fix(op-node): derive a finalized hash on `ELSync` when sync status is `syncStatusFinishedELButNotFinalized`

[joshieDo]

The current implementation of EL sync provides an unsafe head for the EL to facilitate catch-up, with the expectation that it handles any resulting reorganizations.

However, once the EL is caught up and while CL sync demands a finalized state, the next FCU is assigned a finalized hash that matches the unsafe one. Although the likelihood of issues arising from this is low, it is technically incorrect behavior. If a reorg occurs, it could be irreversible for the EL, given that finalized hashes are not expected to be reversible.

Additionally, op-node only uses ELSync if there are no finalized blocks in the EL; otherwise, it switches to CLSync. However, in scenarios such as a node restart after a week, it is still preferable from the EL's perspective to initiate EL sync. By enabling the derivation of a genuine finalized hash, we can eliminate this constraint and avoid the risk associated with treating an unsafe hash as finalized on every restart.

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[github-actions[bot]]

This PR is stale because it has been open 14 days with no activity. Remove stale label or comment or this will be closed in 5 days.

[tynes]

@trianglesphere Can we follow up with the reth team on next steps here? They are blocked and are not sure how to proceed

[tynes]

@trianglesphere this has been handled via a different PR correct? So we can close this?

[trianglesphere]

@tynes @joshieDo, yes handling the genesis case of finalization has been fixed. The op-node still immediately finalizes.

[tynes]

Closing this then, thanks @trianglesphere

[joshieDo]

op-reth does not use snap sync elsync mode from op-node triggers a staged-sync style on op-reth. this is just an optimized way of executing large ranges of blocks (eg. from genesis to unsafe.)

op-node requires that if a L2 block is marked as finalized, the EL client has the full state available at the block.

Seems to me this is related to capability of the EL to be able to build a block from a block marked as finalized in the event of a safe/unsafe reorg/invalidation. Is the interpretation correct? If so, op-reth can do it.

In your PR, you walk back from a block which has the full state available to a block which may not have the full state available.

if by available means: can EL re-execute from the block that got marked as finalized - then yes op-reth can do it from the block we traverse back.to

given the above, would this be acceptable? if op-reth { traverse back method } else { as is currently }