diff --git a/go/buscalls/buscalls.go b/go/buscalls/buscalls.go
new file mode 100644
index 0000000..44e007d
--- /dev/null
+++ b/go/buscalls/buscalls.go
@@ -0,0 +1,382 @@
+// Package buscalls is the contract of the calls a bundle makes on its own bus state through the tool runner, over the
+// bundle's pipe (novox/hq ADR 0595 §9, ADR 0597 §10, design 25 § 12.5): the object store's, a stream's read-back and
+// fill, a work queue's size and dead letters, and the ledger's. Each call names an entry by the local name its module
+// asks for it by in `requires`; the tool runner serves it from the module's membership's bindings, its own entries
+// only. Only the shapes and the method names are here: what the tool runner refuses, and why, is its own.
+//
+// It is a package of its own, imported only by the modules that use these calls and by the tool runner, so a change
+// here rebuilds those and not the module library's importers (ADR 0595 §9). It imports nothing of mesh-sdk.
+package buscalls
+
+import (
+	"encoding/json"
+	"fmt"
+	"strings"
+	"time"
+)
+
+// MetaCall is where in a `tools/call`'s `_meta` the tool runner hands a bundle the id of the tool call in flight: the id
+// ApplyRequest.Call names, so the runner stamps the caller it proved for that call as the operation's author (novox/hq
+// ADR 0597 §7). The runner writes `_meta`; a caller writes only `arguments`, so no caller can name another call.
+const MetaCall = "mesh/call"
+
+// The methods a bundle asks the tool runner, one per call.
+const (
+	ObjectsPut    = "mesh/objects.put"
+	ObjectsGet    = "mesh/objects.get"
+	ObjectsList   = "mesh/objects.list"
+	ObjectsDelete = "mesh/objects.delete"
+	ObjectsInfo   = "mesh/objects.info"
+	ObjectsWatch  = "mesh/objects.watch"
+
+	StreamRead = "mesh/stream.read"
+	StreamFill = "mesh/stream.fill"
+
+	WorkQueueSize = "mesh/workqueue.size"
+	WorkQueueDead = "mesh/workqueue.dead"
+
+	LedgerApply   = "mesh/ledger.apply"
+	LedgerGet     = "mesh/ledger.get"
+	LedgerHistory = "mesh/ledger.history"
+	LedgerWatch   = "mesh/ledger.watch"
+	LedgerQuery   = "mesh/ledger.query"
+	// The ledger's repairs, which the tool runner also serves as tools of every module owning a ledger, its own
+	// ledgers only (design 25 § 12.5).
+	LedgerRebuild  = "mesh/ledger.rebuild"
+	LedgerReindex  = "mesh/ledger.reindex"
+	LedgerSnapshot = "mesh/ledger.snapshot"
+	LedgerLag      = "mesh/ledger.lag"
+)
+
+// The methods the tool runner sends the bundle for a watch it asked, each naming the watch by its id, as `mesh/log`
+// does for a log.
+const (
+	ObjectsWatched = "mesh/objects"
+	LedgerWatched  = "mesh/ledger"
+)
+
+// Fill is how much an entry holds against its cap: its messages (or objects), its bytes and its cap in bytes.
+type Fill struct {
+	Count    uint64 `json:"count"`
+	Bytes    uint64 `json:"bytes"`
+	MaxBytes uint64 `json:"max_bytes"`
+}
+
+// Done is the answer of a call that answers nothing but that it was done.
+type Done struct{}
+
+// --- the object store
+
+// ObjectsPutRequest stores one object whole under its name, replacing one of that name.
+type ObjectsPutRequest struct {
+	Objects     string `json:"objects"`
+	Name        string `json:"name"`
+	Data        []byte `json:"data"`
+	Description string `json:"description,omitempty"`
+}
+
+// ObjectsNameRequest names one object of an object store: get, delete.
+type ObjectsNameRequest struct {
+	Objects string `json:"objects"`
+	Name    string `json:"name"`
+}
+
+// ObjectsRequest names an object store: list, info.
+type ObjectsRequest struct {
+	Objects string `json:"objects"`
+}
+
+// ObjectsWatchRequest asks the tool runner to send every object stored or deleted, as ObjectsChange under the watch's id.
+type ObjectsWatchRequest struct {
+	Objects string `json:"objects"`
+	Watch   string `json:"watch"`
+}
+
+// ObjectInfo is one object as its store holds it: put's answer, and each of list's.
+type ObjectInfo struct {
+	Name        string    `json:"name"`
+	Size        uint64    `json:"size"`
+	Chunks      uint32    `json:"chunks"`
+	Digest      string    `json:"digest"`
+	Description string    `json:"description,omitempty"`
+	Modified    time.Time `json:"modified"`
+	Deleted     bool      `json:"deleted,omitempty"`
+}
+
+// ObjectData is get's answer: the object's info and its bytes.
+type ObjectData struct {
+	Info ObjectInfo `json:"info"`
+	Data []byte     `json:"data"`
+}
+
+// ObjectsListed is list's answer: every object the store holds.
+type ObjectsListed struct {
+	Objects []ObjectInfo `json:"objects"`
+}
+
+// ObjectsChange is one object stored or deleted, sent under ObjectsWatched; Current says it was there when the watch
+// began.
+type ObjectsChange struct {
+	Watch   string     `json:"watch"`
+	Object  ObjectInfo `json:"object"`
+	Current bool       `json:"current"`
+}
+
+// --- a stream
+
+// StreamReadRequest reads a module's own stream from a sequence on, at most Limit messages, Subjects narrowing it.
+type StreamReadRequest struct {
+	Stream   string `json:"stream"`
+	From     uint64 `json:"from"`
+	Subjects string `json:"subjects,omitempty"`
+	Limit    int    `json:"limit,omitempty"`
+}
+
+// StreamRequest names a stream: fill.
+type StreamRequest struct {
+	Stream string `json:"stream"`
+}
+
+// StreamMessage is one message of a stream.
+type StreamMessage struct {
+	Sequence uint64          `json:"sequence"`
+	Subject  string          `json:"subject"`
+	Body     json.RawMessage `json:"body"`
+	At       time.Time       `json:"at"`
+}
+
+// StreamPage is read's answer: the messages in order, the sequence to read on from (0 when nothing follows) and the
+// stream's last sequence when it was read.
+type StreamPage struct {
+	Messages []StreamMessage `json:"messages"`
+	Next     uint64          `json:"next"`
+	Last     uint64          `json:"last"`
+}
+
+// StreamFilled is fill's answer: the stream's fill and its first and last sequence.
+type StreamFilled struct {
+	Fill
+	First uint64 `json:"first"`
+	Last  uint64 `json:"last"`
+}
+
+// --- a work queue
+
+// WorkQueueRequest names a work queue: size.
+type WorkQueueRequest struct {
+	Queue string `json:"queue"`
+}
+
+// WorkQueueDeadRequest asks a work queue's dead letters, at most Limit of them.
+type WorkQueueDeadRequest struct {
+	Queue string `json:"queue"`
+	Limit int    `json:"limit,omitempty"`
+}
+
+// WorkQueueSized is size's answer: the messages waiting to be taken, against the queue's cap.
+type WorkQueueSized struct {
+	Fill
+}
+
+// DeadLetter is one message delivered as often as its queue allows and never settled.
+type DeadLetter struct {
+	Sequence   uint64          `json:"sequence"`
+	Subject    string          `json:"subject"`
+	Deliveries int             `json:"deliveries"`
+	Body       json.RawMessage `json:"body,omitempty"`
+	At         time.Time       `json:"at"`
+}
+
+// WorkQueueDeadLetters is dead's answer.
+type WorkQueueDeadLetters struct {
+	Dead []DeadLetter `json:"dead"`
+}
+
+// --- the ledger (ADR 0597)
+
+// ApplyRequest applies one operation to one instance of a ledger. Call is the id of the tool call the operation
+// serves, as the tool runner handed it under MetaCall, whose caller the tool runner proved and stamps as the author
+// (ADR 0597 §7); empty, the operation carries the owning module's account alone. An author the bundle writes into Body
+// is never taken as the author.
+type ApplyRequest struct {
+	Ledger    string          `json:"ledger"`
+	Instance  string          `json:"instance"`
+	Operation string          `json:"operation"`
