reEncodedSignData property
Optional: the signing payload re-derived from the transaction you are ABOUT TO BROADCAST. Recovering against signData alone proves the device signed something you asked for — this closes the second half: that it is the transaction still in your hands (payloads can legitimately change between build and send, e.g. a blockhash refresh in your own state).
Implementation
final Uint8List? reEncodedSignData;