## Issue Addressed
NA
## Proposed Changes
Fixes an issue introduced in #3574 where I erroneously assumed that a `crossbeam_channel` multiple receiver queue was a *broadcast* queue. This is incorrect, each message will be received by *only one* receiver. The effect of this mistake is these logs:
```
Sep 20 06:56:17.001 INFO Synced slot: 4736079, block: 0xaa8a…180d, epoch: 148002, finalized_epoch: 148000, finalized_root: 0x2775…47f2, exec_hash: 0x2ca5…ffde (verified), peers: 6, service: slot_notifier
Sep 20 06:56:23.237 ERRO Unable to validate attestation error: CommitteeCacheWait(RecvError), peer_id: 16Uiu2HAm2Jnnj8868tb7hCta1rmkXUf5YjqUH1YPj35DCwNyeEzs, type: "aggregated", slot: Slot(4736047), beacon_block_root: 0x88d318534b1010e0ebd79aed60b6b6da1d70357d72b271c01adf55c2b46206c1
```
## Additional Info
NA
## Proposed Changes
Improve the payload pruning feature in several ways:
- Payload pruning is now entirely optional. It is enabled by default but can be disabled with `--prune-payloads false`. The previous `--prune-payloads-on-startup` flag from #3565 is removed.
- Initial payload pruning on startup now runs in a background thread. This thread will always load the split state, which is a small fraction of its total work (up to ~300ms) and then backtrack from that state. This pruning process ran in 2m5s on one Prater node with good I/O and 16m on a node with slower I/O.
- To work with the optional payload pruning the database function `try_load_full_block` will now attempt to load execution payloads for finalized slots _if_ pruning is currently disabled. This gives users an opt-out for the extensive traffic between the CL and EL for reconstructing payloads.
## Additional Info
If the `prune-payloads` flag is toggled on and off then the on-startup check may not see any payloads to delete and fail to clean them up. In this case the `lighthouse db prune_payloads` command should be used to force a manual sweep of the database.
## Issue Addressed
https://github.com/ethereum/beacon-APIs/pull/222
## Proposed Changes
Update Lighthouse's randao verification API to match the `beacon-APIs` spec. We implemented the API before spec stabilisation, and it changed slightly in the course of review.
Rather than a flag `verify_randao` taking a boolean value, the new API uses a `skip_randao_verification` flag which takes no argument. The new spec also requires the randao reveal to be present and equal to the point-at-infinity when `skip_randao_verification` is set.
I've also updated the `POST /lighthouse/analysis/block_rewards` API to take blinded blocks as input, as the execution payload is irrelevant and we may want to assess blocks produced by builders.
## Additional Info
This is technically a breaking change, but seeing as I suspect I'm the only one using these parameters/APIs, I think we're OK to include this in a patch release.
## Issue Addressed
Closes https://github.com/sigp/lighthouse/issues/3556
## Proposed Changes
Delete finalized execution payloads from the database in two places:
1. When running the finalization migration in `migrate_database`. We delete the finalized payloads between the last split point and the new updated split point. _If_ payloads are already pruned prior to this then this is sufficient to prune _all_ payloads as non-canonical payloads are already deleted by the head pruner, and all canonical payloads prior to the previous split will already have been pruned.
2. To address the fact that users will update to this code _after_ the merge on mainnet (and testnets), we need a one-off scan to delete the finalized payloads from the canonical chain. This is implemented in `try_prune_execution_payloads` which runs on startup and scans the chain back to the Bellatrix fork or the anchor slot (if checkpoint synced after Bellatrix). In the case where payloads are already pruned this check only imposes a single state load for the split state, which shouldn't be _too slow_. Even so, a flag `--prepare-payloads-on-startup=false` is provided to turn this off after it has run the first time, which provides faster start-up times.
There is also a new `lighthouse db prune_payloads` subcommand for users who prefer to run the pruning manually.
## Additional Info
The tests have been updated to not rely on finalized payloads in the database, instead using the `MockExecutionLayer` to reconstruct them. Additionally a check was added to `check_chain_dump` which asserts the non-existence or existence of payloads on disk depending on their slot.
