diff --git a/pkg/roomkeysender/roomkeysender.go b/pkg/roomkeysender/roomkeysender.go
index a577151a4..948557df7 100644
--- a/pkg/roomkeysender/roomkeysender.go
+++ b/pkg/roomkeysender/roomkeysender.go
@@ -25,21 +25,41 @@ func NewSender(pub Publisher) *Sender {
 	return &Sender{pub: pub}
 }
 
-// Send publishes evt to the room key update subject for the given user account.
-// The event is accepted by value; Send stamps its own Timestamp before publishing.
-// The value copy is intentional: Send must not mutate the caller's struct.
+// Marshal stamps the event Timestamp and serializes it once into a payload that
+// can be fanned out to many accounts via SendData without re-marshaling per
+// recipient. The event is accepted by value; Marshal must not mutate the
+// caller's struct.
 //
 //nolint:gocritic // hugeParam: by-value is intentional for immutability; the copy cost is acceptable.
-func (s *Sender) Send(account string, evt model.RoomKeyEvent) error {
+func (s *Sender) Marshal(evt model.RoomKeyEvent) ([]byte, error) {
 	evt.Timestamp = time.Now().UTC().UnixMilli()
 	// #nosec G117 -- RoomKeyEvent.PrivateKey is the intended payload: room-key distribution to the authorized account over its auth-callout-gated per-user subject, not a leak
 	data, err := json.Marshal(evt)
 	if err != nil {
-		return fmt.Errorf("marshal room key event: %w", err)
+		return nil, fmt.Errorf("marshal room key event: %w", err)
 	}
+	return data, nil
+}
+
+// SendData publishes an already-marshaled payload (from Marshal) to the room key
+// update subject for the given user account.
+func (s *Sender) SendData(account string, data []byte) error {
 	subj := subject.RoomKeyUpdate(account)
 	if err := s.pub.Publish(subj, data); err != nil {
 		return fmt.Errorf("publish room key event: %w", err)
 	}
 	return nil
 }
+
+// Send publishes evt to the room key update subject for the given user account.
+// The event is accepted by value; Send stamps its own Timestamp before publishing.
+// The value copy is intentional: Send must not mutate the caller's struct.
+//
+//nolint:gocritic // hugeParam: by-value is intentional for immutability; the copy cost is acceptable.
+func (s *Sender) Send(account string, evt model.RoomKeyEvent) error {
+	data, err := s.Marshal(evt)
+	if err != nil {
+		return err
+	}
+	return s.SendData(account, data)
+}
diff --git a/pkg/roomkeysender/roomkeysender_test.go b/pkg/roomkeysender/roomkeysender_test.go
index e1d184bd9..0a50f9b92 100644
--- a/pkg/roomkeysender/roomkeysender_test.go
+++ b/pkg/roomkeysender/roomkeysender_test.go
@@ -110,3 +110,48 @@ func TestSender_Send(t *testing.T) {
 		})
 	}
 }
+
+// TestSender_Marshal verifies Marshal stamps a timestamp and serializes the
+// event once into reusable bytes, without mutating the caller's struct.
+func TestSender_Marshal(t *testing.T) {
+	evt := model.RoomKeyEvent{RoomID: "room-1", Version: 7, PrivateKey: []byte{0x01, 0x02}}
+	before := evt
+	before.PrivateKey = append([]byte(nil), evt.PrivateKey...)
+
+	sender := roomkeysender.NewSender(&mockPublisher{})
+	data, err := sender.Marshal(evt)
+	require.NoError(t, err)
+
+	// Non-mutation contract: Marshal takes the event by value.
+	assert.Equal(t, before, evt, "Marshal must not mutate the caller's RoomKeyEvent")
+
+	var got model.RoomKeyEvent
+	require.NoError(t, json.Unmarshal(data, &got))
+	assert.Equal(t, evt.RoomID, got.RoomID)
+	assert.Equal(t, evt.Version, got.Version)
+	assert.Equal(t, evt.PrivateKey, got.PrivateKey)
+	assert.Greater(t, got.Timestamp, int64(0), "Marshal must stamp a timestamp")
+}
+
+// TestSender_SendData publishes pre-marshaled bytes verbatim to the account's
+// room-key subject — the marshal-once fan-out building block.
+func TestSender_SendData(t *testing.T) {
+	t.Run("publishes bytes to the account subject", func(t *testing.T) {
+		pub := &mockPublisher{}
+		sender := roomkeysender.NewSender(pub)
+		payload := []byte(`{"roomId":"r","version":3}`)
+
+		require.NoError(t, sender.SendData("alice", payload))
+		assert.Equal(t, "chat.user.alice.event.room.key", pub.subject)
+		assert.Equal(t, payload, pub.data, "SendData must publish the bytes verbatim")
+	})
+
+	t.Run("wraps publish errors", func(t *testing.T) {
+		sentinel := errors.New("connection lost")
+		sender := roomkeysender.NewSender(&mockPublisher{err: sentinel})
+		err := sender.SendData("bob", []byte("{}"))
+		require.Error(t, err)
+		assert.Contains(t, err.Error(), "publish room key event")
+		assert.ErrorIs(t, err, sentinel)
+	})
+}
diff --git a/room-worker/handler.go b/room-worker/handler.go
index 466bdc996..3d1c21910 100644
--- a/room-worker/handler.go
+++ b/room-worker/handler.go
@@ -325,7 +325,8 @@ func (h *Handler) processRemoveMember(ctx context.Context, data []byte) error {
 
