feat: standard l2 genesis

[tynes]

Description

Add design doc for standard L2 genesis

Tracking ticket: https://github.com/ethereum-optimism/optimism/issues/12302

[tynes]

I am adding more information, thank you for the review so far

[tynes]

Here is a link to the audit plan for this feature: https://www.notion.so/oplabs/Isthmus-Smart-Contract-Audit-113f153ee16280448ebbd1b628c26ff2?pvs=4

[tynes]

Noticed something here: https://github.com/ethereum-optimism/optimism/blob/dcdf2b7693192f5bca0353bf22729f26c6240ea9/op-node/rollup/types.go#L43

The op-node starts deriving on the L1 block after what is in its config. This means we need SystemConfig.startBlock() - 1 rather than the start block itself. Two options on how to handle this:

• Have the genesis generation script fill in start block - 1 into the rollup config
• Make the starting L1 block be optional in the rollup config and use the startBlock() value as the starting point if its not present

I lean towards the second, it removes config overhead

[ajsutton]

I think the second is doable so long as op-node can load it from the latest L1 block reliably. Otherwise it doesn't know which block the system config first existed in. In most cases (probably not all) op-node walks along L1 from the start block forwards loading data from the block its up to so it has a consistent view. This would need to be a case where it always goes to the latest value. The start block has to be immutable so that seems reasonable to me.

[maurelian]

Tracking the startblock config topic here: https://github.com/ethereum-optimism/optimism/issues/12579

[tynes]

@maurelian Can I get an approval on this so we can merge?