We store the transfer-ID counter per remote sender:

We can easily extend it to 64 bits and thus eliminate the differences in transfer deduplication between cyclic- and monotonic transfer-ID transfers.

The transfer-ID timeout then could default to ~2 seconds and the corresponding parameter could be removed from the API. The user could still change it if necessary directly in the subscription struct, but this is only for arcane use cases. In the worst case, if the remote node restarts and loses the transfer-ID state, prior to the expiration of the transfer-ID timeout we could lose up to 16 transfers.