, Modules: []delivery.PlacedModule{{Module: "prov"}, {Module: overlay.Name}}}},
+		records:   map[string]delivery.NodeRecord{"n1": {Node: "n1", TunnelKey: publicKey(t)}, "n2": {Node: "n2", TunnelKey: publicKey(t)}},
+		modules:   map[string]delivery.Module{"prov": {Manifest: delivery.ManifestDigest(prov)}, "cons": {Manifest: delivery.ManifestDigest(cons)}},
+		manifests: map[string][]byte{delivery.ManifestDigest(prov): prov, delivery.ManifestDigest(cons): cons}}
+	given := map[string]*delivery.Placement{}
+	for n, p := range b.placements {
+		p := p
+		given[n] = &p
+	}
+	a := Answer(ctx, b, Mesh{}, Scope{Node: "n1", Placements: given}, map[string]string{"cons": "src2:" + strings.Repeat("1", 64)}, nil, "h", 1)
+	if a.Verdict != delivery.CandidateRefused || !strings.Contains(a.Refused, "prov on n2 lacks container-runtime") {
+		t.Errorf("a refusal for want of n2's provider = %+v", a)
+	}
+}
+
+// A node that reaches no artifact store says what its composition holds of one (issue 1126: ace and g14 answered
+// "reaches no artifact store", and nothing said why).
+func noStoreReachedSaysWhy(t *testing.T) {
+	in := compose.Input{Catalogue: map[string]catalogue.Manifest{
+		"distribution": {Module: "distribution", Serves: map[string]map[string]any{catalogue.ArtifactStoreProvision: {"port": 5000}}}},
+		Nodes: []compose.Node{{Name: "g14", Assigned: []string{"adwaita"}}, {Name: "novox", Assigned: []string{"distribution"}}}}
+	if got := storeSought(in); got != "the composition holds g14, novox; artifact-store is served by distribution on novox, none of it on the private network with a port" {
+		t.Errorf("said %q", got)
+	}
+	in.Nodes = in.Nodes[:1]
+	if got := storeSought(in); got != "the composition holds g14; no module placed there serves artifact-store" {
+		t.Errorf("said %q", got)
+	}
+}

go/compose/frombus/frombus.go

@@ -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.
@@ -113,12 +123,21 @@ type Mesh struct {
 //
 // InOwn is the modules the composing node runs inside its own composition (InOwn of what it runs), composed there again
 // (compose.Node.InOwn) rather than cut out as modules no build is given for (issue 1126).
+//
+// Running is what the composing node runs; of it, its own composition (`<node>.node`) is given to the composition
+// (compose.Node.RunsOwn), so a module folded there that names a build of the old form is left to the node, carried
+// as it runs (issue 1126). Nil composes every folded module from its manifest.
 type Scope struct {
 	Node       string
 	Every      bool
 	KeptAt     map[string]string
 	Placements map[string]*delivery.Placement
 	InOwn      []string
+	Running    []delivery.Composed
+	// SameValue, in an answer, says whether two sealed values open to the same value (the node opens them with its own
+	// key), so a differing resource shows a value sealed again as such (delivery.CompareComposedWith). Nil shows them
+	// as differing.
+	SameValue func(a, b string) (same, known bool)
 }
 
 // InOwn is, of the modules p places on its node, those whose resources the node's own composition it runs
@@ -154,6 +173,13 @@ func InOwn(running []delivery.Composed, p delivery.Placement) []string {
 
