Merge pull request 'mesh-grants: publish memberships for new placements now; the user list, assertions and grants in shadow (ADR 0547 milestone 1)' (#53) from fix/1945-memberships into main

Reviewed-on: #53
2026-10-25 22:44:11 +00:00
parent ce7d60cb6e 26ba7404bf
commit 2a856e2a76
16 changed files with 3285 additions and 0 deletions
@@ -0,0 +1,220 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/process"
+)
+
+// requestWithin bounds one request to the bus: a read the bus refuses is answered by no reply, so the bound is how a
+// refusal is told from a slow answer. It is no clock of the part's work: nothing is ever started by it.
+const requestWithin = 10 * time.Second
+
+// bucketOf is the bucket a read names: `<module>.<state>` is `<module>_<state>`.
+func bucketOf(state string) string {
+	at := strings.LastIndex(state, ".")
+	if at <= 0 {
+		return state
+	}
+	return state[:at] + "_" + state[at+1:]
+}
+
+// busReader reads other parts' state on the bus, and keeps every value of a state it watches, so a composition reads
+// those from memory. A bucket it cannot open (refused, or not there yet) is an error of the call, never the end.
+type busReader struct {
+	ctx context.Context
+	js  jetstream.JetStream
+
+	mu      sync.Mutex
+	kvs     map[string]jetstream.KeyValue
+	world   map[string]map[string][]byte
+	settled map[string]bool
+}
+
+func newBusReader(ctx context.Context, js jetstream.JetStream) *busReader {
+	return &busReader{ctx: ctx, js: js, kvs: map[string]jetstream.KeyValue{}, world: map[string]map[string][]byte{},
+		settled: map[string]bool{}}
+}
+
+func (b *busReader) kv(state string) (jetstream.KeyValue, error) {
+	b.mu.Lock()
+	kv, ok := b.kvs[state]
+	b.mu.Unlock()
+	if ok {
+		return kv, nil
+	}
+	ctx, cancel := context.WithTimeout(b.ctx, requestWithin)
+	defer cancel()
+	kv, err := b.js.KeyValue(ctx, bucketOf(state))
+	if err != nil {
+		if errors.Is(err, context.DeadlineExceeded) {
+			err = fmt.Errorf("no answer in %s: a read the bus refuses is answered by none (%w)", requestWithin, err)
+		}
+		return nil, fmt.Errorf("the bucket %s cannot be opened: %w", bucketOf(state), err)
+	}
+	b.mu.Lock()
+	b.kvs[state] = kv
+	b.mu.Unlock()
+	return kv, nil
+}
+
+func (b *busReader) Keys(state string) ([]string, error) {
+	b.mu.Lock()
+	if b.settled[state] {
+		out := make([]string, 0, len(b.world[state]))
+		for k := range b.world[state] {
+			out = append(out, k)
+		}
+		b.mu.Unlock()
+		sort.Strings(out)
+		return out, nil
+	}
+	b.mu.Unlock()
+	kv, err := b.kv(state)
+	if err != nil {
+		return nil, err
+	}
+	ctx, cancel := context.WithTimeout(b.ctx, requestWithin)
+	defer cancel()
+	keys, err := kv.Keys(ctx)
+	if errors.Is(err, jetstream.ErrNoKeysFound) {
+		return []string{}, nil
+	}
+	return keys, err
+}
+
+func (b *busReader) Get(state, key string) ([]byte, bool, error) {
+	b.mu.Lock()
+	if b.settled[state] {
+		v, ok := b.world[state][key]
+		b.mu.Unlock()
+		return v, ok, nil
+	}
+	b.mu.Unlock()
+	kv, err := b.kv(state)
+	if err != nil {
+		return nil, false, err
+	}
+	ctx, cancel := context.WithTimeout(b.ctx, requestWithin)
+	defer cancel()
+	e, err := kv.Get(ctx, key)
+	if errors.Is(err, jetstream.ErrKeyNotFound) {
+		return nil, false, nil
+	}
+	if err != nil {
+		return nil, false, err
+	}
+	return e.Value(), true, nil
+}
+
+// Watch keeps every value of a state from now on and hands each change after what stands to changed; it returns once
+// what stands is held. The watch ending is handed to ended, and the state is read from the bus again until watched.
+func (b *busReader) Watch(state string, changed func(string, []byte), ended func(error)) error {
+	kv, err := b.kv(state)
+	if err != nil {
+		return err
+	}
+	w, err := kv.WatchAll(b.ctx)
+	if err != nil {
+		return fmt.Errorf("the bucket %s cannot be watched: %w", bucketOf(state), err)
+	}
+	put := func(e jetstream.KeyValueEntry) {
+		b.mu.Lock()
+		defer b.mu.Unlock()
+		if b.world[state] == nil {
+			b.world[state] = map[string][]byte{}
+		}
+		if e.Operation() == jetstream.KeyValuePut {
+			b.world[state][e.Key()] = e.Value()
+		} else {
+			delete(b.world[state], e.Key())
+		}
+	}
+	lost := func(err error) {
+		w.Stop()
+		b.mu.Lock()
+		b.settled[state] = false
+		delete(b.world, state)
+		delete(b.kvs, state)
+		b.mu.Unlock()
+		ended(err)
+	}
+	settling, stop := context.WithTimeout(b.ctx, requestWithin)
+	defer stop()
+settle:
+	for {
+		select {
+		case <-settling.Done():
+			w.Stop()
+			if b.ctx.Err() != nil {
+				return b.ctx.Err()
+			}
+			return fmt.Errorf("the watch of %s handed nothing in %s: a watch the bus refuses is answered by none", bucketOf(state), requestWithin)
+		case e, ok := <-w.Updates():
+			if !ok {
+				w.Stop()
+				return fmt.Errorf("the watch of %s ended before it held what stands", bucketOf(state))
+			}
+			if e == nil {
+				break settle
+			}
+			put(e)
+		}
+	}
+	b.mu.Lock()
+	b.settled[state] = true
+	b.mu.Unlock()
+	go func() {
+		for {
+			select {
+			case <-b.ctx.Done():
+				w.Stop()
+				return
+			case e, ok := <-w.Updates():
+				if !ok {
+					lost(errors.New("the server ended it"))
+					return
+				}
+				if e != nil {
+					put(e)
+					var value []byte
+					if e.Operation() == jetstream.KeyValuePut {
+						value = e.Value()
+					}
+					changed(e.Key(), value)
+				}
+			}
+		}
+	}()
+	return nil
+}
+
+// ownStore is the part's own state on its process connection: a state it did not announce, or one the bus refuses,
+// fails the call, named.
+type ownStore struct{ c *process.Conn }
+
+func (s ownStore) Get(state, key string) ([]byte, uint64, bool, error) {
+	e, err := s.c.State(state).Get(key)
+	if err != nil || e == nil {
+		return nil, 0, false, err
+	}
+	return e.Value, e.Revision, true, nil
+}
+
+func (s ownStore) Put(state, key string, value []byte) (uint64, error) {
+	return s.c.State(state).Put(key, json.RawMessage(value))
+}
+
+// emitting is the process connection as the part's emitter: its events, with no options.
+type emitting struct{ c *process.Conn }
+
+func (e emitting) Emit(event string, body any) error { return e.c.Emit(event, body) }
@@ -0,0 +1,128 @@
+// Command mesh-grants is the grants part (novox/hq ADR 0547 clauses 5 to 8, issue 1945): a process on its own bus
+// credential that watches placement, the assigner's wants, the indexer's manifests, the builder's builds, mesh-config's
+// resolved values and the node agents' haves, and on every change composes each assignment's membership, the bus's user
+// list and each manifest's buckets, logs and streams with the bus composer the controller uses (mesh-sdk buscompose).
+//
+// **Memberships are published for real** (the operator, 2026-10-25 22:31): since release 6 nobody publishes them, so a
+// module placed since cannot serve its seat or reach a new state. Each is published on the assignments stream only when
+// it differs from the one last published there. **The user list, the assertions and the grants stay in shadow** until
+// the operator's take-over, which this milestone always refuses: they are composed, compared with what the bus loaded
+// and holds (through the bus module's own read tools) and kept in the part's own state, and take no effect.
+//
+// It holds no timer, and never exits for a refused read, write or publish: a refusal is said and tried again at the next
+// event.
+//
+// **No seat in this milestone.** ADR 0547 clause 5 gives the part the seat `mesh-grants`; a `mesh-*` seat must be in
+// mesh-sdk's own seat list, which the running controller's composer does not know, so the part serves module tools
+// (grants_*) and claims no seat until take-over. The composer grants the membership publish by the module's name,
+// mesh-grants.
+//
+// Started by the tool runner, with no credential of its own, it serves those tools (a process never serves, ADR 0436).
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"os/signal"
+	"strings"
+	"syscall"
+
+	"github.com/nats-io/nats.go"
+	"github.com/nats-io/nats.go/jetstream"
+
+	stdio "git.novox.be/novox/mesh-sdk/go"
+	"git.novox.be/novox/mesh-sdk/go/announce"
+	"git.novox.be/novox/mesh-sdk/go/process"
+
+	"mesh-grants/internal/grants"
+)
+
+func main() {
+	if os.Getenv("MESH_BROKER_FILE") == "" {
+		if err := serveTools(); err != nil {
+			fmt.Fprintln(os.Stderr, "mesh-grants:", err)
+			os.Exit(1)
+		}
+		return
+	}
+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+	defer stop()
+	if err := run(ctx, os.Getenv, os.Stderr); err != nil {
+		fmt.Fprintln(os.Stderr, "mesh-grants:", err)
+		os.Exit(1)
+	}
+}
+
+// keptStates is what the part keeps, each readable (ADR 0495 §2-§3): the view and a session read them.
+func keptStates() []announce.State {
+	var out []announce.State
+	for _, s := range grants.States {
+		out = append(out, announce.State{Name: s, Readable: true})
+	}
+	return out
+}
+
+// run is the process: it returns when ctx ends, or when it has no credential or cannot dial the bus at all. A bucket or
+// read the bus refuses never ends it.
+func run(ctx context.Context, getenv func(string) string, logOut io.Writer) error {
+	logger := log.New(logOut, "mesh-grants: ", log.LstdFlags)
+	path := strings.TrimSpace(getenv("MESH_BROKER_FILE"))
+	if path == "" {
+		return errors.New("MESH_BROKER_FILE is not set, so there is no credential to read the bus with")
+	}
+	account, err := process.ReadAccount(path)
+	if err != nil {
+		return err
+	}
+	f := &grants.Follower{Logf: logger.Printf}
+	conn, err := process.Connect(account, nats.Name(account.Node+"."+account.Module), nats.RetryOnFailedConnect(true),
+		nats.ReconnectHandler(func(*nats.Conn) { f.Wake() }))
+	if err != nil {
+		return err
+	}
+	defer conn.Close()
+	if err := conn.Keeps(keptStates()...); err != nil {
+		logger.Printf("what the part keeps could not be said on the bus, so its readers are not granted until it is: %v", err)
+	}
+	// The reads of other parts' state, on a connection of the same account: a read the bus refuses is said and composed
+	// past (busReader), never the end of the process.
+	opts := []nats.Option{
+		nats.Name(account.Node + "." + account.Module + ".reads"),
+		nats.UserInfo(account.User, account.Password),
+		nats.CustomInboxPrefix(account.InboxPrefix()),
+		nats.MaxReconnects(-1),
+		nats.RetryOnFailedConnect(true),
+		nats.ReconnectHandler(func(*nats.Conn) { f.Wake() }),
+	}
+	if strings.TrimSpace(account.Fingerprint) != "" {
+		opts = append(opts, nats.Secure(process.PinnedToFingerprint(account.Fingerprint)))
+	}
+	nc, err := nats.Connect(account.URL, opts...)
+	if err != nil {
+		return fmt.Errorf("connecting to the bus: %w", err)
+	}
+	defer nc.Close()
+	js, err := jetstream.New(nc)
+	if err != nil {
+		return err
+	}
+	bus := newBusReader(ctx, js)
+	f.Part = &grants.Part{Read: bus, Call: conn, Store: ownStore{conn}, Emit: emitting{conn},
+		Publish: memberships{ctx: ctx, nc: nc, js: js}}
+	f.Watch = bus
+	f.Asked = func(wake func()) error {
+		return conn.State(grants.StateUserList).Watch(grants.KeyAsked, func(c stdio.StateChange) error {
+			if !c.Current {
+				wake()
+			}
+			return nil
+		})
+	}
+	logger.Printf("started on the account %s: publishing memberships; the user list, assertions and grants in shadow", account.User)
+	f.Run(ctx)
+	return nil
+}
@@ -0,0 +1,55 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strconv"
+
+	"github.com/nats-io/nats.go"
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/membership"
+)
+
+// memberships publishes each membership on the assignments stream, last per subject, over the one last read there
+// (ExpectLastSequencePerSubject, so a membership another writer published meanwhile is not overwritten, issues 930 and
+// 934), and reads the last one by a direct get of its subject. The one place the part publishes on the bus.
+type memberships struct {
+	ctx context.Context
+	nc  *nats.Conn
+	js  jetstream.JetStream
+}
+
+func (m memberships) LastMembership(node, module string) ([]byte, uint64, bool, error) {
+	ctx, cancel := context.WithTimeout(m.ctx, requestWithin)
+	defer cancel()
+	msg, err := m.nc.RequestWithContext(ctx, membership.DirectGetSubject(node, module), nil)
+	if err != nil {
+		if errors.Is(err, context.DeadlineExceeded) {
+			err = fmt.Errorf("no answer in %s: a read the bus refuses is answered by none (%w)", requestWithin, err)
+		}
+		return nil, 0, false, err
+	}
+	switch status := msg.Header.Get("Status"); status {
+	case "":
+	case "404":
+		return nil, 0, false, nil
+	default:
+		return nil, 0, false, fmt.Errorf("the assignments stream answered %s %s", status, msg.Header.Get("Description"))
+	}
+	seq, err := strconv.ParseUint(msg.Header.Get("Nats-Sequence"), 10, 64)
+	if err != nil {
+		return nil, 0, false, fmt.Errorf("the membership of %s on %s carries no sequence", module, node)
+	}
+	return msg.Data, seq, true, nil
+}
+
+func (m memberships) PublishMembership(node, module string, body []byte, after uint64) error {
+	ctx, cancel := context.WithTimeout(m.ctx, requestWithin)
+	defer cancel()
+	if _, err := m.js.Publish(ctx, membership.Subject(node, module), body, jetstream.WithExpectLastSequencePerSubject(after)); err != nil {
+		return fmt.Errorf("the membership of %s on %s after sequence %d: %w", module, node, after, err)
+	}
+	return nil
+}
@@ -0,0 +1,116 @@
+package main
+
+import (
+	"encoding/json"
+
+	stdio "git.novox.be/novox/mesh-sdk/go"
+
+	"mesh-grants/internal/grants"
+)
+
+// The part's tools, served through the tool runner from its bundle (ADR 0436: a process never serves). They read and
+// write through the runtime as the module: its own states, the reads its manifest names, the bus module's read tools.
+
+// runtimeReader reads another part's state through the runtime, `<module>.<state>`.
+type runtimeReader struct{}
+
+func (runtimeReader) Keys(state string) ([]string, error) { return stdio.State(state).Keys() }
+
+func (runtimeReader) Get(state, key string) ([]byte, bool, error) {
+	e, err := stdio.State(state).Get(key)
+	if err != nil || e == nil {
+		return nil, false, err
+	}
+	return e.Value, true, nil
+}
+
+// runtimeStore is the part's own state through the runtime.
+type runtimeStore struct{}
+
+func (runtimeStore) Get(state, key string) ([]byte, uint64, bool, error) {
+	e, err := stdio.State(state).Get(key)
+	if err != nil || e == nil {
+		return nil, 0, false, err
+	}
+	return e.Value, e.Revision, true, nil
+}
+
+func (runtimeStore) Put(state, key string, value []byte) (uint64, error) {
+	return stdio.State(state).Put(key, json.RawMessage(value))
+}
+
+// runtimeBus calls tools and says events through the runtime.
+type runtimeBus struct{}
+
+func (runtimeBus) Call(key string, body any) (json.RawMessage, error) { return stdio.Ask(key, body) }
+func (runtimeBus) Emit(event string, body any) error                  { return stdio.Emit(event, body) }
+
+func schema(properties map[string]string, required ...string) map[string]any {
+	props := map[string]any{}
+	for name, description := range properties {
+		props[name] = map[string]any{"type": "string", "description": description}
+	}
+	out := map[string]any{"type": "object", "properties": props}
+	if len(required) > 0 {
+		out["required"] = required
+	}
+	return out
+}
+
+// toolsOf are the part's tools over a part (grants.Tools names them).