+	Body      json.RawMessage `json:"body,omitempty"`
+	Call      string          `json:"call,omitempty"`
+}
+
+// Applied is apply's answer: the operation was taken, with its sequence in the instance's history; StateBehind says
+// the state could not follow because its bucket is full, and catches up at the next apply after room is made (ADR
+// 0597 §6).
+type Applied struct {
+	Taken       bool   `json:"taken"`
+	Sequence    uint64 `json:"sequence"`
+	StateBehind bool   `json:"state_behind,omitempty"`
+}
+
+// Author is who an operation is by, as `apply` stamped it (ADR 0597 §7): the owning module's account, and the caller
+// of the tool call it served, as the tool runner proved it.
+type Author struct {
+	Account string `json:"account"`
+	Caller  string `json:"caller,omitempty"`
+}
+
+// InstanceRequest names one instance of a ledger: get, snapshot.
+type InstanceRequest struct {
+	Ledger   string `json:"ledger"`
+	Instance string `json:"instance"`
+}
+
+// InstanceState is get's answer: the instance's state and the sequence of the last operation it holds.
+type InstanceState struct {
+	Instance string          `json:"instance"`
+	State    json.RawMessage `json:"state"`
+	Sequence uint64          `json:"sequence"`
+}
+
+// HistoryRequest reads an instance's operations from a sequence on, at most Limit of them.
+type HistoryRequest struct {
+	Ledger   string `json:"ledger"`
+	Instance string `json:"instance"`
+	From     uint64 `json:"from,omitempty"`
+	Limit    int    `json:"limit,omitempty"`
+}
+
+// Operation is one operation as the history keeps it.
+type Operation struct {
+	Sequence  uint64          `json:"sequence"`
+	Instance  string          `json:"instance"`
+	Operation string          `json:"operation"`
+	Body      json.RawMessage `json:"body,omitempty"`
+	Author    Author          `json:"author"`
+	At        time.Time       `json:"at"`
+}
+
+// HistoryPage is history's answer: the operations oldest first, the sequence to read on from (0 when nothing
+// follows) and the instance's last sequence when it was read.
+type HistoryPage struct {
+	Operations []Operation `json:"operations"`
+	Next       uint64      `json:"next"`
+	Last       uint64      `json:"last"`
+}
+
+// LedgerWatchRequest asks the tool runner to send every change of the instances Instances names (an instance, with
+// `*` for one name and `>` for the rest) as InstanceChange under the watch's id: the current states first.
+type LedgerWatchRequest struct {
+	Ledger    string `json:"ledger"`
+	Instances string `json:"instances"`
+	Watch     string `json:"watch"`
+}
+
+// InstanceChange is one instance's new state, sent under LedgerWatched; Current says it was the state when the watch
+// began.
+type InstanceChange struct {
+	Watch    string          `json:"watch"`
+	Instance string          `json:"instance"`
+	State    json.RawMessage `json:"state"`
+	Sequence uint64          `json:"sequence"`
+	Current  bool            `json:"current"`
+}
+
+// QueryRequest reads a declared index of a ledger: the entries whose key Key names (a key, with `*` for one name and
+// `>` for the rest; empty is every key), at most Limit of them.
+type QueryRequest struct {
+	Ledger string `json:"ledger"`
+	Index  string `json:"index"`
+	Key    string `json:"key,omitempty"`
+	Limit  int    `json:"limit,omitempty"`
+}
+
+// IndexEntry is the value of one key of a declared index (IndexKey): the instance it points at, and the sequence of
+// the operation it was written from. The owner's watcher and the tool runner's reindex both write it so.
+type IndexEntry struct {
+	Instance string `json:"instance"`
+	Sequence uint64 `json:"sequence"`
+}
+
+// IndexKey is the key of an instance in a declared index: the values of the index's fields, in its order, then the
+// parts of the instance's path, all joined by ".". Each value and each path part is encoded (keyToken): every byte
+// outside [A-Za-z0-9_-] is written "=" and two upper-case hex digits ("." is "=2E", " " is "=20", "=" is "=3D"), so two
+// different keys never meet and every part is a token the bus takes. `17950.listing.a17` is the key of price 17950
+// and instance `listing/a17`. The owner's watcher and the tool runner's reindex both write it, so a reindex leaves the
+// index as the watcher keeps it.
+func IndexKey(fields []string, instance string) string {
+	parts := make([]string, 0, len(fields)+2)
+	for _, f := range fields {
+		parts = append(parts, keyToken(f))
+	}
+	for _, p := range strings.Split(instance, "/") {
+		parts = append(parts, keyToken(p))
+	}
+	return strings.Join(parts, ".")
+}
+
+// keyToken is v with every byte outside [A-Za-z0-9_-] written "=" and two upper-case hex digits (IndexKey).
+func keyToken(v string) string {
+	var b strings.Builder
+	for i := 0; i < len(v); i++ {
+		c := v[i]
+		if c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z' || c >= '0' && c <= '9' || c == '_' || c == '-' {
+			b.WriteByte(c)
+			continue
+		}
+		fmt.Fprintf(&b, "=%02X", c)
+	}
+	return b.String()
+}
+
+// QueryAnswer is query's answer.
+type QueryAnswer struct {
+	Entries []IndexEntry `json:"entries"`
+}
+
+// RebuildFrom is what a rebuild derives the state from: the history, or the snapshot and the operations after it.
+const (
+	RebuildFromHistory  = "history"
+	RebuildFromSnapshot = "snapshot"
+)
+
+// RebuildRequest derives an instance's state again (every instance's when Instance is empty), From the history or the
+// snapshot.
+type RebuildRequest struct {
+	Ledger   string `json:"ledger"`
+	Instance string `json:"instance,omitempty"`
+	From     string `json:"from,omitempty"`
+}
+
+// ReindexRequest builds a declared index again from the history.
+type ReindexRequest struct {
+	Ledger string `json:"ledger"`
+	Index  string `json:"index"`
+}
+
+// LedgerRequest names a ledger: lag.
+type LedgerRequest struct {
+	Ledger string `json:"ledger"`
+}
+
+// Repaired is the answer of rebuild, reindex and snapshot: how many instances (or index entries) it wrote.
+type Repaired struct {
+	Written int `json:"written"`
+}
+
+// InstanceLag is one instance whose state or snapshot is behind its history: the sequences each holds.
+type InstanceLag struct {
+	Instance string `json:"instance"`
+	History  uint64 `json:"history"`
+	State    uint64 `json:"state"`
+	Snapshot uint64 `json:"snapshot"`
+}
+
+// IndexLag is how far one declared index is behind the history.
+type IndexLag struct {
+	Index  string `json:"index"`
+	Behind uint64 `json:"behind"`
+}
+
+// Lagged is lag's answer: every instance and index behind its history; none when nothing is behind.
+type Lagged struct {
+	Instances []InstanceLag `json:"instances,omitempty"`
+	Indexes   []IndexLag    `json:"indexes,omitempty"`
+}
diff --git a/go/buscompose/accounts.go b/go/buscompose/accounts.go
index 924afc7..38c79a1 100644
--- a/go/buscompose/accounts.go
+++ b/go/buscompose/accounts.go
@@ -31,7 +31,8 @@ type ClaimedSeat struct {
 // WantedAccount is one key of the grants part's state `accounts`: an account the mesh needs, without its password.
 type WantedAccount struct {
 	User string `json:"user"`
-	// Kind is KindModule (KindNodeTools for the runtime, named as a module is), KindProcess or KindProvisioner.
+	// Kind is KindModule (KindNodeTools for the runtime, named as a module is), KindProcess, KindProvisioner or
+	// KindLedger.
 	Kind   Kind   `json:"kind"`
 	Node   string `json:"node"`
 	Module string `json:"module"`
@@ -46,8 +47,12 @@ type WantedAccount struct {
 	At time.Time `json:"at"`
 }
 
