diff --git a/cmd/membershipd/users_cli.go b/cmd/membershipd/users_cli.go
index e21276c..5dedeff 100644
--- a/cmd/membershipd/users_cli.go
+++ b/cmd/membershipd/users_cli.go
@@ -65,7 +65,7 @@ const defaultDBPath = "./local_files/unibus.db"
 // openStore opens the membership store at path, exiting on failure. Migrations
 // (including 002_users.sql) are applied by membership.Open, so a fresh database
 // gets the users table on first use of the CLI.
-func openStore(path string) *membership.Store {
+func openStore(path string) membership.Store {
 	store, err := membership.Open(path)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "membershipd user: open store %q: %v\n", path, err)
diff --git a/dev/feature_flags.json b/dev/feature_flags.json
index 8fc10d1..f58b826 100644
--- a/dev/feature_flags.json
+++ b/dev/feature_flags.json
@@ -14,6 +14,13 @@
       "description": "TLS on the NATS data plane using the project's self-signed CA (deploy/tls/). Server opts in via membershipd --tls-cert/--tls-key; clients pin ca.crt via client.Connect(caPath).",
       "added": "2026-06-07",
       "enabled_at": "2026-06-07"
+    },
+    "decentralized": {
+      "enabled": false,
+      "issue": "0003",
+      "description": "Control-plane state on replicated JetStream KV instead of local SQLite (branch-by-abstraction membership.Store: sqliteStore default OFF, jetstreamStore ON). The route cluster (0003a) and the KV store (0003b) ship behind this flag; the membershipd boot wiring that selects the KV store completes with the session/reconnect redesign (0003e) and is activated on the multi-node deploy (0003f). OFF keeps the single-node SQLite control plane unchanged.",
+      "added": "2026-06-07",
+      "enabled_at": null
     }
   }
 }
diff --git a/pkg/client/client_test.go b/pkg/client/client_test.go
index c556cd8..7b441d4 100644
--- a/pkg/client/client_test.go
+++ b/pkg/client/client_test.go
@@ -31,7 +31,7 @@ type testHarness struct {
 	ctrlURL string
 	ns      *server.Server
 	httpts  *httptest.Server
-	store   *membership.Store
+	store   membership.Store
 	srv     *membership.Server
 }
 