+func toolsOf(p *grants.Part) []stdio.Tool {
+	return []stdio.Tool{
+		{Name: grants.ToolGrants, Description: "What the grants part holds of grants (novox/hq ADR 0547 clause 6): in this milestone it " +
+			"writes none (grants.<module>.<fp> from the third milestone, clause 5), and shows beside it the grants the controller " +
+			"wrote (mesh-controller_grants), all or one module's with the accounts each names. Read-only.",
+			Input: schema(map[string]string{"module": "one module"}),
+			Run:   func(a map[string]any) (any, error) { return p.Grants(grants.Answer(a, "module")) }},
+		{Name: grants.ToolMembership, Description: "One module's membership on one node (ADR 0547 clause 6): as composed now from the " +
+			"bus's records with the bus composer, and what the part's process published of it at its last pass (published, " +
+			"unchanged, or why not: a shadow difference names what publishing would lose), with what the composition cannot " +
+			"read. Read-only.",
+			Input: schema(map[string]string{"node": "the machine", "module": "the module"}, "node", "module"),
+			Run: func(a map[string]any) (any, error) {
+				return p.MembershipOf(grants.Answer(a, "node"), grants.Answer(a, "module"))
+			}},
+		{Name: grants.ToolUserList, Description: "The bus's user list in shadow (ADR 0547 clauses 6 and 8): the list the grants part " +
+			"composed (digest, revision, users), what the bus node says it loaded (source, revision, digest, users, error), and how " +
+			"they differ: users added, users dropped (and of those, gone from placement), each user's grant differences, the " +
+			"assignments left out, and every input the bus does not carry, named. Read-only.",
+			Run: func(map[string]any) (any, error) { return p.UserList() }},
+		{Name: grants.ToolComposeNow, Description: "Compose again now (ADR 0547 clause 6), as the part does on every change it hears: asks " +
+			"the part's process (which alone holds the grant to publish a membership) to compose the memberships, the user list and " +
+			"the assertions, publish each membership that differs from the one last published, and keep what changed in its own " +
+			"state (one revision when an input changed, none when not), saying user-list-changed and membership-changed. Answers " +
+			"the ask and the last pass; grants_user_list shows the pass that answers it. A membership is published only when it is " +
+			"the first or only adds to the last one; any loss stays a shadow difference, named. The user list, assertions and " +
+			"grants stay in shadow. It cannot ask the controller to write a module's grant again: the controller serves no such " +
+			"verb, and the answer says so.",
+			Run: func(a map[string]any) (any, error) { return p.AskCompose(stdio.CallerOf(a)) }},
+		{Name: grants.ToolAssert, Description: "One module's buckets, logs and streams (ADR 0547 clause 6), composed from its manifest at " +
+			"the indexer's trunk with their limits, beside what the bus holds (through the bus module's nats_streams). In shadow it " +
+			"asserts nothing, and says so.",
+			Input: schema(map[string]string{"module": "the module"}, "module"),
+			Run:   func(a map[string]any) (any, error) { return p.AssertOne(grants.Answer(a, "module")) }},
+		{Name: grants.ToolTakeOver, Description: "The operator's switch to the grants part's list (ADR 0547 clause 8), refused without the " +
+			"operator's credential (a person's account), refused while any user of the shadow list differs from the loaded list (but " +
+			"those placement no longer names), naming them; in this milestone always refused, since the enrolment users and the " +
+			"persons cannot be composed. Every ask is recorded in the part's state takeover.",
+			Input: schema(map[string]string{"why": "why, kept with the act"}, "why"),
+			Run: func(a map[string]any) (any, error) {
+				return nil, p.TakeOver(stdio.CallerOf(a), grants.Answer(a, "why"))
+			}},
+		{Name: grants.ToolHandBack, Description: "The operator's switch back to the controller's list (ADR 0547 clause 8), refused without " +
+			"the operator's credential; in shadow there is nothing to hand back, and it says so. Every ask is recorded.",
+			Input: schema(map[string]string{"why": "why, kept with the act"}, "why"),
+			Run: func(a map[string]any) (any, error) {
+				return nil, p.HandBack(stdio.CallerOf(a), grants.Answer(a, "why"))
+			}},
+	}
+}
+
+// serveTools serves the tools to the runtime until it stops.
+func serveTools() error {
+	p := &grants.Part{Read: runtimeReader{}, Call: runtimeBus{}, Store: runtimeStore{}, Emit: runtimeBus{}}
+	return stdio.Serve("", toolsOf(p))
+}
@@ -0,0 +1,16 @@
+module mesh-grants
+
+go 1.26.0
+
+require (
+	git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261025215021-b7b5c6ef27a0
+	github.com/nats-io/nats.go v1.54.0
+)
+
+require (
+	github.com/klauspost/compress v1.20.0 // indirect
+	github.com/nats-io/nkeys v0.4.16 // indirect
+	github.com/nats-io/nuid v1.0.1 // indirect
+	golang.org/x/crypto v0.57.0 // indirect
+	golang.org/x/sys v0.48.0 // indirect
+)
@@ -0,0 +1,26 @@
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261025215021-b7b5c6ef27a0 h1:8dKGrZzPthx/jZlV9Bjm2lWGNORUTETmq2vxKN+MRV0=
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261025215021-b7b5c6ef27a0/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
+github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op h1:Z/MZK75wC/NSrkgqeNIa7jexam9uWzhLmFTSCPI/kn0=
+github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op/go.mod h1:FQyySiasQQM8735Ddel3MRojmy4dA1IqCeyJ5jmPMbI=
+github.com/google/go-tpm v0.9.8 h1:slArAR9Ft+1ybZu0lBwpSmpwhRXaa85hWtMinMyRAWo=
+github.com/google/go-tpm v0.9.8/go.mod h1:h9jEsEECg7gtLis0upRBQU+GhYVH6jMjrFxI8u6bVUY=
+github.com/klauspost/compress v1.20.0 h1:a3C1ke2ohxFymNlb2HWAHjDeKCI90scRskErZkR0ezA=
+github.com/klauspost/compress v1.20.0/go.mod h1:LUdAzn7YLVvxLpc7y3V1m40wESHTgc1422pwwBSKYuI=
+github.com/minio/highwayhash v1.0.4 h1:asJizugGgchQod2ja9NJlGOWq4s7KsAWr5XUc9Clgl4=
+github.com/minio/highwayhash v1.0.4/go.mod h1:GGYsuwP/fPD6Y9hMiXuapVvlIUEhFhMTh0rxU3ik1LQ=
+github.com/nats-io/jwt/v2 v2.8.1 h1:V0xpGuD/N8Mi+fQNDynXohVvp7ZztevW5io8CUWlPmU=
+github.com/nats-io/jwt/v2 v2.8.1/go.mod h1:nWnOEEiVMiKHQpnAy4eXlizVEtSfzacZ1Q43LIRavZg=
+github.com/nats-io/nats-server/v2 v2.11.17 h1:GKEghcFK6A+aFx11Yf1LjgLC3txAwvyhnYzhBIQZA8I=
+github.com/nats-io/nats-server/v2 v2.11.17/go.mod h1:B1sFVz4StNosQ903ak4N1G01Fl/9f8e06mXpFIE2K24=
+github.com/nats-io/nats.go v1.54.0 h1:vsXoOxjHp/GmPUN+EcI7uOf/uB+iAP+kEsAFNQN0yzA=
+github.com/nats-io/nats.go v1.54.0/go.mod h1:y+DZoD1oBOYfZTU681eTUiUjI0vbqYGixNVFHcjHJ0k=
+github.com/nats-io/nkeys v0.4.16 h1:rd5oAuLOb8mnAycB0xleuEBNS1pVVnN0fv/FF34Eypg=
+github.com/nats-io/nkeys v0.4.16/go.mod h1:llLgWoI0o4z/Q57q2R1kHfmocyhGV6VG/U18Glg1Afs=
+github.com/nats-io/nuid v1.0.1 h1:5iA8DT8V7q8WK2EScv2padNa/rTESc1KdnPw4TC2paw=
+github.com/nats-io/nuid v1.0.1/go.mod h1:19wcPz3Ph3q0Jbyiqsd0kePYG7A95tJPxeL+1OSON2c=
+golang.org/x/crypto v0.57.0 h1:3ZVCjf8Ggz7zneR/EHRVx68Ctf+2pmIMP2UFhh9cC6M=
+golang.org/x/crypto v0.57.0/go.mod h1:Fdz0i5U6CoizGwLda9DttjSk6qlZo25zYNtR+ycvuZA=
+golang.org/x/sys v0.48.0 h1:bbX/i/6MgT9BVLM9RT1thmxL04yeTAhbEz4SyadbXoo=
+golang.org/x/sys v0.48.0/go.mod h1:hNLxWAXmnKAxqDtdwIYC4bM9oQPEecfsnNMuSxOs3og=
+golang.org/x/time v0.15.0 h1:bbrp8t3bGUeFOx08pvsMYRTCVSMk89u4tKbNOZbp88U=
+golang.org/x/time v0.15.0/go.mod h1:Y4YMaQmXwGQZoFaVFk4YpCt4FLQMYKZe9oeV/f4MSno=
@@ -0,0 +1,760 @@
+package manifest
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"slices"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+
+	"mesh-grants/internal/grants"
+)
+
+// fakeBus is the bus as the part sees it: other parts' states to read (refusing those named), the bus module's read
+// tools, the part's own states and its events. It records every write, call and event, so a row can prove nothing was
+// published or asserted.
+type fakeBus struct {
+	mu       sync.Mutex
+	states   map[string]map[string][]byte
+	refused  map[string]bool
+	loaded   []grants.User
+	streams  []map[string]any
+	own      map[string]map[string][]byte
+	revs     map[string]uint64
+	refuseTo map[string]bool
+	calls    []string
+	events   []string
+	writes   []string
+	// The assignments stream: each subject's last membership and sequence, every publish, and whether it is refused.
+	stream    map[string][]byte
+	seqs      map[string]uint64
+	seq       uint64
+	publishes []string
+	refusePub bool
+	// hold, when set, keeps every nats_users call waiting until it is closed: a pass waiting on the bus.
+	hold chan struct{}
+}
+
+func (b *fakeBus) LastMembership(node, module string) ([]byte, uint64, bool, error) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	subject := "mesh.assignment." + node + "." + module
+	v, ok := b.stream[subject]
+	return v, b.seqs[subject], ok, nil
+}
+
+func (b *fakeBus) PublishMembership(node, module string, body []byte, after uint64) error {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	subject := "mesh.assignment." + node + "." + module
+	if b.refusePub {
+		return errors.New("Permissions Violation for Publish to " + subject)
+	}
+	if b.seqs[subject] != after {
+		return fmt.Errorf("wrong last sequence for %s: %d", subject, b.seqs[subject])
+	}
+	if b.stream == nil {
+		b.stream, b.seqs = map[string][]byte{}, map[string]uint64{}
+	}
+	b.seq++
+	b.stream[subject], b.seqs[subject] = body, b.seq
+	b.publishes = append(b.publishes, subject)
+	return nil
+}
+
+func newFakeBus() *fakeBus {
+	return &fakeBus{states: map[string]map[string][]byte{}, refused: map[string]bool{}, own: map[string]map[string][]byte{},
+		revs: map[string]uint64{}, refuseTo: map[string]bool{}}
+}
+
+func (b *fakeBus) put(state, key string, v any) {
+	raw, err := json.Marshal(v)
+	if err != nil {
+		panic(err)
+	}
+	if b.states[state] == nil {
+		b.states[state] = map[string][]byte{}
+	}
+	b.states[state][key] = raw
+}
+
+func (b *fakeBus) Keys(state string) ([]string, error) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if b.refused[state] {
+		return nil, errors.New("Permissions Violation for Publish to $JS.API.STREAM.INFO.KV_" + state)
+	}
+	var out []string
+	for k := range b.states[state] {
+		out = append(out, k)
+	}
+	slices.Sort(out)
+	return out, nil
+}
+
+func (b *fakeBus) Get(state, key string) ([]byte, bool, error) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if b.refused[state] {
+		return nil, false, errors.New("refused")
+	}
+	v, ok := b.states[state][key]
+	return v, ok, nil
+}
+
+func (b *fakeBus) Call(key string, body any) (json.RawMessage, error) {
+	b.mu.Lock()
+	hold := b.hold
+	b.mu.Unlock()
+	if hold != nil && key == grants.CallUsers {
+		<-hold
+	}
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	b.calls = append(b.calls, key)
+	args, _ := body.(map[string]any)
+	switch key {
+	case grants.CallUsers:
+		part, _ := args["user"].(string)
+		if part == "" {
+			var names []map[string]any
+			for _, u := range b.loaded {
+				names = append(names, map[string]any{"user": u.User, "publish_grants": len(u.Publish)})
+			}
+			return json.Marshal(map[string]any{"users": names})
+		}
+		var out []grants.User
+		for _, u := range b.loaded {
+			if strings.Contains(u.User, part) {
+				out = append(out, u)
+			}
+		}
+		return json.Marshal(map[string]any{"users": out})
+	case grants.CallStreams:
+		return json.Marshal(map[string]any{"detail": b.streams})
+	}
+	return nil, fmt.Errorf("no tool %s", key)
+}
+
+func (b *fakeBus) ownGet(state, key string) ([]byte, uint64, bool, error) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	v, ok := b.own[state][key]
+	return v, b.revs[state+"/"+key], ok, nil
+}
+
+type ownStore struct{ b *fakeBus }
+
+func (s ownStore) Get(state, key string) ([]byte, uint64, bool, error) { return s.b.ownGet(state, key) }
+func (s ownStore) Put(state, key string, value []byte) (uint64, error) {
+	b := s.b
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if b.refuseTo[state] {
+		return 0, errors.New("Permissions Violation for Publish to $KV.mesh-grants_" + state)
+	}
+	b.writes = append(b.writes, state)
+	if b.own[state] == nil {
+		b.own[state] = map[string][]byte{}
+	}
+	b.own[state][key] = value
+	b.revs[state+"/"+key]++
+	return b.revs[state+"/"+key], nil
+}
+
+func (b *fakeBus) Emit(event string, _ any) error {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	b.events = append(b.events, event)
+	return nil
+}
+
+func (b *fakeBus) count(key string) int {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	n := 0
+	for _, c := range b.calls {
+		if c == key {
+			n++
+		}
+	}
+	return n
+}
+
+// manifestOf is a fixture manifest of one module, in the indexer's two buckets.
+func (b *fakeBus) manifestOf(module, raw string) {
+	digest := delivery.ManifestDigest([]byte(raw))
+	b.put(grants.ReadManifests, digest, delivery.Manifest{V: delivery.Version, Module: module, JSON: raw})
+	b.put(grants.ReadModules, module, delivery.Module{V: delivery.Version, FP2: "src2:" + strings.Repeat("ab", 32), Manifest: digest, Repository: "novox/x", Commit: "c"})
+}
+
+func (b *fakeBus) assign(node, module string) {
+	b.put(grants.ReadAssignments, node+"."+module, map[string]any{"node": node, "module": module, "assigned": "2026-10-25T20:00:00Z"})
+}
+
+const (
+	natsManifest = `{"module":"nats","version":"1","claims":[{"name":"mesh-broker"}],"own-secrets":{"broker":"/var/lib/nats/broker"}}`
+	xManifest    = `{"module":"mod-x","version":"1","own-secrets":{"broker":"/var/lib/x/broker"},"state":[{"name":"kept","history":3}],` +
+		`"streams":[{"name":"things","events":["thing.added"],"max-age-days":2,"max-mib":5}],"logs":[{"name":"history"}]}`
+	yManifest = `{"module":"mod-y","version":"1","own-secrets":{"broker":"/var/lib/y/broker"},"reads":["mod-x.kept"]}`
+)
+
+// fixture is a mesh of two machines: a runs the bus and mod-x, b runs mod-y; the bus node's agent loaded a list.
+func fixture() *fakeBus {
+	b := newFakeBus()
+	b.manifestOf("nats", natsManifest)
+	b.manifestOf("mod-x", xManifest)
+	b.manifestOf("mod-y", yManifest)
+	b.assign("a", "nats")
+	b.assign("a", "mod-x")
+	b.assign("b", "mod-y")
+	b.put(grants.ReadAssignments, "b.gone", map[string]any{"node": "b", "module": "gone", "assigned": "2026-10-01T00:00:00Z", "ended": "2026-10-02T00:00:00Z"})
+	b.put(grants.ReadHave, "a.node", map[string]any{"v": 1})
+	b.put(grants.ReadHave, "b.node", map[string]any{"v": 1})
+	b.put(grants.ReadHave, "a.nats", delivery.Have{V: delivery.Version, Phase: delivery.PhaseRunning, Health: delivery.HealthOK,
+		UserList: &delivery.UserListWritten{Source: "a.nats.src2", Revision: 7, Wanted: "sha256:aa", Digest: "sha256:aa", Users: 6}})
+	b.put(grants.ReadControllerGrant, "mod-x.0123456789ab0123456789ab0123456789ab0123456789ab0123456789ab0123", delivery.ControllerGrant{V: delivery.Version, Accounts: []string{"a.mod-x"}})
+	return b
+}
+
+func partOn(b *fakeBus) *grants.Part {
+	return &grants.Part{Read: b, Call: b, Store: ownStore{b}, Emit: b, Publish: b, Now: func() time.Time { return time.Date(2026, 10, 25, 22, 0, 0, 0, time.UTC) }}
+}
+
+// shadowOf is the list the part composes from b's records now.