 // Input is the composition input for s, read through r.
 func Input(ctx context.Context, r Reader, mesh Mesh, s Scope) (compose.Input, error) {
+	return input(ctx, r, mesh, s, nil)
+}
+
+// input is Input; with refuse set, a module placed on the composing node whose build cannot be read or taken in is
+// handed to refuse and composed as a stub (compose.Stub, kept for that node alone) rather than ending the read, so a
+// node's answer names every module it cannot compose (issue 1126).
+func input(ctx context.Context, r Reader, mesh Mesh, s Scope, refuse func(module string, err error)) (compose.Input, error) {
 	placements, err := r.Placements(ctx)
 	if err != nil {
 		return compose.Input{}, fmt.Errorf("frombus: placement: %w", err)
@@ -203,6 +229,13 @@ func Input(ctx context.Context, r Reader, mesh Mesh, s Scope) (compose.Input, er
 			}
 		}
 	}
+	// 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)
@@ -280,6 +313,22 @@ func Input(ctx context.Context, r Reader, mesh Mesh, s Scope) (compose.Input, er
 				}
 				n.InOwn[module] = true
 			}
+			for i := range s.Running {
+				if s.Running[i].Module == "" {
+					own := s.Running[i]
+					n.RunsOwn = &own
+					// Its bus membership as it runs it: the controller composes it from its store, which the node does
+					// not read; until the grants part hands memberships sealed to the node, the node's own composition
+					// carries the one it runs (issue 1126, seed #531 on novox: "bus-membership in what runs, not
+					// composed", which applied would have taken the node's bus credential away).
+					if sealed := membershipOf(own); sealed != "" {
+						if in.BusMemberships == nil {
+							in.BusMemberships = map[string]string{}
+						}
+						in.BusMemberships[s.Node] = sealed
+					}
+				}
+			}
 		}
 		in.Nodes = append(in.Nodes, n)
 		in.Holdings = append(in.Holdings, p.Held()...)
@@ -309,7 +358,7 @@ func Input(ctx context.Context, r Reader, mesh Mesh, s Scope) (compose.Input, er
 		if _, ok := records[s.Node]; !ok {
 			return compose.Input{}, fmt.Errorf("frombus: %s has written no record of itself yet", s.Node)
 		}
-		if err := fromBuilds(ctx, r, &in, s, placements[s.Node], modules, read, parse); err != nil {
+		if err := fromBuilds(ctx, r, &in, s, placements[s.Node], modules, read, parse, refuse); err != nil {
 			return compose.Input{}, err
 		}
 		// Its own modules' secrets, sealed to its own key by the vault: a composition carries them sealed (ADR 0550 §5).
@@ -358,7 +407,29 @@ func Compose(ctx context.Context, r Reader, mesh Mesh, s Scope, fps map[string]s
 // by the one take-in rule (takein.Manifest), a templates archive read in the artifact store as the node reaches it
 // (issue 1126).
 func fromBuilds(ctx context.Context, r Reader, in *compose.Input, s Scope, p delivery.Placement, modules map[string]delivery.Module,
-	read func(module, digest string) (catalogue.Manifest, error), parse func([]byte) (catalogue.Manifest, error)) error {
+	read func(module, digest string) (catalogue.Manifest, error), parse func([]byte) (catalogue.Manifest, error),
+	refuse func(module string, err error)) error {
+	// stub keeps a refused module in the composition as a stub for this node alone (compose.Stub): what it provides
+	// and requires still shapes the rest.
+	stub := func(module string, err error) {
+		refuse(module, err)
+		for i := range in.Nodes {
+			if in.Nodes[i].Name != s.Node {
+				continue
+			}
+			man, ok := in.Nodes[i].Kept[module]
+			if !ok {
+				man, ok = in.Catalogue[module]
+			}
+			if !ok {
+				return
+			}
+			if in.Nodes[i].Kept == nil {
+				in.Nodes[i].Kept = map[string]catalogue.Manifest{}
+			}
+			in.Nodes[i].Kept[module] = compose.Stub(man)
+		}
+	}
 	address, addressErr := "", error(nil)
 	addressed := false
 	archive := func(ctx context.Context, reference, digest string) ([]byte, error) {
@@ -370,7 +441,7 @@ func fromBuilds(ctx context.Context, r Reader, in *compose.Input, s Scope, p del
 		case addressErr != nil:
 			return nil, addressErr
 		case address == "":
-			return nil, fmt.Errorf("%s reaches no artifact store", s.Node)
+			return nil, fmt.Errorf("%s reaches no artifact store (%s)", s.Node, storeSought(*in))
 		}
 		return r.Archive(ctx, catalogue.Routed(reference, address), digest)
 	}
@@ -409,14 +480,23 @@ func fromBuilds(ctx context.Context, r Reader, in *compose.Input, s Scope, p del
 		}
 		b, err := r.Build(ctx, pm.Module, m.FP2)
 		if err != nil {
-			return fmt.Errorf("frombus: the build of %s at %s: %w", pm.Module, m.FP2, err)
+			err = fmt.Errorf("frombus: the build of %s at %s: %w", pm.Module, m.FP2, err)
+			if refuse == nil {
+				return err
+			}
+			stub(pm.Module, err)
+			continue
 		}
 		if b == nil || b.State != delivery.BuildDone {
 			continue // no done build at the trunk's: composed from the indexer's manifest, as before
 		}
 		resolved, err := built(pm.Module, m.FP2, b)
 		if err != nil {
-			return err
+			if refuse == nil {
+				return err
+			}
+			stub(pm.Module, err)
+			continue
 		}
 		in.Catalogue[pm.Module] = resolved
 	}
@@ -427,15 +507,22 @@ func fromBuilds(ctx context.Context, r Reader, in *compose.Input, s Scope, p del
 		for _, module := range sortedKeys(s.KeptAt) {
 			fp := s.KeptAt[module]
 			b, err := r.Build(ctx, module, fp)
-			if err != nil {
-				return fmt.Errorf("frombus: the build of %s at %s: %w", module, fp, err)
+			switch {
+			case err != nil:
+				err = fmt.Errorf("frombus: the build of %s at %s: %w", module, fp, err)
+			case b == nil || b.State != delivery.BuildDone:
+				err = fmt.Errorf("frombus: %s is wanted at %s, of which the builder holds no done build", module, fp)
 			}
-			if b == nil || b.State != delivery.BuildDone {
-				return fmt.Errorf("frombus: %s is wanted at %s, of which the builder holds no done build", module, fp)
+			var resolved catalogue.Manifest
+			if err == nil {
+				resolved, err = built(module, fp, b)
 			}
-			resolved, err := built(module, fp, b)
 			if err != nil {
-				return err
+				if refuse == nil {
+					return err
+				}
+				stub(module, err)
+				continue
 			}
 			if in.Nodes[i].Kept == nil {
 				in.Nodes[i].Kept = map[string]catalogue.Manifest{}
@@ -613,3 +700,42 @@ func sortedKeys[V any](m map[string]V) []string {
 	sort.Strings(out)
 	return out
 }
+
+// storeSought says, for a node that reaches no artifact store, what the composition holds of one: the nodes it holds and
+// where each module serving the artifact store is placed, so the refusal names why (issue 1126).
+func storeSought(in compose.Input) string {
+	var nodes, where []string
+	for _, n := range in.Nodes {
+		nodes = append(nodes, n.Name)
+		for _, a := range n.Assigned {
+			if m, ok := in.Catalogue[a]; ok {
+				if _, serves := m.Serves[catalogue.ArtifactStoreProvision]; serves {
+					where = append(where, a+" on "+n.Name)
+				}
+			}
+		}
+	}
+	sort.Strings(nodes)
+	sort.Strings(where)
+	said := "the composition holds " + strings.Join(nodes, ", ")
+	if len(where) == 0 {
+		return said + "; no module placed there serves " + catalogue.ArtifactStoreProvision
+	}
+	return said + "; " + catalogue.ArtifactStoreProvision + " is served by " + strings.Join(where, ", ") +
+		", none of it on the private network with a port"
+}
+
+// membershipOf is the sealed value of the bus membership resource (catalogue.BusMembershipID) of a node's own
+// composition, or "".
+func membershipOf(own delivery.Composed) string {
+	for _, raw := range own.Resources {
+		var r struct {
+			ID     string `json:"id"`
+			Sealed string `json:"sealed"`
+		}
+		if json.Unmarshal(raw, &r) == nil && r.ID == catalogue.BusMembershipID() {
+			return r.Sealed
+		}
+	}
+	return ""
+}

