fix(oplog-collections-transformer): error on empty ALL_SITE_IDS instead of silent drop

publishUserStatus ranged ALL_SITE_IDS and, when empty/misconfigured, emitted
nothing and returned nil — silently dropping every statusText change. Return a
transient error when no destination resolves so the event Naks and stays visible
rather than being dropped. A startup hard-fail will replace the per-event error later.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012X9qhQT4NwmCHjdndwNtFD

Author: claude

data-migration/oplog-collections-transformer/users.go

@@ -114,6 +114,7 @@ func (h *handler) publishUserStatus(ctx context.Context, account, statusText str
 		StatusText: statusText,
 		Timestamp:  now,
 	})
+	sent := 0
 	for _, dest := range h.allSiteIDs {
 		if dest == "" {
 			continue
@@ -128,6 +129,13 @@ func (h *handler) publishUserStatus(ctx context.Context, account, statusText str
 		if err := h.pub.Publish(ctx, evt); err != nil {
 			return fmt.Errorf("publish user_status_updated to %q: %w", dest, err)
 		}
+		sent++
+	}
+	if sent == 0 {
+		// No destination sites: a statusText change would be lost. Surface a (transient) error
+		// so the event Naks and is visible rather than silently dropped — ALL_SITE_IDS is empty
+		// or misconfigured. (Future: hard-fail at startup instead of per-event.)
+		return fmt.Errorf("no destination sites for user_status_updated (account %q): ALL_SITE_IDS empty", account)
 	}
 	return nil
 }

data-migration/oplog-collections-transformer/users_test.go

@@ -110,6 +110,27 @@ func TestHandleUser_StatusTextUpdate_FansToAllSites(t *testing.T) {
 	assert.ElementsMatch(t, []string{testSiteID, "s2"}, dests)
 }
 
+func TestHandleUser_StatusTextUpdate_NoSites_ReturnsError(t *testing.T) {
+	pub := &fakePublisher{}
+	doc := `{"_id":"u1","username":"alice","statusText":"in a meeting"}`
+	h := newTestHandler(pub, &fakeTarget{}, &fakeLookup{doc: []byte(doc)})
+	h.allSiteIDs = nil // misconfigured: ALL_SITE_IDS empty
+
+	ev := oplogEvent{
+		Op:                "update",
+		Collection:        usersColl,
+		EventID:           "e1",
+		DocumentKey:       json.RawMessage(`{"_id":"u1"}`),
+		UpdateDescription: json.RawMessage(`{"updatedFields":{"statusText":"in a meeting"}}`),
+	}
+	err := h.handleUser(context.Background(), ev)
+	// Empty destinations must surface an error (Nak/visible), never a silent skip or drop.
+	require.Error(t, err)
+	assert.NotErrorIs(t, err, migration.ErrSkipped)
+	assert.NotErrorIs(t, err, migration.ErrPoison)
+	assert.Empty(t, pub.events)
+}
+
 func TestHandleUser_NonStatusUpdate_NoFanout(t *testing.T) {
 	pub := &fakePublisher{}
 	doc := `{"_id":"u1","username":"alice","customFields":{"deptName":"NewDept"}}`