 // rotateAndFanOut generates v+1, fans it out to survivors, then commits via Valkey Rotate.
 // Fan-out before Rotate is intentional so survivors hold v+1 before broadcast-worker switches.
-func (h *Handler) rotateAndFanOut(ctx context.Context, roomID string, currentPair *roomkeystore.VersionedKeyPair, survivors []model.Subscription) error {
+// survivorAccounts is a pre-computed post-deletion snapshot of the room's member accounts.
+func (h *Handler) rotateAndFanOut(ctx context.Context, roomID string, currentPair *roomkeystore.VersionedKeyPair, survivorAccounts []string) error {
 	newPair, err := roomkeystore.GenerateKeyPair()
 	if err != nil {
 		return fmt.Errorf("generate room key: %w", err)
@@ -335,7 +336,7 @@ func (h *Handler) rotateAndFanOut(ctx context.Context, roomID string, currentPai
 		predictedVersion = currentPair.Version + 1
 	}
 	versioned := &roomkeystore.VersionedKeyPair{Version: predictedVersion, KeyPair: *newPair}
-	h.fanOutRoomKeyToSurvivors(ctx, roomID, versioned, survivors)
+	h.fanOutRoomKeyToSurvivors(ctx, roomID, versioned, survivorAccounts)
 
 	if currentPair == nil {
 		if _, err := h.keyStore.Set(ctx, roomID, *newPair); err != nil {
@@ -400,12 +401,14 @@ func (h *Handler) processRemoveIndividual(ctx context.Context, req *model.Remove
 		return fmt.Errorf("reconcile member counts: %w", err)
 	}
 
-	// Rotate after delete + reconcile; ListByRoom returns post-deletion survivors.
-	survivors, listErr := h.store.ListByRoom(ctx, req.RoomID)
+	// Rotate after delete + reconcile; GetSubscriptionAccounts returns the
+	// post-deletion survivor accounts (projected — fan-out only needs accounts,
+	// not full subscription docs).
+	survivorAccounts, listErr := h.store.GetSubscriptionAccounts(ctx, req.RoomID)
 	if listErr != nil {
 		return fmt.Errorf("list survivors for key fan-out (room %s): %w", req.RoomID, listErr)
 	}
-	if err := h.rotateAndFanOut(ctx, req.RoomID, currentPair, survivors); err != nil {
+	if err := h.rotateAndFanOut(ctx, req.RoomID, currentPair, survivorAccounts); err != nil {
 		return fmt.Errorf("rotate and fan-out room key after remove-individual: %w", err)
 	}
 