+func shadowOf(t *testing.T, b *fakeBus) []grants.User {
+	t.Helper()
+	recs, _ := grants.Records(grants.ReadInputs(b, &grants.Manifests{}))
+	users, err := grants.ComposeUsers(recs)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return users
+}
+
+func names(us []grants.User) []string {
+	var out []string
+	for _, u := range us {
+		out = append(out, u.User)
+	}
+	return out
+}
+
+func gapNamed(gs []grants.Gap, input string) bool {
+	return slices.ContainsFunc(gs, func(g grants.Gap) bool { return strings.Contains(g.Input, input) })
+}
+
+// TestGrants is the grants part's one table of checks (ADR 0547 clauses 5 to 8 in shadow, issue 1945): its manifest,
+// the shadow list composed from bus values, the compare, each tool, that nothing is published or asserted, and that a
+// refused read or write never stops it.
+func TestGrants(t *testing.T) {
+	t.Run("manifest", func(t *testing.T) {
+		raw, err := os.ReadFile("module.json")
+		if err != nil {
+			t.Fatal(err)
+		}
+		m, err := catalogue.ParseManifest(raw)
+		if err != nil {
+			t.Fatalf("mesh-sdk's manifest reader refuses the manifest: %v", err)
+		}
+		if m.Module != "mesh-grants" || len(m.Claims) != 0 {
+			t.Errorf("module %q claims %v: the part claims no seat until mesh-sdk's seat list names mesh-grants", m.Module, m.Claims)
+		}
+		for _, row := range []struct {
+			what      string
+			got, want []string
+		}{
+			{"reads", m.Reads, grants.Reads},
+			{"invokes", m.Invokes, grants.Invokes},
+			{"emits", m.Emits, grants.Emits},
+			{"tools", m.Tools, grants.Tools},
+		} {
+			if !slices.Equal(slices.Sorted(slices.Values(row.got)), slices.Sorted(slices.Values(row.want))) {
+				t.Errorf("%s = %v, the program's are %v", row.what, row.got, row.want)
+			}
+		}
+		var states []string
+		for _, s := range m.State {
+			states = append(states, s.Name)
+		}
+		if !slices.Equal(slices.Sorted(slices.Values(states)), grants.States) {
+			t.Errorf("state = %v, want %v", states, grants.States)
+		}
+		if _, ok := m.OwnSecrets["broker"]; !ok || len(m.OwnSecrets) != 1 || m.SecretsOwner != "mesh-grants" {
+			t.Errorf("own-secrets %v owner %q: a credential of its own, broker", m.OwnSecrets, m.SecretsOwner)
+		}
+	})
+
+	t.Run("no timer, no create, a publish only of memberships", func(t *testing.T) {
+		forbidden := []string{"time.Tick", "time.NewTicker", "time.Sleep", "time.After", "time.NewTimer", "time.AfterFunc",
+			"PublishMsg", "CreateStream", "CreateKeyValue", "CreateOrUpdate", "UpdateStream", "UpdateKeyValue",
+			"CreateObjectStore", "EnsureStream", "RaiseBuckets", "RaiseLogs", ".Create("}
+		// The one publish: a membership, on its own subject, in publish.go.
+		publishOnly := filepath.Join("cmd", "mesh-grants", "publish.go")
+		files := 0
+		for _, root := range []string{"cmd", "internal"} {
+			err := filepath.WalkDir(root, func(path string, d fs.DirEntry, err error) error {
+				if err != nil || d.IsDir() || !strings.HasSuffix(path, ".go") || strings.HasSuffix(path, "_test.go") {
+					return err
+				}
+				files++
+				src, err := os.ReadFile(path)
+				if path != publishOnly && (strings.Contains(string(src), ".Publish(") || strings.Contains(string(src), "mesh.assignment")) {
+					t.Errorf("%s publishes: only publish.go publishes, and only memberships", path)
+				}
+				if path == publishOnly && strings.Count(string(src), ".Publish(") != 1 {
+					t.Errorf("publish.go publishes other than one membership")
+				}
+				for _, f := range forbidden {
+					if strings.Contains(string(src), f) {
+						t.Errorf("%s holds %s: the part holds no timer and creates or asserts nothing", path, f)
+					}
+				}
+				return err
+			})
+			if err != nil {
+				t.Fatal(err)
+			}
+		}
+		if files < 8 {
+			t.Fatalf("read %d source files, want the program's", files)
+		}
+	})
+
+	t.Run("shadow list from bus values", func(t *testing.T) {
+		for _, row := range []struct {
+			name  string
+			bend  func(*fakeBus)
+			users []string
+			gap   string
+		}{
+			{"every record on the bus", func(*fakeBus) {},
+				[]string{"a.mod-x", "a.nats", "b.mod-y", "controller", "node.a", "node.b"}, "enrolment tokens"},
+			{"a manifest missing is a gap and its user is left out", func(b *fakeBus) { delete(b.states[grants.ReadModules], "mod-y") },
+				[]string{"a.mod-x", "a.nats", "controller", "node.a", "node.b"}, "manifest of mod-y"},
+			{"a want's built manifest is composed, not the trunk's", func(b *fakeBus) {
+				built := strings.Replace(xManifest, `"history":3}]`, `"history":3},{"name":"newer"}]`, 1)
+				digest := delivery.ManifestDigest([]byte(built))
+				b.put(grants.ReadManifests, digest, delivery.Manifest{V: delivery.Version, Module: "mod-x", JSON: built})
+				fp := "src2:" + strings.Repeat("cd", 32)
+				b.put(grants.ReadWants, "want.a.mod-x", delivery.Want{V: delivery.Version, FP: fp, Composed: "sha256:" + strings.Repeat("ef", 32)})
+				key, _ := delivery.BuilderBuildKey("mod-x", fp)
+				b.put(grants.ReadBuilds, key, map[string]any{"v": delivery.Version, "state": "done", "manifest": digest})
+			}, []string{"a.mod-x", "a.nats", "b.mod-y", "controller", "node.a", "node.b"}, "enrolment tokens"},
+			{"placement refused is a gap; the machines come from the haves", func(b *fakeBus) { b.refused[grants.ReadAssignments] = true },
+				[]string{"controller", "node.a", "node.b"}, grants.ReadAssignments},
+		} {
+			t.Run(row.name, func(t *testing.T) {
+				b := fixture()
+				row.bend(b)
+				in := grants.ReadInputs(b, &grants.Manifests{})
+				recs, left := grants.Records(in)
+				users, err := grants.ComposeUsers(recs)
+				if err != nil {
+					t.Fatal(err)
+				}
+				if got := names(users); !slices.Equal(got, row.users) {
+					t.Errorf("users = %v, want %v", got, row.users)
+				}
+				if !gapNamed(append(in.Gaps, left...), row.gap) {
+					t.Errorf("gaps %v name no %q", in.Gaps, row.gap)
+				}
+				if strings.HasPrefix(row.name, "a want's") {
+					x := users[slices.IndexFunc(users, func(u grants.User) bool { return u.User == "a.mod-x" })]
+					if !slices.Contains(x.Publish, "$KV.mod-x_newer.>") {
+						t.Errorf("a.mod-x is not granted the state its wanted build declares: %v", x.Publish)
+					}
+				}
+			})
+		}
+		b := fixture()
+		users := shadowOf(t, b)
+		y := users[slices.IndexFunc(users, func(u grants.User) bool { return u.User == "b.mod-y" })]
+		if !slices.Contains(y.Publish, "$JS.API.DIRECT.GET.KV_mod-x_kept.>") {
+			t.Errorf("b.mod-y reads mod-x.kept and is not granted its direct get: %v", y.Publish)
+		}
+	})
+
+	t.Run("compare", func(t *testing.T) {
+		b := fixture()
+		shadow := shadowOf(t, b)
+		in := grants.ReadInputs(b, &grants.Manifests{})
+		changed := slices.Clone(shadow)
+		x := slices.IndexFunc(changed, func(u grants.User) bool { return u.User == "a.mod-x" })
+		changed[x].Publish = append(slices.Clone(changed[x].Publish[1:]), "extra.subject")
+		for _, row := range []struct {
+			name                 string
+			loaded               []grants.User
+			added, dropped, gone []string
+			differ               []string
+			equal                bool
+		}{
+			{"equal", shadow, nil, nil, nil, nil, true},
+			{"one user the bus lacks", shadow[1:], []string{shadow[0].User}, nil, nil, nil, false},
+			{"one loaded user still placed", append(slices.Clone(shadow), grants.User{User: "a.mod-x.worker"}), nil, []string{"a.mod-x.worker"}, nil, nil, false},
+			{"one loaded user placement no longer names", append(slices.Clone(shadow), grants.User{User: "b.gone"}), nil, []string{"b.gone"}, []string{"b.gone"}, nil, true},
+			{"grants differ", changed, nil, nil, nil, []string{"a.mod-x"}, false},
+		} {
+			t.Run(row.name, func(t *testing.T) {
+				c := grants.Compare(shadow, row.loaded, grants.Placed(in))
+				var differ []string
+				for _, d := range c.Differ {
+					differ = append(differ, d.User)
+				}
+				if !slices.Equal(c.Added, nonNil(row.added)) || !slices.Equal(c.Dropped, nonNil(row.dropped)) ||
+					!slices.Equal(c.Gone, row.gone) || !slices.Equal(differ, row.differ) || c.Equal() != row.equal {
+					t.Errorf("compare = %+v", c)
+				}
+				if row.name == "grants differ" && (len(c.Differ[0].PublishAdded) != 1 || c.Differ[0].PublishDropped[0] != "extra.subject") {
+					t.Errorf("the grant difference is not named: %+v", c.Differ[0])
+				}
+			})
+		}
+	})
+
+	t.Run("tools", func(t *testing.T) {
+		b := fixture()
+		b.loaded = shadowOf(t, b)
+		b.streams = []map[string]any{{"name": "KV_mod-x_kept", "subjects": []string{"$KV.mod-x_kept.>"}, "retention": "limits", "max_per_subject": 3}}
+		p := partOn(b)
+
+		got, _ := p.UserList()
+		if !strings.Contains(fmt.Sprint(got), "nothing composed yet") {
+			t.Errorf("user-list before any composition = %v", got)
+		}
+		first := p.Compose()
+		if !first.Written || first.Revision != 1 || !first.UserList.Compare.Equal() || first.UserList.Users != 6 {
+			t.Fatalf("first composition = %+v", first)
+		}
+		if len(first.Published) != 3 || len(b.publishes) != 3 {
+			t.Errorf("the first composition published %v, want the three assignments' memberships", first.Published)
+		}
+		// The second pass says each membership unchanged (published at the first); the third writes nothing at all.
+		if again := p.Compose(); again.Written || again.Revision != 1 || len(again.Published) != 0 || again.AssertionsWritten != 0 {
+			t.Errorf("a composition with no input changed wrote or published: %+v", again)
+		}
+		if third := p.Compose(); third.Written || third.MembershipsWritten != 0 || len(third.Published) != 0 || len(b.publishes) != 3 {
+			t.Errorf("a membership equal to the one last published was published again, or a state written: %+v", third)
+		}
+		// mod-x placed on b too: b.mod-x is added and its first membership published; a.mod-x's would lose the module's
+		// plain subject (mod-x now runs on two machines), a loss, so it stays a shadow difference.