+// LedgersSecret is the tool runner's own secret holding its machine's ledger accounts, a map of module to credential
+// (ADR 0597 §9).
+const LedgersSecret = "ledgers"
+
 // mintedKinds are the kinds of account the vault mints (ADR 0561 §1).
-var mintedKinds = []Kind{KindModule, KindNodeTools, KindProcess, KindProvisioner}
+var mintedKinds = []Kind{KindModule, KindNodeTools, KindProcess, KindProvisioner, KindLedger}
 
 // principal is the account as the composer names it.
 func (w WantedAccount) principal() Principal {
@@ -93,9 +98,12 @@ func (w WantedAccount) Same(o WantedAccount) bool {
 }
 
 // OwnSecret is the module's own secret the account is held in: `broker`, `broker-<process id>` or `provisioner-broker`
-// (the controller's names, ADR 0436 §2, ADR 0349 §11).
+// (the controller's names, ADR 0436 §2, ADR 0349 §11); a ledger account in the tool runner's `ledgers`, which keeps every
+// ledger account of its machine, by module (ADR 0597 §9).
 func (w WantedAccount) OwnSecret() string {
 	switch w.Kind {
+	case KindLedger:
+		return LedgersSecret
 	case KindProcess:
 		return "broker-" + w.Process
 	case KindProvisioner:
diff --git a/go/buscompose/names_test.go b/go/buscompose/names_test.go
index dd76d2a..2f0b5cc 100644
--- a/go/buscompose/names_test.go
+++ b/go/buscompose/names_test.go
@@ -18,4 +18,18 @@ func TestTheBusNamesAgree(t *testing.T) {
 	if LogStreamName("mesh-delivery-builder", "build-log") == "" || LogSubject("mesh-delivery-builder", "build-log") == "" {
 		t.Fatal("a log has no stream or subject")
 	}
+	// 1966/AC20: a ledger's history and snapshot subjects are one contract, which the grants part grants a ledger
+	// account its publish on.
+	if h, sn := LedgerHistorySubject("m", "records"), LedgerSnapshotSubject("m", "records"); h != "mesh.ledger.m.records.history" ||
+		sn != "mesh.ledger.m.records.snapshot" {
+		t.Fatalf("a ledger's subjects are %q and %q", h, sn)
+	}
+	// 1966/AC23: a wanted account of kind ledger for m on a names the user ledger.a.m and the own secret ledgers.
+	ledger := WantedAccount{User: "ledger.a.m", Kind: KindLedger, Node: "a", Module: "m", URL: "nats://10.0.0.1:4222"}
+	if got := (Principal{Kind: KindLedger, Node: "a", Module: "m"}).Username(); got != "ledger.a.m" {
+		t.Fatalf("a ledger account is named %q", got)
+	}
+	if err := ledger.Valid(); err != nil || ledger.OwnSecret() != "ledgers" {
+		t.Fatalf("a wanted ledger account: %v, held in %q", err, ledger.OwnSecret())
+	}
 }
diff --git a/go/buscompose/nats.go b/go/buscompose/nats.go
index 72cd670..f7f8ba8 100644
--- a/go/buscompose/nats.go
+++ b/go/buscompose/nats.go
@@ -44,8 +44,26 @@ const (
 	// exactly what its bus says — never root, never the operator account, and never able to answer a tool
 	// call or a seat's verb (§3). One per process and machine.
 	KindProcess Kind = "process"
+	// KindLedger is one module assignment's ledger credential (novox/hq ADR 0597 §9, design 25 § 12.4): held by that
+	// machine's tool runner, never by the module's own code, and the only account that publishes on that module's ledger
+	// histories and snapshots. One per module assignment, whose module asks for a ledger in `requires`.
+	KindLedger Kind = "ledger"
 )
 
