pay_to_node: raise failure_msg if we received a trampoline error from the next onion.

that way, the error is sent back to the payer

electrum/lnworker.py

@@ -1523,8 +1523,6 @@ class LNWallet(LNWorker):
                         self.network.path_finder.update_inflight_htlcs(htlc_log.route, add_htlcs=False)
                     return
                 # htlc failed
-                if (attempts is not None and len(log) >= attempts) or (attempts is None and time.time() - paysession.start_time > self.PAYMENT_TIMEOUT):
-                    raise PaymentFailure('Giving up after %d attempts'%len(log))
                 # if we get a tmp channel failure, it might work to split the amount and try more routes
                 # if we get a channel update, we might retry the same route and amount
                 route = htlc_log.route
@@ -1537,6 +1535,11 @@ class LNWallet(LNWorker):
                 self.logger.info(f"error reported by {erring_node_id.hex()}")
                 if code == OnionFailureCode.MPP_TIMEOUT:
                     raise PaymentFailure(failure_msg.code_name())
+                # errors returned by the next trampoline.
+                if fwd_trampoline_onion and code in [
+                        OnionFailureCode.TRAMPOLINE_FEE_INSUFFICIENT,
+                        OnionFailureCode.TRAMPOLINE_EXPIRY_TOO_SOON]:
+                    raise failure_msg
                 # trampoline
                 if self.uses_trampoline():
                     paysession.handle_failed_trampoline_htlc(
@@ -1544,6 +1547,9 @@ class LNWallet(LNWorker):
                 else:
                     self.handle_error_code_from_failed_htlc(
                         route=route, sender_idx=sender_idx, failure_msg=failure_msg, amount=htlc_log.amount_msat)
+                # max attempts or timeout
+                if (attempts is not None and len(log) >= attempts) or (attempts is None and time.time() - paysession.start_time > self.PAYMENT_TIMEOUT):
+                    raise PaymentFailure('Giving up after %d attempts'%len(log))
         finally:
             paysession.is_active = False
             if paysession.can_be_deleted():