diff --git a/pkg/membership/auth_test.go b/pkg/membership/auth_test.go
index 4cff562..ee73cfe 100644
--- a/pkg/membership/auth_test.go
+++ b/pkg/membership/auth_test.go
@@ -22,7 +22,7 @@ import (
 // with a fresh store + blob store, and seeds one active admin ("alice").
 type authHarness struct {
 	ts       *httptest.Server
-	store    *Store
+	store    Store
 	alice    cs.Identity
 	alicePub string // hex
 }
diff --git a/pkg/membership/jetstream_store.go b/pkg/membership/jetstream_store.go
new file mode 100644
index 0000000..0ab63a5
--- /dev/null
+++ b/pkg/membership/jetstream_store.go
@@ -0,0 +1,510 @@
+package membership
+
+// jetstreamStore is the JetStream KV implementation of Store (issue 0003b): the
+// control-plane state (rooms, members, sealed room keys, the user allowlist)
+// lives in replicated JetStream Key/Value buckets instead of a process-local
+// SQLite file. Any node in the cluster reads and writes the same buckets, and
+// JetStream's RAFT layer keeps them consistent across replicas, so the HTTP
+// control plane becomes effectively stateless: any membershipd can serve any
+// request. It is selected only when the `decentralized` flag is on; sqliteStore
+// stays the default.
+//
+// Key layout (every path segment is a single KV token — ULIDs, RawURL endpoint
+// ids and lowercase-hex keys never contain a '.', so '.' is a safe separator and
+// a "<prefix>.*" watch enumerates exactly one trailing token):
+//
+//	rooms            roomID                       -> RoomInfo (JSON)
+//	members          roomID.endpoint              -> Member   (JSON, carries Role)
+//	rooms_by_member  endpoint.roomID              -> role     (reverse index for ListRoomsForEndpoint)
+//	room_keys        roomID.endpoint.epoch        -> sealed_key bytes
+//	users            signPubHex                   -> User     (JSON)
+//
+// Consistency caveat: KV has no multi-key transaction, so a multi-write op
+// (CreateRoom, AddMember) is a short sequence of single-key writes. The order is
+// chosen so a partial failure leaves a recoverable state (the room/member row
+// before its reverse index or sealed key), and writes are idempotent (Put
+// overwrites), which is also what makes the SQLite->KV migration (0003c) safe to
+// re-run.
+//
+// Fail-closed: every read uses a bounded context, and IsAuthorized/HasAdmin
+// return false on ANY backend error (a KV quorum loss or timeout denies access
+// rather than admitting it), mirroring the SQLite store's behavior.
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"sort"
+	"strconv"
+	"time"
+
+	"github.com/nats-io/nats.go/jetstream"
+)
+
+// Bucket names (alphanumeric/dash/underscore only — no dots, per KV rules).
+const (
+	bucketRooms     = "UNIBUS_rooms"
+	bucketMembers   = "UNIBUS_members"
+	bucketByMember  = "UNIBUS_rooms_by_member"
+	bucketRoomKeys  = "UNIBUS_room_keys"
+	bucketUsers     = "UNIBUS_users"
+	defaultKVOpTime = 5 * time.Second
+)
+
+// JetStreamConfig configures the KV-backed store.
+type JetStreamConfig struct {
+	// Replicas is the per-bucket replication factor (R1..R5). Use 1 for a single
+	// node or a 1-2 node rollout, 3 for real HA (quorum 2/3). Scaling R1->R3 in
+	// place is an operational step (nats kv update) done when the third node
+	// joins; it does not require reopening the store.
+	Replicas int
+	// OpTimeout bounds every KV operation so a stalled backend fails closed
+	// instead of hanging a request. Zero uses defaultKVOpTime.
+	OpTimeout time.Duration
+}
+
+type jetstreamStore struct {
+	rooms     jetstream.KeyValue
+	members   jetstream.KeyValue
+	byMember  jetstream.KeyValue
+	keys      jetstream.KeyValue
+	users     jetstream.KeyValue
+	opTimeout time.Duration
+}
+
+// OpenJetStream creates (or opens) the five KV buckets on js with the configured
+// replication factor and returns a Store backed by them. The JetStream context
+// belongs to the caller (it owns the NATS connection); Close is a no-op.
+func OpenJetStream(js jetstream.JetStream, cfg JetStreamConfig) (Store, error) {
+	if cfg.Replicas <= 0 {
+		cfg.Replicas = 1
+	}
+	opTimeout := cfg.OpTimeout
+	if opTimeout <= 0 {
+		opTimeout = defaultKVOpTime
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
+	defer cancel()
+
+	s := &jetstreamStore{opTimeout: opTimeout}
+	for _, b := range []struct {
+		name string
+		dst  *jetstream.KeyValue
+	}{
+		{bucketRooms, &s.rooms},
+		{bucketMembers, &s.members},
+		{bucketByMember, &s.byMember},
+		{bucketRoomKeys, &s.keys},
+		{bucketUsers, &s.users},
+	} {
+		kv, err := js.CreateOrUpdateKeyValue(ctx, jetstream.KeyValueConfig{
+			Bucket:   b.name,
+			Replicas: cfg.Replicas,
+			History:  1,
+			Storage:  jetstream.FileStorage,
+		})
+		if err != nil {
+			return nil, fmt.Errorf("membership: open KV bucket %q (replicas=%d): %w", b.name, cfg.Replicas, err)
+		}
+		*b.dst = kv
+	}
+	return s, nil
+}
+
+// Close releases nothing: the JetStream context and NATS connection are owned by
+// the caller, which closes them on shutdown.
+func (s *jetstreamStore) Close() error { return nil }
+
+func (s *jetstreamStore) ctx() (context.Context, context.CancelFunc) {
+	return context.WithTimeout(context.Background(), s.opTimeout)
+}
+
+// ---- key helpers ----------------------------------------------------------
+
+func memberKey(roomID, endpoint string) string   { return roomID + "." + endpoint }
+func byMemberKey(endpoint, roomID string) string  { return endpoint + "." + roomID }
+func sealedKey(roomID, endpoint string, e int) string {
+	return roomID + "." + endpoint + "." + strconv.Itoa(e)
+}
+
+// watchEntries collects every current entry whose key matches pattern (a KV
+// watch with a "<prefix>.*" wildcard), draining the watcher until the nil marker
+// that signals "all initial values delivered". Tombstones are skipped.
+func (s *jetstreamStore) watchEntries(kv jetstream.KeyValue, pattern string) ([]jetstream.KeyValueEntry, error) {
+	ctx, cancel := s.ctx()
+	defer cancel()
+	w, err := kv.Watch(ctx, pattern, jetstream.IgnoreDeletes())
+	if err != nil {
+		return nil, err
+	}
+	defer w.Stop()
+	var out []jetstream.KeyValueEntry
+	for {
+		select {
+		case e := <-w.Updates():
+			if e == nil {
+				return out, nil // initial snapshot complete
+			}
+			out = append(out, e)
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		}
+	}
+}
+
+// ---- rooms / members / keys ----------------------------------------------
+
+func (s *jetstreamStore) CreateRoom(info RoomInfo, ownerSignPub, ownerKexPub, ownerSealedKey []byte) error {
+	ctx, cancel := s.ctx()
+	defer cancel()
+
+	info.Epoch = 1
+	roomJSON, err := json.Marshal(info)
+	if err != nil {
+		return fmt.Errorf("membership: marshal room: %w", err)
+	}
+	// Create (not Put) so a duplicate room id is rejected, matching SQLite's
+	// PRIMARY KEY behavior.
+	if _, err := s.rooms.Create(ctx, info.RoomID, roomJSON); err != nil {
+		if errors.Is(err, jetstream.ErrKeyExists) {
+			return fmt.Errorf("membership: room %q already exists", info.RoomID)
+		}
+		return fmt.Errorf("membership: create room: %w", err)
+	}
+
+	owner := Member{Endpoint: info.OwnerEndpoint, Role: "owner", SignPub: ownerSignPub, KexPub: ownerKexPub}
+	if err := s.putMember(ctx, info.RoomID, owner); err != nil {
+		return err
+	}
+	if info.Encrypt {
+		if _, err := s.keys.Put(ctx, sealedKey(info.RoomID, info.OwnerEndpoint, 1), ownerSealedKey); err != nil {
+			return fmt.Errorf("membership: put owner key: %w", err)
+		}
+	}
+	return nil
+}
+
+// putMember writes the member row and its reverse index together.
+func (s *jetstreamStore) putMember(ctx context.Context, roomID string, m Member) error {
+	mb, err := json.Marshal(m)
+	if err != nil {
+		return fmt.Errorf("membership: marshal member: %w", err)
+	}
+	if _, err := s.members.Put(ctx, memberKey(roomID, m.Endpoint), mb); err != nil {
+		return fmt.Errorf("membership: put member: %w", err)
+	}
+	if _, err := s.byMember.Put(ctx, byMemberKey(m.Endpoint, roomID), []byte(m.Role)); err != nil {
+		return fmt.Errorf("membership: put member index: %w", err)
+	}
+	return nil
+}
+
+func (s *jetstreamStore) GetRoom(roomID string) (RoomInfo, error) {
+	ctx, cancel := s.ctx()
+	defer cancel()
+	e, err := s.rooms.Get(ctx, roomID)
+	if err != nil {
+		if errors.Is(err, jetstream.ErrKeyNotFound) {
+			return RoomInfo{}, fmt.Errorf("membership: get room %q: %w", roomID, ErrNotFound)
+		}
+		return RoomInfo{}, fmt.Errorf("membership: get room %q: %w", roomID, err)
+	}
+	var info RoomInfo
+	if err := json.Unmarshal(e.Value(), &info); err != nil {
+		return RoomInfo{}, fmt.Errorf("membership: unmarshal room %q: %w", roomID, err)
+	}
+	return info, nil
+}
+
+func (s *jetstreamStore) AddMember(roomID string, m Member, epoch int, sealedKeyBytes []byte) error {
+	ctx, cancel := s.ctx()
+	defer cancel()
+	if err := s.putMember(ctx, roomID, m); err != nil {
+		return err
+	}
+	if len(sealedKeyBytes) > 0 {
+		if _, err := s.keys.Put(ctx, sealedKey(roomID, m.Endpoint, epoch), sealedKeyBytes); err != nil {
+			return fmt.Errorf("membership: put member key: %w", err)
+		}
+	}
+	return nil
+}
+
+func (s *jetstreamStore) GetMember(roomID, endpoint string) (Member, error) {
+	ctx, cancel := s.ctx()
+	defer cancel()
+	e, err := s.members.Get(ctx, memberKey(roomID, endpoint))
+	if err != nil {
+		if errors.Is(err, jetstream.ErrKeyNotFound) {
+			return Member{}, fmt.Errorf("membership: get member %q/%q: %w", roomID, endpoint, ErrNotFound)
+		}
+		return Member{}, fmt.Errorf("membership: get member %q/%q: %w", roomID, endpoint, err)
+	}
+	var m Member
+	if err := json.Unmarshal(e.Value(), &m); err != nil {
+		return Member{}, fmt.Errorf("membership: unmarshal member: %w", err)
+	}
+	return m, nil
+}
+
+func (s *jetstreamStore) ListMembers(roomID string) ([]Member, error) {
+	entries, err := s.watchEntries(s.members, roomID+".*")
+	if err != nil {
+		return nil, fmt.Errorf("membership: list members %q: %w", roomID, err)
