Interop: op-supervisor devnet 1 readiness

[protolambda]

op-supervisor status:

• PR open
• Fixes X-head updating to handle edge-cases:
  • Empty blocks, using DB work that landed Friday
  • Difference between future blocks and conflicting blocks
• Needs better testing:
  • Existing tests stub the DB, but make a lot of assumptions, and little coverage.
    • In favor of instead randomizing / fuzzing the DB:
      Create a DB, fill it with random data, and see if the x-head can be progressed.
  • Existing tests lock us into some earlier prototype-ish code abstractions:
    • Too synchronous
    • Slow: frequent map lookups, poor usage pattern of the heads DB
• X-unsafe head progression works now:
  • Had to fix the prior fix to genesis block insertion;
    the empty-DB case is recognized correctly now.
• X-safe head progression is broken:
  • op-supervisor polls op-geth for safe, to update local-safe.
  • But op-geth serves cross-safe, not local-safe.
  • And x-safe will only update after op-node learns from op-supervisor.
  • Thus stuck at genesis forever.
  • To fix: the node should not be polling the op-geth node for safe or finalized data.
    Instead, it should poll the op-node for safe and finalized data.
    • When using op-node, we can use the sync-status endpoint,
      and retrieve the finalized L1 block, and the derived-from info, at the same time.
• X-finalized progression is broken:
  • As in prior op-node implementation change: cross-finalized is a bad idea.
    We should have just 1 level of finality in op-node / op-geth.
  • To fix: to determine what to finalize, the op-supervisor needs:
    • per L2:
      • what the latest cross-safe value is.
      • recent history of cross-safe L2 values, per L1 derived-from value,
        until we have the safety-index which covers a deeper history
        (see design doc).
    • global:
      • what the L1 finalized block is
  • We can then update cross-finalized of each L2 chain
    to the latest cross-safe value recognized in the recent history
    of the latest finalized L1 block.

[protolambda]

Closing this:

• cross-safe update fixes will be tracked in a separate issue
• supervisor is being updated to take data from op-node, and not wait for local-safe from geth when it only has cross-safe info
• L2 finality falls into place once we have data that registers what L2 block was cross-safe at which L1 point