@@ -608,13 +611,15 @@ func (h *Handler) processRemoveOrg(ctx context.Context, req *model.RemoveMemberR
 		return fmt.Errorf("reconcile member counts: %w", err)
 	}
 
-	// Rotate only when something was actually deleted; ListByRoom returns post-deletion survivors.
+	// Rotate only when something was actually deleted; GetSubscriptionAccounts
+	// returns the post-deletion survivor accounts (projected — fan-out only
+	// needs accounts, not full subscription docs).
 	if len(accounts) > 0 {
-		survivors, listErr := h.store.ListByRoom(ctx, req.RoomID)
+		survivorAccounts, listErr := h.store.GetSubscriptionAccounts(ctx, req.RoomID)
 		if listErr != nil {
 			return fmt.Errorf("list survivors for key fan-out (room %s): %w", req.RoomID, listErr)
 		}
-		if err := h.rotateAndFanOut(ctx, req.RoomID, currentPair, survivors); err != nil {
+		if err := h.rotateAndFanOut(ctx, req.RoomID, currentPair, survivorAccounts); err != nil {
 			return fmt.Errorf("rotate and fan-out room key after remove-org: %w", err)
 		}
 	}
@@ -1821,21 +1826,18 @@ func (h *Handler) natsServerCreateDM(m otelnats.Msg) {
 	natsutil.ReplyJSON(m.Msg, reply)
 }
 
-// fanOutRoomKeyToSurvivors sends the already-fetched room key to every room member in survivors
-// (local + remote). NATS supercluster routes user-subjects to home sites.
-// survivors is a pre-computed post-deletion snapshot supplied by the caller; pair must be non-nil.
-func (h *Handler) fanOutRoomKeyToSurvivors(ctx context.Context, roomID string, pair *roomkeystore.VersionedKeyPair, survivors []model.Subscription) {
+// fanOutRoomKeyToSurvivors sends the already-fetched room key to every survivor
+// account (local + remote). NATS supercluster routes user-subjects to home
+// sites. survivorAccounts is a pre-computed post-deletion snapshot supplied by
+// the caller; pair must be non-nil.
+func (h *Handler) fanOutRoomKeyToSurvivors(ctx context.Context, roomID string, pair *roomkeystore.VersionedKeyPair, survivorAccounts []string) {
 	// PublicKey omitted: server-side only, read from Valkey by broadcast-worker.
 	evt := model.RoomKeyEvent{
 		RoomID:     roomID,
 		Version:    pair.Version,
 		PrivateKey: pair.KeyPair.PrivateKey,
 	}
-	accounts := make([]string, len(survivors))
-	for i := range survivors {
-		accounts[i] = survivors[i].User.Account
-	}
-	h.fanOutKey(ctx, roomID, accounts, &evt)
+	h.fanOutKey(ctx, roomID, survivorAccounts, &evt)
 }
 
 // buildAndFanOutRoomKey publishes pair as a RoomKeyEvent to every account in users.
@@ -1859,10 +1861,12 @@ func (h *Handler) buildAndFanOutRoomKey(ctx context.Context, roomID string, pair
 	return nil
 }
 