+	}
+	out := make([]Member, 0, len(entries))
+	for _, e := range entries {
+		var m Member
+		if err := json.Unmarshal(e.Value(), &m); err != nil {
+			return nil, fmt.Errorf("membership: unmarshal member: %w", err)
+		}
+		out = append(out, m)
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i].Endpoint < out[j].Endpoint })
+	return out, nil
+}
+
+func (s *jetstreamStore) ListRoomsForEndpoint(endpoint string) ([]RoomMembership, error) {
+	entries, err := s.watchEntries(s.byMember, endpoint+".*")
+	if err != nil {
+		return nil, fmt.Errorf("membership: list rooms for endpoint %q: %w", endpoint, err)
+	}
+	out := make([]RoomMembership, 0, len(entries))
+	for _, e := range entries {
+		// Key is "<endpoint>.<roomID>"; the roomID is everything after the dot.
+		roomID := e.Key()[len(endpoint)+1:]
+		info, err := s.GetRoom(roomID)
+		if err != nil {
+			if errors.Is(err, ErrNotFound) {
+				continue // index points at a removed room: skip, stay consistent
+			}
+			return nil, err
+		}
+		out = append(out, RoomMembership{RoomInfo: info, Role: string(e.Value())})
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i].RoomID < out[j].RoomID })
+	return out, nil
+}
+
+func (s *jetstreamStore) GetSealedKey(roomID, endpoint string, epoch int) (int, []byte, error) {
+	if epoch > 0 {
+		ctx, cancel := s.ctx()
+		defer cancel()
+		e, err := s.keys.Get(ctx, sealedKey(roomID, endpoint, epoch))
+		if err != nil {
+			if errors.Is(err, jetstream.ErrKeyNotFound) {
+				return 0, nil, fmt.Errorf("membership: get sealed key %q/%q@%d: %w", roomID, endpoint, epoch, ErrNotFound)
+			}
+			return 0, nil, fmt.Errorf("membership: get sealed key %q/%q@%d: %w", roomID, endpoint, epoch, err)
+		}
+		return epoch, e.Value(), nil
+	}
+	// epoch <= 0: latest. Enumerate "<roomID>.<endpoint>.*" and take the max.
+	entries, err := s.watchEntries(s.keys, roomID+"."+endpoint+".*")
+	if err != nil {
+		return 0, nil, fmt.Errorf("membership: get latest sealed key %q/%q: %w", roomID, endpoint, err)
+	}
+	bestEpoch, bestVal := -1, []byte(nil)
+	for _, e := range entries {
+		k := e.Key()
+		ep, perr := strconv.Atoi(k[len(roomID)+1+len(endpoint)+1:])
+		if perr != nil {
+			continue
+		}
+		if ep > bestEpoch {
+			bestEpoch, bestVal = ep, e.Value()
+		}
+	}
+	if bestEpoch < 0 {
+		return 0, nil, fmt.Errorf("membership: get latest sealed key %q/%q: %w", roomID, endpoint, ErrNotFound)
+	}
+	return bestEpoch, bestVal, nil
+}
+
+func (s *jetstreamStore) PutSealedKeys(roomID string, epoch int, keys map[string][]byte) error {
+	ctx, cancel := s.ctx()
+	defer cancel()
+	for endpoint, sealed := range keys {
+		if _, err := s.keys.Put(ctx, sealedKey(roomID, endpoint, epoch), sealed); err != nil {
+			return fmt.Errorf("membership: put sealed key for %q: %w", endpoint, err)
+		}
+	}
+	return nil
+}
+
+func (s *jetstreamStore) BumpEpoch(roomID string, newEpoch int) error {
+	// Read-modify-write the room's epoch. The control plane serializes rekeys per
+	// room (owner-signed), so the lost-update window is not exercised in practice.
+	info, err := s.GetRoom(roomID)
+	if err != nil {
+		return fmt.Errorf("membership: bump epoch %q->%d: %w", roomID, newEpoch, err)
+	}
+	info.Epoch = newEpoch
+	b, err := json.Marshal(info)
+	if err != nil {
+		return fmt.Errorf("membership: marshal room: %w", err)
+	}
+	ctx, cancel := s.ctx()
+	defer cancel()
+	if _, err := s.rooms.Put(ctx, roomID, b); err != nil {
+		return fmt.Errorf("membership: bump epoch %q->%d: %w", roomID, newEpoch, err)
+	}
+	return nil
+}
+
+func (s *jetstreamStore) RemoveMember(roomID, endpoint string) error {
+	ctx, cancel := s.ctx()
+	defer cancel()
+	// Drop the member row and its reverse index. Past-epoch sealed keys are left
+	// intact (they only decrypt data the member could already read), matching the
+	// SQLite store.
+	if err := s.members.Delete(ctx, memberKey(roomID, endpoint)); err != nil && !errors.Is(err, jetstream.ErrKeyNotFound) {
+		return fmt.Errorf("membership: remove member %q/%q: %w", roomID, endpoint, err)
+	}
+	if err := s.byMember.Delete(ctx, byMemberKey(endpoint, roomID)); err != nil && !errors.Is(err, jetstream.ErrKeyNotFound) {
+		return fmt.Errorf("membership: remove member index %q/%q: %w", roomID, endpoint, err)
+	}
+	return nil
+}
+
+// ---- users (the bus allowlist) -------------------------------------------
+
+func (s *jetstreamStore) AddUser(signPub, handle, role string) error {
+	signPub = normalizeSignPub(signPub)
+	if signPub == "" || handle == "" {
+		return fmt.Errorf("membership: AddUser: sign_pub and handle required")
+	}
+	if role == "" {
+		role = RoleMember
+	}
+	if role != RoleAdmin && role != RoleMember {
+		return fmt.Errorf("membership: AddUser: invalid role %q (want %q or %q)", role, RoleAdmin, RoleMember)
+	}
+	u := User{SignPub: signPub, Handle: handle, Role: role, Status: StatusActive, CreatedAt: nowRFC3339()}
+	b, err := json.Marshal(u)
+	if err != nil {
+		return fmt.Errorf("membership: marshal user: %w", err)
+	}
+	ctx, cancel := s.ctx()
+	defer cancel()
+	if _, err := s.users.Create(ctx, signPub, b); err != nil {
+		if errors.Is(err, jetstream.ErrKeyExists) {
+			return ErrUserExists
+		}
+		return fmt.Errorf("membership: insert user: %w", err)
+	}
+	return nil
+}
+
+func (s *jetstreamStore) GetUser(signPub string) (User, error) {
+	signPub = normalizeSignPub(signPub)
+	ctx, cancel := s.ctx()
+	defer cancel()
+	e, err := s.users.Get(ctx, signPub)
+	if err != nil {
+		if errors.Is(err, jetstream.ErrKeyNotFound) {
+			return User{}, fmt.Errorf("membership: get user %q: %w", signPub, ErrNotFound)
+		}
+		return User{}, fmt.Errorf("membership: get user %q: %w", signPub, err)
+	}
+	var u User
+	if err := json.Unmarshal(e.Value(), &u); err != nil {
+		return User{}, fmt.Errorf("membership: unmarshal user: %w", err)
+	}
+	return u, nil
+}
+
+func (s *jetstreamStore) ListUsers() ([]User, error) {
+	ctx, cancel := s.ctx()
+	w, err := s.users.WatchAll(ctx, jetstream.IgnoreDeletes())
+	if err != nil {
+		cancel()
+		return nil, fmt.Errorf("membership: list users: %w", err)
+	}
+	defer cancel()
+	defer w.Stop()
+	var out []User
+	for {
+		select {
+		case e := <-w.Updates():
+			if e == nil {
+				sort.Slice(out, func(i, j int) bool {
+					if out[i].Handle != out[j].Handle {
+						return out[i].Handle < out[j].Handle
+					}
+					return out[i].SignPub < out[j].SignPub
+				})
+				return out, nil
+			}
+			var u User
+			if err := json.Unmarshal(e.Value(), &u); err != nil {
+				return nil, fmt.Errorf("membership: unmarshal user: %w", err)
+			}
+			out = append(out, u)
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		}
+	}
+}
+
+func (s *jetstreamStore) RevokeUser(signPub string) error {
+	signPub = normalizeSignPub(signPub)
+	u, err := s.GetUser(signPub)
+	if err != nil {
+		if errors.Is(err, ErrNotFound) {
+			return fmt.Errorf("membership: revoke user %q: no active user with that key", signPub)
+		}
+		return fmt.Errorf("membership: revoke user %q: %w", signPub, err)
+	}
+	if u.Status != StatusActive {
+		return fmt.Errorf("membership: revoke user %q: no active user with that key", signPub)
+	}
+	u.Status = StatusRevoked
+	u.RevokedAt = nowRFC3339()
+	b, err := json.Marshal(u)
+	if err != nil {
+		return fmt.Errorf("membership: marshal user: %w", err)
+	}
+	ctx, cancel := s.ctx()
+	defer cancel()
+	if _, err := s.users.Put(ctx, signPub, b); err != nil {
+		return fmt.Errorf("membership: revoke user %q: %w", signPub, err)
+	}
+	return nil
+}
+
+// IsAuthorized reports whether signPub is an active bus user. Any backend error
+// (including a KV quorum loss or timeout) yields false: fail closed.
+func (s *jetstreamStore) IsAuthorized(signPub string) bool {
+	signPub = normalizeSignPub(signPub)
+	if signPub == "" {
+		return false
+	}
+	ctx, cancel := s.ctx()
+	defer cancel()
+	e, err := s.users.Get(ctx, signPub)
+	if err != nil {
+		return false
+	}
+	var u User
+	if err := json.Unmarshal(e.Value(), &u); err != nil {
+		return false
+	}
+	return u.Status == StatusActive
+}
+
+// HasAdmin reports whether at least one active admin exists. On any backend
+// error it returns false, keeping the admin-gated endpoints closed (conservative).
+func (s *jetstreamStore) HasAdmin() bool {
+	users, err := s.ListUsers()
+	if err != nil {
+		return false
+	}
+	for _, u := range users {
+		if u.Role == RoleAdmin && u.Status == StatusActive {
+			return true
+		}
+	}
+	return false
+}
diff --git a/pkg/membership/jetstream_store_test.go b/pkg/membership/jetstream_store_test.go
new file mode 100644
index 0000000..effad8c
--- /dev/null
+++ b/pkg/membership/jetstream_store_test.go
@@ -0,0 +1,275 @@
+package membership
+
+import (
+	"bytes"
+	"errors"
+	"net"
+	"testing"
+	"time"
+
+	"github.com/enmanuel/unibus/pkg/embeddednats"
+	"github.com/nats-io/nats.go"
+	"github.com/nats-io/nats.go/jetstream"
+	server "github.com/nats-io/nats-server/v2/server"
+)
+
+func kvFreePort(t *testing.T) int {
+	t.Helper()
+	l, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("free port: %v", err)
+	}
+	defer l.Close()
+	return l.Addr().(*net.TCPAddr).Port
+}
+
+// newKVStore boots a single-node embedded NATS with JetStream and opens a
+// jetstreamStore (R1) over it, returning the store plus the server and
+// connection so a test can shut the backend down to exercise fail-closed paths.
+func newKVStore(t *testing.T) (*jetstreamStore, *server.Server, *nats.Conn) {
+	t.Helper()
+	ns, err := embeddednats.StartServer(embeddednats.ServerConfig{
+		StoreDir: t.TempDir(),
+		Host:     "127.0.0.1",
+		Port:     kvFreePort(t),
+	})
+	if err != nil {
+		t.Fatalf("embedded nats: %v", err)
+	}
+	nc, err := nats.Connect(ns.ClientURL())
+	if err != nil {
+		ns.Shutdown()
+		t.Fatalf("nats connect: %v", err)
+	}
+	js, err := jetstream.New(nc)
+	if err != nil {
+		nc.Close()
+		ns.Shutdown()
+		t.Fatalf("jetstream: %v", err)
+	}
