User should have a way to know that a transaction changed its state

[danielabrozzoni]

Right now if users want to know if a transaction was removed from the chain, or dropped from the mempool, they need to compare two versions of list_unspent obtained in different moments.

We should investigate if we can provide some method to do this on our end.

The use case for this is: a user just synced with the backend, wants to know which transactions disappeared.

Edit: this can be further generalized to be a way to notify users when transactions/utxos change state (confirmation, drop from mempool, reorg, but also replacement, etc)

[evanlinjin]

Right now if users want to know if a transaction was removed from the chain, or dropped from the mempool, they need to compare two versions of list_unspent obtained in different moments.

Module	Data type	Method(s) to compare state with
bdk_chain	UTXOs	TxGraph::filter_chain_unspents, TxGraph::try_filter_chain_unspents
bdk_chain	Transactions	TxGraph::list_chain_txs, TxGraph::try_list_chain_txs
bdk_wallet	UTXOs	Wallet::list_unspent
bdk_wallet	Transactions	Wallet::transactions

[LLFourn]

Before introducing a way of notifying users of a state change we should have a way of determining the current state of a transaction more precisely. Right now we only have canonical (confirmed or unconfirmed) or not canonical. This is not enough -- I want to know why a transaction is non-canonical. This is usually a conflict was confirmed or seen more recently.

In terms of listing I think we should have a way of listing all transactions in the order they were first seen (see: #106) and what the current state of them is. You usually don't want to just forget about a transaction when you've broadcast it. RBF happens infrequently enough it's better to leave it in the app's transaction list and just indicate that the tx was replaced by another.

[notmandatory]

A potentially big change I think we should push to 2.0 milestone.