go/compose/frombus/frombus_test.go

@@ -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) {
@@ -119,6 +121,11 @@ func publicKey(t *testing.T) string {
 // controller's store fills for compose's own two-machine mesh (compose's aMesh: anchor the hub, laptop), and that Input
 // composes; a node reads only its own config values; what cannot be composed is refused, naming it.
 func TestInput(t *testing.T) {
+	// Issue 1126, the seed's shadow: every refusal named, an old-form module left to the node, and no store reached
+	// saying why (answer_rows_test.go).
+	t.Run("every refusal, and an old build left to the node", answerNamesEveryRefusalAndLeavesAnOldBuildToTheNode)
+	t.Run("no store reached says why", noStoreReachedSaysWhy)
+	t.Run("another node not resolved is named", otherNodeNotResolvedIsNamed)
 	ctx := context.Background()
 	xterm, err := os.ReadFile("../../catalogue/testdata/catalogue-835bf22b-xterm.module.json")
 	if err != nil {
@@ -211,6 +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)
 	}

go/compose/input.go

@@ -23,6 +23,7 @@ import (
 	"strings"
 
 	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
 )
 
 // Input is everything the composition reads. Each field is what one read of the controller's inventory answers, named
@@ -194,6 +195,11 @@ type Node struct {
 	// resources into the node's own, as the controller's composed writer does, unless fps gives one of the new form.
 	// The private network's module (overlay.Name), which nobody builds, is folded whether or not it is named here.
 	InOwn map[string]bool
+	// RunsOwn is the node's own composition (`<node>.node`) as it runs, when the node composes itself: a module folded
+	// there (InOwn) whose manifest names a build (NamesBuild) runs a build of the old form only the controller holds,
+	// so it is left to the node: Compositions composes it as a stub (Stub) and carries its resources as they run, each
+	// after the resource it runs after (issue 1126). Nil composes every folded module from its manifest, as before.
+	RunsOwn *delivery.Composed
 }
 
 // Place is where a node is, as its placement says (inv.Overlay).

go/compose/network.go

@@ -24,6 +24,9 @@ type composer struct {
 	in   Input
 	said []string
 	seen map[string]bool
+	// unhostable is, from the last look at the rest of the mesh, each module assigned to another node that this
+	// composition finds that node cannot run: what it would have offered is missing here (issue 1126, probe #532).
+	unhostable []string
 }
 
 func newComposer(in Input) *composer { return &composer{in: in, seen: map[string]bool{}} }

go/compose/resolve.go

@@ -3,6 +3,7 @@ package compose
 import (
 	"fmt"
 	"slices"
+	"strings"
 