-// fanOutKey distributes evt to every account via h.keySender.Send using up to
-// h.keyFanoutWorkers concurrent goroutines. Per-account errors are logged and
-// counted via roomkeymetrics; partial fan-out is acceptable because JetStream
-// redelivers on permanent failure and recipients are idempotent on key version.
+// fanOutKey distributes evt to every account using up to h.keyFanoutWorkers
+// concurrent goroutines. The event is marshaled exactly once and the resulting
+// bytes are published to each account — on a giant room this avoids one
+// json.Marshal per recipient. Per-account errors are logged and counted via
+// roomkeymetrics; partial fan-out is acceptable because JetStream redelivers on
+// permanent failure and recipients are idempotent on key version.
 //
 // evt is taken by pointer so the 80-byte struct isn't copied per fan-out call;
 // callers must not mutate it after passing it in.
@@ -1870,6 +1874,15 @@ func (h *Handler) fanOutKey(ctx context.Context, roomID string, accounts []strin
 	if len(accounts) == 0 {
 		return
 	}
+	data, err := h.keySender.Marshal(*evt)
+	if err != nil {
+		// Marshaling a RoomKeyEvent effectively never fails; if it somehow does,
+		// no recipient can be served, so count the whole batch and bail. The
+		// caller treats fan-out as best-effort and JetStream redelivers.
+		slog.Error("marshal room key for fan-out", "error", err, "roomId", roomID, "accounts", len(accounts))
+		roomkeymetrics.FanoutErrors.Add(ctx, int64(len(accounts)), metric.WithAttributes(attribute.String("roomId", roomID)))
+		return
+	}
 	workers := h.keyFanoutWorkers
 	if workers <= 0 {
 		// Defensive default for tests and any future construction path that
@@ -1890,7 +1903,7 @@ func (h *Handler) fanOutKey(ctx context.Context, roomID string, accounts []strin
 				<-sem
 				wg.Done()
 			}()
-			if err := h.keySender.Send(acct, *evt); err != nil {
+			if err := h.keySender.SendData(acct, data); err != nil {
 				slog.Error("send room key", "error", err, "account", acct, "roomId", roomID)
 				roomkeymetrics.FanoutErrors.Add(ctx, 1, metric.WithAttributes(attribute.String("roomId", roomID)))
 			}
diff --git a/room-worker/handler_test.go b/room-worker/handler_test.go
index 752ab14e7..229000f05 100644
--- a/room-worker/handler_test.go
+++ b/room-worker/handler_test.go
@@ -395,7 +395,7 @@ func TestHandler_ProcessRemoveMember_SelfLeave_IndividualOnly(t *testing.T) {
 	store.EXPECT().
 		ReconcileMemberCounts(gomock.Any(), roomID).Return(nil)
 	store.EXPECT().
-		ListByRoom(gomock.Any(), roomID).Return(nil, nil)
+		GetSubscriptionAccounts(gomock.Any(), roomID).Return(nil, nil)
 
 	var published []publishedMsg
 	h := NewHandler(store, siteID, func(_ context.Context, subj string, data []byte, _ string) error {
@@ -582,7 +582,7 @@ func TestHandler_ProcessRemoveMember_OwnerRemovesIndividual(t *testing.T) {
 	store.EXPECT().
 		ReconcileMemberCounts(gomock.Any(), roomID).Return(nil)
 	store.EXPECT().
-		ListByRoom(gomock.Any(), roomID).Return(nil, nil)
+		GetSubscriptionAccounts(gomock.Any(), roomID).Return(nil, nil)
 	store.EXPECT().
 		GetUser(gomock.Any(), requester).
 		Return(&model.User{ID: "u_alice", Account: requester, SiteID: siteID, EngName: "Alice", ChineseName: "愛"}, nil)
@@ -1168,7 +1168,7 @@ func TestHandler_ProcessRemoveMember_OwnerRemovesOrg(t *testing.T) {
 	store.EXPECT().
 		ReconcileMemberCounts(gomock.Any(), roomID).Return(nil) // recount after removal
 	store.EXPECT().
-		ListByRoom(gomock.Any(), roomID).Return(nil, nil)
+		GetSubscriptionAccounts(gomock.Any(), roomID).Return(nil, nil)
 	store.EXPECT().
 		GetUser(gomock.Any(), requester).
 		Return(&model.User{ID: "u_alice", Account: requester, SiteID: siteID, EngName: "Alice", ChineseName: "愛"}, nil)
@@ -1242,7 +1242,7 @@ func TestHandler_ProcessRemoveMember_CrossSiteOutbox(t *testing.T) {
 	store.EXPECT().
 		ReconcileMemberCounts(gomock.Any(), roomID).Return(nil)
 	store.EXPECT().
-		ListByRoom(gomock.Any(), roomID).Return(nil, nil)
+		GetSubscriptionAccounts(gomock.Any(), roomID).Return(nil, nil)
 