+		b.assign("b", "mod-x")
+		moved := p.Compose()
+		if !moved.Written || moved.Revision != 2 || !slices.Equal(moved.Published, []string{"b.mod-x"}) || len(moved.NotPublished) != 1 || !strings.HasPrefix(moved.NotPublished[0], "a.mod-x: "+grants.ShadowDifference) || moved.UserList.Compare.Equal() ||
+			!slices.Equal(moved.UserList.Compare.Added, []string{"b.mod-x"}) {
+			t.Errorf("a composition after placement moved = %+v", moved)
+		}
+		got, _ = p.UserList()
+		ul, _ := got.(map[string]any)
+		if st, ok := ul["written"].(grants.UserListState); !ok || st.Loaded == nil || st.Loaded.Digest != "sha256:aa" || st.BusNode != "a" ||
+			ul["revision"] != uint64(2) || !gapNamed(st.Gaps, "people") {
+			t.Errorf("user-list = %+v", got)
+		}
+
+		a, err := p.AssertOne("mod-x")
+		as, _ := a.(grants.Assertion)
+		if err != nil || as.Asserted || as.Says != grants.ShadowAsserts || len(as.Items) != 3 {
+			t.Fatalf("assert = %+v, %v", a, err)
+		}
+		for _, it := range as.Items {
+			if it.Stream == "KV_mod-x_kept" && len(it.Differences) != 0 {
+				t.Errorf("a bucket the bus holds as composed differs: %v", it.Differences)
+			}
+			if it.Stream == "THINGS" && !slices.Contains(it.Differences, "the bus holds no stream THINGS") {
+				t.Errorf("a stream the bus lacks is not named: %+v", it)
+			}
+		}
+
+		ms, _ := p.MembershipOf("a", "mod-x")
+		if mo, _ := ms.(map[string]any); !strings.Contains(fmt.Sprint(mo["published"]), "last_pass") || mo["composed"] == nil {
+			t.Errorf("membership = %v", ms)
+		}
+		gr, _ := p.Grants("mod-x")
+		if g, _ := gr.(map[string]any); g["writes"] != grants.WritesNoGrant || g["count"] != 1 {
+			t.Errorf("grants = %v", gr)
+		}
+
+		b.loaded = append(b.loaded, grants.User{User: "b.gone"})
+		for _, row := range []struct {
+			name, act, caller string
+			says, never       []string
+		}{
+			{"take-over without the operator's credential", "take-over", "shanks.node-tools", []string{"operator's alone"}, nil},
+			{"hand-back without the operator's credential", "hand-back", "unproven", []string{"operator's alone"}, nil},
+			{"take-over while a user differs names it", "take-over", "person.operator", []string{"users differ", "b.mod-x", grants.NotComposable}, []string{"b.gone"}},
+			{"hand-back in shadow", "hand-back", "person.operator", []string{"nothing to hand back"}, nil},
+		} {
+			t.Run(row.name, func(t *testing.T) {
+				var err error
+				if row.act == "take-over" {
+					err = p.TakeOver(row.caller, "a row")
+				} else {
+					err = p.HandBack(row.caller, "a row")
+				}
+				if err == nil {
+					t.Fatalf("%s by %s was not refused", row.act, row.caller)
+				}
+				for _, s := range row.says {
+					if !strings.Contains(err.Error(), s) {
+						t.Errorf("refusal %q does not say %q", err, s)
+					}
+				}
+				for _, s := range row.never {
+					if strings.Contains(err.Error(), s) {
+						t.Errorf("refusal %q names %q", err, s)
+					}
+				}
+				raw, _, _, _ := b.ownGet(grants.StateTakeover, grants.KeySwitch)
+				var s grants.Switch
+				_ = json.Unmarshal(raw, &s)
+				last := s.Acts[len(s.Acts)-1]
+				if s.State != grants.Shadow || last.Act != row.act || last.By != row.caller || last.Refused == "" {
+					t.Errorf("the act is not recorded: %+v", s)
+				}
+			})
+		}
+		t.Run("take-over with only a user placement no longer names is refused for want of records alone", func(t *testing.T) {
+			b.states[grants.ReadAssignments] = nil
+			b.assign("a", "nats")
+			b.assign("a", "mod-x")
+			b.assign("b", "mod-y")
+			b.loaded = append(shadowOf(t, b), grants.User{User: "b.gone"})
+			err := p.TakeOver("person.operator", "lists agree")
+			if err == nil || strings.Contains(err.Error(), "differ") || !strings.Contains(err.Error(), grants.NotComposable) {
+				t.Errorf("take-over = %v, want refused for the enrolment users and persons alone", err)
+			}
+		})
+
+		t.Run("only memberships published, nothing asserted", func(t *testing.T) {
+			for _, s := range b.publishes {
+				if !strings.HasPrefix(s, "mesh.assignment.") {
+					t.Errorf("published on %s", s)
+				}
+			}
+			for _, w := range b.writes {
+				if !slices.Contains(grants.States, w) {
+					t.Errorf("wrote %s, which is not the part's own state", w)
+				}
+			}
+			for _, c := range b.calls {
+				if c != grants.CallUsers && c != grants.CallStreams {
+					t.Errorf("called %s: the part calls only the bus module's read tools", c)
+				}
+			}
+			for _, e := range b.events {
+				if !slices.Contains(grants.Emits, e) {
+					t.Errorf("said %s", e)
+				}
+			}
+		})
+	})
+
+	t.Run("memberships: a first or an additive one published, a loss never", func(t *testing.T) {
+		const key = "a.mod-x"
+		composed := func(b *fakeBus) map[string]any {
+			recs, _ := grants.Records(grants.ReadInputs(b, &grants.Manifests{}))
+			raw, _ := json.Marshal(grants.Memberships(recs)[key].Membership)
+			var m map[string]any
+			_ = json.Unmarshal(raw, &m)
+			return m
+		}
+		for _, row := range []struct {
+			name      string
+			last      func(map[string]any) map[string]any
+			published bool
+			names     string
+		}{
+			{"a first membership is published", nil, true, ""},
+			{"an additive change is published, the private network carried", func(m map[string]any) map[string]any {
+				delete(m, "state")
+				m["mesh"] = []any{"10.0.0.1"}
+				return m
+			}, true, ""},
+			{"a change that drops verified-sender is not published, and named", func(m map[string]any) map[string]any {
+				m["seat-traffic"] = map[string]any{"kinds": []any{map[string]any{"seat": "channel", "kind": "telegram", "capabilities": []any{"verified-sender"}}}}
+				return m
+			}, false, "verified-sender"},
+			{"a change that drops any other field is not published", func(m map[string]any) map[string]any {
+				m["serves"] = append(m["serves"].([]any), map[string]any{"subject": "mesh.mod.mod-x.tool.gone"})
+				return m
+			}, false, "tool.gone"},
+		} {
+			t.Run(row.name, func(t *testing.T) {
+				b := fixture()
+				b.loaded = shadowOf(t, b)
+				if row.last != nil {
+					raw, _ := json.Marshal(row.last(composed(b)))
+					b.stream = map[string][]byte{"mesh.assignment." + key: raw}
+					b.seqs = map[string]uint64{"mesh.assignment." + key: 4}
+				}
+				res := partOn(b).Compose()
+				if got := slices.Contains(res.Published, key); got != row.published {
+					t.Fatalf("published %v, not published %v", res.Published, res.NotPublished)
+				}
+				if row.published {
+					if row.last != nil && !strings.Contains(string(b.stream["mesh.assignment."+key]), "10.0.0.1") {
+						t.Errorf("the private network of the last membership is not carried: %s", b.stream["mesh.assignment."+key])
+					}
+					return
+				}
+				said := strings.Join(res.NotPublished, "\n")
+				if !strings.Contains(said, grants.ShadowDifference) || !strings.Contains(said, row.names) {
+					t.Errorf("the loss is not named: %s", said)
+				}
+				ms, _ := partOn(b).MembershipOf("a", "mod-x")
+				if !strings.Contains(fmt.Sprint(ms), row.names) {
+					t.Errorf("grants_membership does not name what would be lost: %v", ms)
+				}
+			})
+		}
+		t.Run("a refused publish: no exit, said, published at the next event", func(t *testing.T) {
+			b := fixture()
+			b.loaded = shadowOf(t, b)
+			b.refusePub = true
+			p := partOn(b)
+			refused := p.Compose()
+			if len(refused.Published) != 0 || len(refused.NotPublished) != 3 || !strings.Contains(refused.NotPublished[0], "Permissions Violation") {
+				t.Errorf("a refused publish = %+v: said, and nothing published", refused)
+			}
+			b.refusePub = false
+			if next := p.Compose(); !slices.Equal(next.Published, []string{"a.mod-x", "a.nats", "b.mod-y"}) {
+				t.Errorf("the next event published %v", next.Published)
+			}
+		})
+		t.Run("a tool answers while a pass waits on the bus", func(t *testing.T) {
+			b := fixture()
+			b.loaded = shadowOf(t, b)
+			b.hold = make(chan struct{})
+			p := partOn(b)
+			done := make(chan struct{})
+			go func() { p.Compose(); close(done) }()
+			answered := make(chan struct{})
+			go func() {
+				_, _ = p.UserList()
+				_, _ = p.MembershipOf("a", "mod-x")
+				_, _ = p.Grants("")
+				_ = p.Last()
+				close(answered)
+			}()
+			select {
+			case <-answered:
+			case <-time.After(10 * time.Second):
+				t.Error("a tool waited on the pass's round trip")
+			}
+			close(b.hold)
+			<-done
+		})
+	})
+
+	t.Run("a refused read or write never stops it", func(t *testing.T) {
+		b := fixture()
+		b.loaded = shadowOf(t, b)
+		b.refuseTo[grants.StateMemberships] = true
+		res := partOn(b).Compose()
+		if !res.Written || len(res.Errors) == 0 || !strings.Contains(strings.Join(res.Errors, " "), "memberships") {
+			t.Errorf("a refused write of memberships = %+v: the user list is written all the same, the refusal said", res)
+		}
+		w := &fakeWatcher{refuse: map[string]int{grants.ReadModules: 1}, opened: make(chan string, 16)}
+		var logged []string
+		var lmu sync.Mutex
+		f := &grants.Follower{Part: partOn(b), Watch: w, Logf: func(format string, args ...any) {
+			lmu.Lock()
+			logged = append(logged, fmt.Sprintf(format, args...))
+			lmu.Unlock()
+		}}
+		ctx, cancel := context.WithCancel(context.Background())
+		done := make(chan struct{})
+		go func() { f.Run(ctx); close(done) }()
+		waitOpened(t, w, grants.ReadAssignments)
+		if r := f.Refused(); r[grants.ReadModules] == "" {
+			waitFor(t, func() bool { return f.Refused()[grants.ReadModules] != "" })
+		}
+		w.change(grants.ReadAssignments, "a.mod-x")
+		waitOpened(t, w, grants.ReadModules)
+		waitFor(t, func() bool { return len(f.Refused()) == 0 })
+		select {
+		case <-done:
+			t.Fatal("the follower stopped")
+		default:
+		}
+		cancel()
+		<-done
+		lmu.Lock()
+		defer lmu.Unlock()
+		if !strings.Contains(strings.Join(logged, "\n"), "cannot be watched yet") {
+			t.Errorf("the refusal was not said: %v", logged)
+		}
+	})
+}
+
+func nonNil(s []string) []string {
+	if s == nil {
+		return []string{}
+	}
+	return s
+}
+
+// fakeWatcher refuses a state's first watches as told, and hands changes to the watches it opened.
+type fakeWatcher struct {
+	mu      sync.Mutex
+	refuse  map[string]int
+	changes map[string]func(string, []byte)
+	opened  chan string
+}
+
+func (w *fakeWatcher) Watch(state string, changed func(string, []byte), _ func(error)) error {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	if w.refuse[state] > 0 {
+		w.refuse[state]--
+		return errors.New("Permissions Violation for Publish to $JS.API.STREAM.INFO.KV_" + state)
+	}
+	if w.changes == nil {
+		w.changes = map[string]func(string, []byte){}
+	}
+	w.changes[state] = changed
+	w.opened <- state
+	return nil
+}
+
+func (w *fakeWatcher) change(state, key string) {
+	w.mu.Lock()
+	h := w.changes[state]
+	w.mu.Unlock()
+	h(key, []byte(`{}`))
+}
+
+func waitOpened(t *testing.T, w *fakeWatcher, state string) {
+	t.Helper()
+	deadline := time.After(10 * time.Second)
+	for {
+		select {
+		case s := <-w.opened:
+			if s == state {
+				return
+			}
+		case <-deadline:
+			t.Fatalf("%s was never watched", state)
+		}
+	}
+}
+
+func waitFor(t *testing.T, ok func() bool) {
+	t.Helper()
+	for end := time.Now().Add(10 * time.Second); time.Now().Before(end); time.Sleep(10 * time.Millisecond) {
+		if ok() {
+			return
+		}
+	}
+	t.Fatal("never came")
+}
@@ -0,0 +1,127 @@
+package grants
+
+import (
+	"encoding/json"
+	"fmt"
+	"slices"
+	"sort"
+
+	"git.novox.be/novox/mesh-sdk/go/buscompose"
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+)
+
+// Item is one bucket, log or stream a manifest declares, as composed, beside what the bus holds of it.
+type Item struct {
+	Kind   string `json:"kind"`
+	Stream string `json:"stream"`
+	// Composed is what an assertion would ask for; Held what the bus holds, absent when it holds no such stream.
+	Composed Limits  `json:"composed"`
+	Held     *Limits `json:"held,omitempty"`
+	// Differences says how they differ, in words; empty when they agree in what can be read from here.
+	Differences []string `json:"differences,omitempty"`
+}
+
+// Limits are the facts of a stream an assertion sets and the bus module's nats_streams reads back. Its size cap is not
+// read back by that tool, so it is composed and not compared.
+type Limits struct {
+	Subjects      []string `json:"subjects"`
+	Retention     string   `json:"retention"`
+	MaxAgeHours   int      `json:"max_age_hours,omitempty"`
+	MaxPerSubject int      `json:"max_per_subject,omitempty"`
+	MaxBytes      int64    `json:"max_bytes,omitempty"`
+}
+
+// Assertion is one module's declared buckets, logs and streams, composed and compared. Asserted is always false in
+// shadow: nothing is created or changed.
+type Assertion struct {
+	Module   string `json:"module"`
+	Manifest string `json:"manifest"`
+	Items    []Item `json:"items"`
+	Asserted bool   `json:"asserted"`
+	Says     string `json:"says"`
+}
+
+// ShadowAsserts is what every assertion says in this milestone.
+const ShadowAsserts = "in shadow: composed and compared, nothing asserted (ADR 0547 clause 5 asserts from take-over)"
+
+// Composed is a module's buckets, logs and streams as an assertion would ask for them. Pure.
+func Composed(m catalogue.Manifest) []Item {
+	var out []Item
+	for _, b := range bucketsOf(m) {
+		per := b.History
+		if per < 1 {
+			per = 1
+		}
+		out = append(out, Item{Kind: "bucket", Stream: "KV_" + b.Bucket(), Composed: Limits{
+			Subjects: []string{"$KV." + b.Bucket() + ".>"}, Retention: string(buscompose.RetentionLimits),
+			MaxAgeHours: b.TTLSeconds / 3600, MaxPerSubject: per}})
+	}
+	for _, l := range logsOf(m) {
+		c := l.Config()
+		out = append(out, Item{Kind: "log", Stream: l.Stream(), Composed: Limits{Subjects: set(c.Subjects),
+			Retention: string(buscompose.RetentionLimits), MaxAgeHours: int(c.MaxAge.Hours()), MaxBytes: c.MaxBytes}})
+	}
+	for _, s := range streamsOf(m) {
+		st := s.Stream()
+		out = append(out, Item{Kind: "stream", Stream: st.Name, Composed: Limits{Subjects: set(st.Subjects),
+			Retention: string(st.Retention), MaxAgeHours: st.MaxAge / 3600, MaxBytes: st.MaxBytes}})
+	}
+	return out
+}
+
+// HeldStreams reads every stream the bus holds through its module's nats_streams, by name.
+func HeldStreams(c Caller) (map[string]Limits, error) {
+	raw, err := c.Call(CallStreams, map[string]any{})
+	if err != nil {
+		return nil, fmt.Errorf("%s: %w", CallStreams, err)
+	}
+	var got struct {
+		Detail []struct {
+			Name          string   `json:"name"`
+			Subjects      []string `json:"subjects"`
+			Retention     string   `json:"retention"`
+			MaxAgeHours   int      `json:"max_age_hours"`
+			MaxPerSubject int      `json:"max_per_subject"`
+		} `json:"detail"`
+	}
+	if err := json.Unmarshal(unwrap(raw), &got); err != nil {
+		return nil, fmt.Errorf("%s answered no streams: %w", CallStreams, err)
+	}
+	out := map[string]Limits{}
+	for _, s := range got.Detail {
+		out[s.Name] = Limits{Subjects: set(s.Subjects), Retention: s.Retention, MaxAgeHours: s.MaxAgeHours, MaxPerSubject: s.MaxPerSubject}
+	}
+	return out, nil
+}
+
+// Assert composes a module's items and compares each with what the bus holds; held nil is not read. It asserts nothing.
+func Assert(module, digest string, m catalogue.Manifest, held map[string]Limits, heldErr error) Assertion {
+	a := Assertion{Module: module, Manifest: digest, Items: Composed(m), Says: ShadowAsserts}
+	for i := range a.Items {
+		it := &a.Items[i]
+		if heldErr != nil {
+			it.Differences = []string{"what the bus holds was not read: " + heldErr.Error()}
+			continue
+		}
+		h, ok := held[it.Stream]
+		if !ok {
+			it.Differences = []string{"the bus holds no stream " + it.Stream}
+			continue
+		}
+		it.Held = &h
+		if !slices.Equal(h.Subjects, it.Composed.Subjects) {
+			it.Differences = append(it.Differences, fmt.Sprintf("subjects %v held, %v composed", h.Subjects, it.Composed.Subjects))
+		}
+		if h.Retention != it.Composed.Retention {
+			it.Differences = append(it.Differences, fmt.Sprintf("retention %s held, %s composed", h.Retention, it.Composed.Retention))
+		}
+		if h.MaxAgeHours != it.Composed.MaxAgeHours {
+			it.Differences = append(it.Differences, fmt.Sprintf("age %d h held, %d h composed", h.MaxAgeHours, it.Composed.MaxAgeHours))
+		}
+		if it.Kind == "bucket" && max(h.MaxPerSubject, 1) != it.Composed.MaxPerSubject {
+			it.Differences = append(it.Differences, fmt.Sprintf("history %d held, %d composed", h.MaxPerSubject, it.Composed.MaxPerSubject))
+		}
+	}
+	sort.SliceStable(a.Items, func(i, j int) bool { return a.Items[i].Stream < a.Items[j].Stream })
+	return a
+}
@@ -0,0 +1,171 @@
+package grants
+
+import (
+	"context"
+	"encoding/json"
+	"sync"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// Watcher watches another part's state: changed hears each change after what stands, ended hears the watch end. A watch
+// refused (a read not granted yet, a bucket not there) is an error, and is tried again at the next wake.
+type Watcher interface {
+	Watch(state string, changed func(key string, value []byte), ended func(error)) error
+}
+
+// Followed are the states whose change composes again: placement, the indexer's manifests by module, the resolved
+// config values, the node agents' haves (a machine's first have, and the bus node's loaded list) and the assigner's
+// wants (the manifest each machine is wanted to run).
+var Followed = []string{ReadAssignments, ReadModules, ReadResolved, ReadHave, ReadWants}
+
+// Follower composes again on every change it hears, never on a timer. It never stops for a refusal: a watch it cannot
+// open is said, composed without, and opened again at the next wake (any change it does hear, or a reconnect).
+type Follower struct {
+	Part  *Part
+	Watch Watcher
+	Logf  func(string, ...any)
+	// Asked watches the part's own ask to compose now (a tool's compose-now), waking at each; nil watches none.
+	Asked func(wake func()) error
+
+	wake    chan struct{}
+	once    sync.Once
+	mu      sync.Mutex
+	asked   bool
+	watched map[string]bool
+	refused map[string]string
+	have    map[string]string
+}
+
+func (f *Follower) init() {
+	f.once.Do(func() {
+		f.wake = make(chan struct{}, 1)
+		f.watched, f.refused, f.have = map[string]bool{}, map[string]string{}, map[string]string{}
+	})
+}
+
+// Wake asks for one more composition: after a change, and after a reconnect.
+func (f *Follower) Wake() {
+	f.init()
+	select {
+	case f.wake <- struct{}{}:
+	default:
+	}
+}
+
+// Refused is every watch refused at the last try, with why.
+func (f *Follower) Refused() map[string]string {
+	f.init()
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	out := map[string]string{}
+	for k, v := range f.refused {
+		out[k] = v
+	}
+	return out
+}
+
+func (f *Follower) logf(format string, args ...any) {
+	if f.Logf != nil {
+		f.Logf(format, args...)
+	}
+}
+
+// heard says whether a change composes again: every change but a have's, and of the haves a machine's first and the
+// bus module's loaded list moving.