+	st, err := OpenJetStream(js, JetStreamConfig{Replicas: 1, OpTimeout: 2 * time.Second})
+	if err != nil {
+		nc.Close()
+		ns.Shutdown()
+		t.Fatalf("open jetstream store: %v", err)
+	}
+	t.Cleanup(func() {
+		nc.Close()
+		ns.Shutdown()
+		ns.WaitForShutdown()
+	})
+	return st.(*jetstreamStore), ns, nc
+}
+
+// TestJetStreamStoreRoomsCRUD is the golden path: an encrypted room with an owner
+// and an invited member round-trips through every room/member/key method.
+func TestJetStreamStoreRoomsCRUD(t *testing.T) {
+	s, _, _ := newKVStore(t)
+
+	roomID := newULID()
+	owner := "owner-ep-1"
+	info := RoomInfo{RoomID: roomID, Subject: "room.kv", Encrypt: true, Persist: true, SignMsgs: true, OwnerEndpoint: owner}
+	ownerSealed := []byte("sealed-owner-epoch1")
+	if err := s.CreateRoom(info, []byte("owner-sign"), []byte("owner-kex"), ownerSealed); err != nil {
+		t.Fatalf("CreateRoom: %v", err)
+	}
+
+	// GetRoom returns epoch 1 and the policy.
+	got, err := s.GetRoom(roomID)
+	if err != nil {
+		t.Fatalf("GetRoom: %v", err)
+	}
+	if got.Epoch != 1 || got.Subject != "room.kv" || !got.Encrypt || got.OwnerEndpoint != owner {
+		t.Fatalf("GetRoom mismatch: %+v", got)
+	}
+
+	// Owner is a member with role "owner".
+	om, err := s.GetMember(roomID, owner)
+	if err != nil {
+		t.Fatalf("GetMember owner: %v", err)
+	}
+	if om.Role != "owner" || !bytes.Equal(om.SignPub, []byte("owner-sign")) {
+		t.Fatalf("owner member mismatch: %+v", om)
+	}
+
+	// Owner's sealed key at epoch 1.
+	ep, sealed, err := s.GetSealedKey(roomID, owner, 1)
+	if err != nil || ep != 1 || !bytes.Equal(sealed, ownerSealed) {
+		t.Fatalf("GetSealedKey owner: ep=%d sealed=%q err=%v", ep, sealed, err)
+	}
+
+	// Invite a member with a sealed key at epoch 1.
+	bob := "member-ep-bob"
+	bobSealed := []byte("sealed-bob-epoch1")
+	if err := s.AddMember(roomID, Member{Endpoint: bob, Role: "member", SignPub: []byte("bob-sign"), KexPub: []byte("bob-kex")}, 1, bobSealed); err != nil {
+		t.Fatalf("AddMember: %v", err)
+	}
+
+	// ListMembers returns both, sorted by endpoint.
+	members, err := s.ListMembers(roomID)
+	if err != nil {
+		t.Fatalf("ListMembers: %v", err)
+	}
+	if len(members) != 2 {
+		t.Fatalf("ListMembers want 2, got %d (%+v)", len(members), members)
+	}
+
+	// Bob can find the room via the reverse index.
+	rooms, err := s.ListRoomsForEndpoint(bob)
+	if err != nil {
+		t.Fatalf("ListRoomsForEndpoint: %v", err)
+	}
+	if len(rooms) != 1 || rooms[0].RoomID != roomID || rooms[0].Role != "member" {
+		t.Fatalf("ListRoomsForEndpoint mismatch: %+v", rooms)
+	}
+
+	// Latest sealed key (epoch <= 0) resolves to epoch 1 for bob.
+	lep, lsealed, err := s.GetSealedKey(roomID, bob, 0)
+	if err != nil || lep != 1 || !bytes.Equal(lsealed, bobSealed) {
+		t.Fatalf("GetSealedKey latest bob: ep=%d err=%v", lep, err)
+	}
+
+	// Rekey to epoch 2 (bump + new sealed keys), then latest resolves to 2.
+	if err := s.BumpEpoch(roomID, 2); err != nil {
+		t.Fatalf("BumpEpoch: %v", err)
+	}
+	if err := s.PutSealedKeys(roomID, 2, map[string][]byte{owner: []byte("owner-epoch2")}); err != nil {
+		t.Fatalf("PutSealedKeys: %v", err)
+	}
+	got2, _ := s.GetRoom(roomID)
+	if got2.Epoch != 2 {
+		t.Fatalf("after BumpEpoch want epoch 2, got %d", got2.Epoch)
+	}
+	lep2, _, err := s.GetSealedKey(roomID, owner, 0)
+	if err != nil || lep2 != 2 {
+		t.Fatalf("latest owner key after rekey: ep=%d err=%v", lep2, err)
+	}
+
+	// Remove bob; he disappears from members and his reverse index.
+	if err := s.RemoveMember(roomID, bob); err != nil {
+		t.Fatalf("RemoveMember: %v", err)
+	}
+	if _, err := s.GetMember(roomID, bob); !errors.Is(err, ErrNotFound) {
+		t.Fatalf("GetMember after remove want ErrNotFound, got %v", err)
+	}
+	rooms2, _ := s.ListRoomsForEndpoint(bob)
+	if len(rooms2) != 0 {
+		t.Fatalf("ListRoomsForEndpoint after remove want 0, got %d", len(rooms2))
+	}
+}
+
+// TestJetStreamStoreUsers exercises the allowlist: add, lookup, authorize,
+// revoke (which flips IsAuthorized), and the admin gate.
+func TestJetStreamStoreUsers(t *testing.T) {
+	s, _, _ := newKVStore(t)
+
+	const aliceHex = "aa11"
+	if s.HasAdmin() {
+		t.Fatalf("fresh store should have no admin")
+	}
+	if err := s.AddUser(aliceHex, "alice", RoleAdmin); err != nil {
+		t.Fatalf("AddUser: %v", err)
+	}
+	if !s.HasAdmin() {
+		t.Fatalf("HasAdmin should be true after adding an admin")
+	}
+	if !s.IsAuthorized(aliceHex) {
+		t.Fatalf("alice should be authorized")
+	}
+	// Case-insensitive lookup (keys are normalized lowercase).
+	if !s.IsAuthorized("AA11") {
+		t.Fatalf("uppercase hex should normalize and authorize")
+	}
+	u, err := s.GetUser(aliceHex)
+	if err != nil || u.Handle != "alice" || u.Role != RoleAdmin || u.Status != StatusActive {
+		t.Fatalf("GetUser mismatch: %+v err=%v", u, err)
+	}
+
+	// Duplicate add is rejected with ErrUserExists.
+	if err := s.AddUser(aliceHex, "alice2", RoleMember); !errors.Is(err, ErrUserExists) {
+		t.Fatalf("duplicate AddUser want ErrUserExists, got %v", err)
+	}
+
+	if err := s.AddUser("bb22", "bob", RoleMember); err != nil {
+		t.Fatalf("AddUser bob: %v", err)
+	}
+	users, err := s.ListUsers()
+	if err != nil || len(users) != 2 {
+		t.Fatalf("ListUsers want 2, got %d err=%v", len(users), err)
+	}
+
+	// Revoke alice: authorization flips off immediately.
+	if err := s.RevokeUser(aliceHex); err != nil {
+		t.Fatalf("RevokeUser: %v", err)
+	}
+	if s.IsAuthorized(aliceHex) {
+		t.Fatalf("revoked user must not be authorized")
+	}
+	if s.HasAdmin() {
+		t.Fatalf("after revoking the only admin, HasAdmin must be false")
+	}
+	// Revoking again is an error (no active user).
+	if err := s.RevokeUser(aliceHex); err == nil {
+		t.Fatalf("re-revoke should error")
+	}
+}
+
+// TestJetStreamStoreNotFound checks the ErrNotFound mapping for misses.
+func TestJetStreamStoreNotFound(t *testing.T) {
+	s, _, _ := newKVStore(t)
+	if _, err := s.GetRoom("nope"); !errors.Is(err, ErrNotFound) {
+		t.Fatalf("GetRoom miss want ErrNotFound, got %v", err)
+	}
+	if _, err := s.GetMember("nope", "x"); !errors.Is(err, ErrNotFound) {
+		t.Fatalf("GetMember miss want ErrNotFound, got %v", err)
+	}
+	if _, _, err := s.GetSealedKey("nope", "x", 1); !errors.Is(err, ErrNotFound) {
+		t.Fatalf("GetSealedKey miss want ErrNotFound, got %v", err)
+	}
+	if _, _, err := s.GetSealedKey("nope", "x", 0); !errors.Is(err, ErrNotFound) {
+		t.Fatalf("GetSealedKey latest miss want ErrNotFound, got %v", err)
+	}
+	if _, err := s.GetUser("ffff"); !errors.Is(err, ErrNotFound) {
+		t.Fatalf("GetUser miss want ErrNotFound, got %v", err)
+	}
+}
+
+// TestJetStreamStoreIsAuthorizedFailClosed is the error path mandated by the
+// issue: when the KV backend is unavailable (here the NATS server is shut down),
+// IsAuthorized must DENY, never admit. A previously-authorized identity flips to
+// unauthorized once the backend cannot be reached.
+func TestJetStreamStoreIsAuthorizedFailClosed(t *testing.T) {
+	s, ns, nc := newKVStore(t)
+
+	const aliceHex = "abcd"
+	if err := s.AddUser(aliceHex, "alice", RoleAdmin); err != nil {
+		t.Fatalf("AddUser: %v", err)
+	}
+	if !s.IsAuthorized(aliceHex) {
+		t.Fatalf("alice should be authorized while the backend is up")
+	}
+
+	// Take the KV backend away: close the client and stop the server. Every
+	// subsequent KV Get fails, and the store must fail closed.
+	nc.Close()
+	ns.Shutdown()
+	ns.WaitForShutdown()
+
+	// Bound the assertion: IsAuthorized internally caps each op at OpTimeout, so
+	// this returns well before the test deadline.
+	done := make(chan bool, 1)
+	go func() { done <- s.IsAuthorized(aliceHex) }()
+	select {
+	case authorized := <-done:
+		if authorized {
+			t.Fatalf("KV backend down but IsAuthorized returned true: NOT fail-closed")
+		}
+	case <-time.After(10 * time.Second):
+		t.Fatalf("IsAuthorized hung when the backend was down (no bounded timeout)")
+	}
+
+	// HasAdmin is likewise conservative: backend down -> false (gates stay closed).
+	if s.HasAdmin() {
+		t.Fatalf("KV backend down but HasAdmin returned true: NOT fail-closed")
+	}
+}
diff --git a/pkg/membership/server.go b/pkg/membership/server.go
index c5a2724..75136cf 100644
--- a/pkg/membership/server.go
+++ b/pkg/membership/server.go
@@ -3,7 +3,6 @@ package membership
 import (
 	"bytes"
 	"context"
-	"database/sql"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -56,7 +55,7 @@ const (
 // rate limiting, and read endpoints (GET) are unauthenticated. Hardening
 // (mTLS, capabilities, rate limits) is a later phase.
 type Server struct {
-	store    *Store
+	store    Store
 	blobs    *blobstore.Store
 	mux      *http.ServeMux
 	authMode AuthMode
@@ -79,7 +78,7 @@ type Server struct {
 // tests that have not migrated to signed requests yet). It installs a per-IP
 // rate limiter with the package defaults; loopback dev behavior is unchanged
 // because the burst comfortably exceeds any single client's request rate.
-func NewServer(store *Store, blobs *blobstore.Store, authMode AuthMode) *Server {
+func NewServer(store Store, blobs *blobstore.Store, authMode AuthMode) *Server {
 	s := &Server{
 		store:    store,
 		blobs:    blobs,
@@ -456,7 +455,7 @@ func (s *Server) handleGetKey(w http.ResponseWriter, r *http.Request) {
 	}
 	ep, sealed, err := s.store.GetSealedKey(roomID, endpoint, epoch)
 	if err != nil {
-		if errors.Is(err, sql.ErrNoRows) {
+		if errors.Is(err, ErrNotFound) {
 			writeErr(w, http.StatusForbidden,
 				"not invited to this encrypted room: no key has been sealed for your identity. Ask the room owner to invite you before joining.")
 			return
diff --git a/pkg/membership/store.go b/pkg/membership/store.go
index 6e4a7e2..fb57257 100644
--- a/pkg/membership/store.go
+++ b/pkg/membership/store.go
@@ -13,6 +13,7 @@ package membership
 import (
 	"database/sql"
 	"embed"
+	"errors"
 	"fmt"
 	"io/fs"
 	"sort"
@@ -26,6 +27,14 @@ import (
 //go:embed migrations/*.sql
 var migrationsFS embed.FS
 