 	"git.novox.be/novox/mesh-sdk/go/catalogue"
 )
@@ -203,7 +204,7 @@ func (c *composer) resolution(nodeName string) (catalogue.Resolution, error) {
 		return catalogue.Resolution{}, err
 	}
 	shelf := c.shelfFor(node)
-	world, _, _, err := c.theRestOfTheMesh(nodeName)
+	world, _, left, err := c.theRestOfTheMesh(nodeName)
 	if err != nil {
 		return catalogue.Resolution{}, err
 	}
@@ -226,6 +227,19 @@ func (c *composer) resolution(nodeName string) (catalogue.Resolution, error) {
 			Account: node.Account, AccountHome: node.AccountHome,
 			AgentAccount: node.AgentAccount, AgentAccountHome: node.AgentAccountHome}, world)
 	if err != nil {
+		// What another node's set would have offered is missing when that set does not resolve here: said with the
+		// refusal, so "nothing provides" is read beside why (issue 1126, probe #532).
+		if len(left) > 0 {
+			var why []string
+			for _, l := range left {
+				why = append(why, l.String())
+			}
+			err = fmt.Errorf("%w\n\nand %d node(s) offer nothing here, as they could not be resolved: %s", err, len(left), strings.Join(why, "; "))
+		}
+		if len(c.unhostable) > 0 {
+			err = fmt.Errorf("%w\n\nand these modules offer nothing here, as their node cannot run them in this composition: %s",
+				err, strings.Join(c.unhostable, "; "))
+		}
 		// The node's own set does not compose: the only failure a mesh-wide gatherer may pass over.
 		return catalogue.Resolution{}, notResolvable{err}
 	}

go/compose/rest.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"sort"
+	"strings"
 
 	"git.novox.be/novox/mesh-sdk/go/catalogue"
 )
@@ -100,6 +101,7 @@ func (c *composer) theRestOfTheMesh(exclude string) (catalogue.World, Passes, []
 	var left []LeftOut
 	offered := map[string][]catalogue.Provider{}
 	var firstHeld []catalogue.Held
+	c.unhostable = nil
 	for _, o := range others {
 		got, err := catalogue.Resolve(shelf, o.assigned, o.node, catalogue.World{Unchecked: true, Holdings: holdings})
 		if err != nil {
@@ -107,6 +109,9 @@ func (c *composer) theRestOfTheMesh(exclude string) (catalogue.World, Passes, []
 			left = append(left, LeftOut{Node: o.node.Name, Err: err})
 			continue
 		}
+		for _, u := range got.Unhostable {
+			c.unhostable = append(c.unhostable, fmt.Sprintf("%s on %s lacks %s", u.Module, o.node.Name, strings.Join(u.Missing, ", ")))
+		}
 		firstHeld = append(firstHeld, got.Claims...)
 		for _, m := range got.Modules {
 			for _, name := range m.OffersAt(catalogue.ScopeMesh) {

go/delivery/composed_compare.go

@@ -28,6 +28,13 @@ type Comparison struct {
 // resource is equal it says what else differs (their order, the files filled, the data, the node's own parts, a file
 // carried by digest).
 func CompareComposed(composed map[string]Composed, running []Composed) Comparison {
+	return CompareComposedWith(composed, running, nil)
+}
+
+// CompareComposedWith is CompareComposed showing, for each module that differs, every differing resource with both
+// bodies masked (MaskedPair); sameValue, when given, says whether two sealed values open to the same value (the node
+// opens them with its own key), so a value sealed again reads as such.
+func CompareComposedWith(composed map[string]Composed, running []Composed, sameValue func(a, b string) (same, known bool)) Comparison {
 	name := func(c Composed) string {
 		if c.Module == "" {
 			return HaveNodeWord
@@ -60,7 +67,7 @@ func CompareComposed(composed map[string]Composed, running []Composed) Compariso
 		case !composedHere:
 			out.Removed = append(out.Removed, m)
 		default:
-			if d, ok := compareOne(m, a, b); ok {
+			if d, ok := compareOne(m, a, b, sameValue); ok {
 				out.Same = append(out.Same, m)
 			} else {
 				out.Differs = append(out.Differs, d)
@@ -71,7 +78,7 @@ func CompareComposed(composed map[string]Composed, running []Composed) Compariso
 }
 