+func (f *Follower) heard(state, key string, value []byte) bool {
+	if state != ReadHave {
+		return true
+	}
+	node, module, isNode, err := delivery.ParseHaveKey(key)
+	if err != nil {
+		return false
+	}
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	if isNode {
+		if _, seen := f.have[node]; seen {
+			return false
+		}
+		f.have[node] = ""
+		return true
+	}
+	if module != BusModule {
+		return false
+	}
+	var h struct {
+		UserList json.RawMessage `json:"user-list"`
+	}
+	_ = json.Unmarshal(value, &h)
+	was, seen := f.have[key]
+	f.have[key] = string(h.UserList)
+	return !seen || was != string(h.UserList)
+}
+
+// open opens every watch not open yet; one refused is said and left for the next wake.
+func (f *Follower) open() {
+	if f.Asked != nil && !f.asked {
+		if err := f.Asked(f.Wake); err != nil {
+			f.logf("a tool's ask to compose now cannot be heard yet (%v): tried again at the next change", err)
+		} else {
+			f.asked = true
+		}
+	}
+	for _, state := range Followed {
+		f.mu.Lock()
+		open := f.watched[state]
+		f.mu.Unlock()
+		if open {
+			continue
+		}
+		state := state
+		err := f.Watch.Watch(state, func(key string, value []byte) {
+			if f.heard(state, key, value) {
+				f.Wake()
+			}
+		}, func(err error) {
+			f.mu.Lock()
+			f.watched[state] = false
+			f.mu.Unlock()
+			f.logf("the watch of %s ended (%v): opened again at the next change", state, err)
+			f.Wake()
+		})
+		f.mu.Lock()
+		if err != nil {
+			f.refused[state] = err.Error()
+			f.logf("%s cannot be watched yet (%v): composed without it, and tried again at the next change or reconnect", state, err)
+		} else {
+			f.watched[state] = true
+			delete(f.refused, state)
+		}
+		f.mu.Unlock()
+	}
+}
+
+// Run composes at start and after every change until ctx ends. It returns only when ctx ends.
+func (f *Follower) Run(ctx context.Context) {
+	f.init()
+	f.Wake()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-f.wake:
+			f.open()
+			res := f.Part.Pass()
+			for _, e := range res.Errors {
+				f.logf("%s", e)
+			}
+			if len(res.Published) > 0 {
+				f.logf("published %d memberships: %v", len(res.Published), res.Published)
+			}
+			if len(res.NotPublished) > 0 {
+				f.logf("%d memberships not published, tried again at the next event; the first: %s", len(res.NotPublished), res.NotPublished[0])
+			}
+			if res.Written {
+				f.logf("the shadow list moved to revision %d: %d users, %d differing from the loaded list",
+					res.Revision, res.UserList.Users, len(res.UserList.Compare.Differing()))
+			}
+		}
+	}
+}
@@ -0,0 +1,329 @@
+// Package grants is the grants part in shadow (novox/hq ADR 0547 clauses 5 to 8, issue 1945): it composes the bus's user
+// list, each module's membership and each manifest's buckets, logs and streams from what the bus holds, with the bus
+// composer the controller uses (mesh-sdk buscompose), and compares them with what the bus loaded and holds. It writes only
+// its own state and takes no effect: it publishes no membership, asserts nothing, writes no grant and no user list the
+// bus node reads, until the operator's take-over, which this milestone always refuses.
+package grants
+
+import (
+	"encoding/json"
+	"fmt"
+	"slices"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// The states of other parts the grants part reads, as its manifest's reads name them (`<module>.<state>`).
+const (
+	ReadAssignments     = "mesh-controller.assignments"
+	ReadControllerGrant = "mesh-controller.grants"
+	ReadModules         = "mesh-delivery-indexer.modules"
+	ReadManifests       = "mesh-delivery-indexer.manifests"
+	ReadHave            = "node-engine.have"
+	ReadResolved        = "mesh-config.resolved"
+	ReadWants           = "mesh-delivery-assigner.wants"
+	ReadBuilds          = "mesh-delivery-builder.builds"
+)
+
+// Reads is every state the part reads, in the manifest's order.
+var Reads = []string{ReadAssignments, ReadControllerGrant, ReadModules, ReadManifests, ReadResolved, ReadHave, ReadWants, ReadBuilds}
+
+// The bus module's tools the part calls, as its manifest's invokes name them: read-only, each.
+const (
+	CallUsers   = "nats.nats_users"
+	CallUserCan = "nats.nats_user_can"
+	CallStreams = "nats.nats_streams"
+)
+
+// Invokes is every tool the part calls.
+var Invokes = []string{CallUsers, CallUserCan, CallStreams}
+
+// Reader reads another part's state, named `<module>.<state>`. A refusal (a read not granted yet, a bucket not there) is
+// an error the part names as a gap and composes past: it never stops for one.
+type Reader interface {
+	Keys(state string) ([]string, error)
+	Get(state, key string) ([]byte, bool, error)
+}
+
+// Caller calls another module's tool, `<module>.<tool>`, and answers its result.
+type Caller interface {
+	Call(key string, body any) (json.RawMessage, error)
+}
+
+// Gap is an input the shadow cannot read from the bus, named with why: never guessed.
+type Gap struct {
+	Input string `json:"input"`
+	Why   string `json:"why"`
+}
+
+// Standing gaps: what the controller composes from its own store, which no bus value carries in this milestone.
+var standingGaps = []Gap{
+	{Input: "enrolment tokens", Why: "the live enrolment tokens are in the controller's store alone: no enrolment user is composed"},
+	{Input: "people", Why: "the people and the tools they may invoke are in the controller's store alone: no person user is composed"},
+	{Input: "seat holdings", Why: "who holds each seat held once for the mesh is in the controller's store alone: a mesh seat claimed on two machines is composed as held on both"},
+	{Input: "announced states", Why: "the controller does not announce its states-announced readable, so every read is composed from `reads`, as when announcements cannot be read"},
+	{Input: "credentials", Why: "the shadow holds no hash, so a user it composes that the loaded list lacks may be one left out for want of a credential"},
+}
+
+// assignment is a key of the controller's assignments as composing needs it (mesh-controller internal/chain Assignment):
+// a value that names no time assigned (a module pulled in), has ended, or waits in a state, is no assignment.
+type assignment struct {
+	Node     string    `json:"node"`
+	Module   string    `json:"module"`
+	Assigned time.Time `json:"assigned,omitzero"`
+	Ended    time.Time `json:"ended,omitzero"`
+	State    string    `json:"state,omitempty"`
+}
+
+func (a assignment) stands() bool { return !a.Assigned.IsZero() && a.Ended.IsZero() && a.State == "" }
+
+// resolved is a key of mesh-config's resolved values, `<node>.<module>.<key>`.
+type resolved struct {
+	Node   string          `json:"node"`
+	Module string          `json:"module"`
+	Key    string          `json:"key"`
+	Value  json.RawMessage `json:"value,omitempty"`
+}
+
+// Inputs is what the shadow composes from, read from the bus.
+type Inputs struct {
+	// Nodes is every machine seen: in a node agent's have or a standing assignment.
+	Nodes []string
+	// Assigned is each machine's standing assignments, sorted.
+	Assigned map[string][]string
+	// Manifests is each module's manifest at the indexer's trunk, by module.
+	Manifests map[string]catalogue.Manifest
+	// Digests is each module's manifest digest, by module.
+	Digests map[string]string
+	// Running is the manifest a machine is wanted to run, by `<node>.<module>`: the one the builder built at the
+	// fingerprint the assigner's want names. An assignment with none is composed from the trunk's manifest.
+	Running map[string]catalogue.Manifest
+	// Values is each resolved config value, by `<node>/<module>/<key>`.
+	Values map[string]any
+	// BusNode is the machine running the bus's module, and Loaded what its node agent says it loaded.
+	BusNode string
+	Loaded  *delivery.UserListWritten
+	Gaps    []Gap
+}
+
+// BusModule is the bus's module: it holds mesh-broker.
+const BusModule = "nats"
+
+// Manifests caches manifests by digest: a digest names one manifest for ever.
+type Manifests struct {
+	mu     sync.Mutex
+	parsed map[string]catalogue.Manifest
+}
+
+func (c *Manifests) get(r Reader, digest string) (catalogue.Manifest, error) {
+	// The lock guards the map alone, never a read on the bus: a tool never waits on a pass's round trip.
+	c.mu.Lock()
+	m, ok := c.parsed[digest]
+	c.mu.Unlock()
+	if ok {
+		return m, nil
+	}
+	raw, found, err := r.Get(ReadManifests, digest)
+	if err != nil {
+		return catalogue.Manifest{}, err
+	}
+	if !found {
+		return catalogue.Manifest{}, fmt.Errorf("the indexer holds no manifest %s", digest)
+	}
+	v, err := delivery.DecodeManifest(raw)
+	if err != nil {
+		return catalogue.Manifest{}, err
+	}
+	m, err = catalogue.ParseManifest([]byte(v.JSON))
+	if err != nil {
+		return catalogue.Manifest{}, fmt.Errorf("the manifest %s is refused by mesh-sdk's reader: %w", digest, err)
+	}
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.parsed == nil {
+		c.parsed = map[string]catalogue.Manifest{}
+	}
+	c.parsed[digest] = m
+	return m, nil
+}
+
+// each reads every current value of a state; a refusal is a gap and an empty map.
+func each(r Reader, state string, gaps *[]Gap) map[string][]byte {
+	keys, err := r.Keys(state)
+	if err != nil {
+		*gaps = append(*gaps, Gap{Input: state, Why: "refused or absent: " + err.Error()})
+		return map[string][]byte{}
+	}
+	out := map[string][]byte{}
+	for _, k := range keys {
+		v, found, err := r.Get(state, k)
+		if err != nil {
+			*gaps = append(*gaps, Gap{Input: state + " " + k, Why: err.Error()})
+			continue
+		}
+		if found {
+			out[k] = v
+		}
+	}
+	return out
+}
+
+// ReadInputs reads what the shadow composes from. It never fails: what it cannot read is a gap.
+func ReadInputs(r Reader, cache *Manifests) Inputs {
+	in := Inputs{Assigned: map[string][]string{}, Manifests: map[string]catalogue.Manifest{}, Digests: map[string]string{},
+		Running: map[string]catalogue.Manifest{},
+		Values:  map[string]any{}, Gaps: append([]Gap(nil), standingGaps...)}
+	nodes := map[string]bool{}
+	for _, raw := range each(r, ReadAssignments, &in.Gaps) {
+		var a assignment
+		if json.Unmarshal(raw, &a) != nil || !a.stands() || a.Node == "" || a.Module == "" {
+			continue
+		}
+		nodes[a.Node] = true
+		in.Assigned[a.Node] = append(in.Assigned[a.Node], a.Module)
+		if a.Module == BusModule {
+			in.BusNode = a.Node
+		}
+	}
+	haveKeys, err := r.Keys(ReadHave)
+	if err != nil {
+		in.Gaps = append(in.Gaps, Gap{Input: ReadHave, Why: "refused or absent: " + err.Error()})
+	}
+	for _, k := range haveKeys {
+		if node, _, isNode, err := delivery.ParseHaveKey(k); err == nil && isNode {
+			nodes[node] = true
+		}
+	}
+	in.Gaps = append(in.Gaps, Gap{Input: "machines", Why: "read from the node agents' haves and the assignments: a machine with neither is not seen"})
+	for n := range nodes {
+		in.Nodes = append(in.Nodes, n)
+	}
+	sort.Strings(in.Nodes)
+	if in.BusNode != "" {
+		if raw, found, err := r.Get(ReadHave, in.BusNode+"."+BusModule); err != nil {
+			in.Gaps = append(in.Gaps, Gap{Input: "the loaded list's have", Why: err.Error()})
+		} else if found {
+			if h, err := delivery.DecodeHave(raw); err == nil {
+				in.Loaded = h.UserList
+			}
+		}
+	}
+	wanted := map[string]bool{}
+	for node := range in.Assigned {
+		sort.Strings(in.Assigned[node])
+		for _, m := range in.Assigned[node] {
+			wanted[m] = true
+		}
+	}
+	modules := make([]string, 0, len(wanted))
+	for m := range wanted {
+		modules = append(modules, m)
+	}
+	sort.Strings(modules)
+	// The seats every module declares, across the whole catalogue: read every module the indexer holds, not only the
+	// assigned ones, since a seat is declared by one module and held by another.
+	indexed, err := r.Keys(ReadModules)
+	if err != nil {
+		in.Gaps = append(in.Gaps, Gap{Input: ReadModules, Why: "refused or absent: " + err.Error()})
+	}
+	for _, module := range indexed {
+		raw, found, err := r.Get(ReadModules, module)
+		if err != nil || !found {
+			continue
+		}
+		v, err := delivery.DecodeModule(raw)
+		if err == nil && v.Manifest == "" {
+			err = fmt.Errorf("the indexer's value names no manifest digest")
+		}
+		if err != nil {
+			if wanted[module] {
+				in.Gaps = append(in.Gaps, Gap{Input: "manifest of " + module, Why: err.Error()})
+			}
+			continue
+		}
+		m, err := cache.get(r, v.Manifest)
+		if err != nil {
+			if wanted[module] {
+				in.Gaps = append(in.Gaps, Gap{Input: "manifest of " + module, Why: err.Error()})
+			}
+			continue
+		}
+		in.Manifests[module] = m
+		in.Digests[module] = v.Manifest
+	}
+	for _, module := range modules {
+		if _, ok := in.Manifests[module]; !ok && !gapNamed(in.Gaps, "manifest of "+module) {
+			in.Gaps = append(in.Gaps, Gap{Input: "manifest of " + module,
+				Why: "assigned, and the indexer holds no manifest of it at the trunk (a module registered from outside the indexed repositories): composed with no authority"})
+		}
+	}
+	// What each machine is wanted to run: the want's fingerprint, the builder's build of it, the manifest it built.
+	var fromTrunk []string
+	for key, raw := range each(r, ReadWants, &in.Gaps) {
+		node, module, err := delivery.ParseWantKey(key)
+		if err != nil || !slices.Contains(in.Assigned[node], module) {
+			continue
+		}
+		w, err := delivery.DecodeWant(raw)
+		if err != nil {
+			fromTrunk = append(fromTrunk, node+"."+module)
+			continue
+		}
+		if w.Removed || w.FP == "" {
+			continue
+		}
+		bk, err := delivery.BuilderBuildKey(module, w.FP)
+		if err != nil {
+			continue
+		}
+		braw, found, err := r.Get(ReadBuilds, bk)
+		if err != nil || !found {
+			fromTrunk = append(fromTrunk, node+"."+module)
+			continue
+		}
+		b, err := delivery.DecodeBuilderBuild(braw)
+		if err != nil || b.Manifest == "" {
+			fromTrunk = append(fromTrunk, node+"."+module)
+			continue
+		}
+		if m, err := cache.get(r, b.Manifest); err == nil {
+			in.Running[node+"."+module] = m
+		} else {
+			fromTrunk = append(fromTrunk, node+"."+module)
+		}
+	}
+	if len(fromTrunk) > 0 {
+		sort.Strings(fromTrunk)
+		in.Gaps = append(in.Gaps, Gap{Input: "wanted manifests", Why: "no build record names the manifest at the wanted fingerprint, so the trunk's is used: " + strings.Join(fromTrunk, ", ")})
+	}
+	for _, raw := range each(r, ReadResolved, &in.Gaps) {
+		var v resolved
+		if json.Unmarshal(raw, &v) != nil || v.Node == "" || v.Module == "" || v.Key == "" || len(v.Value) == 0 {
+			continue
+		}
+		var value any
+		if json.Unmarshal(v.Value, &value) == nil {
+			in.Values[v.Node+"/"+v.Module+"/"+v.Key] = value
+		}
+	}
+	sortGaps(in.Gaps)
+	return in
+}
+
+func gapNamed(gaps []Gap, input string) bool {
+	for _, g := range gaps {
+		if g.Input == input {
+			return true
+		}
+	}
+	return false
+}
+
+func sortGaps(g []Gap) {
+	sort.SliceStable(g, func(i, j int) bool { return strings.Compare(g[i].Input, g[j].Input) < 0 })
+}
@@ -0,0 +1,195 @@
+package grants
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"reflect"
+	"slices"
+	"sort"
+	"strings"
+
+	"git.novox.be/novox/mesh-sdk/go/buscompose"
+	"git.novox.be/novox/mesh-sdk/go/membership"
+)
+
+// Memberships are published for real from this milestone (the operator, 2026-10-25 22:31): since release 6 nobody
+// publishes them, so a module placed since cannot serve its seat or reach a new state. The user list, the assertions and
+// the grants stay in shadow until take-over.
+
+// MembershipGaps are what a membership carries that the part cannot compose from the bus.