+// ErrNotFound is the store-agnostic "no such record" sentinel. Both backends
+// (SQLite and JetStream KV) return it, wrapped, when a lookup misses, so callers
+// distinguish "not invited / no key yet" from a genuine backend failure without
+// depending on a specific driver's error (the SQLite store maps sql.ErrNoRows to
+// it; the KV store maps a missing key to it). This is what lets the control
+// plane stay storage-agnostic under the branch-by-abstraction of issue 0003b.
+var ErrNotFound = errors.New("membership: not found")
+
 // Member is a participant of a room with their published public keys.
 type Member struct {
 	Endpoint string `json:"endpoint"`
@@ -45,14 +54,58 @@ type RoomInfo struct {
 	OwnerEndpoint string
 }
 
-// Store is the SQLite-backed membership/key store.
-type Store struct {
+// Store is the membership/key control-plane store: the authoritative source of
+// room metadata, the member directory, per-epoch sealed room keys, and the bus
+// user allowlist. It is an interface (branch-by-abstraction, issue 0003b) with
+// two implementations: sqliteStore (the default, single-node, local SQLite) and
+// jetstreamStore (rooms/members/keys/users on replicated JetStream KV, selected
+// when the `decentralized` flag is on). Every lookup miss returns ErrNotFound
+// (wrapped); every implementation MUST fail closed (IsAuthorized returns false
+// on any backend error), so a KV quorum loss denies rather than admits.
+type Store interface {
+	// Rooms / members / keys.
+	CreateRoom(info RoomInfo, ownerSignPub, ownerKexPub, ownerSealedKey []byte) error
+	GetRoom(roomID string) (RoomInfo, error)
+	AddMember(roomID string, m Member, epoch int, sealedKey []byte) error
+	GetMember(roomID, endpoint string) (Member, error)
+	ListMembers(roomID string) ([]Member, error)
+	ListRoomsForEndpoint(endpoint string) ([]RoomMembership, error)
+	GetSealedKey(roomID, endpoint string, epoch int) (int, []byte, error)
+	PutSealedKeys(roomID string, epoch int, keys map[string][]byte) error
+	BumpEpoch(roomID string, newEpoch int) error
+	RemoveMember(roomID, endpoint string) error
+
+	// Users (the bus allowlist).
+	AddUser(signPub, handle, role string) error
+	GetUser(signPub string) (User, error)
+	ListUsers() ([]User, error)
+	RevokeUser(signPub string) error
+	IsAuthorized(signPub string) bool
+	HasAdmin() bool
+
+	// Lifecycle.
+	Close() error
+}
+
+// sqliteStore is the SQLite-backed implementation of Store (the default,
+// single-node backend). It stays the production default while the
+// `decentralized` flag is off.
+type sqliteStore struct {
 	db *sql.DB
 }
 