 // compareOne is one module's comparison: true when the digests agree, else what differs first.
-func compareOne(module string, composed, running Composed) (ModuleDiffers, bool) {
+func compareOne(module string, composed, running Composed, sameValue func(a, b string) (bool, bool)) (ModuleDiffers, bool) {
 	composed, running = withoutBusUsers(composed), withoutBusUsers(running)
 	dc, errC := ComposedDigestOf(composed)
 	dr, errR := ComposedDigestOf(running)
@@ -99,17 +106,35 @@ func compareOne(module string, composed, running Composed) (ModuleDiffers, bool)
 	for id := range rb {
 		ids[id] = true
 	}
+	var first ModuleDiffers
+	found := false
+	var bodies []ResourceBodies
 	for _, id := range sortedKeys(ids) {
 		x, inA := ra[id]
 		y, inB := rb[id]
+		why := ""
 		switch {
 		case !inB:
-			return differs(id, "composed, and not in what runs")
+			why = "composed, and not in what runs"
 		case !inA:
-			return differs(id, "in what runs, and not composed")
+			why = "in what runs, and not composed"
 		case !bytes.Equal(x, y):
-			return differs(id, "the resource differs")
+			why = "the resource differs"
+		default:
+			continue
 		}
+		if !found {
+			first, _ = differs(id, why)
+			found = true
+		}
+		if len(bodies) < MaxBodies {
+			c, r := MaskedPair(x, y, sameValue)
+			bodies = append(bodies, ResourceBodies{ID: id, Why: why, Composed: cut(c), Running: cut(r)})
+		}
+	}
+	if found {
+		first.Bodies = bodies
+		return first, false
 	}
 	switch {
 	case !jsonEqual(a.Filled, b.Filled):
@@ -165,3 +190,162 @@ func resourcesByID(resources []json.RawMessage) map[string][]byte {
 	}
 	return out
 }
+
+// cut is s cut at MaxBody bytes, saying so.
+func cut(s string) string {
+	if len(s) <= MaxBody {
+		return s
+	}
+	return s[:MaxBody] + "… (cut at " + strconv.Itoa(MaxBody) + " bytes)"
+}
+
+// secretWords are the words of a key whose value may hold a secret or a sealed one: masked in a shown body.
+var secretWords = []string{"sealed", "secret", "password", "passwd", "token", "private", "key", "credential", "jwt", "salt", "hash"}
+
+func secretKey(k string) bool {
+	k = strings.ToLower(k)
+	for _, w := range secretWords {
+		if strings.Contains(k, w) {
+			return true
+		}
+	}
+	return false
+}
+
+// MaskedPair is two bodies of one resource (either may be nil) as JSON text with every value under a key a secret could
+// be in (secretWords, at any depth) masked: "<masked: the same on both sides>", "<masked: another seal of the same
+// value>" or "<masked: another value>" when sameValue says so, "<masked: differs>" otherwise, "<masked>" on one side
+// alone. A body that is not JSON is shown as its length only.
+func MaskedPair(composed, running json.RawMessage, sameValue func(a, b string) (same, known bool)) (string, string) {
+	var a, b any
+	okA := composed != nil && json.Unmarshal(composed, &a) == nil
+	okB := running != nil && json.Unmarshal(running, &b) == nil
+	if okA && okB {
+		a, b = maskBoth(a, b, sameValue)
+	} else if okA {
+		a, _ = maskBoth(a, nil, nil)
+	} else if okB {
+		_, b = maskBoth(nil, b, nil)
+	}
+	show := func(v any, raw json.RawMessage, ok bool) string {
+		if raw == nil {
+			return ""
+		}
+		if !ok {
+			return "<not JSON: " + strconv.Itoa(len(raw)) + " bytes>"
+		}
+		var out bytes.Buffer
+		enc := json.NewEncoder(&out)
+		enc.SetEscapeHTML(false)
+		_ = enc.Encode(v)
+		return strings.TrimSuffix(out.String(), "\n")
+	}
+	return show(a, composed, okA), show(b, running, okB)
+}
+
+func maskBoth(a, b any, sameValue func(a, b string) (bool, bool)) (any, any) {
+	ma, isA := a.(map[string]any)
+	mb, isB := b.(map[string]any)
+	if isA || isB {
+		outA, outB := map[string]any{}, map[string]any{}
+		keys := map[string]bool{}
+		for k := range ma {
+			keys[k] = true
+		}
+		for k := range mb {
+			keys[k] = true
+		}
+		for k := range keys {
+			va, inA := ma[k]
+			vb, inB := mb[k]
+			if secretKey(k) {
+				word := maskWord(va, vb, inA && inB, sameValue)
+				if inA {
+					outA[k] = word
+				}
+				if inB {
+					outB[k] = word
+				}
+				continue
+			}
+			x, y := maskBoth(va, vb, sameValue)
+			if inA {
+				outA[k] = x
+			}
+			if inB {
+				outB[k] = y
+			}
+		}
+		var ra, rb any
+		if isA {
+			ra = outA
+		} else {
+			ra = a
+		}
+		if isB {
+			rb = outB
+		} else {
+			rb = b
+		}
+		return ra, rb
+	}
+	la, isLA := a.([]any)
+	lb, isLB := b.([]any)
+	if isLA || isLB {
+		outA := make([]any, len(la))
+		outB := make([]any, len(lb))
+		for i := range max(len(la), len(lb)) {
+			var x, y any
+			if i < len(la) {
+				x = la[i]
+			}
+			if i < len(lb) {
+				y = lb[i]
+			}
+			x, y = maskBoth(x, y, sameValue)
+			if i < len(la) {
+				outA[i] = x
+			}
+			if i < len(lb) {
+				outB[i] = y
+			}
+		}
+		var ra, rb any = a, b
+		if isLA {
+			ra = outA
+		}
+		if isLB {
+			rb = outB
+		}
+		return ra, rb
+	}
+	return a, b
+}
+
+func maskWord(a, b any, both bool, sameValue func(a, b string) (bool, bool)) string {
+	if !both {
+		return "<masked>"
+	}
+	x, _ := json.Marshal(a)
+	y, _ := json.Marshal(b)
+	if bytes.Equal(x, y) {
+		return "<masked: the same on both sides>"
+	}
+	if sameValue != nil {
+		sa, okA := a.(string)
+		sb, okB := b.(string)
+		if !okA {
+			sa = string(x)
+		}
+		if !okB {
+			sb = string(y)
+		}
+		if same, known := sameValue(sa, sb); known {
+			if same {
+				return "<masked: another seal of the same value>"
+			}
+			return "<masked: another value>"
+		}
+	}
+	return "<masked: differs>"
+}

