diff --git a/go/process/consumers.go b/go/process/consumers.go
new file mode 100644
index 00000000..80ffb536
--- /dev/null
+++ b/go/process/consumers.go
@@ -0,0 +1,122 @@
+package process
+
+import (
+	"context"
+	"encoding/json"
+	"sync"
+	"time"
+
+	"github.com/nats-io/nats.go/jetstream"
+)
+
+// ConsumersState is the name of the state a module keeps its durable consumers' facts in, one key per consumer by its name,
+// history 1 (design 47 G A-166, A-176): what a module's tool reads of a consumer, since a tool runs in a runtime of its own and
+// cannot read the consumer's information.
+const ConsumersState = "consumers"
+
+// ConsumerFacts is one durable consumer as ConsumerLedger keeps it.
+type ConsumerFacts struct {
+	// Stream and Name are the consumer's stream and its name.
+	Stream string `json:"stream"`
+	Name   string `json:"name"`
+	// Acknowledged is the stream sequence of the last message applied.
+	Acknowledged uint64 `json:"acknowledged"`
+	// Pending is the messages the consumer has not been given yet, as the last message said.
+	Pending uint64 `json:"pending"`
+	// LastEvent is the subject of the last event applied and LastAt its own `at`, or when the bus stored it where it has none.
+	LastEvent string    `json:"last-event,omitempty"`
+	LastAt    time.Time `json:"last-at,omitempty"`
+	// OldestUnacknowledged is when the oldest message delivered and not yet applied was delivered; zero when none is.
+	OldestUnacknowledged time.Time `json:"oldest-unacknowledged,omitempty"`
+}
+
+// ConsumerSink stores one key of the module's state consumers.
+type ConsumerSink func(ctx context.Context, key string, value []byte) error
+
+// ConsumerLedger writes a durable consumer's facts into the module's state consumers after each message delivered and each message
+// applied, so a tool reads them and nothing is read on a timer (design 47 G A-166, A-176). One ledger serves one consumer.
+type ConsumerLedger struct {
+	stream, name string
+	sink         ConsumerSink
+	now          func() time.Time
+	logf         func(string, ...any)
+
+	mu     sync.Mutex
+	facts  ConsumerFacts
+	unacks map[uint64]time.Time // delivered and not applied, by stream sequence
+}
+
+// NewConsumerLedger is the ledger of the consumer name on stream, writing through sink; a nil now is the clock and a nil logf says
+// nothing.
+func NewConsumerLedger(stream, name string, sink ConsumerSink, now func() time.Time, logf func(string, ...any)) *ConsumerLedger {
+	if now == nil {
+		now = time.Now
+	}
+	if logf == nil {
+		logf = func(string, ...any) {}
+	}
+	return &ConsumerLedger{stream: stream, name: name, sink: sink, now: now, logf: logf, unacks: map[uint64]time.Time{},
+		facts: ConsumerFacts{Stream: stream, Name: name}}
+}
+
+// Delivered notes that m was given to the consumer, and writes the facts.
+func (l *ConsumerLedger) Delivered(m jetstream.Msg) {
+	md, err := m.Metadata()
+	if err != nil {
+		l.logf("consumers: %s's message has no metadata, its delivery is not kept: %v", l.name, err)
+		return
+	}
+	l.mu.Lock()
+	l.unacks[md.Sequence.Stream] = l.now().UTC()
+	l.facts.Pending = md.NumPending
+	l.mu.Unlock()
+	l.write()
+}
+
+// Applied notes that m was applied and acknowledged, at the event's own `at` (zero: when the bus stored it), and writes the facts.