-// Open opens (creating if needed) the SQLite database at path and applies all
-// embedded migrations idempotently.
-func Open(path string) (*Store, error) {
+// Open opens (creating if needed) the SQLite database at path, applies all
+// embedded migrations idempotently, and returns it as a Store. It remains the
+// default control-plane backend; the JetStream KV store is opened separately
+// (OpenJetStream) when decentralization is enabled.
+func Open(path string) (Store, error) {
+	return openSQLite(path)
+}
+
+// openSQLite is the concrete constructor, returning *sqliteStore so internal
+// callers (e.g. the SQLite->KV migration) can use SQLite-specific helpers that
+// are not part of the storage-agnostic Store interface.
+func openSQLite(path string) (*sqliteStore, error) {
 	// _pragma busy_timeout avoids spurious "database is locked" under concurrent
 	// HTTP handlers; foreign_keys kept off — we manage referential integrity in code.
 	dsn := fmt.Sprintf("file:%s?_pragma=busy_timeout(5000)&_pragma=journal_mode(WAL)", path)
@@ -64,7 +117,7 @@ func Open(path string) (*Store, error) {
 		db.Close()
 		return nil, fmt.Errorf("membership: ping db: %w", err)
 	}
-	s := &Store{db: db}
+	s := &sqliteStore{db: db}
 	if err := s.applyMigrations(); err != nil {
 		db.Close()
 		return nil, err
@@ -73,11 +126,11 @@ func Open(path string) (*Store, error) {
 }
 