go/delivery/composed_signature_test.go

@@ -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)
+		}
+	}
 }

go/delivery/delivery.go

@@ -410,8 +410,20 @@ type HaveNode struct {
 	// its shadow composer whenever an answer changes, removed when the candidate key goes. The node applies nothing of a
 	// candidate.
 	Candidates map[string]CandidateAnswer `json:"candidates,omitempty"`
+	// Composes is whose compositions the node applies: its own (ComposesOwn, the catalogue places it) or the
+	// controller's (ComposesController); ComposesWhy says why in words. Written by the node agent at each start, so a
+	// node returning to the controller's compositions when its placement key is deleted says so (issue 1126). Empty
+	// from an engine older than the field.
+	Composes    string `json:"composes,omitempty"`
+	ComposesWhy string `json:"composes-why,omitempty"`
 }
 
+// Whose compositions a node applies (HaveNode.Composes).
+const (
+	ComposesOwn        = "own"
+	ComposesController = "controller"
+)
+
 // Presence is whether a node or a part's instance is online; the entry's own time says since when. The watchman
 // writes it.
 type Presence struct {
@@ -506,6 +518,11 @@ func DecodeHave(data []byte) (Have, error) {
 }
 
 func (n HaveNode) check() error {
+	switch n.Composes {
+	case "", ComposesOwn, ComposesController:
+	default:
+		return fmt.Errorf("delivery: a node composes %q, neither %s nor %s", n.Composes, ComposesOwn, ComposesController)
+	}
 	for group, a := range n.Candidates {
 		if group == "" {
 			return fmt.Errorf("delivery: a node's candidate answer names no group")
@@ -590,7 +607,8 @@ func SameHaveNode(a, b HaveNode) bool {
 	return a.V == b.V && a.Composed == b.Composed && sameJSON(a.Windows, b.Windows) && sameJSON(a.Busy, b.Busy) &&
 		sameJSON(a.Strays, b.Strays) && sameJSON(a.Filters, b.Filters) && sameJSON(a.Profile, b.Profile) &&
 		(a.Record == nil) == (b.Record == nil) && (a.Record == nil || SameNodeRecord(*a.Record, *b.Record)) &&
-		jsonEqual(a.Sealed, b.Sealed) && jsonEqual(a.Candidates, b.Candidates)
+		jsonEqual(a.Sealed, b.Sealed) && jsonEqual(a.Candidates, b.Candidates) && a.Composes == b.Composes &&
+		a.ComposesWhy == b.ComposesWhy
 }
 
 // SamePresence says whether two presences are the same value.

go/delivery/noderecord.go

@@ -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 {

go/delivery/noderecord_test.go

@@ -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)

go/delivery/placement_candidate.go

@@ -132,8 +132,20 @@ type CandidateAnswer struct {
 	Refusals []ModuleRefused `json:"refusals,omitempty"`
 	// Refused is why the node could not compose with the candidate at all; Refusals is then empty.
 	Refused string `json:"refused,omitempty"`
+	// Returns is, for a head that deletes the node's placement file, what the node does then: it returns to the
+	// controller's compositions (ReturnsToController), as a node the catalogue does not place composes none of its own
+	// (issue 1126: the seed's revert). Same, Differs, Added and Removed then compare the controller's compositions at
+	// the node's wants with what it runs, and the verdict is theirs; a want the controller holds no composition for is
+	// refused (Refused, without Returns).
+	Returns string `json:"returns,omitempty"`
+	// Note is what the node says of how it answered, in words, beside the verdict: a pass that ran over a minute, inputs
+	// it waited for (issue 1126: the shadow shows its work). It changes no verdict.
+	Note string `json:"note,omitempty"`
 }
 
