Goals of this issue

• Track all ongoing work on assumeutxo until mainnet params are included in a release
• Categorize the work into critical/optional for mainnet readiness
• Conceptual discussion on assumeutxo topics that may or may not be critical for mainnet readiness

The initial categorizations here are suggestions and changes should be discussed here in the issue. Obviously let me know if I missed anything.

Critical Issues/PRs

• validation: assumeutxo params mainnet #28553 - The mainnet params themselves
• p2p: For assumeutxo, download snapshot chain before background chain #29519 - Stop syncing non-snapshot chain from peers that are already connected
• assumeutxo: Drop block height from metadata #30598 - Resolving implicit-integer-sign-change in ActivateSnapshot #30514
• assumeutxo: Don't load a snapshot if it's not in the best header chain #30320 - Deny loading if snapshot is not in best header chain
• Assumeutxo: bugfix on loadtxoutset with a divergent chain + test #29996 - Bugfix and additional test coverage
• rpc: Avoid getchaintxstats invalid results #29720 - RPC fixes for missing values, addressing assumeutxo: nTx and nChainTx in RPC results are off #29328
• rpc: Optimize serialization and enhance metadata of dumptxoutset output #29612 (which fixes Possible savings in dumptxoutset serialization format (~20%) #25675) - Improves size of dump, critical because it is not backwards compatible
• assumeutxo: Fix -reindex before snapshot was validated #29726 - Fix -reindex behavior
• assumeutxo: Get rid of faked nTx and nChainTx values #29370 - Get rid of faked nTx and nChainTx values (closing issues discussed in assumeutxo: nTx and nChainTx violations in CheckBlockIndex #29261)
• assumeutxo: Check snapshot base block is not in invalid chain #30267 - Prevent issues from loading dump for invalid block

Optional Issues/PRs

(Attempted a rough ordering by importance)

• Show transactions as not fully confirmed during background validation #28616 (which fixes assumeutxo: Ensure transactions are not presented as confirmed until background sync is complete #28598) - Show background chain funds as not fully confirmed in GUI
• test: assumeutxo: add missing tests in wallet_assumeutxo.py #30455 - Additional wallet tests
• refactor: Improve assumeutxo state representation #30214 - First part of assumeutxo state and locking cleanup #28608
• Pause IBD during AssumeUTXO snapshot load #29993 - Improve usability
• assumeutxo state and locking cleanup #28608 (draft) - State and locking cleanup
• assumeutxo: Add dumptxoutset height param, remove shell scripts #29553 - dumptxoutset with height param
• test: assumeutxo: check that UTXO-querying RPCs operate on snapshot chainstate #30636
• rpc: Return errors in loadtxoutset that currently go to logs #30497
• test, assumeutxo: Remove resolved todo comments and add new test #30403 - Additional test coverage and cleanup
• validation: Check if mempool exists before size check in ActivateSnapshot #30388 - Optimization for testing performance
• (obsolete) assumeutxo, rpc: Improve EOF error when reading snapshot metadata in loadtxoutset #28670 - Improved error handling for loadtxoutset
• test: Test new header sync behavior in loadtxoutset #29478 - Additional test coverage for loadtxoutset
• test: Validate UTXO snapshot with coin height > base height & amount > MAX_MONEY supply #29617 - Additional test coverage
• test: Assumeutxo: ensure failure when importing a snapshot twice #29973 - Additional test coverage
• test: Assumeutxo: snapshots with less work should not be loaded #29428 - Additional test coverage

Critical conceptual discussion

• RFC: Assumeutxo and large forks and reorgs #30288
• Agreement on a rule of thumb which height we choose once there is consensus for mainnet readiness, i.e. how to choose the height for validation: assumeutxo params mainnet #28553 once we are close to an upcoming release. I think the earlier we discuss this the better, so that this doesn't get in the way later.

Optional conceptual discussion

These were taken from #28553 and the original assumeutxo PR.

• Distribution of snapshots - This recently came up here and here. There are multiple levels to this topic but I believe that this is not critical either way. If it were critical then, at the most basic level, we would probably provide an "official" torrent/download link for the dump with the release. It would be great if one or more contributors could do that (@Sjors did this in validation: assumeutxo params for testnet and signet #28516 for example) and are willing to maintain this for a reasonable amount of time but it is not critical IMO because anyone can use dumptxoutset to recreate the dump and then share it any way they like. So there is no need to provide this service from within the project. I think anyone who plans to distribute the dump to other users (think of downstream projects like BTCPayServer, Raspiblitz, Umbrel, Greenlight etc.) should validate the dump like this at least once anyway. And there may even be options for distribution possible for downstream projects that we can not even think of right now but if we don't make the feature available they can also not be explored.
• Usage of MuHash Use muhash for assumeUTXO snapshot  #27669 - While it would be nice to have this I don't think it is blocking because this can still be introduced later without invalidating existing dumps.
• Make params configurable/not hardcoded params - I think it would be good to stay on the safe side for now and make the feature available to the public as originally planned. If the feature sees wide adoption and requests for more flexibility come in that would be the right point to explore this further.
• Should old hashes be removed from source code at some point? - Obviously not relevant for the first mainnet params
• How frequently should we update testnet/signet params and is there any way to deal with the possibility that these chains may get nuked at some point?