Key reading:

• https://www.notion.so/arbitrum/Reimbursing-Mini-Stakes-In-Band-in-BoLD-f7d27046d6304c2ab6933a152b83057d

Current approach:

• Only the root edge of the block level challenge is ever confirmed by time. We don’t care about confirming any other edges by time. The only other confirmation type that exists is by one step proof win, which happens at the small step challenge level
• Each time the root, block challenge edge tracker “ticks”, it updates its inherited timer using the bold challenge manager’s in-memory honest tree. It uses a recursive computation to figure out its inherited timer. If that inherited timer is >= 1 CHALLENGE PERIOD, the edge tracker initiates a “confirmation job”
• Right now, edge trackers have 3 main moves they can make: bisect, open subchallenge, one step prove. There are certain conditions that must be met for the finite state machine to decide which action to take. However, we need to add additional conditions as described below
  Revamp:
• We can confirm any “root” edge by time, and we should do so. That is, we should not only confirm the block challenge root edge, but also the subchallenge root edges. It is important they reach “confirmed” status so that their bonds can be reimbursed
• We change the rules of when the honest validator can make certain moves. That is, it should only open a subchallenge, bisect, or one step prove if the normal conditions for those actions are met AND additional “path timer” conditions are met (more on this later)
• We change how the code determines if an edge is “confirmable by time” to use path weight / essential path rules instead of the current approach

Terminology remapping:

• Path weight: the sum of the local timers along a path of edges up to some root edge
• Node: can be taken to mean edge
• Refinement node: a subchallenge root edge
• Terminal node: the edge that a subchallenge root edge claims at a higher level
• Proof node: any lowest level subchallenge edge

Places to change:

• Change the conditions for tryToConfirm edge in the edge tracker file to use a function called IsConfirmableEssentialNode, which checks all the path weights from that edge to its essential root have a minimum of 1 CHALLENGE_PERIOD. The logic or checking all path weights have that minimum is implemented in challenge-manager/challenge-tree/paths.go using a min heap
• Change the Act() function in bisections, subchallenges, or one step proofs to consider not acting if the path weight of the edge to its closest essential ancestor is >= 1 CHALLENGE_PERIOD
• Evaluate if any changes need to be made to confirmation_job.go
• Check in our e2e test that we also confirm the essential root edges in addition to winning the challenge