Properly handle concurrent closing types

[pm47]

We are emitting a ChannelCloseOutgoingPayment db event only for the first known closing tx, and are ignoring any concurrent transactions -- even if they do win the confirmation race.

This can happen when rbf-ing a cooperative close, or if we have a combination of force closes.

[haanhvu]

I'm working on this as a contributor. In case someone already started working on this, please let me know so that I'll find another issue. Thanks!

[haanhvu]

I have been digging into the codebase and this is how I understand:

Currently we are emitting a ChannelCloseOutgoingPayment for the first known closing transaction here:

lightning-kmp/modules/core/src/commonMain/kotlin/fr/acinq/lightning/io/Peer.kt

Lines 994 to 1007 in cbd454d

	_eventsFlow.emit(ChannelClosing(channelId))
	ChannelCloseOutgoingPayment(
	id = UUID.randomUUID(),
	recipientAmount = action.amount,
	address = action.address,
	isSentToDefaultAddress = action.isSentToDefaultAddress,
	miningFee = action.miningFee,
	channelId = channelId,
	txId = action.txId,
	createdAt = currentTimestampMillis(),
	confirmedAt = null,
	lockedAt = currentTimestampMillis(), // channel close are not splices, they are final
	closingType = action.closingType
	)

So instead of doing this, we should add WatchConfirmed to all closing transactions, and only emit ChannelCloseOutgoingPayment when WatchConfirmedTriggered.

Could any member of the project help answering if this is the right approach or not?