+// ReturnsToController is what a node answers a head that deletes its placement file.
+const ReturnsToController = "the head deletes this node's placement: it returns to the controller's compositions"
+
 // ModuleDiffers is one module the node runs and the candidate still places whose composition is not the one it runs:
 // both digests (Composed with the candidate, Running what runs), the first resource that differs by its id, or empty
 // when every resource is equal, and why in words.
@@ -143,8 +155,26 @@ type ModuleDiffers struct {
 	Running  string `json:"running,omitempty"`
 	Resource string `json:"resource,omitempty"`
 	Why      string `json:"why"`
+	// Bodies is every resource that differs, both sides, each value a secret could be in masked (issue 1126: the shadow
+	// shows its work, so why a module differs is read, not guessed). At most MaxBodies, each side cut at MaxBody bytes.
+	Bodies []ResourceBodies `json:"bodies,omitempty"`
 }
 
+// ResourceBodies is one differing resource of a module: its id, why, and its body composed and as it runs, masked
+// (MaskedPair); a side that does not hold it is empty.
+type ResourceBodies struct {
+	ID       string `json:"id"`
+	Why      string `json:"why"`
+	Composed string `json:"composed,omitempty"`
+	Running  string `json:"running,omitempty"`
+}
+
+// The bounds of a module's shown bodies.
+const (
+	MaxBodies = 20
+	MaxBody   = 8192
+)
+
 // ModuleAdded is one module the candidate places on the node and the node does not run: its composition's digest when
 // it composed, and the values not yet issued for it (its own secrets, its grants, a host port), each in the words the
 // composition stood in for it with.
@@ -187,6 +217,10 @@ func (a CandidateAnswer) check() error {
 	if a.Refused != "" && len(a.Same)+len(a.Differs)+len(a.Added)+len(a.Removed)+len(a.Refusals) > 0 {
 		return fmt.Errorf("delivery: a candidate the node could not compose names modules")
 	}
+	if a.Returns != "" && (a.Refused != "" || len(a.Refusals) > 0) {
+		return fmt.Errorf("delivery: a candidate the node returns to the controller's compositions on is compared, never refused: " +
+			"a composition the controller holds none of is refused without returning")
+	}
 	for _, d := range a.Differs {
 		if d.Module == "" || d.Why == "" {
 			return fmt.Errorf("delivery: a candidate difference names no module or no why")

