Transactions confirmed transitively question

[thunderbiscuit]

I'm trying to wrap my mind around transitively confirmed transactions (https://github.com/bitcoindevkit/bdk/pull/1733/files).

When would you find yourself in possession of a transaction that doesn't have an anchor with its "true confirmation block", but only through a block that confirms a transaction that spent this tx? I understand why if we know about a transaction B that spends an output created in transaction A, then it must be that A was confirmed at some point, but when does that come into play?

I basically want to be able to answer a user-layer question that would be something like: "So if I see this transaction as "transitively confirmed"... what should I do? Can I ask my TxGraph to perform the required steps to update itself? What are my next steps? For one I can't display the block a tx was confirmed in to my users, but this seems like a surfacing of something deeper and I wonder if there are other internal issues I should address. Is my syncing wrong in some way that the TxGraph could not procure the correct block that the transaction was confirmed in and has to rely on a secondary transaction to ensure canonicalism?"

That's the sort of question going through my mind as I see a transaction with a ChainPosition enum that can potentially be confirmed transitively and want to make sure I react appropriately when/if I come across them.

Thank you @evanlinjin for getting the conversation going on this on Discord. I'm still not 100% clear on how to proceed if ever I come across one of those however, and that tells me I need to understand better the circumstances where this variant would come up.