Tasks:

• Double-check whether we need something from #7768 #9954
• Protobuf: responses should be enums: see what is missing from ABCI++: Update new protos to use enum instead of bool #8158 [Estimation: 0.5 days]
• Block data exposed to App: follow abci++: only include meaningful header fields in data passed-through to application #8216 and take the parts still missing (mainly FinalizeBlock) [Estimation: 1 day]
• Double-check if there is something we need from abci++: Remove intermediate protos #8414 (probably not)
• See what metrics we are still missing from consensus: add additional metrics for abci++ data #8480 (mainly vote extensions)
• Redundant params in FinalizeBlock, and obsolete methods (BeginBlock, etc). Double check that changes in Removed redundant params in FinalizeBlock #8598 and/or Remove obsolete abci methods, no longer called by ABCI++ Tendermint #8633 are unnecessary
• Move app_hash from Commit to FinalizeBlock: follow abci: Move app_hash parameter from Commit to FinalizeBlock #8664
• Compare the status of abci's types.proto in feature/abci++vef and v0.36.x and make sure no changes are related to vote extensions and FinalizeBlock
• Crash in all cases of undefined app behavior #8206
• Update description of BlockSync p2p messages in spec #9002
• [Optional]: Run a testnet on DO (200 node test) as smoke test on this branch
• Once we are code complete, and all CI tests pass, merge branch back into main
• Fix and unit-test condition vote.Height < 0 in Vote::ValidateBasic in v0.37.x and v0.34.x

DoD:

• No errors in CI
• No major concerns if testnets were run
• Branch feature/abci++vef has been merged back into main