go/delivery/placement_test.go

@@ -229,19 +229,33 @@ func TestPlacement(t *testing.T) {
 			"refused": {Head: "h1", Revision: 3, Verdict: CandidateRefused, Refused: "unbound postgres"},
 			"added":   {Head: "h1", Verdict: CandidateDiffers, Same: []string{"node"}, Added: []ModuleAdded{{Module: "app", Unissued: []string{"app/token"}}}, Removed: []string{"old"}},
 			"a value": {Head: "h1", Verdict: CandidateRefused, Same: []string{"node"}, Refusals: []ModuleRefused{{Module: "db", Why: "stands in for db/password"}}},
+			// A head that deletes the node's placement file: the node returns to the controller's compositions (issue 1126,
+			// the seed's revert, mesh-catalog #526).
+			"returns": {Head: "h1", Verdict: CandidateSame, Returns: ReturnsToController, Same: []string{"app", "node"}},
+			"returns, the controller's differs": {Head: "h1", Verdict: CandidateDiffers, Returns: ReturnsToController, Same: []string{"node"},
+				Differs: []ModuleDiffers{{Module: "app", Resource: "file:/etc/app", Why: "the resource differs"}}, Removed: []string{"old"}},
 		}
-		n := HaveNode{Composed: "sha256:" + strings.Repeat("a", 64), Sealed: []string{"box"}, Candidates: answers}
+		n := HaveNode{Composed: "sha256:" + strings.Repeat("a", 64), Sealed: []string{"box"}, Candidates: answers,
+			Composes: ComposesOwn, ComposesWhy: "the catalogue places it (placement.n1)"}
 		raw, err := EncodeHaveNode(n)
 		if err != nil {
 			t.Fatal(err)
 		}
 		back, err := DecodeHaveNode(raw)
-		if err != nil || !SameHaveNode(back, HaveNode{V: Version, Composed: n.Composed, Sealed: n.Sealed, Candidates: answers}) {
+		if err != nil || !SameHaveNode(back, HaveNode{V: Version, Composed: n.Composed, Sealed: n.Sealed, Candidates: answers,
+			Composes: ComposesOwn, ComposesWhy: n.ComposesWhy}) {
 			t.Fatalf("a node's answers changed on the way: %+v, %v", back, err)
 		}
-		if SameHaveNode(back, HaveNode{V: Version, Composed: n.Composed, Sealed: n.Sealed}) {
+		if SameHaveNode(back, HaveNode{V: Version, Composed: n.Composed, Sealed: n.Sealed, Composes: ComposesOwn, ComposesWhy: n.ComposesWhy}) {
 			t.Error("a node's have without its answers counts as the same")
 		}
+		if SameHaveNode(back, HaveNode{V: Version, Composed: n.Composed, Sealed: n.Sealed, Candidates: answers,
+			Composes: ComposesController, ComposesWhy: n.ComposesWhy}) {
+			t.Error("a node's have composing otherwise counts as the same")
+		}
+		if _, err := EncodeHaveNode(HaveNode{Composes: "both"}); err == nil {
+			t.Error("a node composing neither its own nor the controller's was taken")
+		}
 		// CompareComposed: the bus's user list is left out on both sides; anything else that differs is named.
 		file := func(id, content string) json.RawMessage {
 			return json.RawMessage(`{"id":"` + id + `","type":"file","module":"nats","path":"/etc/` + id + `","mode":"0600","content":"` + content + `"}`)
@@ -269,6 +283,39 @@ func TestPlacement(t *testing.T) {
 				t.Errorf("%s: differs %+v, want %s: %s with both digests", name, c.Differs, tc.resource, tc.why)
 			}
 		}
+		// Issue 1126, the shadow shows its work: every differing resource with both bodies, each value a secret could be
+		// in masked (never a secret in an answer), saying whether the two sides hold the same value.
+		sealedFile := func(id, sealed, mode string) json.RawMessage {
+			return json.RawMessage(`{"id":"` + id + `","type":"file","module":"nats","path":"/etc/` + id + `","mode":"` + mode + `","sealed":"` + sealed + `"}`)
+		}
+		shown := CompareComposedWith(map[string]Composed{"k": comp(sealedFile("a", "box-1", "0600"), sealedFile("b", "box-2", "0600"), file("c", "x"))},
+			[]Composed{comp(sealedFile("a", "box-1", "0644"), sealedFile("b", "box-3", "0600"), file("c", "y"))},
+			func(a, b string) (same, known bool) { return a == "box-2" && b == "box-3", true })
+		if len(shown.Differs) != 1 || len(shown.Differs[0].Bodies) != 3 {
+			t.Fatalf("every differing resource is not shown: %+v", shown.Differs)
+		}
+		for _, row := range []struct{ id, has, hasNot string }{
+			{"a", `"mode":"0600"`, "box-1"},
+			{"b", "another seal of the same value", "box-2"},
+			{"c", `"content":"x"`, ""},
+		} {
+			var body ResourceBodies
+			for _, b := range shown.Differs[0].Bodies {
+				if b.ID == row.id {
+					body = b
+				}
+			}
+			both := body.Composed + body.Running
+			if !strings.Contains(both, row.has) || (row.hasNot != "" && strings.Contains(both, row.hasNot)) {
+				t.Errorf("%s shown as %+v", row.id, body)
+			}
+		}
+		if c, r := MaskedPair(json.RawMessage(`{"env":{"DB_PASSWORD":"hunter2","PORT":"80"},"list":[{"token":"t1"}]}`),
+			json.RawMessage(`{"env":{"DB_PASSWORD":"hunter3","PORT":"81"},"list":[{"token":"t1"}]}`), nil); strings.Contains(c+r, "hunter") ||
+			strings.Contains(c+r, `"t1"`) || !strings.Contains(r, `"PORT":"81"`) || !strings.Contains(c, "<masked: differs>") ||
+			!strings.Contains(c, "<masked: the same on both sides>") {
+			t.Errorf("masked as %s and %s", c, r)
+		}
 		if c := CompareComposed(nil, []Composed{{Node: "novox", Resources: []json.RawMessage{}}}); len(c.Removed) != 1 || c.Removed[0] != "node" {
 			t.Errorf("the node's own composition run and not composed is removed: %+v", c)
 		}
@@ -285,6 +332,8 @@ func TestPlacement(t *testing.T) {
 			"same with an added":  {Head: "h", Verdict: CandidateSame, Added: []ModuleAdded{{Module: "a"}}},
 			"differs refusing":    {Head: "h", Verdict: CandidateDiffers, Removed: []string{"a"}, Refusals: []ModuleRefused{{Module: "b", Why: "x"}}},
 			"refused and modules": {Head: "h", Verdict: CandidateRefused, Refused: "x", Same: []string{"a"}},
+			"returns refusing":    {Head: "h", Verdict: CandidateRefused, Returns: ReturnsToController, Refusals: []ModuleRefused{{Module: "b", Why: "x"}}},
+			"returns refused":     {Head: "h", Verdict: CandidateRefused, Returns: ReturnsToController, Refused: "x"},
 		} {
 			if _, err := EncodeHaveNode(HaveNode{Candidates: map[string]CandidateAnswer{"g": a}}); err == nil {
 				t.Errorf("%s: taken", name)

go/delivery/signers.go

@@ -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) }