 // Close closes the underlying database.
-func (s *Store) Close() error { return s.db.Close() }
+func (s *sqliteStore) Close() error { return s.db.Close() }
 
 // applyMigrations runs every embedded migration in lexical order, tolerating
 // the "already applied" errors that SQLite's non-idempotent DDL produces.
-func (s *Store) applyMigrations() error {
+func (s *sqliteStore) applyMigrations() error {
 	files, err := fs.Glob(migrationsFS, "migrations/*.sql")
 	if err != nil {
 		return fmt.Errorf("membership: glob migrations: %w", err)
@@ -103,7 +156,7 @@ func nowRFC3339() string { return time.Now().UTC().Format(time.RFC3339Nano) }
 // CreateRoom inserts a room at epoch 1, registers the owner as a member with
 // role "owner", and stores the owner's sealed key for epoch 1. Idempotent
 // inserts are not used: a duplicate room_id returns an error.
-func (s *Store) CreateRoom(info RoomInfo, ownerSignPub, ownerKexPub, ownerSealedKey []byte) error {
+func (s *sqliteStore) CreateRoom(info RoomInfo, ownerSignPub, ownerKexPub, ownerSealedKey []byte) error {
 	tx, err := s.db.Begin()
 	if err != nil {
 		return fmt.Errorf("membership: begin: %w", err)
@@ -142,7 +195,7 @@ func (s *Store) CreateRoom(info RoomInfo, ownerSignPub, ownerKexPub, ownerSealed
 }
 
 // GetRoom returns room metadata (including current epoch).
-func (s *Store) GetRoom(roomID string) (RoomInfo, error) {
+func (s *sqliteStore) GetRoom(roomID string) (RoomInfo, error) {
 	var info RoomInfo
 	var enc, per, sgn int
 	err := s.db.QueryRow(
@@ -158,7 +211,7 @@ func (s *Store) GetRoom(roomID string) (RoomInfo, error) {
 
 // AddMember inserts a member at the given role and stores their sealed key for
 // the supplied epoch.
-func (s *Store) AddMember(roomID string, m Member, epoch int, sealedKey []byte) error {
+func (s *sqliteStore) AddMember(roomID string, m Member, epoch int, sealedKey []byte) error {
 	tx, err := s.db.Begin()
 	if err != nil {
 		return fmt.Errorf("membership: begin: %w", err)
@@ -185,7 +238,7 @@ func (s *Store) AddMember(roomID string, m Member, epoch int, sealedKey []byte)
 }
 
 // GetMember returns a single member of a room.
-func (s *Store) GetMember(roomID, endpoint string) (Member, error) {
+func (s *sqliteStore) GetMember(roomID, endpoint string) (Member, error) {
 	var m Member
 	err := s.db.QueryRow(
 		`SELECT endpoint, role, sign_pub, kex_pub FROM members WHERE room_id = ? AND endpoint = ?`,
@@ -198,7 +251,7 @@ func (s *Store) GetMember(roomID, endpoint string) (Member, error) {
 }
 
 // ListMembers returns all members of a room ordered by endpoint.
-func (s *Store) ListMembers(roomID string) ([]Member, error) {
+func (s *sqliteStore) ListMembers(roomID string) ([]Member, error) {
 	rows, err := s.db.Query(
 		`SELECT endpoint, role, sign_pub, kex_pub FROM members WHERE room_id = ? ORDER BY endpoint`,
 		roomID,
@@ -230,7 +283,7 @@ type RoomMembership struct {
 // ListRoomsForEndpoint returns every room the given endpoint is a member of,
 // with the room's current metadata and the endpoint's role, ordered by room id.
 // An endpoint that is in no rooms yields an empty slice (not an error).
-func (s *Store) ListRoomsForEndpoint(endpoint string) ([]RoomMembership, error) {
+func (s *sqliteStore) ListRoomsForEndpoint(endpoint string) ([]RoomMembership, error) {
 	rows, err := s.db.Query(
 		`SELECT r.room_id, r.subject, r.key_epoch, r.encrypt, r.persist, r.sign_msgs, r.owner_endpoint, m.role
 		 FROM members m JOIN rooms r ON r.room_id = m.room_id
@@ -257,7 +310,7 @@ func (s *Store) ListRoomsForEndpoint(endpoint string) ([]RoomMembership, error)
 
