Summary
Problem Definition
The index where the blob starts had two initial purposes:
- It was needed to create compact fraud proofs for blob inclusion proofs.
- It was needed to create the square out of the transactions alone in the absence of any constraints on blob placement.
We are solving the first by committing to proving the correctness of the square layout in the future using a ZK proof, thereby removing the need for the index for fraud proofs.
The second initial purpose was removed when we moved to a deterministic square construction. With that the index was no longer needed for blob placements as it can be deterministically derived from the list of transactions. Each blob has to follow the blob share commitment rules and cannot be placed at an index that does not respect the rules.
One of the dependencies to unblock FBSS is that the creation of blocks and squares is deterministic, and that blocks are proven to be included in the square. This is done much more easily if it is over the same data. We can only set the index wrapper if we have a square, and if we delay square construction, we don't know the positions of the blobs yet.
This change also commits to using validity proofs for the square layout and the state transition function.
Proposal
Remove the index wrapper