+// LedgerHistorySubject and LedgerSnapshotSubject are the subject prefixes of one ledger's history and of its instances'
+// snapshots (novox/hq ADR 0597 §1, §8, §9): an instance's subject is the prefix, ".", and the instance's path with each
+// "/" written "." (`decision/0290` is `….decision.0290`). One contract: the grants part grants a ledger account its
+// publish on them, the tool runner appends and snapshots on them, and the bus module creates the history's stream over
+// them.
+func LedgerHistorySubject(module, local string) string {
+	return "mesh.ledger." + module + "." + local + ".history"
+}
+
+// LedgerSnapshotSubject is the subject prefix of one ledger's instances' snapshots (LedgerHistorySubject).
+func LedgerSnapshotSubject(module, local string) string {
+	return "mesh.ledger." + module + "." + local + ".snapshot"
+}
+
 // Seat is a role on the bus as a principal relates to it: the subjects it accepts, and those it
 // emits (novox/hq ADR 0118, design 29 §5).
 type Seat struct {
@@ -272,6 +290,10 @@ func (p Principal) Username() string {
 			return p.Login
 		}
 		return "node." + p.Node
+	case KindLedger:
+		// `ledger.<machine>.<module>`: never `<node>.<module>`, which is the module's own account or the tool runner's,
+		// so the module's code never holds it.
+		return "ledger." + p.Node + "." + p.Module
 	case KindProvisioner:
 		// Named for the machine, as a node is: one client per machine, whichever module runs it, and never
 		// `<node>.<module>`, which is the module's own account or the tool runner's.
diff --git a/go/catalogue/busstate.go b/go/catalogue/busstate.go
new file mode 100644
index 0000000..21dc379
--- /dev/null
+++ b/go/catalogue/busstate.go
@@ -0,0 +1,207 @@
+package catalogue
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"strings"
+)
+
+// Bus state is what a module keeps on the bus, asked for as a provision of the bus module in `requires` (novox/hq ADR
+// 0595 §1, design 32 § 4): an entry of `requires` in its typed long form, the local name, the storage type, the template
+// and the template's options. This is the contract only (ADR 0578 §7, ADR 0593 §1): the entry's shape, decoded
+// leniently. Every rule that judges an entry (a template known, an option within its bound, a fixed setting not given)
+// is the indexer's judge's.
+
+// The storage types (design 25 § 12.1): the stream is the base; the key-value bucket, the object store and the ledger
+// are built on it, each with calls of its own (ADR 0595 §2).
+const (
+	StorageStream      = "stream"
+	StorageKeyValue    = "key-value"
+	StorageObjectStore = "object-store"
+	StorageLedger      = "ledger"
+)
+
+// The six templates, each a storage type with a predefined configuration (ADR 0595 §2, design 25 § 12.1): state on
+// key-value, events, work queue and log on stream, objects on object store, ledger on ledger. A bare stream names
+// none and gives its own Configuration.
+const (
+	TemplateState     = "state"
+	TemplateEvents    = "events"
+	TemplateWorkQueue = "work-queue"
+	TemplateLog       = "log"
+	TemplateObjects   = "objects"
+	TemplateLedger    = "ledger"
+)
+
+// The option names, a template's settings a module may change (design 25 § 12.1's table), written as the old sections
+// wrote them, so a module that moves carries its old settings as options unchanged (ADR 0595 §11). Which option a
+// template takes, and its bound, is the judge's.
+const (
+	// OptionPastValues is how many past values a state's key keeps (the old `state`'s `history`).
+	OptionPastValues = "history"
+	// OptionTimeToLive is how long a state's value lives, in seconds.
+	OptionTimeToLive = "ttl-seconds"
+	// OptionLifetimePerKey is whether a state's key may be given a lifetime of its own.
+	OptionLifetimePerKey = "key-ttl"
+	// OptionPerMachine is whether a state is kept one bucket per machine.
+	OptionPerMachine = "per-machine"
+	// OptionAgeDays is how long a stream keeps a message, in days.
+	OptionAgeDays = "max-age-days"
+	// OptionCapMiB is the cap of a stream, a bucket or an object store, in MiB.
+	OptionCapMiB = "max-mib"
+	// OptionGrant names the trusted config value granting another module a part of it (ADR 0363 §4, ADR 0592 §9).
+	OptionGrant = "grant"
+	// OptionDeliveries is how many times a work queue's message is delivered before it is a dead letter.
+	OptionDeliveries = "max-deliveries"
+	// OptionDuplicates is how long, in seconds, a work queue detects a message sent twice.
+	OptionDuplicates = "duplicates"
+)
+
+// ConfigWhenFull is what a configuration of its own says a bare stream does when full: WhenFullRefuse or
+// WhenFullDropOldest. In a template it is fixed, never an option (ADR 0595 §3).
+const (
+	ConfigWhenFull     = "when-full"
+	WhenFullRefuse     = "refuse"
+	WhenFullDropOldest = "drop-oldest"
+)
+
+// The ledger effects, what an operation does to an instance's state (ADR 0597 §2): one of this fixed set.
+const (
+	// EffectSetFields sets the state's fields to the operation's Fields.
+	EffectSetFields = "set-fields"
+	// EffectSetEntry sets one entry of the state's map Into, under the key the operation's field Key holds, to its Fields.
+	EffectSetEntry = "set-entry"
+	// EffectAppend appends the operation's Fields to the state's list Into.
+	EffectAppend = "append"
+	// EffectRemove removes the entry of the map Into under the operation's field Key, or, naming no Into, the instance's
+	// state.
+	EffectRemove = "remove"
+)
+
+// LedgerType is one type of a ledger (ADR 0597 §1): a schema and the operations allowed on it, with its indexes. An
+// instance of it is named by a path whose first part is the type's name (`decision/0290`).
+type LedgerType struct {
+	Name string `json:"name"`
+	// Schema is the type's fields, by name.
+	Schema map[string]LedgerField `json:"schema"`
+	// Operations are the operations allowed on an instance, each with its effect.
+	Operations []LedgerOperation `json:"operations"`
+	// Indexes are its declared indexes, each a second key-value bucket kept by a watcher (ADR 0597 §4).
+	Indexes []LedgerIndex `json:"indexes,omitempty"`
+}
+
+// LedgerField is one field of a ledger type's schema.
+type LedgerField struct {
+	// Type is the field's value type, as the schema names it.
+	Type string `json:"type"`
+	// DigestOf names the text field this field is the digest of (ADR 0597 §2): `apply` refuses an operation whose
+	// digest does not match its text.
+	DigestOf string `json:"digest-of,omitempty"`
+}
+
+// LedgerOperation is one operation a ledger type allows, and its effect on the state.
+type LedgerOperation struct {
+	Name string `json:"name"`
+	// Effect is one of the ledger effects (EffectSetFields, EffectSetEntry, EffectAppend, EffectRemove).
+	Effect string `json:"effect"`
+	// Fields are the operation's fields its effect copies into the state; it may carry more (ADR 0597 §2).
+	Fields []string `json:"fields,omitempty"`
+	// Into is the state's map (EffectSetEntry, EffectRemove) or list (EffectAppend) the effect writes.
+	Into string `json:"into,omitempty"`
+	// Key is the operation's field holding the entry's key (EffectSetEntry, EffectRemove).
+	Key string `json:"key,omitempty"`
+	// Sequence and Author are whether the effect also writes the operation's sequence and its proven author.
+	Sequence bool `json:"sequence,omitempty"`
+	Author   bool `json:"author,omitempty"`
+}
+
+// LedgerIndex is one declared index of a ledger type: its name, and the fields it is kept on.
+type LedgerIndex struct {
+	Name string   `json:"name"`
+	On   []string `json:"on"`
+}
+
+// BusStateField is where a stored manifest keeps its bus-state entries: beside `requires`, which stays a plain list of
+// names, as OptionalRequiresKey keeps the optional ones.
+const BusStateField = "bus-state"
+
+// BusStateEntry is one piece of a module's bus state, as its manifest asks for it.
+type BusStateEntry struct {
+	// Name is its local name; the mesh, never the module, names it on the bus (ADR 0201 §4).
+	Name string `json:"name"`
+	// Storage is its storage type (design 25 § 12.1): how the bus keeps it.
+	Storage string `json:"storage"`
+	// Template is the predefined configuration of that storage type it uses; empty for a bare stream, which gives
+	// Configuration instead.
+	Template string `json:"template,omitempty"`
+	// Options are the template's settings the module changes, by option name; each value as the manifest wrote it.
+	Options map[string]json.RawMessage `json:"options,omitempty"`
+	// Configuration is a configuration of the module's own, where no template fits: a bare stream's, or a ledger's
+	// whose history expires (ADR 0595 §2).
+	Configuration map[string]json.RawMessage `json:"configuration,omitempty"`
+	// Types are a ledger's types (ADR 0597 §1), for the storage type ledger only.
+	Types []LedgerType `json:"types,omitempty"`
+}
+
+// isBusStateEntry is whether a `requires` item in its long form asks for bus state: it names a storage type.
+func isBusStateEntry(raw json.RawMessage) bool {
+	var keys map[string]json.RawMessage
+	if json.Unmarshal(raw, &keys) != nil {
+		return false
+	}
+	_, has := keys["storage"]
+	return has
+}
+
+// readBusStateEntry reads one bus-state entry leniently (ADR 0578 §3): a key it does not know, at any depth, is set
+// aside and its path named, never refused. An error is only an entry of the wrong shape.
+func readBusStateEntry(raw json.RawMessage) (BusStateEntry, []string, error) {
+	var tree any
+	dec := json.NewDecoder(bytes.NewReader(raw))
+	dec.UseNumber()
+	if err := dec.Decode(&tree); err != nil {
+		return BusStateEntry{}, nil, err
+	}
+	var aside []string
+	strict := func(e *BusStateEntry) error {
+		b, err := json.Marshal(tree)
+		if err != nil {
+			return err
+		}
+		d := json.NewDecoder(bytes.NewReader(b))
+		d.DisallowUnknownFields()
+		return typedUnknown(d.Decode(e))
+	}
+	for tries := 0; ; tries++ {
+		var e BusStateEntry
+		err := strict(&e)
+		if err == nil {
+			return e, aside, nil
+		}
+		unknown := asUnknownField(err)
+		if unknown == nil || tries > 64 {
+			return BusStateEntry{}, nil, err
+		}
+		path, ok := removalThatHelps(tree, unknown.Field, err.Error(), func() error { var e BusStateEntry; return strict(&e) })
+		if !ok {
+			if removeEvery(tree, unknown.Field) == 0 {
+				return BusStateEntry{}, nil, err
+			}
+			path = "…." + unknown.Field
+		}
+		aside = append(aside, path)
+	}
+}
+
+// setAsideAlso adds paths read without to what a manifest set aside (SetAside), in its words.
+func setAsideAlso(unknown string, paths []string) string {
+	if len(paths) == 0 {
+		return unknown
+	}
+	if unknown == "" {
+		field := paths[0][strings.LastIndex(paths[0], ".")+1:]
+		unknown = fmt.Sprintf("json: unknown field %q", field)
+	}
+	return unknown + " (read without " + strings.Join(paths, ", ") + ")"
+}
diff --git a/go/catalogue/manifest.go b/go/catalogue/manifest.go
index 322afde..897d053 100644
--- a/go/catalogue/manifest.go
+++ b/go/catalogue/manifest.go
@@ -478,6 +478,10 @@ type Manifest struct {
 	// RequireShares is who else may use the bucket a module requires, by requirement (BucketShare, novox/hq ADR 0468
 	// §8): filled from the long form's `shares`, or from the stored form's `requires-shares`; never written by hand.
 	RequireShares map[string][]BucketShare `json:"-"`
+	// BusState is what the module keeps on the bus, each entry asked for in `requires` in its typed long form
+	// (BusStateEntry, novox/hq ADR 0595 §1); its local name is never in Requires, which names provisions. Stored
+	// beside `requires` (BusStateField), which stays a plain list of names.
+	BusState []BusStateEntry `json:"bus-state,omitempty"`
 