 	var published []publishedMsg
 	h := NewHandler(store, localSite, func(_ context.Context, subj string, data []byte, _ string) error {
@@ -1534,7 +1534,7 @@ func TestHandler_ProcessRemoveIndividual_OutboxFailurePropagates(t *testing.T) {
 	store.EXPECT().
 		ReconcileMemberCounts(gomock.Any(), roomID).Return(nil)
 	store.EXPECT().
-		ListByRoom(gomock.Any(), roomID).Return(nil, nil)
+		GetSubscriptionAccounts(gomock.Any(), roomID).Return(nil, nil)
 
 	outboxSubj := subject.Outbox(localSite, userSite, "member_removed")
 	publish := func(_ context.Context, subj string, _ []byte, _ string) error {
@@ -1573,7 +1573,7 @@ func TestHandler_ProcessRemoveOrg_OutboxFailurePropagates(t *testing.T) {
 	store.EXPECT().DeleteSubscriptionsByAccounts(gomock.Any(), roomID, []string{"carol"}).Return(int64(1), nil)
 	store.EXPECT().DeleteRoomMember(gomock.Any(), roomID, model.RoomMemberOrg, orgID).Return(nil)
 	store.EXPECT().ReconcileMemberCounts(gomock.Any(), roomID).Return(nil)
-	store.EXPECT().ListByRoom(gomock.Any(), roomID).Return(nil, nil)
+	store.EXPECT().GetSubscriptionAccounts(gomock.Any(), roomID).Return(nil, nil)
 	store.EXPECT().GetUser(gomock.Any(), requester).
 		Return(&model.User{ID: "u_alice", Account: requester, SiteID: localSite, EngName: "Alice", ChineseName: "愛"}, nil)
 
@@ -3635,14 +3635,12 @@ func TestFanOutRoomKeyToSurvivors_SendsToAllSurvivorsIncludingRemoteSite(t *test
 	pair := &roomkeystore.VersionedKeyPair{Version: 5, KeyPair: roomkeystore.RoomKeyPair{
 		PrivateKey: bytes.Repeat([]byte{0x03}, 32),
 	}}
-	survivors := []model.Subscription{
-		{User: model.SubscriptionUser{Account: "alice"}, RoomID: "r1", SiteID: "site-a"},
-		{User: model.SubscriptionUser{Account: "bob"}, RoomID: "r1", SiteID: "site-a"},
-		{User: model.SubscriptionUser{Account: "remote-carol"}, RoomID: "r1", SiteID: "site-b"},
-	}
+	// Survivor accounts span the local site (alice, bob) and a remote site
+	// (remote-carol); the caller projects these out of the subscriptions.
+	survivorAccounts := []string{"alice", "bob", "remote-carol"}
 
 	h := NewHandler(store, "site-a", func(_ context.Context, _ string, _ []byte, _ string) error { return nil }, nil, keySender)
-	h.fanOutRoomKeyToSurvivors(context.Background(), "r1", pair, survivors)
+	h.fanOutRoomKeyToSurvivors(context.Background(), "r1", pair, survivorAccounts)
 	// alice, bob (site-a) and remote-carol (site-b) all receive the new key.
 	assert.ElementsMatch(t, []string{
 		"chat.user.alice.event.room.key",
@@ -4115,7 +4113,7 @@ func TestHandler_ProcessRemoveIndividual_SelfLeave_Content(t *testing.T) {
 	store.EXPECT().DeleteRoomMember(gomock.Any(), roomID, model.RoomMemberIndividual, "u_b").Return(nil)
 	store.EXPECT().DeleteSubscription(gomock.Any(), roomID, "bob").Return(int64(1), nil)
 	store.EXPECT().ReconcileMemberCounts(gomock.Any(), roomID).Return(nil)
-	store.EXPECT().ListByRoom(gomock.Any(), roomID).Return([]model.Subscription{}, nil)
+	store.EXPECT().GetSubscriptionAccounts(gomock.Any(), roomID).Return([]string{}, nil)
 
