diff --git a/pkg/service/setup/migration_readiness_test.go b/pkg/service/setup/migration_readiness_test.go
index c54e1d41..d4cd21b6 100644
--- a/pkg/service/setup/migration_readiness_test.go
+++ b/pkg/service/setup/migration_readiness_test.go
@@ -331,3 +331,48 @@ func TestMigrationDataReadinessExplainsPresetsDroppedByFull(t *testing.T) {
 		t.Errorf("action = %q, want it to point at the missing source", notReady.Action)
 	}
 }
+
+// TestMigrationSummaryReportsDataReadiness: the pre-flight panel must show a
+// refusal before the user commits, rather than showing all-green and failing
+// with a 409 at Apply.
+func TestMigrationSummaryReportsDataReadiness(t *testing.T) {
+	t.Run("refusal", func(t *testing.T) {
+		m, _, deviceIP := newMigrationReadinessFixture(t, `<presets/>`)
+
+		// No persisted snapshot, so the check refuses.
+		summary, err := m.GetMigrationSummary(deviceIP, "http://aftertouch.example:8000", "", nil)
+		if err != nil {
+			t.Fatalf("GetMigrationSummary: %v", err)
+		}
+
+		if summary.DataReadyError == "" {
+			t.Error("summary hid a refusal that Apply would hit")
+		}
+	})
+
+	t.Run("warning", func(t *testing.T) {
+		m, ds, deviceIP := newMigrationReadinessFixture(t, `<presets/>`)
+		if err := ds.SavePresets(readinessAccount, readinessDevice, nil); err != nil {
+			t.Fatalf("SavePresets: %v", err)
+		}
+		if err := ds.SaveDeviceInfo(readinessAccount, "SIBLING01", &models.ServiceDeviceInfo{
+			DeviceID:  "SIBLING01",
+			AccountID: readinessAccount,
+			Name:      "Sibling Speaker",
+		}); err != nil {
+			t.Fatalf("SaveDeviceInfo sibling: %v", err)
+		}
+
+		summary, err := m.GetMigrationSummary(deviceIP, "http://aftertouch.example:8000", "", nil)
+		if err != nil {
+			t.Fatalf("GetMigrationSummary: %v", err)
+		}
+
+		if summary.DataReadyError != "" {
+			t.Errorf("summary reported a refusal for a shared account: %q", summary.DataReadyError)
+		}
+		if len(summary.DataReadyWarnings) != 1 {
+			t.Errorf("warnings = %v, want one about the device count", summary.DataReadyWarnings)
+		}
+	})
+}
diff --git a/pkg/service/setup/setup.go b/pkg/service/setup/setup.go
index 57ac70fb..6f38f736 100644
--- a/pkg/service/setup/setup.go
+++ b/pkg/service/setup/setup.go
@@ -80,6 +80,12 @@ type MigrationSummary struct {
 	CurrentResolvConf        string      `json:"current_resolv_conf,omitempty"`
 	PlannedResolv            string      `json:"planned_resolv,omitempty"`
 	IsMigrated               bool        `json:"is_migrated"`
+	// Data readiness, so the pre-flight panel can show a refusal before the
+	// user commits to Apply instead of only surfacing it as a 409 afterwards.
+	// DataReadyError is the reason migration will be refused; empty means it
+	// will proceed. DataReadyWarnings are advisory and do not block.
+	DataReadyError    string   `json:"data_ready_error,omitempty"`
+	DataReadyWarnings []string `json:"data_ready_warnings,omitempty"`
 	// Per-axis migration signals — IsMigrated is the OR of these. The UI
 	// displays them individually so users can see partial states (e.g.
 	// URLs flipped via telnet but the on-disk XML hasn't caught up, or
@@ -303,6 +309,13 @@ func (m *Manager) GetMigrationSummary(deviceIP, targetURL, proxyURL string, opti
 		SSHSuccess: false,
 	}
 
+	// Same read-only check MigrateSpeaker runs, reported rather than enforced.
+	if warnings, err := m.checkMigrationDataReady(deviceIP); err != nil {
+		summary.DataReadyError = err.Error()
+	} else {
+		summary.DataReadyWarnings = warnings
+	}
+
 	// Run the telnet preflight in parallel with the SSH-based probes below.
 	// Both transports are queried independently: SSH gives access to
 	// /etc/hosts, /etc/resolv.conf and the on-device XML config; telnet's