 	// Emits are the events this module publishes, named **locally**: `order.placed`, not a subject
 	// and not a routing key. The mesh derives where it lands (design 29 §1), so reorganising the
@@ -1556,18 +1560,21 @@ func (m *Manifest) UnmarshalJSON(raw []byte) error {
 	}
 	var optionalRequires map[string]bool
 	var requireShares map[string][]BucketShare
+	var busState []BusStateEntry
+	var busStateAside []string
 	if requires, ok := keys["requires"]; ok && string(requires) != "null" {
-		names, optional, shares, err := readRequires(requires)
+		read, err := readRequires(requires)
 		if err != nil {
 			return err
 		}
-		plainNames, err := json.Marshal(names)
+		plainNames, err := json.Marshal(read.names)
 		if err != nil {
 			return err
 		}
 		keys["requires"] = plainNames
-		optionalRequires = optional
-		requireShares = shares
+		optionalRequires = read.optional
+		requireShares = read.shares
+		busState, busStateAside = read.busState, read.aside
 	}
 	// The stored form's shares (RequireSharesKey).
 	if stored, ok := keys[RequireSharesKey]; ok {
@@ -1631,7 +1638,9 @@ func (m *Manifest) UnmarshalJSON(raw []byte) error {
 		}
 	}
 	*m = Manifest(fields)
-	m.unknown = unknown
+	m.unknown = setAsideAlso(unknown, busStateAside)
+	// A bus-state entry of `requires`, beside those of the stored form (BusStateField).
+	m.BusState = append(m.BusState, busState...)
 	m.forms = forms
 	m.OptionalRequires = optionalRequires
 	m.RequireShares = requireShares
diff --git a/go/catalogue/optional_requirements.go b/go/catalogue/optional_requirements.go
index 48fcef5..dcfd4c7 100644
--- a/go/catalogue/optional_requirements.go
+++ b/go/catalogue/optional_requirements.go
@@ -21,34 +21,59 @@ type requirementForm struct {
 	Shares []BucketShare `json:"shares,omitempty"`
 }
 
-// readRequires reads `requires` in both of its forms — a bare name, or {name, optional} — into the
-// names and which of them are optional.
-func readRequires(raw json.RawMessage) ([]string, map[string]bool, map[string][]BucketShare, error) {
+// requiresRead is `requires` as readRequires read it.
+type requiresRead struct {
+	names    []string
+	optional map[string]bool
+	shares   map[string][]BucketShare
+	// busState are the entries asking for bus state (BusStateEntry), never named in names, which name provisions; aside
+	// the paths of the keys they had that this package does not know, set aside (ADR 0578 §3).
+	busState []BusStateEntry
+	aside    []string
+}
+
+// readRequires reads `requires` in its forms — a bare name, {name, optional}, or a bus-state entry (BusStateEntry,
+// novox/hq ADR 0595 §1) — into the names of the provisions, which of them are optional, and the bus-state entries,
+// whose local names stay off the names: a local name is no provision, and nothing provides it.
+func readRequires(raw json.RawMessage) (requiresRead, error) {
 	var entries []json.RawMessage
 	if err := json.Unmarshal(raw, &entries); err != nil {
-		return nil, nil, nil, fmt.Errorf("requires: a list of names, or of {name, optional}: %w", err)
+		return requiresRead{}, fmt.Errorf("requires: a list of names, or of {name, optional}: %w", err)
 	}
 	var names []string
 	optional := map[string]bool{}
 	var shares map[string][]BucketShare
+	var busState []BusStateEntry
+	var aside []string
 	for i, e := range entries {
 		var plain string
 		if err := json.Unmarshal(e, &plain); err == nil {
 			names = append(names, plain)
 			continue
 		}
+		if isBusStateEntry(e) {
+			entry, unknown, err := readBusStateEntry(e)
+			if err != nil {
+				return requiresRead{}, fmt.Errorf("requires[%d]: a bus-state entry is {name, storage, template, options, configuration, types} (novox/hq ADR 0595 §1): %w", i, err)
+			}
+			busState = append(busState, entry)
+			for _, path := range unknown {
+				aside = append(aside, fmt.Sprintf("requires[%d]%s", i, path))
+			}
+			continue
+		}
 		var full requirementForm
 		dec := json.NewDecoder(bytes.NewReader(e))
 		dec.DisallowUnknownFields()
 		if err := dec.Decode(&full); err != nil {
-			return nil, nil, nil, fmt.Errorf("requires[%d]: a name, or {name, optional} (novox/hq ADR 0330): %w", i, err)
+			return requiresRead{}, fmt.Errorf("requires[%d]: a name, or {name, optional} (novox/hq ADR 0330): %w", i, err)
 		}
 		if strings.TrimSpace(full.Name) == "" {
-			return nil, nil, nil, fmt.Errorf("requires[%d] names no requirement: {name, optional}", i)
+			return requiresRead{}, fmt.Errorf("requires[%d] names no requirement: {name, optional}", i)
 		}
 		names = append(names, full.Name)
 		if err := checkBucketShares(full.Name, full.Shares); err != nil {
-			return nil, nil, nil, fmt.Errorf("requires[%d]: %w", i, err)
+			return requiresRead{}, fmt.Errorf("requires[%d]: %w", i, err)
 		}
 		if len(full.Shares) > 0 {
 			if shares == nil {
@@ -63,7 +88,7 @@ func readRequires(raw json.RawMessage) ([]string, map[string]bool, map[string][]
 	if len(optional) == 0 {
 		optional = nil
 	}
-	return names, optional, shares, nil
+	return requiresRead{names: names, optional: optional, shares: shares, busState: busState, aside: aside}, nil
 }
 
 // OptionalRequiresKey is where a stored manifest keeps which of its requirements are optional: beside
diff --git a/go/catalogue/optional_requirements_test.go b/go/catalogue/optional_requirements_test.go
index 9f0aa04..d6d9cb3 100644
--- a/go/catalogue/optional_requirements_test.go
+++ b/go/catalogue/optional_requirements_test.go
@@ -2,6 +2,7 @@ package catalogue
 
 import (
 	"encoding/json"
+	"reflect"
 	"strings"
 	"testing"
 )
@@ -9,9 +10,8 @@ import (
 // A requirement a module can run without (novox/hq ADR 0330, issue 166). The shape of the issue:
 // grafana runs without a data source and requires `influxdb-api` softly; a mesh without influxdb
 // could not assign grafana at all, and one with influxdb in its catalogue would have had it installed
-// for grafana.
-
-func TestARequirementIsHardUnlessMarkedOptional(t *testing.T) {
+// for grafana. And `requires` in its typed long form, a module's bus state (novox/hq ADR 0595 §1).
+func TestARequirementsLongForm(t *testing.T) {
 	m := mustParse(t, `{"module":"grafana","version":"1",
 		"requires":["route",{"name":"influxdb-api","optional":true},{"name":"oidc-client"}]}`)
 	if strings.Join(m.Requires, " ") != "route influxdb-api oidc-client" {
@@ -24,23 +24,12 @@ func TestARequirementIsHardUnlessMarkedOptional(t *testing.T) {
 		t.Error("a requirement marked optional read as hard")
 	}
 	// And written back as it was read, so a manifest through the store keeps its form.
-	raw, err := json.Marshal(m)
-	if err != nil {
-		t.Fatal(err)
-	}
-	var again Manifest
-	if err := json.Unmarshal(raw, &again); err != nil {
-		t.Fatal(err)
-	}
+	again := roundTrip(t, m)
 	if !again.IsOptional("influxdb-api") || again.IsOptional("route") || len(again.Requires) != 3 {
-		t.Fatalf("written and read back, it says %v optional %v (%s)", again.Requires, again.OptionalRequires, raw)
+		t.Fatalf("written and read back, it says %v optional %v", again.Requires, again.OptionalRequires)
 	}
-	if strings.Contains(string(raw), `"name":`) {
-		t.Errorf("a requirement was stored in the long form: %s", raw)
-	}
-}
 