 	var published []publishedMsg
 	h := &Handler{store: store, siteID: "site-a", publish: func(_ context.Context, subj string, data []byte, _ string) error {
@@ -4145,7 +4143,7 @@ func TestHandler_ProcessRemoveIndividual_RemovedByOther_Content(t *testing.T) {
 	store.EXPECT().DeleteRoomMember(gomock.Any(), roomID, model.RoomMemberIndividual, "u_b").Return(nil)
 	store.EXPECT().DeleteSubscription(gomock.Any(), roomID, "bob").Return(int64(1), nil)
 	store.EXPECT().ReconcileMemberCounts(gomock.Any(), roomID).Return(nil)
-	store.EXPECT().ListByRoom(gomock.Any(), roomID).Return([]model.Subscription{}, nil)
+	store.EXPECT().GetSubscriptionAccounts(gomock.Any(), roomID).Return([]string{}, nil)
 	store.EXPECT().GetUser(gomock.Any(), "alice").
 		Return(&model.User{ID: "u_a", Account: "alice", SiteID: "site-a", EngName: "Alice", ChineseName: "愛"}, nil)
 
@@ -4257,7 +4255,7 @@ func TestHandler_ProcessRemoveOrg_OtherOrgCovers_PreservesSub(t *testing.T) {
 	// MUST NOT be called — alice is still covered by the sibling org.
 	store.EXPECT().DeleteSubscriptionsByAccounts(gomock.Any(), gomock.Any(), gomock.Any()).Times(0)
 	// MUST NOT rotate — no survivors were displaced.
-	store.EXPECT().ListByRoom(gomock.Any(), gomock.Any()).Times(0)
+	store.EXPECT().GetSubscriptionAccounts(gomock.Any(), gomock.Any()).Times(0)
 	// The X org row still gets deleted; the count gets reconciled.
 	store.EXPECT().DeleteRoomMember(gomock.Any(), roomID, model.RoomMemberOrg, "X").Return(nil)
 	store.EXPECT().ReconcileMemberCounts(gomock.Any(), roomID).Return(nil)
diff --git a/room-worker/keyfanout_test.go b/room-worker/keyfanout_test.go
index 1f944856b..f0f798f67 100644
--- a/room-worker/keyfanout_test.go
+++ b/room-worker/keyfanout_test.go
@@ -132,6 +132,60 @@ func TestFanOutKey_PublishesEveryAccount(t *testing.T) {
 	require.Len(t, got, accounts, "must publish once per account")
 }
 
+// dataRecordingPublisher records the raw payload slice of every Publish call
+// WITHOUT copying, so a test can compare backing-array identity across calls.
+// Safe because fanOutKey marshals once and never mutates the buffer after it is
+// handed to Publish.
+type dataRecordingPublisher struct {
+	mu       sync.Mutex
+	payloads [][]byte
+}
+
+func (d *dataRecordingPublisher) Publish(_ string, data []byte) error {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	d.payloads = append(d.payloads, data)
+	return nil
+}
+
+func (d *dataRecordingPublisher) snapshot() [][]byte {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	out := make([][]byte, len(d.payloads))
+	copy(out, d.payloads)
+	return out
+}
+
+// TestFanOutKey_MarshalsOnce asserts the event is serialized exactly once and
+// the same buffer is fanned out to every recipient. It compares backing-array
+// identity (same first-element address) rather than byte-equality: two
+// json.Marshal calls always allocate distinct buffers, so a per-recipient
+// re-marshal is caught deterministically even when every marshal lands in the
+// same millisecond and produces identical JSON.
+func TestFanOutKey_MarshalsOnce(t *testing.T) {
+	const accounts = 50
+
+	dp := &dataRecordingPublisher{}
+	h := newFanoutTestHandler(t, roomkeysender.NewSender(dp), 8)
+
+	accts := make([]string, accounts)
+	for i := range accts {
+		accts[i] = fmt.Sprintf("acct-%03d", i)
+	}
+	evt := model.RoomKeyEvent{RoomID: "r", Version: 2, PrivateKey: []byte{0xaa, 0xbb}}
+	h.fanOutKey(context.Background(), "r", accts, &evt)
+
+	payloads := dp.snapshot()
+	require.Len(t, payloads, accounts)
+	first := payloads[0]
+	require.NotEmpty(t, first)
+	for i, p := range payloads {
+		require.NotEmpty(t, p, "payload %d is empty", i)
+		assert.True(t, &p[0] == &first[0],
+			"payload %d is a distinct allocation; event was marshaled more than once", i)
+	}
+}
+
 func TestFanOutKey_NoAccountsIsNoOp(t *testing.T) {
 	rp := &recordingPublisher{}
 	h := newFanoutTestHandler(t, roomkeysender.NewSender(rp), 16)
diff --git a/room-worker/mock_store_test.go b/room-worker/mock_store_test.go
index 3d5f71dcd..e71da84d2 100644
--- a/room-worker/mock_store_test.go
+++ b/room-worker/mock_store_test.go
@@ -293,21 +293,6 @@ func (mr *MockSubscriptionStoreMockRecorder) ListAddMemberCandidates(ctx, orgIDs
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "ListAddMemberCandidates", reflect.TypeOf((*MockSubscriptionStore)(nil).ListAddMemberCandidates), ctx, orgIDs, directAccounts, roomID)
 }
 