+var MembershipGaps = []Gap{
+	{Input: "membership: private network and received contributions", Why: "kept in each node's composition, which only that node reads: carried over from the membership last published, none for a first one"},
+	{Input: "membership: root-free machines", Why: "judged by the controller on the bus at its composition, not kept: a verified sender is composed as from no root-free machine"},
+}
+
+// Publisher publishes a membership on the assignments stream (membership.Subject), last per subject, and reads the one
+// last published there. A refusal (the grant not yet on the bus) is an error the part says and tries again at the next
+// event.
+type Publisher interface {
+	LastMembership(node, module string) (body []byte, seq uint64, found bool, err error)
+	PublishMembership(node, module string, body []byte, after uint64) error
+}
+
+// Membership is one module's membership on one node, as composed now, and what became of its publishing.
+type Membership struct {
+	Node       string                `json:"node"`
+	Module     string                `json:"module"`
+	Digest     string                `json:"digest"`
+	Membership membership.Membership `json:"membership"`
+	// Published says what became of it at the last pass: "published", "unchanged" (equal to the one last published),
+	// or why it was not.
+	Published string `json:"published"`
+}
+
+// Memberships composes every assignment's membership from the records (buscompose.MembershipFor, as the controller's
+// parked composition pass, mesh-controller 003eee8a, issued them), by `<node>.<module>`. Pure.
+func Memberships(r buscompose.Records) map[string]Membership {
+	where := buscompose.PlacementsOf(r, r.Interchangeable)
+	out := map[string]Membership{}
+	for node, declared := range r.Assigned {
+		for _, d := range declared {
+			m := buscompose.MembershipFor(node, d, where)
+			out[node+"."+d.Module] = Membership{Node: node, Module: d.Module, Digest: digestOf(m), Membership: m}
+		}
+	}
+	return out
+}
+
+func digestOf(m membership.Membership) string {
+	raw, _ := json.Marshal(m)
+	sum := sha256.Sum256(raw)
+	return "sha256:" + hex.EncodeToString(sum[:])
+}
+
+// Published words of a membership's last pass.
+const (
+	MembershipPublished = "published"
+	MembershipUnchanged = "unchanged"
+)
+
+// publish publishes m when it differs from the membership last published for its assignment, carrying that one's private
+// network and received contributions; it answers m as published (or why not) and whether it was published now.
+func publish(p Publisher, m Membership) (Membership, bool) {
+	if p == nil {
+		m.Published = "not published: no publisher here (only the part's process publishes)"
+		return m, false
+	}
+	was, seq, found, err := p.LastMembership(m.Node, m.Module)
+	if err != nil {
+		m.Published = "not published: the membership last published cannot be read: " + err.Error()
+		return m, false
+	}
+	if found {
+		var last membership.Membership
+		if json.Unmarshal(was, &last) == nil {
+			m.Membership.Mesh, m.Membership.Receives = last.Mesh, last.Receives
+			m.Digest = digestOf(m.Membership)
+		}
+	}
+	body, err := json.Marshal(m.Membership)
+	if err != nil {
+		m.Published = "not published: " + err.Error()
+		return m, false
+	}
+	if found && sameMembership(was, body) {
+		m.Published = MembershipUnchanged
+		return m, false
+	}
+	// Only a first membership, or one that only adds to the last, is published (the lead's decision, review of 1ff5049):
+	// composed with no root-free judgement, a kind's verified-sender would be dropped, and the operator's approvals by
+	// a channel would no longer be honoured. Any loss stays a shadow difference, named.
+	if found {
+		if lost := Losses(was, body); len(lost) > 0 {
+			m.Published = ShadowDifference + strings.Join(lost, "; ")
+			return m, false
+		}
+	}
+	if err := p.PublishMembership(m.Node, m.Module, body, seq); err != nil {
+		m.Published = fmt.Sprintf("not published (tried again at the next event): %v", err)
+		return m, false
+	}
+	m.Published = MembershipPublished
+	return m, true
+}
+
+// sameMembership says two memberships say the same, whatever the order of their fields. Pure.
+func sameMembership(was, now []byte) bool {
+	var a, b any
+	if json.Unmarshal(was, &a) != nil || json.Unmarshal(now, &b) != nil {
+		return false
+	}
+	return reflect.DeepEqual(a, b)
+}
+
+// ShadowDifference opens what a membership's pass says when it was not published because it would lose something.
+const ShadowDifference = "not published, a shadow difference: publishing would lose "
+
+// Losses names everything the last membership holds that now drops or weakens: a field gone, a value changed, a list
+// element (a capability, a kind, a served address, a seat, a state, a stream) with no element in now that holds all of it.
+// Empty means now holds all the last one did, and maybe more. Pure.
+func Losses(last, now []byte) []string {
+	var a, b any
+	if json.Unmarshal(last, &a) != nil {
+		return nil
+	}
+	if json.Unmarshal(now, &b) != nil {
+		return []string{"the new membership is not JSON"}
+	}
+	return losses("", a, b)
+}
+
+func losses(path string, last, now any) []string {
+	switch l := last.(type) {
+	case map[string]any:
+		n, ok := now.(map[string]any)
+		if !ok {
+			return []string{fmt.Sprintf("%s: %s", name(path), brief(last))}
+		}
+		keys := make([]string, 0, len(l))
+		for k := range l {
+			keys = append(keys, k)
+		}
+		sort.Strings(keys)
+		var out []string
+		for _, k := range keys {
+			nv, ok := n[k]
+			if !ok {
+				out = append(out, fmt.Sprintf("%s: %s", name(path+"."+k), brief(l[k])))
+				continue
+			}
+			out = append(out, losses(path+"."+k, l[k], nv)...)
+		}
+		return out
+	case []any:
+		n, _ := now.([]any)
+		var out []string
+		for i, e := range l {
+			if !slices.ContainsFunc(n, func(c any) bool { return len(losses("", e, c)) == 0 }) {
+				out = append(out, fmt.Sprintf("%s[%d]: %s", name(path), i, brief(e)))
+			}
+		}
+		return out
+	}
+	if !reflect.DeepEqual(last, now) {
+		return []string{fmt.Sprintf("%s: %s, now %s", name(path), brief(last), brief(now))}
+	}
+	return nil
+}
+
+func name(path string) string {
+	if path == "" {
+		return "the membership"
+	}
+	return strings.TrimPrefix(path, ".")
+}
+
+// brief is a value in JSON, cut at 200 bytes.
+func brief(v any) string {
+	raw, _ := json.Marshal(v)
+	if len(raw) > 200 {
+		return string(raw[:200]) + "…"
+	}
+	return string(raw)
+}
@@ -0,0 +1,342 @@
+package grants
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// The part's own states, as its manifest declares them, and the keys of the two that hold one value.
+const (
+	StateUserList    = "user-list"
+	StateMemberships = "memberships"
+	StateAssertions  = "assertions"
+	StateTakeover    = "takeover"
+	KeyList          = "list"
+	KeySwitch        = "switch"
+	// KeyPass is the last pass's result, and KeyAsked a tool's ask to compose again now, both in StateUserList.
+	KeyPass  = "pass"
+	KeyAsked = "asked"
+)
+
+// States is every state the part keeps.
+var States = []string{StateAssertions, StateMemberships, StateTakeover, StateUserList}
+
+// The events the part says.
+const (
+	EventUserList   = "user-list-changed"
+	EventMembership = "membership-changed"
+)
+
+// Emits is every event the part says.
+var Emits = []string{EventMembership, EventUserList}
+
+// Shadow is the switch's one state in this milestone: the bus node follows the controller's list.
+const Shadow = "shadow"
+
+// Store is the part's own state, by local name: the only thing the part writes.
+type Store interface {
+	Get(state, key string) ([]byte, uint64, bool, error)
+	Put(state, key string, value []byte) (uint64, error)
+}
+
+// Emitter says one of the part's events.
+type Emitter interface {
+	Emit(event string, body any) error
+}
+
+// UserListState is the value of `user-list` in shadow: the list the grants part composed (users and grants, no hashes),
+// what the bus loaded, and how they differ. Inputs is the digest of all it says but At: a value is written again only
+// when it changes.
+type UserListState struct {
+	V      int    `json:"v"`
+	Mode   string `json:"mode"`
+	Inputs string `json:"inputs"`
+	Digest string `json:"digest"`
+	Users  int    `json:"users"`
+	// LeftOut are the assignments the shadow list leaves out, each with why.
+	LeftOut []Gap                     `json:"left_out"`
+	Compare Comparison                `json:"compare"`
+	Loaded  *delivery.UserListWritten `json:"loaded,omitempty"`
+	BusNode string                    `json:"bus_node,omitempty"`
+	Gaps    []Gap                     `json:"gaps"`
+	At      time.Time                 `json:"at"`
+}
+
+func (s UserListState) inputs() string {
+	s.At, s.Inputs = time.Time{}, ""
+	raw, _ := json.Marshal(s)
+	sum := sha256.Sum256(raw)
+	return "sha256:" + hex.EncodeToString(sum[:])
+}
+
+// Result is what one composition did.
+type Result struct {
+	UserList            UserListState `json:"user_list"`
+	Revision            uint64        `json:"revision"`
+	Written             bool          `json:"written"`
+	Memberships         int           `json:"memberships"`
+	MembershipsWritten  int           `json:"memberships_written"`
+	Published           []string      `json:"published,omitempty"`
+	NotPublished        []string      `json:"not_published,omitempty"`
+	Assertions          int           `json:"assertions"`
+	AssertionsWritten   int           `json:"assertions_written"`
+	Errors              []string      `json:"errors,omitempty"`
+	PublishedOrAsserted string        `json:"published_or_asserted"`
+}
+
+// NothingTakesEffect is what every composition says it did on the bus beyond its own state and the memberships.
+const NothingTakesEffect = "memberships only (on the assignments stream, a first one or one that only adds to the last published; a loss stays a shadow difference); the user list, assertions and grants stay in shadow until take-over"
+
+// Part is the grants part: it reads, calls and writes through these, and nothing else.
+type Part struct {
+	Read  Reader
+	Call  Caller
+	Store Store
+	Emit  Emitter
+	// Publish publishes memberships: the process's connection; nil in the tools, which ask the process instead.
+	Publish Publisher
+	Now     func() time.Time
+
+	cache Manifests
+	mu    sync.Mutex
+	last  Result
+}
+
+func (p *Part) now() time.Time {
+	if p.Now == nil {
+		return time.Now().UTC()
+	}
+	return p.Now().UTC()
+}
+
+// Compose composes the user list, the memberships and the assertions from what the bus holds now, compares them, and
+// writes each of its own keys whose value changed, saying each change. It never stops at a refusal: a read refused is
+// a gap, a write refused is said in Errors, and the next event composes again.
+func (p *Part) Compose() Result {
+	// No lock is held across a round trip on the bus: the reads, calls, publishes and writes below take none, and the
+	// lock is taken only to keep the result, so a tool answers while a pass waits on the bus.
+	res := Result{PublishedOrAsserted: NothingTakesEffect}
+	defer func() {
+		p.mu.Lock()
+		p.last = res
+		p.mu.Unlock()
+	}()
+	in := ReadInputs(p.Read, &p.cache)
+	recs, left := Records(in)
+	st := UserListState{V: 1, Mode: Shadow, LeftOut: left, Loaded: in.Loaded, BusNode: in.BusNode,
+		Gaps: append(append([]Gap(nil), in.Gaps...), MembershipGaps...), At: p.now()}
+	if st.LeftOut == nil {
+		st.LeftOut = []Gap{}
+	}
+	users, err := ComposeUsers(recs)
+	if err != nil {
+		res.Errors = append(res.Errors, "the shadow list could not be composed: "+err.Error())
+	}
+	st.Digest, st.Users = Digest(users), len(users)
+	loaded, err := LoadedUsers(p.Call)
+	st.Compare = Compare(users, loaded, Placed(in))
+	if err != nil {
+		st.Compare.Unread = err.Error()
+	}
+	st.Inputs = st.inputs()
+	res.UserList = st
+	if raw, rev, found, err := p.Store.Get(StateUserList, KeyList); err != nil {
+		res.Errors = append(res.Errors, fmt.Sprintf("its own %s cannot be read: %v", StateUserList, err))
+	} else {
+		var was UserListState
+		if found && json.Unmarshal(raw, &was) == nil && was.Inputs == st.Inputs {
+			res.Revision = rev
+		} else if data, err := json.Marshal(st); err == nil {
+			if rev, err := p.Store.Put(StateUserList, KeyList, data); err != nil {
+				res.Errors = append(res.Errors, fmt.Sprintf("its own %s cannot be written: %v", StateUserList, err))
+			} else {
+				res.Revision, res.Written = rev, true
+				p.say(&res, EventUserList, map[string]any{"digest": st.Digest, "revision": rev, "users": st.Users,
+					"differing": len(st.Compare.Differing()), "mode": Shadow})
+			}
+		}
+	}
+	ms := Memberships(recs)
+	res.Memberships = len(ms)
+	for _, key := range sortedKeys(ms) {
+		m, now := publish(p.Publish, ms[key])
+		switch {
+		case now:
+			res.Published = append(res.Published, key)
+			p.say(&res, EventMembership, map[string]any{"node": m.Node, "module": m.Module, "digest": m.Digest, "published": true})
+		case m.Published != MembershipUnchanged:
+			res.NotPublished = append(res.NotPublished, key+": "+m.Published)
+		}
+		data, _ := json.Marshal(m)
+		if p.changed(&res, StateMemberships, key, data) {
+			res.MembershipsWritten++
+		}
+	}
+	held, heldErr := HeldStreams(p.Call)
+	for _, module := range sortedKeys(in.Manifests) {
+		if !assigned(in, module) {
+			continue
+		}
+		a := Assert(module, in.Digests[module], in.Manifests[module], held, heldErr)
+		res.Assertions++
+		data, _ := json.Marshal(a)
+		if p.changed(&res, StateAssertions, module, data) {
+			res.AssertionsWritten++
+		}
+	}
+	if _, _, found, err := p.Store.Get(StateTakeover, KeySwitch); err == nil && !found {
+		data, _ := json.Marshal(Switch{V: 1, State: Shadow, Acts: []Act{}})
+		if _, err := p.Store.Put(StateTakeover, KeySwitch, data); err != nil {
+			res.Errors = append(res.Errors, fmt.Sprintf("its own %s cannot be written: %v", StateTakeover, err))
+		}
+	}
+	return res
+}
+
+// Last is the result of the last pass this part made, kept under the lock alone.
+func (p *Part) Last() Result {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	return p.last
+}
+
+func assigned(in Inputs, module string) bool {
+	for _, ms := range in.Assigned {
+		for _, m := range ms {
+			if m == module {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+// changed writes key when its value differs from the one held, and says whether it wrote.
+func (p *Part) changed(res *Result, state, key string, data []byte) bool {
+	raw, _, found, err := p.Store.Get(state, key)
+	if err != nil {
+		res.Errors = append(res.Errors, fmt.Sprintf("its own %s %s cannot be read: %v", state, key, err))
+		return false
+	}
+	if found && bytes.Equal(raw, data) {
+		return false
+	}
+	if _, err := p.Store.Put(state, key, data); err != nil {
+		res.Errors = append(res.Errors, fmt.Sprintf("its own %s %s cannot be written: %v", state, key, err))
+		return false
+	}
+	return true
+}
+
+func (p *Part) say(res *Result, event string, body any) {
+	if p.Emit == nil {
+		return
+	}
+	if err := p.Emit.Emit(event, body); err != nil {
+		res.Errors = append(res.Errors, fmt.Sprintf("the event %s could not be said: %v", event, err))
+	}
+}
+
+func sortedKeys[V any](m map[string]V) []string {
+	out := make([]string, 0, len(m))
+	for k := range m {
+		out = append(out, k)
+	}
+	sort.Strings(out)
+	return out
+}
+
+// Switch is the value of `takeover`: which list the bus node follows, and every act on the switch.
+type Switch struct {
+	V     int    `json:"v"`
+	State string `json:"state"`
+	Acts  []Act  `json:"acts"`
+}
+
+// Act is one take-over or hand-back asked, done or refused.
+type Act struct {
+	Act     string    `json:"act"`
+	By      string    `json:"by"`
+	Why     string    `json:"why,omitempty"`
+	At      time.Time `json:"at"`
+	Refused string    `json:"refused,omitempty"`
+}
+
+// keptActs is how many acts the switch keeps, newest last.
+const keptActs = 50
+
+// Operator says whether a caller is the operator's credential: a person's own bus account (`person.<name>`), which no
+// session of an agent holds (an agent calls as its machine's tool runner).
+func Operator(caller string) bool {
+	name, ok := strings.CutPrefix(caller, "person.")
+	return ok && name != ""
+}
+
+// NotComposable is why take-over is refused in this milestone, whatever the lists say.
