feat(core): Inform user about transaction finalization in Bitcoin replacement transactions.

core/src/apps/bitcoin/sign_tx/approvers.py

@@ -170,6 +170,10 @@ class BasicApprover(Approver):
 
             if self.external_in > self.orig_external_in:
                 description = "PayJoin"
+            elif tx_info.rbf_disabled() and any(
+                not orig.rbf_disabled() for orig in orig_txs
+            ):
+                description = "Finalize transaction"
             elif len(orig_txs) > 1:
                 description = "Transaction meld"
             else:

core/src/apps/bitcoin/sign_tx/tx_info.py

@@ -69,6 +69,10 @@ _BIP32_MAX_LAST_ELEMENT = const(1000000)
 # Setting nSequence to this value for every input in a transaction disables nLockTime.
 _SEQUENCE_FINAL = const(0xFFFFFFFF)
 
+# Setting nSequence to a value greater than this for every input in a transaction
+# disables replace-by-fee opt-in.
+_MAX_BIP125_RBF_SEQUENCE = const(0xFFFFFFFD)
+
 
 class TxInfoBase:
     def __init__(self, signer: Signer) -> None:
@@ -122,6 +126,9 @@ class TxInfoBase:
     def lock_time_disabled(self) -> bool:
         return self.min_sequence == _SEQUENCE_FINAL
 
+    def rbf_disabled(self) -> bool:
+        return self.min_sequence > _MAX_BIP125_RBF_SEQUENCE
+
     def get_tx_check_digest(self) -> bytes:
         return self.h_tx_check.get_digest()