Suppose I'm writing an app that uses the Bitcoin blockchain to store small amounts of data - eg. hashes, I write a tx to a block and later that block becomes orphaned. The tx probably will get confirmed in the forked chain, either at the same height or later.

But if not, is it considered an abuse of the protocol to refer to the orphan block in my app - for example storing a reference to the orphan block in a database so the tx can be retrieved later? Are there any guarantees about the availability of orphan blocks, in bitcoind or other implementations, or are they prune-able ?