+const NotComposable = "the enrolment users and the persons cannot be composed: they live only in the controller's store, and take-over waits until they have records on the bus (ADR 0547 clause 9, version 26)"
+
+// record keeps an act on the switch; a refused write is said in the answer.
+func (p *Part) record(a Act) string {
+	raw, _, found, err := p.Store.Get(StateTakeover, KeySwitch)
+	if err != nil {
+		return fmt.Sprintf("; the act is not recorded: %v", err)
+	}
+	s := Switch{V: 1, State: Shadow}
+	if found {
+		_ = json.Unmarshal(raw, &s)
+	}
+	s.Acts = append(s.Acts, a)
+	if len(s.Acts) > keptActs {
+		s.Acts = s.Acts[len(s.Acts)-keptActs:]
+	}
+	data, _ := json.Marshal(s)
+	if _, err := p.Store.Put(StateTakeover, KeySwitch, data); err != nil {
+		return fmt.Sprintf("; the act is not recorded: %v", err)
+	}
+	return ""
+}
+
+// TakeOver is the operator's switch to the grants part's list. It is refused without the operator's credential, while
+// any user of the shadow list differs from the loaded list (but those both agree are gone), and in this milestone
+// always, since the enrolment users and the persons cannot be composed. Every ask is recorded.
+func (p *Part) TakeOver(caller, why string) error {
+	a := Act{Act: "take-over", By: caller, Why: why, At: p.now()}
+	if !Operator(caller) {
+		a.Refused = fmt.Sprintf("take-over is the operator's alone: %s is not a person's account", caller)
+		return fmt.Errorf("%s%s", a.Refused, p.record(a))
+	}
+	res := p.Compose()
+	var reasons []string
+	if c := res.UserList.Compare; !c.Equal() {
+		if c.Unread != "" {
+			reasons = append(reasons, "the loaded list could not be read: "+c.Unread)
+		}
+		if d := c.Differing(); len(d) > 0 {
+			reasons = append(reasons, fmt.Sprintf("%d users differ between the shadow list and the loaded list: %s", len(d), strings.Join(d, ", ")))
+		}
+	}
+	reasons = append(reasons, NotComposable)
+	a.Refused = "take-over refused: " + strings.Join(reasons, "; ")
+	return fmt.Errorf("%s%s", a.Refused, p.record(a))
+}
+
+// HandBack is the operator's switch back to the controller's list. Refused without the operator's credential, and
+// while the part is in shadow, since the bus node follows the controller's list already. Every ask is recorded.
+func (p *Part) HandBack(caller, why string) error {
+	a := Act{Act: "hand-back", By: caller, Why: why, At: p.now()}
+	if !Operator(caller) {
+		a.Refused = fmt.Sprintf("hand-back is the operator's alone: %s is not a person's account", caller)
+		return fmt.Errorf("%s%s", a.Refused, p.record(a))
+	}
+	a.Refused = "nothing to hand back: the grants part is in shadow and never took over, so the bus node follows the controller's list already"
+	return fmt.Errorf("%s%s", a.Refused, p.record(a))
+}
@@ -0,0 +1,273 @@
+package grants
+
+import (
+	"fmt"
+	"slices"
+	"strings"
+
+	"git.novox.be/novox/mesh-sdk/go/buscompose"
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+)
+
+// Records is what the bus composer composes from, rebuilt from the bus (mesh-controller internal/inventory busrecords.go,
+// BusRecords, read the same way from Inputs instead of the controller's store). Pure. An assigned module whose manifest
+// the indexer does not hold is left out and named, where the controller refuses the whole composition: the shadow
+// composes what it can and says what it could not.
+func Records(in Inputs) (buscompose.Records, []Gap) {
+	var gaps []Gap
+	seats := map[string]catalogue.SeatDeclaration{}
+	declarers := map[string]string{}
+	for _, m := range in.Manifests {
+		for _, s := range m.DefinesSeats {
+			seats[s.Name] = s
+			declarers[s.Name] = m.Module
+		}
+	}
+	for _, own := range catalogue.SeatsWithAProtocol() {
+		seats[own.Name] = catalogue.SeatDeclaration{Name: own.Name, Scope: own.Scope, Accepts: own.Accepts, Emits: own.Emits, Serves: own.Serves}
+	}
+	out := buscompose.Records{Assigned: map[string][]buscompose.Declared{}, People: map[string][]string{},
+		Interchangeable: map[string]bool{}}
+	values := func(provider, setting string) []any {
+		var vs []any
+		for _, node := range in.Nodes {
+			if v, ok := in.Values[node+"/"+provider+"/"+setting]; ok && slices.Contains(in.Assigned[node], provider) {
+				vs = append(vs, v)
+			}
+		}
+		return vs
+	}
+	for _, node := range in.Nodes {
+		out.Nodes = append(out.Nodes, node)
+		manifestOf := func(module string) (catalogue.Manifest, bool) {
+			if m, ok := in.Running[node+"."+module]; ok {
+				return m, true
+			}
+			m, ok := in.Manifests[module]
+			return m, ok
+		}
+		var here []catalogue.Manifest
+		for _, module := range in.Assigned[node] {
+			if m, ok := manifestOf(module); ok {
+				here = append(here, m)
+			}
+		}
+		for _, module := range in.Assigned[node] {
+			m, known := manifestOf(module)
+			if !known {
+				gaps = append(gaps, Gap{Input: module + " on " + node, Why: "left out of the shadow list: no manifest to derive what it may say from"})
+				continue
+			}
+			d := declaredFor(m, seats, declarers)
+			for _, sr := range catalogue.ReadsGranted(m, here, node) {
+				d.KeyedReads = append(d.KeyedReads, buscompose.KeyedRead{Read: sr.Read, Key: sr.Key})
+			}
+			d.Hears, d.HearsAStream, d.Consumes = hearsOf(m, in.Manifests, node, values, d.Consumes)
+			out.Assigned[node] = append(out.Assigned[node], d)
+			if m.Instances == catalogue.InstancesInterchangeable {
+				out.Interchangeable[m.Module] = true
+			}
+		}
+	}
+	return out, gaps
+}
+
+// declaredFor is mesh-controller's declaredFor (internal/inventory/busrecords.go), copied: one module's manifest as the
+// composer needs it.
+func declaredFor(m catalogue.Manifest, seats map[string]catalogue.SeatDeclaration, declarers map[string]string) buscompose.Declared {
+	var fromModules []string
+	var watches []buscompose.Seat
+	for _, c := range m.Consumes {
+		emitter, event, named := strings.Cut(c, ".")
+		if named {
+			if s, isASeat := seats[emitter]; isASeat && s.Kinded {
+				ev := strings.TrimSuffix(event, ".*")
+				if catalogue.SeatSays(s.Emits, ev) {
+					watches = append(watches, buscompose.Seat{Name: s.Name, Scope: s.Scope, Emits: []string{ev},
+						Kinded: true, Proofs: s.Proofs, DeclaredBy: declarers[s.Name]})
+					continue
+				}
+			}
+			if s, isASeat := seats[emitter]; isASeat && catalogue.SeatSays(s.Emits, event) {
+				watches = append(watches, buscompose.Seat{Name: s.Name, Emits: []string{event}})
+				continue
+			}
+		}
+		fromModules = append(fromModules, c)
+	}
+	d := buscompose.Declared{
+		Module: m.Module, Emits: m.EmitsAll(), Consumes: fromModules, Watches: watches, Serves: m.Tools,
+		Invokes: m.Invokes, Waits: waitsOf(m, seats), State: bucketsOf(m), Reads: m.Reads, Logs: logsOf(m),
+		Streams: streamsOf(m), Queues: queueOwnersOf(m), Processes: processesOf(m), Checks: catalogue.HealthChecks(m),
+		RunsAs: m.RunsAs, Issued: issuedTools(m),
+	}
+	for _, b := range m.Bundles {
+		if len(b.Loads) > 0 {
+			d.Loads = true
+		}
+	}
+	if _, reads := m.OwnSecrets["broker"]; !reads {
+		d.NoAccount = true
+	}
+	if _, reads := m.OwnSecrets[buscompose.ProvisionerSecret]; reads && m.ClaimsSeat(buscompose.NodeProvisionerSeat) {
+		d.ProvisionsNode = true
+	}
+	d.SnapshotsTheBus = m.ClaimsSeat(catalogue.BrokerSeat)
+	for _, c := range m.Claims {
+		if s, hasAProtocol := seats[c.Name]; hasAProtocol {
+			held := asSeat(s, declarers[s.Name])
+			held.Kind = c.Kind
+			held.Capabilities = c.Capabilities
+			d.Holds = append(d.Holds, held)
+		}
+	}
+	for _, name := range m.Uses {
+		if s, declaredSomewhere := seats[name]; declaredSomewhere {
+			d.Uses = append(d.Uses, asSeat(s, declarers[s.Name]))
+		}
+	}
+	return d
+}
+
+func waitsOf(m catalogue.Manifest, seats map[string]catalogue.SeatDeclaration) []buscompose.Wait {
+	var out []buscompose.Wait
+	for _, w := range m.Waits {
+		emitter, event, _ := strings.Cut(w, ".")
+		first, _, _ := strings.Cut(event, ".")
+		wait := buscompose.Wait{Name: w, Emitter: emitter, Event: event}
+		if s, isASeat := seats[emitter]; isASeat {
+			switch {
+			case s.Kinded && catalogue.SeatSays(s.Emits, first):
+				wait.Seat, wait.Last = true, "kind"
+			case s.NamedByCaller(first) && catalogue.SeatSays(s.Emits, first):
+				wait.Seat, wait.Last = true, "asker"
+			case catalogue.SeatSays(s.Emits, event):
+				wait.Seat = true
+			}
+		}
+		out = append(out, wait)
+	}
+	return out
+}
+
+func issuedTools(m catalogue.Manifest) []string {
+	var out []string
+	for _, o := range m.Provides {
+		if tool, issued := m.IssuedCredentialOf(o.Name); issued && !slices.Contains(out, tool) {
+			out = append(out, tool)
+		}
+	}
+	return out
+}
+
+func bucketsOf(m catalogue.Manifest) []buscompose.Bucket {
+	var out []buscompose.Bucket
+	for _, s := range m.State {
+		out = append(out, buscompose.Bucket{Module: m.Module, Name: s.Name, History: s.History, TTLSeconds: s.TTLSeconds,
+			PerMachine: s.PerMachine, KeyTTL: s.KeyTTL})
+	}
+	return out
+}
+
+func logsOf(m catalogue.Manifest) []buscompose.Log {
+	var out []buscompose.Log
+	for _, l := range m.Logs {
+		out = append(out, buscompose.Log{Module: m.Module, Name: l.Name, MaxMiB: l.Cap()})
+	}
+	return out
+}
+
+func asSeat(s catalogue.SeatDeclaration, declarer string) buscompose.Seat {
+	seat := buscompose.Seat{Name: s.Name, Scope: s.Scope, Accepts: s.Accepts, Emits: s.Emits,
+		Serves: catalogue.VerbNames(s.Serves), Kinded: s.Kinded, ByCaller: s.ByCaller, Proofs: s.Proofs, DeclaredBy: declarer}
+	if own, ok := catalogue.SeatNamed(s.Name); ok && own.PulledByKind {
+		seat.PulledByKind = true
+	}
+	for _, r := range s.Records {
+		if declarer != "" {
+			seat.Records = append(seat.Records, buscompose.BucketName(declarer, r))
+		}
+	}
+	return seat
+}
+
+func streamsOf(m catalogue.Manifest) []buscompose.ModuleStream {
+	var out []buscompose.ModuleStream
+	for _, s := range m.Streams {
+		events := make([]string, 0, len(s.Events))
+		for _, e := range s.Events {
+			events = append(events, buscompose.WirePattern(e))
+		}
+		out = append(out, buscompose.ModuleStream{Module: m.Module, Name: s.BusName(), Events: events,
+			MaxAgeDays: s.Days(), MaxMiB: s.Cap(), Restricted: s.Grant != nil,
+			WorkQueue: s.Retention == catalogue.StreamRetentionWorkQueue, Duplicates: s.Duplicates})
+	}
+	return out
+}
+
+func queueOwnersOf(m catalogue.Manifest) []buscompose.QueueOwner {
+	buses := m.ProcessBuses()
+	if len(buses) == 0 {
+		return nil
+	}
+	byName := map[string]catalogue.StreamDeclaration{}
+	for _, s := range m.Streams {
+		byName[s.Name] = s
+	}
+	var out []buscompose.QueueOwner
+	for _, r := range m.Resources {
+		id := fmt.Sprint(r["id"])
+		b, declared := buses[id]
+		if !declared {
+			continue
+		}
+		for _, q := range b.Queues {
+			s, known := byName[q]
+			if !known || s.Retention != catalogue.StreamRetentionWorkQueue {
+				continue
+			}
+			out = append(out, buscompose.QueueOwner{Process: id, Stream: s.BusName(), MaxDeliver: s.MaxDeliveries})
+		}
+	}
+	return out
+}
+
+func processesOf(m catalogue.Manifest) []buscompose.ProcessPrincipal {
+	buses := m.ProcessBuses()
+	if len(buses) == 0 {
+		return nil
+	}
+	queues := queueOwnersOf(m)
+	var out []buscompose.ProcessPrincipal
+	for _, r := range m.Resources {
+		id := fmt.Sprint(r["id"])
+		b, declared := buses[id]
+		if !declared {
+			continue
+		}
+		pr := buscompose.ProcessPrincipal{Process: id, Emits: b.Emits, State: b.State, Asks: b.Asks, Invokes: b.Invokes}
+		for _, q := range queues {
+			if q.Process == id {
+				pr.Queues = append(pr.Queues, q)
+			}
+		}
+		out = append(out, pr)
+	}
+	return out
+}
+
+func hearsOf(m catalogue.Manifest, declared map[string]catalogue.Manifest, node string, values func(provider, setting string) []any,
+	consumes []string) ([]buscompose.Heard, bool, []string) {
+	reading := m
+	reading.Consumes = consumes
+	parts, touches, onEvents := catalogue.Hearing(reading, declared, node, values)
+	var out []buscompose.Heard
+	for _, p := range parts {
+		h := buscompose.Heard{Stream: p.Stream.BusName(), Emitter: p.Emitter, Restricted: p.Stream.Grant != nil}
+		for _, pattern := range p.Patterns {
+			h.Filters = append(h.Filters, buscompose.ModuleStreamSubject(p.Emitter, buscompose.WirePattern(pattern)))
+		}
+		out = append(out, h)
+	}
+	return out, touches, onEvents
+}
@@ -0,0 +1,187 @@
+package grants
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"sort"
+	"strings"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// The part's tools, as its manifest lists them. Module tools in this milestone: a `mesh-*` seat must be in mesh-sdk's own
+// seat list, which the running controller's composer does not know, so the part claims no seat until take-over.
+const (
+	ToolGrants     = "grants_grants"
+	ToolMembership = "grants_membership"
+	ToolUserList   = "grants_user_list"
+	ToolComposeNow = "grants_compose_now"
+	ToolAssert     = "grants_assert"
+	ToolTakeOver   = "grants_take_over"
+	ToolHandBack   = "grants_hand_back"
+)
+
+// Tools is every tool, in the manifest's order.
+var Tools = []string{ToolGrants, ToolMembership, ToolUserList, ToolComposeNow, ToolAssert, ToolTakeOver, ToolHandBack}
+
+// WritesNoGrant is what grants says of the part's own grants in this milestone.
+const WritesNoGrant = "none: the grants part writes no grants.<module>.<fp> before ADR 0547's third milestone (clause 5); the controller's are beside"
+
+// Grants answers the tool grants: what the part writes of grants (none), and the controller's, one module's or all.
+func (p *Part) Grants(module string) (any, error) {
+	keys, err := p.Read.Keys(ReadControllerGrant)
+	if err != nil {
+		return map[string]any{"writes": WritesNoGrant, "controller_unread": err.Error()}, nil
+	}
+	type grant struct {
+		Module      string   `json:"module"`
+		Fingerprint string   `json:"fingerprint"`
+		Accounts    []string `json:"accounts,omitempty"`
+	}
+	out := []grant{}
+	for _, k := range keys {
+		m, fp, err := delivery.ParseControllerGrantKey(k)
+		if err != nil || (module != "" && m != module) {
+			continue
+		}
+		g := grant{Module: m, Fingerprint: fp}
+		if module != "" {
+			if raw, found, err := p.Read.Get(ReadControllerGrant, k); err == nil && found {
+				if v, err := delivery.DecodeControllerGrant(raw); err == nil {
+					g.Accounts = v.Accounts
+				}
+			}
+		}
+		out = append(out, g)
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i].Module+out[i].Fingerprint < out[j].Module+out[j].Fingerprint })
+	return map[string]any{"writes": WritesNoGrant, "controller": out, "count": len(out)}, nil
+}
+
+// MembershipOf answers the tool membership: one module on one node as composed now, and as last published by the
+// part's process (its state memberships says what became of each at the last pass).