-func TestARequirementsLongFormRefusesWhatItDoesNotKnow(t *testing.T) {
+	// The long form {name, optional} refuses what it does not know.
 	for _, raw := range []string{
 		`{"module":"x","version":"1","requires":[{"name":"influxdb-api","optinal":true}]}`,
 		`{"module":"x","version":"1","requires":[{"optional":true}]}`,
@@ -49,4 +38,94 @@ func TestARequirementsLongFormRefusesWhatItDoesNotKnow(t *testing.T) {
 			t.Errorf("accepted %s", raw)
 		}
 	}
+
+	records := BusStateEntry{Name: "records", Storage: "ledger", Template: "ledger",
+		Options: map[string]json.RawMessage{"max-mib": json.RawMessage(`1024`)}}
+	// A ledger type with each of the four effects.
+	listing := LedgerType{Name: "listing",
+		Schema: map[string]LedgerField{"price": {Type: "number"}, "seen": {Type: "list"}, "notes": {Type: "map"},
+			"text": {Type: "text"}, "digest": {Type: "text", DigestOf: "text"}},
+		Operations: []LedgerOperation{
+			{Name: "priced", Effect: EffectSetFields, Fields: []string{"price"}, Sequence: true, Author: true},
+			{Name: "noted", Effect: EffectSetEntry, Fields: []string{"text", "digest"}, Into: "notes", Key: "title"},
+			{Name: "seen", Effect: EffectAppend, Fields: []string{"at"}, Into: "seen"},
+			{Name: "unnoted", Effect: EffectRemove, Into: "notes", Key: "title"},
+		},
+		Indexes: []LedgerIndex{{Name: "cheapest", On: []string{"price"}}}}
+	typeJSON, err := json.Marshal(listing)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ledger := records
+	ledger.Types = []LedgerType{listing}
+	for _, c := range []struct {
+		name     string
+		requires string
+		names    string
+		busState []BusStateEntry
+		aside    []string
+	}{
+		// 1966/AC1: a plain name and a bus-state entry: Requires names the plain one only, since it names provisions,
+		// and BusState holds the entry whole.
+		{"a plain name and a bus-state entry", `["postgres-database",
+			{"name":"records","storage":"ledger","template":"ledger","options":{"max-mib":1024}}]`,
+			"postgres-database", []BusStateEntry{records}, nil},
+		// 1966/AC2: an unknown key is set aside and named, never refused; the entry decodes.
+		{"a bus-state entry with a key it does not know", `[
+			{"name":"records","storage":"ledger","template":"ledger","colour":"red","options":{"max-mib":1024}}]`,
+			"", []BusStateEntry{records}, []string{"requires[0].colour"}},
+		// 1966/AC3: a ledger type with each of the four effects round-trips through JSON unchanged.
+		{"a ledger with its type", `[{"name":"records","storage":"ledger","template":"ledger","options":{"max-mib":1024},
+			"types":[` + string(typeJSON) + `]}]`, "", []BusStateEntry{ledger}, nil},
+	} {
+		got, err := decodeForTest([]byte(`{"module":"x","version":"1","requires":` + c.requires + `}`))
+		if err != nil {
+			t.Errorf("%s: refused: %v", c.name, err)
+			continue
+		}
+		if strings.Join(got.Requires, " ") != c.names {
+			t.Errorf("%s: requires read as %v, want %s", c.name, got.Requires, c.names)
+		}
+		if !reflect.DeepEqual(got.BusState, c.busState) {
+			t.Errorf("%s: bus state read as %+v, want %+v", c.name, got.BusState, c.busState)
+		}
+		for _, path := range c.aside {
+			if !strings.Contains(got.SetAside(), path) {
+				t.Errorf("%s: %s is not named among what was set aside: %q", c.name, path, got.SetAside())
+			}
+		}
+		if len(c.aside) == 0 && got.SetAside() != "" {
+			t.Errorf("%s: set aside %q", c.name, got.SetAside())
+		}
+		// Stored and read back, the entries stay whole and `requires` stays plain names.
+		back := roundTrip(t, got)
+		if !reflect.DeepEqual(back.BusState, c.busState) || strings.Join(back.Requires, " ") != c.names {
+			t.Errorf("%s: read back as %v %+v", c.name, back.Requires, back.BusState)
+		}
+	}
+}
+
+// roundTrip is m written as the store keeps it and read again; the stored form keeps `requires` plain names.
+func roundTrip(t *testing.T, m Manifest) Manifest {
+	t.Helper()
+	raw, err := json.Marshal(m)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var stored struct {
+		Requires []any `json:"requires"`
+	}
+	if err := json.Unmarshal(raw, &stored); err != nil {
+		t.Fatal(err)
+	}
+	for _, r := range stored.Requires {
+		if _, plain := r.(string); !plain {
+			t.Errorf("a requirement was stored in the long form: %s", raw)
+		}
+	}
+	var again Manifest
+	if err := json.Unmarshal(raw, &again); err != nil {
+		t.Fatalf("%v: %s", err, raw)
+	}
+	return again
 }
diff --git a/go/catalogue/unknown_field.go b/go/catalogue/unknown_field.go
index 5721847..8c2ffe7 100644
--- a/go/catalogue/unknown_field.go
+++ b/go/catalogue/unknown_field.go
@@ -75,7 +75,7 @@ func prunedFields(keys map[string]json.RawMessage) (manifestFields, []string, er
 				removed = append(removed, k)
 				break
 			}
-			path, ok := removalThatHelps(k, tree[k], unknown.Field, err.Error())
+			path, ok := removalThatHelps(tree[k], unknown.Field, err.Error(), func() error { return decodesAlone(k, tree[k]) })
 			if !ok {
 				// The same key unknown in two entries alike: no one removal changes the words.
 				// Every occurrence goes, and the field is judged again.
@@ -113,8 +113,8 @@ func decodesAlone(k string, v any) error {
 }
 
 // removalThatHelps removes, from v, the one occurrence of key whose removal changes what the strict
-// decoder says of field k, and says where it was. Every other occurrence is left as it was.
-func removalThatHelps(k string, v any, key, said string) (string, bool) {
+// decoder says (decodes, which decodes v strictly), and says where it was. Every other occurrence is left as it was.
+func removalThatHelps(v any, key, said string, decodes func() error) (string, bool) {
 	var found bool
 	var where string
 	var walk func(node any, at string) bool
@@ -126,7 +126,7 @@ func removalThatHelps(k string, v any, key, said string) (string, bool) {
 				// Accepted only when the decoder is past it: nothing left, or an unknown key said
 				// elsewhere. A different kind of error means the removal broke the entry; the same
 				// words mean this was not the occurrence it refused.
-				err := decodesAlone(k, v)
+				err := decodes()
 				if err == nil || (asUnknownField(err) != nil && err.Error() != said) {
 					found, where = true, at+"."+key
 					return true
diff --git a/go/delivery/verdicts.go b/go/delivery/verdicts.go
index 15a6a9c..a747897 100644
--- a/go/delivery/verdicts.go
+++ b/go/delivery/verdicts.go
@@ -5,6 +5,8 @@ import (
 	"fmt"
 	"slices"
 	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
 )
 
 // The verdicts on manifests (novox/hq ADR 0578 §1, §3): the indexer judges every manifest it takes in once, with its own
@@ -28,6 +30,11 @@ const (
 	// raises it as a condition beside the indexer's finding.
 	ManifestRefusedEvent = "manifest-refused"
 
+	// ManifestAcceptedEvent is the indexer's event saying a manifest that asks for bus state was accepted
+	// (ManifestAccepted), carrying its bus-state entries whole, so the bus module creates them without reading the
+	// indexer's state (novox/hq ADR 0595 §4, design 25 § 12.2).
+	ManifestAcceptedEvent = "manifest-accepted"
+
 	// ManifestOutgrown is the finding of a manifest the indexer accepted before and a stricter judge finds problems in
 	// (novox/hq ADR 0579 §1): it stays accepted, its problems are the verdict's Warnings, and the watchman raises it as a
 	// warning until the manifest is mended.
@@ -154,3 +161,24 @@ type ManifestRefused struct {
 func RefusedOf(digest string, v ManifestVerdict) ManifestRefused {
 	return ManifestRefused{V: Version, Module: v.Module, Digest: digest, Judge: v.Judge, Problems: v.Problems}
 }
+
+// ManifestAccepted is the body of the indexer's event ManifestAcceptedEvent: the module, the digest of its manifest, the
+// judge, and every bus-state entry the manifest asks for, whole (novox/hq ADR 0595 §4).
+type ManifestAccepted struct {
+	V        int                       `json:"v"`
+	Module   string                    `json:"module"`
+	Digest   string                    `json:"digest"`
+	Judge    string                    `json:"judge"`
+	BusState []catalogue.BusStateEntry `json:"bus-state"`
+}
+
+// AcceptedOf is the event body saying v, the verdict accepting the manifest m of digest.
+func AcceptedOf(digest string, v ManifestVerdict, m catalogue.Manifest) ManifestAccepted {
+	return ManifestAccepted{V: Version, Module: v.Module, Digest: digest, Judge: v.Judge, BusState: m.BusState}
+}
+
+// EventID is the event's id, one per manifest digest and judge, so the bus takes it once:
+// `manifest-accepted-<digest>-<judge>`.
+func (a ManifestAccepted) EventID() string {
+	return ManifestAcceptedEvent + "-" + a.Digest + "-" + a.Judge
+}
diff --git a/go/delivery/verdicts_test.go b/go/delivery/verdicts_test.go
index da05519..ca6cf2f 100644
--- a/go/delivery/verdicts_test.go
+++ b/go/delivery/verdicts_test.go
@@ -1,9 +1,13 @@
 package delivery
 
 import (
+	"encoding/json"
+	"reflect"
 	"strings"
 	"testing"
 	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
 )
 