+func (l *ConsumerLedger) Applied(m jetstream.Msg, at time.Time) {
+	md, err := m.Metadata()
+	if err != nil {
+		l.logf("consumers: %s's message has no metadata, its application is not kept: %v", l.name, err)
+		return
+	}
+	if at.IsZero() {
+		at = md.Timestamp
+	}
+	l.mu.Lock()
+	delete(l.unacks, md.Sequence.Stream)
+	if md.Sequence.Stream > l.facts.Acknowledged {
+		l.facts.Acknowledged = md.Sequence.Stream
+	}
+	l.facts.Pending = md.NumPending
+	l.facts.LastEvent, l.facts.LastAt = m.Subject(), at.UTC()
+	l.mu.Unlock()
+	l.write()
+}
+
+// Facts are the facts now.
+func (l *ConsumerLedger) Facts() ConsumerFacts {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	f := l.facts
+	f.OldestUnacknowledged = time.Time{}
+	for _, t := range l.unacks {
+		if f.OldestUnacknowledged.IsZero() || t.Before(f.OldestUnacknowledged) {
+			f.OldestUnacknowledged = t
+		}
+	}
+	return f
+}
+
+func (l *ConsumerLedger) write() {
+	if l.sink == nil {
+		return
+	}
+	data, err := json.Marshal(l.Facts())
+	if err == nil {
+		err = l.sink(context.Background(), l.name, data)
+	}
+	if err != nil {
+		l.logf("consumers: the facts of %s are not written to the state %s: %v", l.name, ConsumersState, err)
+	}
+}
diff --git a/go/process/consumers_test.go b/go/process/consumers_test.go
new file mode 100644
index 00000000..5f5fb9ce
--- /dev/null
+++ b/go/process/consumers_test.go
@@ -0,0 +1,52 @@
+package process
+
+import (
+	"context"
+	"encoding/json"
+	"testing"
+	"time"
+
+	"github.com/nats-io/nats.go/jetstream"
+)
+
+type ledgerMsg struct {
+	jetstream.Msg
+	subject string
+	seq     uint64
+	pending uint64
+	stored  time.Time
+}
+
+func (m ledgerMsg) Subject() string { return m.subject }
+func (m ledgerMsg) Metadata() (*jetstream.MsgMetadata, error) {
+	return &jetstream.MsgMetadata{Sequence: jetstream.SequencePair{Stream: m.seq, Consumer: m.seq}, NumPending: m.pending, Timestamp: m.stored}, nil
+}
+
+func TestConsumerLedgerKeepsTheFactsAfterEachMessage(t *testing.T) {
+	kept := map[string][]byte{}
+	now := time.Date(2026, 11, 12, 9, 0, 0, 0, time.UTC)
+	l := NewConsumerLedger("EVENTS", "n1_m", func(_ context.Context, key string, value []byte) error { kept[key] = value; return nil }, func() time.Time { return now }, nil)
+	read := func() ConsumerFacts {
+		var f ConsumerFacts
+		if err := json.Unmarshal(kept["n1_m"], &f); err != nil {
+			t.Fatal(err)
+		}
+		return f
+	}
+	a, b := ledgerMsg{subject: "mesh.seat.s.event.a", seq: 7, pending: 1}, ledgerMsg{subject: "mesh.seat.s.event.b", seq: 8, pending: 0}
+	l.Delivered(a)
+	now = now.Add(time.Minute)
+	l.Delivered(b)
+	if f := read(); f.Pending != 0 || !f.OldestUnacknowledged.Equal(now.Add(-time.Minute)) {
+		t.Errorf("after two deliveries: %+v, want pending 0 and the first one's delivery as the oldest unacknowledged", f)
+	}
+	at := now.Add(-time.Hour)
+	l.Applied(a, at)
+	if f := read(); f.Acknowledged != 7 || f.LastEvent != "mesh.seat.s.event.a" || !f.LastAt.Equal(at) || !f.OldestUnacknowledged.Equal(now) {
+		t.Errorf("after the first applied: %+v, want sequence 7, its event and at, and the second one's delivery as the oldest", f)
+	}
+	l.Applied(b, time.Time{})
+	if f := read(); f.Acknowledged != 8 || !f.OldestUnacknowledged.IsZero() {
+		t.Errorf("after both applied: %+v, want sequence 8 and none unacknowledged", f)
+	}
+}