+func (p *Part) MembershipOf(node, module string) (any, error) {
+	if node == "" || module == "" {
+		return nil, errors.New("membership names a node and a module")
+	}
+	in := ReadInputs(p.Read, &p.cache)
+	recs, left := Records(in)
+	m, ok := Memberships(recs)[node+"."+module]
+	out := map[string]any{"node": node, "module": module, "gaps": MembershipGaps}
+	if ok {
+		out["composed"] = m
+	} else {
+		why := fmt.Sprintf("%s is not assigned to %s on the bus", module, node)
+		for _, g := range left {
+			if g.Input == module+" on "+node {
+				why = g.Why
+			}
+		}
+		out["composed"] = why
+	}
+	if raw, rev, found, err := p.Store.Get(StateMemberships, node+"."+module); err != nil {
+		out["published"] = "not readable: " + err.Error()
+	} else if found {
+		out["published"] = map[string]any{"revision": rev, "last_pass": json.RawMessage(raw)}
+	} else {
+		out["published"] = "no pass of the part's process has composed it yet"
+	}
+	return out, nil
+}
+
+// Pass composes and keeps the result as the last pass, for the tools to read.
+func (p *Part) Pass() Result {
+	res := p.Compose()
+	data, _ := json.Marshal(res)
+	if _, err := p.Store.Put(StateUserList, KeyPass, data); err != nil {
+		res.Errors = append(res.Errors, fmt.Sprintf("its own %s %s cannot be written: %v", StateUserList, KeyPass, err))
+	}
+	return res
+}
+
+// NoGrantAgain is what compose-now says of the controller's grants: the controller serves no verb that writes a module's
+// grant again (its issue replaces the account, which is not that), so a grant write it lost stays lost until it composes
+// again; the part writes grants only from ADR 0547's third milestone.
+const NoGrantAgain = "missing: a verb to ask the controller to write a module's grant again (mesh-controller serves none; its issue replaces the bus account, which is not that), so compose-now cannot ask it"
+
+// AskCompose is the tool compose-now: it asks the part's process to compose and publish now (only the process holds the
+// grant to publish a membership), and answers the last pass, whose revision moves when the process answered.
+func (p *Part) AskCompose(caller string) (any, error) {
+	ask, _ := json.Marshal(map[string]any{"by": caller, "at": p.now()})
+	rev, err := p.Store.Put(StateUserList, KeyAsked, ask)
+	if err != nil {
+		return nil, fmt.Errorf("the ask could not be written: %w", err)
+	}
+	out := map[string]any{"asked": rev, "says": "the part's process composes and publishes at this ask; grants_user_list's last pass says what it published",
+		"controller_grants": NoGrantAgain}
+	if raw, prev, found, err := p.Store.Get(StateUserList, KeyPass); err == nil && found {
+		out["last_pass"] = map[string]any{"revision": prev, "result": json.RawMessage(raw)}
+	}
+	return out, nil
+}
+
+// UserList answers the tool user-list: the shadow list as last written, beside what the bus node says it loaded now.
+func (p *Part) UserList() (any, error) {
+	out := map[string]any{"mode": Shadow}
+	raw, rev, found, err := p.Store.Get(StateUserList, KeyList)
+	switch {
+	case err != nil:
+		out["written"] = "not readable: " + err.Error()
+	case !found:
+		out["written"] = "nothing composed yet: grants_compose_now composes it"
+	default:
+		var st UserListState
+		if err := json.Unmarshal(raw, &st); err != nil {
+			return nil, fmt.Errorf("its own user list cannot be read: %w", err)
+		}
+		out["revision"], out["written"] = rev, st
+		if raw, prev, found, err := p.Store.Get(StateUserList, KeyPass); err == nil && found {
+			out["last_pass"] = map[string]any{"revision": prev, "result": json.RawMessage(raw)}
+		}
+		if st.BusNode != "" {
+			if raw, found, err := p.Read.Get(ReadHave, st.BusNode+"."+BusModule); err == nil && found {
+				if h, err := delivery.DecodeHave(raw); err == nil {
+					out["loaded_now"] = h.UserList
+				}
+			}
+		}
+	}
+	return out, nil
+}
+
+// AssertOne answers the tool assert: one module's buckets, logs and streams as composed from its manifest at the
+// indexer's trunk, beside what the bus holds. It asserts nothing.
+func (p *Part) AssertOne(module string) (any, error) {
+	if module == "" {
+		return nil, errors.New("assert names a module")
+	}
+	raw, found, err := p.Read.Get(ReadModules, module)
+	if err != nil {
+		return nil, fmt.Errorf("the indexer's %s cannot be read: %w", module, err)
+	}
+	if !found {
+		return nil, fmt.Errorf("the indexer holds no module %s", module)
+	}
+	v, err := delivery.DecodeModule(raw)
+	if err != nil || v.Manifest == "" {
+		return nil, fmt.Errorf("the indexer names no manifest of %s", module)
+	}
+	m, err := p.cache.get(p.Read, v.Manifest)
+	if err != nil {
+		return nil, err
+	}
+	held, heldErr := HeldStreams(p.Call)
+	return Assert(module, v.Manifest, m, held, heldErr), nil
+}
+
+// Answer is a tool's arguments read as text.
+func Answer(args map[string]any, name string) string {
+	switch v := args[name].(type) {
+	case string:
+		return strings.TrimSpace(v)
+	case bool:
+		return fmt.Sprint(v)
+	}
+	return ""
+}
@@ -0,0 +1,237 @@
+package grants
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"slices"
+	"sort"
+	"strings"
+
+	"git.novox.be/novox/mesh-sdk/go/buscompose"
+)
+
+// User is one bus user and its grants, as the bus module's nats_users answers them: never a password hash.
+type User struct {
+	User           string   `json:"user"`
+	Publish        []string `json:"publish"`
+	Subscribe      []string `json:"subscribe"`
+	AllowResponses bool     `json:"allow_responses"`
+}
+
+// ComposeUsers is the shadow list: every user the composer derives from the records, with its grants. Pure.
+func ComposeUsers(r buscompose.Records) ([]User, error) {
+	principals, err := buscompose.Users(r)
+	if err != nil {
+		return nil, err
+	}
+	out := make([]User, 0, len(principals))
+	for _, p := range principals {
+		perms, err := buscompose.PermissionsFor(p)
+		if err != nil {
+			return nil, fmt.Errorf("%s: %w", p.Username(), err)
+		}
+		out = append(out, User{User: p.Username(), Publish: set(perms.Publish), Subscribe: set(perms.Subscribe),
+			AllowResponses: perms.AllowResponses})
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i].User < out[j].User })
+	return out, nil
+}
+
+func set(in []string) []string {
+	out := slices.Clone(in)
+	sort.Strings(out)
+	out = slices.Compact(out)
+	if out == nil {
+		out = []string{}
+	}
+	return out
+}
+
+// Digest is a list's digest, `sha256:<hex>`, over its users and grants in order.
+func Digest(users []User) string {
+	raw, _ := json.Marshal(users)
+	sum := sha256.Sum256(raw)
+	return "sha256:" + hex.EncodeToString(sum[:])
+}
+
+// LoadedUsers is the list the bus loaded, as its module's nats_users reads it from the file: every user by name, then
+// each one's grants in full.
+func LoadedUsers(c Caller) ([]User, error) {
+	raw, err := c.Call(CallUsers, map[string]any{})
+	if err != nil {
+		return nil, fmt.Errorf("%s: %w", CallUsers, err)
+	}
+	var names struct {
+		Users []struct {
+			User string `json:"user"`
+		} `json:"users"`
+	}
+	if err := json.Unmarshal(unwrap(raw), &names); err != nil {
+		return nil, fmt.Errorf("%s answered no list of users: %w", CallUsers, err)
+	}
+	full := map[string]User{}
+	ask := func(part string) error {
+		raw, err := c.Call(CallUsers, map[string]any{"user": part})
+		if err != nil {
+			return fmt.Errorf("%s %s: %w", CallUsers, part, err)
+		}
+		var got struct {
+			Users []User `json:"users"`
+		}
+		if err := json.Unmarshal(unwrap(raw), &got); err != nil {
+			return fmt.Errorf("%s %s answered no grants: %w", CallUsers, part, err)
+		}
+		for _, u := range got.Users {
+			u.Publish, u.Subscribe = set(u.Publish), set(u.Subscribe)
+			full[u.User] = u
+		}
+		return nil
+	}
+	// Every name with a dot in one call; each name without one (the controller) alone.
+	if err := ask("."); err != nil {
+		return nil, err
+	}
+	out := make([]User, 0, len(names.Users))
+	for _, n := range names.Users {
+		if _, ok := full[n.User]; !ok {
+			if err := ask(n.User); err != nil {
+				return nil, err
+			}
+		}
+		u, ok := full[n.User]
+		if !ok {
+			return nil, fmt.Errorf("%s names %s and gives no grants for it", CallUsers, n.User)
+		}
+		out = append(out, u)
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i].User < out[j].User })
+	return out, nil
+}
+
+// unwrap takes a tool's answer out of an MCP content wrapper, when a runtime hands one.
+func unwrap(raw json.RawMessage) []byte {
+	var wrapped struct {
+		Content []struct {
+			Text string `json:"text"`
+		} `json:"content"`
+	}
+	if json.Unmarshal(raw, &wrapped) == nil && len(wrapped.Content) == 1 && wrapped.Content[0].Text != "" {
+		return []byte(wrapped.Content[0].Text)
+	}
+	return raw
+}
+
+// UserDiff is how one user's grants differ: what the shadow list grants that the loaded list does not, and back.
+type UserDiff struct {
+	User             string   `json:"user"`
+	PublishAdded     []string `json:"publish_added,omitempty"`
+	PublishDropped   []string `json:"publish_dropped,omitempty"`
+	SubscribeAdded   []string `json:"subscribe_added,omitempty"`
+	SubscribeDropped []string `json:"subscribe_dropped,omitempty"`
+	Responses        string   `json:"responses,omitempty"`
+}
+
+// Comparison is the shadow list against the loaded list.
+type Comparison struct {
+	Shadow int `json:"shadow"`
+	Loaded int `json:"loaded"`
+	// Added are users in the shadow list the loaded list lacks (one left out for want of a credential among them);
+	// Dropped are loaded users the shadow list lacks; Gone are those of Dropped whose machine or module placement no
+	// longer names, which both lists agree are gone.
+	Added   []string   `json:"added"`
+	Dropped []string   `json:"dropped"`
+	Gone    []string   `json:"gone,omitempty"`
+	Differ  []UserDiff `json:"differ"`
+	Same    int        `json:"same"`
+	// Unread says the loaded list could not be read, and why: nothing is compared then.
+	Unread string `json:"unread,omitempty"`
+}
+
+// Equal says the two lists agree in every user, but those both agree are gone.
+func (c Comparison) Equal() bool {
+	return c.Unread == "" && len(c.Added) == 0 && len(c.Differ) == 0 && len(c.Dropped) == len(c.Gone)
+}
+
+// Differing names every user that keeps the lists apart: added, dropped and not gone, or granted otherwise.
+func (c Comparison) Differing() []string {
+	var out []string
+	out = append(out, c.Added...)
+	for _, d := range c.Dropped {
+		if !slices.Contains(c.Gone, d) {
+			out = append(out, d)
+		}
+	}
+	for _, d := range c.Differ {
+		out = append(out, d.User)
+	}
+	sort.Strings(out)
+	return out
+}
+
+// Compare compares the shadow list with the loaded one. placed says whether placement still names a loaded user's
+// machine and module; nil names every one. Pure.
+func Compare(shadow, loaded []User, placed func(user string) bool) Comparison {
+	c := Comparison{Shadow: len(shadow), Loaded: len(loaded), Added: []string{}, Dropped: []string{}, Differ: []UserDiff{}}
+	have := map[string]User{}
+	for _, u := range loaded {
+		have[u.User] = u
+	}
+	want := map[string]bool{}
+	for _, s := range shadow {
+		want[s.User] = true
+		l, ok := have[s.User]
+		if !ok {
+			c.Added = append(c.Added, s.User)
+			continue
+		}
+		d := UserDiff{User: s.User, PublishAdded: minus(s.Publish, l.Publish), PublishDropped: minus(l.Publish, s.Publish),
+			SubscribeAdded: minus(s.Subscribe, l.Subscribe), SubscribeDropped: minus(l.Subscribe, s.Subscribe)}
+		if s.AllowResponses != l.AllowResponses {
+			d.Responses = fmt.Sprintf("shadow %v, loaded %v", s.AllowResponses, l.AllowResponses)
+		}
+		if len(d.PublishAdded)+len(d.PublishDropped)+len(d.SubscribeAdded)+len(d.SubscribeDropped) == 0 && d.Responses == "" {
+			c.Same++
+			continue
+		}
+		c.Differ = append(c.Differ, d)
+	}
+	for _, l := range loaded {
+		if !want[l.User] {
+			c.Dropped = append(c.Dropped, l.User)
+			if placed != nil && !placed(l.User) {
+				c.Gone = append(c.Gone, l.User)
+			}
+		}
+	}
+	return c
+}
+
+func minus(a, b []string) []string {
+	var out []string
+	for _, x := range a {
+		if !slices.Contains(b, x) {
+			out = append(out, x)
+		}
+	}
+	return out
+}
+
+// Placed says whether placement still names a user's machine and module: a machine's users (`node.<n>`,
+// `provisioner.<n>`) while the machine is seen, a module's or process's (`<n>.<module>[.<process>]`) while the module is
+// assigned there. The controller, enrolment users and persons are never judged gone from here.
+func Placed(in Inputs) func(user string) bool {
+	return func(user string) bool {
+		parts := strings.Split(user, ".")
+		switch {
+		case len(parts) < 2:
+			return true
+		case parts[0] == "node" || parts[0] == "provisioner":
+			return slices.Contains(in.Nodes, parts[1])
+		case parts[0] == "person" || parts[0] == "enrol":
+			return true
+		}
+		return slices.Contains(in.Nodes, parts[0]) && slices.Contains(in.Assigned[parts[0]], parts[1])
+	}
+}
@@ -0,0 +1,103 @@
+{
+  "module": "mesh-grants",
+  "version": "1",
+  "slug": "grants",
+  "reads": [
+    "mesh-config.resolved",
+    "mesh-controller.assignments",
+    "mesh-controller.grants",
+    "mesh-delivery-assigner.wants",
+    "mesh-delivery-builder.builds",
+    "mesh-delivery-indexer.manifests",
+    "mesh-delivery-indexer.modules",
+    "node-engine.have"
+  ],
+  "invokes": [
+    "nats.nats_streams",
+    "nats.nats_user_can",
+    "nats.nats_users"
+  ],
+  "emits": [
+    "membership-changed",
+    "user-list-changed"
+  ],
+  "tools": [
+    "grants_grants",
+    "grants_membership",
+    "grants_user_list",
+    "grants_compose_now",
+    "grants_assert",
+    "grants_take_over",
+    "grants_hand_back"
+  ],
+  "state": [
+    {
+      "name": "assertions",
+      "history": 5
+    },
+    {
+      "name": "memberships",
+      "history": 5
+    },
+    {
+      "name": "takeover",
+      "history": 20
+    },
+    {
+      "name": "user-list",
+      "history": 20
+    }
+  ],
+  "own-secrets": {
+    "broker": "${dir:state}/broker"
+  },
+  "secrets-owner": "mesh-grants",
+  "resources": [
+    {
+      "id": "account",
+      "type": "user",
+      "name": "mesh-grants",
+      "shell": "/usr/bin/nologin",
+      "home": "/var/lib/mesh-grants"
+    },
+    {
+      "id": "state",
+      "type": "directory",
+      "mode": "0700",
+      "owner": "mesh-grants",
+      "place": ".",
+      "unknown": "program"
+    },
+    {
+      "id": "grants",
+      "type": "process",
+      "name": "mesh-grants",
+      "artifact": "program",
+      "run": [
+        "./mesh-grants"
+      ],
+      "env": {
+        "MESH_BROKER_FILE": "${dir:state}/broker"
+      },
+      "user": "mesh-grants",
+      "health": {
+        "kind": "unit"
+      }
+    }
+  ],
+  "build": {
+    "artifacts": [
+      {
+        "name": "program",
+        "kind": "bundle",
+        "language": "go",
+        "system": "arch",
+        "from": "cmd/mesh-grants",
+        "binary": "mesh-grants",
+        "loads": [
+          "mesh-grants"
+        ]
+      }
+    ]
+  }
+}