 // A verdict on a manifest round-trips, refuses what it cannot be, and a reader takes a missing one as accepted (novox/hq
@@ -72,4 +76,28 @@ func TestAManifestVerdictIsTheContractReadersTake(t *testing.T) {
 	if r, _ := TakeManifestVerdict(m.VerdictOf("x")); r || len(m.VerdictOf("x").Warnings) != 1 {
 		t.Fatalf("an outgrown module: %+v", m.VerdictOf("x"))
 	}
+
+	// 1966/AC6: the accepted event of a manifest with two bus-state entries carries both whole, and its id is
+	// manifest-accepted-<digest>-<judge>.
+	entries := []catalogue.BusStateEntry{
+		{Name: "drafts", Storage: catalogue.StorageKeyValue, Template: catalogue.TemplateState,
+			Options: map[string]json.RawMessage{catalogue.OptionPastValues: json.RawMessage(`5`)}},
+		{Name: "records", Storage: catalogue.StorageLedger, Template: catalogue.TemplateLedger,
+			Types: []catalogue.LedgerType{{Name: "decision", Operations: []catalogue.LedgerOperation{{Name: "submit", Effect: catalogue.EffectSetFields}}}}},
+	}
+	digest := strings.Repeat("d", 64)
+	accepted := AcceptedOf(digest, ManifestVerdict{Module: "mesh-knowledge", State: VerdictAccepted, Judge: "src2:j"},
+		catalogue.Manifest{Module: "mesh-knowledge", BusState: entries})
+	raw, err := json.Marshal(accepted)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var heard ManifestAccepted
+	if err := json.Unmarshal(raw, &heard); err != nil || heard.Module != "mesh-knowledge" || heard.Digest != digest ||
+		heard.V != Version || !reflect.DeepEqual(heard.BusState, entries) {
+		t.Fatalf("the accepted event reads as %+v (%v)", heard, err)
+	}
+	if id := heard.EventID(); id != "manifest-accepted-"+digest+"-src2:j" {
+		t.Fatalf("the accepted event's id is %q", id)
+	}
 }
diff --git a/go/membership/membership.go b/go/membership/membership.go
index 8fd93fd..4f957cb 100644
--- a/go/membership/membership.go
+++ b/go/membership/membership.go
@@ -7,6 +7,8 @@ package membership
 import (
 	"encoding/json"
 	"strings"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
 )
 
 // AssignmentsStream holds every assignment's membership, the newest per subject.
@@ -57,6 +59,36 @@ type Membership struct {
 	Hears   []HeardIssued  `json:"hears,omitempty"`
 	// Waits are the event families a session may wait on through the mesh MCP server (novox/hq ADR 0367 §2).
 	Waits []WaitIssued `json:"waits,omitempty"`
+	// Bindings are the module's bus state as the bus module created it, one per entry its manifest asks for in
+	// `requires` (novox/hq ADR 0595 §1, §7): written by the grants part when it hears the bus module's `created`.
+	Bindings []BusBinding `json:"bindings,omitempty"`
+}
+
+// BusBinding is one bus-state entry's names on the bus, by the local name its module asks for it by (novox/hq ADR 0595
+// §1, design 25 § 12.2): the module names only locally, and reaches its own entries, and only those, through these.
+// Which names are set follows the storage type: a stream's Stream and Subject, a key-value bucket's Bucket, an object
+// store's ObjectStore, and a ledger's History, State, Indexes and Snapshot.
+type BusBinding struct {
+	Local string `json:"local"`
+	// Storage and Template are the entry's storage type and template (catalogue.Storage…, catalogue.Template…).
+	Storage  string `json:"storage"`
+	Template string `json:"template,omitempty"`
+	// Stream and Subject are a stream's name and the subject its messages are on; Subject is also a ledger's history's.
+	Stream  string `json:"stream,omitempty"`
+	Subject string `json:"subject,omitempty"`
+	// Bucket is a key-value bucket's name.
+	Bucket string `json:"bucket,omitempty"`
+	// ObjectStore is an object store's name.
+	ObjectStore string `json:"object-store,omitempty"`
+	// Ledger, for the storage type ledger: its history stream (one subject per instance), its state bucket, each
+	// declared index's bucket by index name, and the subject of the instances' snapshots (ADR 0597 §1, §4, §8).
+	History  string            `json:"history,omitempty"`
+	State    string            `json:"state,omitempty"`
+	Indexes  map[string]string `json:"indexes,omitempty"`
+	Snapshot string            `json:"snapshot,omitempty"`
+	// Types are a ledger's types, copied by the grants part from the entry the manifest-accepted event carries, so the
+	// tool runner checks an operation against its type without reading another part's state (ADR 0596, ADR 0597 §1).
+	Types []catalogue.LedgerType `json:"types,omitempty"`
 }
 
 // Served is one address a tool is answered on.
diff --git a/go/membership/membership_test.go b/go/membership/membership_test.go
index cfce963..e80d346 100644
--- a/go/membership/membership_test.go
+++ b/go/membership/membership_test.go
@@ -4,33 +4,26 @@ import (
 	"encoding/json"
 	"reflect"
 	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
 )
 
