Solved this years ago but no one cared. You create a Merkle tree of your post hashes, as a catalog for your account. The posts can still be individual, but the tree serves as a guide for if anything is missing. You don’t need a chain. Problem is, two devices trying to update the tree (or your chain idea) at once may have a conflict — or during a partition among relays etc — so UI would be needed for fixing the tree. Gets a bit tricky due to many devices due to the CAP theorem.