Zero-fee commitments for mobile wallets

The discussion centers around a proposition to enhance the handling of HTLC (Hashed Time-Locked Contracts) transactions within a blockchain framework, specifically targeting scenarios where transaction fees are a concern. The suggestion involves peers signing two versions of HTLC transactions. The first version is the standard practice, which does not incorporate any transaction fee and consequently requires additional on-chain inputs for execution. This approach, while cost-effective, can complicate the transaction process due to the need for these extra inputs.

The second version introduces a novel approach by including a custom TLV (Type-Length-Value) within the commitment_signed message, setting a high feerate that aligns with the current market conditions. This method aims to expedite the transaction process by ensuring that the fees are adequate to meet the network's requirements for timely processing, addressing the common issue of delayed transactions due to insufficient fees.

However, this proposal raises a question regarding the inclusion of a zero-fee P2A (Pay To Address) transaction within the custom variant. The concern here revolves around the mobile wallet's capability to handle such a transaction under the ephemeral dust policy, which typically requires transactions to have a minimum value to be considered valid and relayable across the network. Specifically, the query is whether, in the case of a zero-fee P2A transaction, the mobile wallet would still necessitate an additional UTXO (Unspent Transaction Output) to spend the P2A output effectively, thereby making the transaction compliant with network relay standards. This point underscores a potential challenge in implementing the proposed solution, highlighting the need for further consideration of how zero-fee transactions interact with existing network policies and the practical implications for users attempting to execute such transactions through mobile wallets.