Add device transfer flow to regV5.

lib/device-transfer/src/main/java/org/signal/devicetransfer/NewDeviceRestoreStatus.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2026 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.signal.devicetransfer;
+
+import androidx.annotation.NonNull;
+
+/**
+ * Progress event posted on the new device as the incoming backup is received and imported.
+ * Posted by the concrete {@code NewDeviceServerTask} in the app module and observed by whichever
+ * UI layer is driving the transfer (app or feature/registration).
+ */
+public final class NewDeviceRestoreStatus {
+
+  private final long messageCount;
+  private final State state;
+
+  public NewDeviceRestoreStatus(long messageCount, @NonNull State state) {
+    this.messageCount = messageCount;
+    this.state = state;
+  }
+
+  public long getMessageCount() {
+    return messageCount;
+  }
+
+  public @NonNull State getState() {
+    return state;
+  }
+
+  public enum State {
+    IN_PROGRESS,
+    TRANSFER_COMPLETE,
+    RESTORE_COMPLETE,
+    FAILURE_VERSION_DOWNGRADE,
+    FAILURE_FOREIGN_KEY,
+    FAILURE_UNKNOWN
+  }
+}