RBF + CPFP (Bump a fee in transaction view) when there's a support for both

[pavlenex]

We're currently facing an interesting UX problem at BTCPay in our wallet. Our wallet is merchant focused, meaning it mostly receives but also sends sometimes. In the next version, we'll have both CPFP and RBF, however the flow for those is a bit different.

Abstraction of these terms would be:

• CPFP (receiver of the tx is bumping/accelerating a tx)
• RBF (sender's of the tx is bumping a tx/accelerating a tx)

For CPFP, multiple transactions can be selected and user can bump a a tx (this is ideal in merchant scenario since you're saving a fee unblocking multiple tx that may ended up stuck in the mempool during a high-fee situation)

For RBF, it's mostly user spending from their wallet, and UX is only for a single transaction, you can't do multiple RBF at once.

Historically we first had CPFP support, where we allowed user to select mutliple tx from a wallet view (or one), and then we showed Bump a tx call to action where they proceed with bumping a tx(s).

Now with introduction of RBF, a single tx from a wallet view can be bumped, and UI there is pretty obvious - Display bump a fee next to a transaction.

Problem comes in ambiguity when you have both CPFP and RBF. Ideally, you could show bump a fee next to a transaction list, user clicks, it does either RBF or CPFP, but what happens if a transaction supports both? Then we need to somehow direct user into making an informed decision on which method to choose. Logically, user will likely choose the method which is cheaper. Okay let's say user selected CPFP, but then ideally you want to show that they can select mutliple transactions that are applicable so that user batches and saves on fees).

I am opening this issue because I wasn't able to find much on RBF/CPFP. I like the Bump a fee abstraction, but we should note that depending on which method is supported flows could be slightly different.

I'll post here our current UI, and hopefully once we figure it out, I'll post how we improved the flow, it may be useful for someone who in the future wants to enrich these sections. It's not really a task or a bug, so feel free to also close it, and I can just add context later on that can be implemented when someone has capacity to tackle this.

I believe the appropriate section would be this one https://bitcoin.design/guide/daily-spending-wallet/activity/#what-is-a-transaction