 // GetSealedKey returns the sealed room key for an endpoint at a given epoch.
 // If epoch <= 0, the latest epoch for that endpoint is returned.
-func (s *Store) GetSealedKey(roomID, endpoint string, epoch int) (int, []byte, error) {
+func (s *sqliteStore) GetSealedKey(roomID, endpoint string, epoch int) (int, []byte, error) {
 	var ep int
 	var sealed []byte
 	var err error
@@ -275,6 +328,12 @@ func (s *Store) GetSealedKey(roomID, endpoint string, epoch int) (int, []byte, e
 		).Scan(&ep, &sealed)
 	}
 	if err != nil {
+		// Map "no such row" to the store-agnostic sentinel so the control plane
+		// can tell "not invited / no key yet" (-> 403 with a helpful message) from
+		// a genuine backend failure, the same way the KV store will.
+		if errors.Is(err, sql.ErrNoRows) {
+			return 0, nil, fmt.Errorf("membership: get sealed key %q/%q@%d: %w", roomID, endpoint, epoch, ErrNotFound)
+		}
 		return 0, nil, fmt.Errorf("membership: get sealed key %q/%q@%d: %w", roomID, endpoint, epoch, err)
 	}
 	return ep, sealed, nil
@@ -282,7 +341,7 @@ func (s *Store) GetSealedKey(roomID, endpoint string, epoch int) (int, []byte, e
 
 // PutSealedKeys stores a batch of sealed keys for the given epoch (endpoint ->
 // sealed bytes), upserting on conflict so a rekey can overwrite stale entries.
-func (s *Store) PutSealedKeys(roomID string, epoch int, keys map[string][]byte) error {
+func (s *sqliteStore) PutSealedKeys(roomID string, epoch int, keys map[string][]byte) error {
 	tx, err := s.db.Begin()
 	if err != nil {
 		return fmt.Errorf("membership: begin: %w", err)
@@ -301,7 +360,7 @@ func (s *Store) PutSealedKeys(roomID string, epoch int, keys map[string][]byte)
 }
 
 // BumpEpoch sets the room's current key_epoch to newEpoch.
-func (s *Store) BumpEpoch(roomID string, newEpoch int) error {
+func (s *sqliteStore) BumpEpoch(roomID string, newEpoch int) error {
 	if _, err := s.db.Exec(`UPDATE rooms SET key_epoch = ? WHERE room_id = ?`, newEpoch, roomID); err != nil {
 		return fmt.Errorf("membership: bump epoch %q->%d: %w", roomID, newEpoch, err)
 	}
@@ -310,7 +369,7 @@ func (s *Store) BumpEpoch(roomID string, newEpoch int) error {
 
 // RemoveMember deletes a member from a room. Their sealed keys for past epochs
 // are left intact (they encrypt only data that member could already read).
-func (s *Store) RemoveMember(roomID, endpoint string) error {
+func (s *sqliteStore) RemoveMember(roomID, endpoint string) error {
 	if _, err := s.db.Exec(`DELETE FROM members WHERE room_id = ? AND endpoint = ?`, roomID, endpoint); err != nil {
 		return fmt.Errorf("membership: remove member %q/%q: %w", roomID, endpoint, err)
 	}
diff --git a/pkg/membership/store_test.go b/pkg/membership/store_test.go
index 2d324cc..83c2c0f 100644
--- a/pkg/membership/store_test.go
+++ b/pkg/membership/store_test.go
@@ -6,10 +6,10 @@ import (
 	"testing"
 )
 
-func openTestStore(t *testing.T) *Store {
+func openTestStore(t *testing.T) *sqliteStore {
 	t.Helper()
 	path := filepath.Join(t.TempDir(), "test.db")
-	s, err := Open(path)
+	s, err := openSQLite(path)
 	if err != nil {
 		t.Fatalf("Open: %v", err)
 	}
diff --git a/pkg/membership/users.go b/pkg/membership/users.go
index 7aeb1c5..3a65597 100644
--- a/pkg/membership/users.go
+++ b/pkg/membership/users.go
@@ -45,7 +45,7 @@ func normalizeSignPub(signPub string) string {
 // AddUser inserts a new bus user. role defaults to RoleMember when empty. It
 // returns ErrUserExists if the sign_pub is already registered (the caller may
 // choose to revoke+re-add or ignore). handle and signPub must be non-empty.
-func (s *Store) AddUser(signPub, handle, role string) error {
+func (s *sqliteStore) AddUser(signPub, handle, role string) error {
 	signPub = normalizeSignPub(signPub)
 	if signPub == "" || handle == "" {
 		return fmt.Errorf("membership: AddUser: sign_pub and handle required")
@@ -74,7 +74,7 @@ func (s *Store) AddUser(signPub, handle, role string) error {
 
 // GetUser returns the user with the given signing public key. It returns
 // sql.ErrNoRows (wrapped) when there is no such user.
-func (s *Store) GetUser(signPub string) (User, error) {
+func (s *sqliteStore) GetUser(signPub string) (User, error) {
 	signPub = normalizeSignPub(signPub)
 	var u User
 	var revoked sql.NullString
@@ -90,7 +90,7 @@ func (s *Store) GetUser(signPub string) (User, error) {
 }
 
 // ListUsers returns every user ordered by handle then sign_pub (stable output).
-func (s *Store) ListUsers() ([]User, error) {
+func (s *sqliteStore) ListUsers() ([]User, error) {
 	rows, err := s.db.Query(
 		`SELECT sign_pub, handle, role, status, created_at, revoked_at FROM users ORDER BY handle, sign_pub`,
 	)
@@ -116,7 +116,7 @@ func (s *Store) ListUsers() ([]User, error) {
 // status flip (not a delete) so the identity stays auditable and IsAuthorized
 // immediately denies it on both planes. Revoking an unknown or already-revoked
 // user returns an error / is a no-op respectively.
-func (s *Store) RevokeUser(signPub string) error {
+func (s *sqliteStore) RevokeUser(signPub string) error {
 	signPub = normalizeSignPub(signPub)
 	res, err := s.db.Exec(
 		`UPDATE users SET status = ?, revoked_at = ? WHERE sign_pub = ? AND status = ?`,
@@ -140,7 +140,7 @@ func (s *Store) RevokeUser(signPub string) error {
 // plane (HTTP request middleware) and the data plane (NATS nkey authenticator),
 // so revoking a user denies access on both without restarting anything. An
 // unknown key, a revoked key, or any query error all yield false (fail closed).
-func (s *Store) IsAuthorized(signPub string) bool {
+func (s *sqliteStore) IsAuthorized(signPub string) bool {
 	signPub = normalizeSignPub(signPub)
 	if signPub == "" {
 		return false
@@ -155,7 +155,7 @@ func (s *Store) IsAuthorized(signPub string) bool {
 // HasAdmin reports whether at least one active admin exists. The control plane
 // uses it to gate user-management endpoints: until the host operator seeds the
 // first admin via the local CLI, those endpoints stay closed (chicken-egg).
-func (s *Store) HasAdmin() bool {
+func (s *sqliteStore) HasAdmin() bool {
 	var one int
 	err := s.db.QueryRow(
 		`SELECT 1 FROM users WHERE role = ? AND status = ? LIMIT 1`, RoleAdmin, StatusActive,