-// ListByRoom mocks base method.
-func (m *MockSubscriptionStore) ListByRoom(ctx context.Context, roomID string) ([]model.Subscription, error) {
-	m.ctrl.T.Helper()
-	ret := m.ctrl.Call(m, "ListByRoom", ctx, roomID)
-	ret0, _ := ret[0].([]model.Subscription)
-	ret1, _ := ret[1].(error)
-	return ret0, ret1
-}
-
-// ListByRoom indicates an expected call of ListByRoom.
-func (mr *MockSubscriptionStoreMockRecorder) ListByRoom(ctx, roomID any) *gomock.Call {
-	mr.mock.ctrl.T.Helper()
-	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "ListByRoom", reflect.TypeOf((*MockSubscriptionStore)(nil).ListByRoom), ctx, roomID)
-}
-
 // ListNewMembersForNewRoom mocks base method.
 func (m *MockSubscriptionStore) ListNewMembersForNewRoom(ctx context.Context, orgIDs, accounts []string, excludeAccount string) ([]string, error) {
 	m.ctrl.T.Helper()
diff --git a/room-worker/store.go b/room-worker/store.go
index 33671ae17..2fad3e93b 100644
--- a/room-worker/store.go
+++ b/room-worker/store.go
@@ -56,8 +56,6 @@ type SubscriptionStore interface {
 	// membership write path (channel, DM, botDM, add-member); the
 	// re-subscribe semantic for botDM is owned by user-service.
 	BulkCreateSubscriptions(ctx context.Context, subs []*model.Subscription) error
-	// ListByRoom returns all subscriptions for roomID across every site.
-	ListByRoom(ctx context.Context, roomID string) ([]model.Subscription, error)
 	// ReconcileMemberCounts recomputes Room.UserCount (non-bot subs) and
 	// Room.AppCount (bot subs) by scanning the subscriptions collection,
 	// then writes both back to the rooms collection in a single update.
diff --git a/room-worker/store_mongo.go b/room-worker/store_mongo.go
index d3ccc0a76..b7127e06b 100644
--- a/room-worker/store_mongo.go
+++ b/room-worker/store_mongo.go
@@ -31,6 +31,10 @@ func NewMongoStore(db *mongo.Database) *MongoStore {
 	}
 }
 
+// ListByRoom returns all subscriptions for roomID across every site. Not part
+// of SubscriptionStore — the handler's hot paths only need accounts (see
+// GetSubscriptionAccounts); this full-document read is retained for integration
+// test verification.
 func (s *MongoStore) ListByRoom(ctx context.Context, roomID string) ([]model.Subscription, error) {
 	cursor, err := s.subscriptions.Find(ctx, bson.M{"roomId": roomID})
 	if err != nil {