+// A credential is read out of a bus address, and the bare address carries no credential and a scheme.
 func TestACredentialIsReadOutOfABusAddress(t *testing.T) {
-	for _, c := range []struct{ in, user, password, bare string }{
-		{"nats://controller:secret@127.0.0.1:4222", "controller", "secret", "nats://127.0.0.1:4222"},
-		{"controller:secret@127.0.0.1:4222", "controller", "secret", "127.0.0.1:4222"},
-		{"nats://127.0.0.1:4222", "", "", "nats://127.0.0.1:4222"},
-		{"127.0.0.1:4222", "", "", "127.0.0.1:4222"},
+	for _, c := range []struct{ in, user, password, bare, schemed string }{
+		{"nats://controller:secret@127.0.0.1:4222", "controller", "secret", "nats://127.0.0.1:4222", "nats://127.0.0.1:4222"},
+		{"controller:secret@127.0.0.1:4222", "controller", "secret", "127.0.0.1:4222", "nats://127.0.0.1:4222"},
+		{"nats://127.0.0.1:4222", "", "", "nats://127.0.0.1:4222", "nats://127.0.0.1:4222"},
+		{"127.0.0.1:4222", "", "", "127.0.0.1:4222", "nats://127.0.0.1:4222"},
 		// A password containing an at-sign: split on the last one.
-		{"nats://controller:a@b@127.0.0.1:4222", "controller", "a@b", "nats://127.0.0.1:4222"},
+		{"nats://controller:a@b@127.0.0.1:4222", "controller", "a@b", "nats://127.0.0.1:4222", "nats://127.0.0.1:4222"},
 	} {
 		user, password, bare := CredentialIn(c.in)
 		if user != c.user || password != c.password || bare != c.bare {
 			t.Errorf("%q read as %q/%q at %q; wanted %q/%q at %q", c.in, user, password, bare, c.user, c.password, c.bare)
 		}
-	}
-}
-
-func TestABareAddressCarriesNoCredentialAndAScheme(t *testing.T) {
-	for in, want := range map[string]string{
-		"nats://controller:secret@10.0.0.1:4222": "nats://10.0.0.1:4222",
-		"controller:secret@10.0.0.1:4222":        "nats://10.0.0.1:4222",
-		"nats://10.0.0.1:4222":                   "nats://10.0.0.1:4222",
-		"10.0.0.1:4222":                          "nats://10.0.0.1:4222",
-	} {
-		if got := BareAddress(in); got != want {
-			t.Errorf("BareAddress(%q) = %q, want %q", in, got, want)
+		if got := BareAddress(c.in); got != c.schemed {
+			t.Errorf("BareAddress(%q) = %q, want %q", c.in, got, c.schemed)
 		}
 	}
 }
@@ -66,6 +59,26 @@ func TestAMembershipRoundTripsAsIssued(t *testing.T) {
 	if !reflect.DeepEqual(in, out) {
 		t.Fatalf("round trip changed it:\n%+v\n%+v", in, out)
 	}
+	// 1966/AC4: a membership with a ledger binding, its types among it, round-trips; one without bindings encodes as before, byte for byte.
+	bound := in
+	bound.Bindings = []BusBinding{{Local: "records", Storage: "ledger", Template: "ledger", History: "forge_records",
+		Subject: "forge_records.>", State: "forge_records_state", Indexes: map[string]string{"search": "forge_records_search"},
+		Snapshot: "forge_records_snapshot.>",
+		Types: []catalogue.LedgerType{{Name: "decision", Schema: map[string]catalogue.LedgerField{"title": {Type: "text"}},
+			Operations: []catalogue.LedgerOperation{{Name: "propose", Effect: catalogue.EffectSetFields, Fields: []string{"title"}}}}}}}
+	boundRaw, err := json.Marshal(bound)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var boundBack Membership
+	if err := json.Unmarshal(boundRaw, &boundBack); err != nil || !reflect.DeepEqual(bound, boundBack) {
+		t.Fatalf("a membership with a ledger binding read back as %+v (%v)", boundBack, err)
+	}
+	before, _ := json.Marshal(Membership{Node: "ace", Module: "forge", Tools: "t", Emits: "e", Serves: []Served{{Subject: "s"}},
+		State: []StateIssued{{Name: "repos", Bucket: "forge_repos", Writes: true}}})
+	if string(before) != `{"node":"ace","module":"forge","serves":[{"subject":"s"}],"emits":"e","tools":"t","state":[{"name":"repos","bucket":"forge_repos","writes":true}]}` {
+		t.Fatalf("a membership without bindings encodes otherwise than before: %s", before)
+	}
 	var wire map[string]json.RawMessage
 	_ = json.Unmarshal(raw, &wire)
 	for _, k := range []string{"receives", "mesh", "seat-traffic"} {
diff --git a/go/packages_list_test.go b/go/packages_list_test.go
index c33e3db..c23b74e 100644
--- a/go/packages_list_test.go
+++ b/go/packages_list_test.go
@@ -1,14 +1,19 @@
 package stdio
 
 import (
+	"encoding/json"
 	"go/ast"
 	"go/parser"
 	"go/token"
 	"io/fs"
 	"path/filepath"
+	"reflect"
 	"slices"
+	"strconv"
 	"strings"
 	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/buscalls"
 )
 
 // meshSDKPackages is every package mesh-sdk holds (novox/hq ADR 0593 §1): what every module shares, the value shapes
@@ -16,7 +21,7 @@ import (
 // Logic only some modules need is its owner module's package. A package added here is a decision to say in the pull
 // request: does every module share it, or is it a shape more than one part reads?
 var meshSDKPackages = []string{
-	".", "announce", "announcetest", "asker", "asks", "buildstep", "buscompose", "busretry", "calladdress", "catalogue",
+	".", "announce", "announcetest", "asker", "asks", "buildstep", "buscalls", "buscompose", "busretry", "calladdress", "catalogue",
 	"composer", "declaration", "delivery", "forgekey", "handacts", "health", "internal/beside", "kvlimit", "membership",
 	"objectlink", "outward", "overlay", "pernode", "process", "provider", "provider/harness", "provisions",
 	"sdkversion", "seal", "testbus",
@@ -56,6 +61,16 @@ func TestMeshSDKHoldsOnlyWhatEveryModuleShares(t *testing.T) {
 		if err != nil {
 			return err
 		}
+		// 1966/AC5: the calls package imports nothing of mesh-sdk but the catalogue's types, so a change here rebuilds
+		// only its importers (ADR 0595 §9).
+		if dir == "buscalls" {
+			for _, imp := range file.Imports {
+				p, _ := strconv.Unquote(imp.Path.Value)
+				if strings.HasPrefix(p, sdkModule) && p != sdkModule+"/catalogue" {
+					t.Errorf("%s imports %s: the calls package imports nothing of mesh-sdk but catalogue (ADR 0595 §9)", path, p)
+				}
+			}
+		}
 		for _, decl := range file.Decls {
 			fn, ok := decl.(*ast.FuncDecl)
 			if !ok {
@@ -90,4 +105,60 @@ func TestMeshSDKHoldsOnlyWhatEveryModuleShares(t *testing.T) {
 			t.Errorf("mesh-sdk's list keeps %s, which is gone: take it off the list", want)
 		}
 	}
+
+	// 1966/AC5: the call an apply names is the id the tool runner hands under `_meta`'s mesh/call.
+	if buscalls.MetaCall != "mesh/call" {
+		t.Errorf("the tool call's id is handed under %q, not mesh/call", buscalls.MetaCall)
+	}
+	// 1966/AC5: an index's key is its fields' values, then the instance's path, joined by "."; its entry names the
+	// instance and the sequence.
+	for _, c := range []struct {
+		fields   []string
+		instance string
+		want     string
+	}{
+		{[]string{"17950", "volvo"}, "listing/a17", "17950.volvo.listing.a17"},
+		// A value holding "." and one that does not meet in no key.
+		{[]string{"a.b"}, "c", "a=2Eb.c"},
+		{[]string{"a"}, "b/c", "a.b.c"},
+		// A title with spaces is a token the bus takes; "=" itself is encoded.
+		{[]string{"How it is checked", "x=y"}, "decision/0290", "How=20it=20is=20checked.x=3Dy.decision.0290"},
+	} {
+		k := buscalls.IndexKey(c.fields, c.instance)
+		if k != c.want {
+			t.Errorf("the index key of %q and %q is %q, want %q", c.fields, c.instance, k, c.want)
+		}
+		for _, token := range strings.Split(k, ".") {
+			if token == "" || strings.ContainsAny(token, " *>\t") {
+				t.Errorf("the index key %q holds a token the bus refuses: %q", k, token)
+			}
+		}
+	}
+	if buscalls.IndexKey([]string{"a.b"}, "c") == buscalls.IndexKey([]string{"a"}, "b/c") {
+		t.Error("two different index keys meet")
+	}
+	entry, _ := json.Marshal(buscalls.IndexEntry{Instance: "listing/a17", Sequence: 3})
+	if string(entry) != `{"instance":"listing/a17","sequence":3}` {
+		t.Errorf("an index entry is %s", entry)
+	}
+	// 1966/AC5: an apply naming the tool call it serves, and its answer with the state behind, round-trip.
+	for _, c := range []struct {
+		name     string
+		in, back any
+	}{
+		{"apply", &buscalls.ApplyRequest{Ledger: "records", Instance: "decision/0290", Operation: "submit",
+			Body: json.RawMessage(`{"why":"x"}`), Call: "call-17"}, &buscalls.ApplyRequest{}},
+		{"applied", &buscalls.Applied{Taken: true, Sequence: 5, StateBehind: true}, &buscalls.Applied{}},
+	} {
+		raw, err := json.Marshal(c.in)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if err := json.Unmarshal(raw, c.back); err != nil || !reflect.DeepEqual(c.in, c.back) {
+			t.Errorf("%s read back as %+v from %s (%v)", c.name, c.back, raw, err)
+		}
+	}
 }
+
+// sdkModule is mesh-sdk's Go module path.
+const sdkModule = "git.novox.be/novox/mesh-sdk/go"