## Issue Addressed
NA
## Proposed Changes
Myself and others (#3678) have observed that when running with lots of validators (e.g., 1000s) the cardinality is too much for Prometheus. I've seen Prometheus instances just grind to a halt when we turn the validator monitor on for our testnet validators (we have 10,000s of Goerli validators). Additionally, the debug log volume can get very high with one log per validator, per attestation.
To address this, the `bn --validator-monitor-individual-tracking-threshold <INTEGER>` flag has been added to *disable* per-validator (i.e., non-aggregated) metrics/logging once the validator monitor exceeds the threshold of validators. The default value is `64`, which is a finger-to-the-wind value. I don't actually know the value at which Prometheus starts to become overwhelmed, but I've seen it work with ~64 validators and I've seen it *not* work with 1000s of validators. A default of `64` seems like it will result in a breaking change to users who are running millions of dollars worth of validators whilst resulting in a no-op for low-validator-count users. I'm open to changing this number, though.
Additionally, this PR starts collecting aggregated Prometheus metrics (e.g., total count of head hits across all validators), so that high-validator-count validators still have some interesting metrics. We already had logging for aggregated values, so nothing has been added there.
I've opted to make this a breaking change since it can be rather damaging to your Prometheus instance to accidentally enable the validator monitor with large numbers of validators. I've crashed a Prometheus instance myself and had a report from another user who's done the same thing.
## Additional Info
NA
## Breaking Changes Note
A new label has been added to the validator monitor Prometheus metrics: `total`. This label tracks the aggregated metrics of all validators in the validator monitor (as opposed to each validator being tracking individually using its pubkey as the label).
Additionally, a new flag has been added to the Beacon Node: `--validator-monitor-individual-tracking-threshold`. The default value is `64`, which means that when the validator monitor is tracking more than 64 validators then it will stop tracking per-validator metrics and only track the `all_validators` metric. It will also stop logging per-validator logs and only emit aggregated logs (the exception being that exit and slashing logs are always emitted).
These changes were introduced in #3728 to address issues with untenable Prometheus cardinality and log volume when using the validator monitor with high validator counts (e.g., 1000s of validators). Users with less than 65 validators will see no change in behavior (apart from the added `all_validators` metric). Users with more than 65 validators who wish to maintain the previous behavior can set something like `--validator-monitor-individual-tracking-threshold 999999`.
## Issue Addressed
Recent discussions with other client devs about optimistic sync have revealed a conceptual issue with the optimisation implemented in #3738. In designing that feature I failed to consider that the execution node checks the `blockHash` of the execution payload before responding with `SYNCING`, and that omitting this check entirely results in a degradation of the full node's validation. A node omitting the `blockHash` checks could be tricked by a supermajority of validators into following an invalid chain, something which is ordinarily impossible.
## Proposed Changes
I've added verification of the `payload.block_hash` in Lighthouse. In case of failure we log a warning and fall back to verifying the payload with the execution client.
I've used our existing dependency on `ethers_core` for RLP support, and a new dependency on Parity's `triehash` crate for the Merkle patricia trie. Although the `triehash` crate is currently unmaintained it seems like our best option at the moment (it is also used by Reth, and requires vastly less boilerplate than Parity's generic `trie-root` library).
Block hash verification is pretty quick, about 500us per block on my machine (mainnet).
The optimistic finalized sync feature can be disabled using `--disable-optimistic-finalized-sync` which forces full verification with the EL.
## Additional Info
This PR also introduces a new dependency on our [`metastruct`](https://github.com/sigp/metastruct) library, which was perfectly suited to the RLP serialization method. There will likely be changes as `metastruct` grows, but I think this is a good way to start dogfooding it.
I took inspiration from some Parity and Reth code while writing this, and have preserved the relevant license headers on the files containing code that was copied and modified.
## Proposed Changes
With proposer boosting implemented (#2822) we have an opportunity to re-org out late blocks.
This PR adds three flags to the BN to control this behaviour:
* `--disable-proposer-reorgs`: turn aggressive re-orging off (it's on by default).
* `--proposer-reorg-threshold N`: attempt to orphan blocks with less than N% of the committee vote. If this parameter isn't set then N defaults to 20% when the feature is enabled.
* `--proposer-reorg-epochs-since-finalization N`: only attempt to re-org late blocks when the number of epochs since finalization is less than or equal to N. The default is 2 epochs, meaning re-orgs will only be attempted when the chain is finalizing optimally.
For safety Lighthouse will only attempt a re-org under very specific conditions:
1. The block being proposed is 1 slot after the canonical head, and the canonical head is 1 slot after its parent. i.e. at slot `n + 1` rather than building on the block from slot `n` we build on the block from slot `n - 1`.
2. The current canonical head received less than N% of the committee vote. N should be set depending on the proposer boost fraction itself, the fraction of the network that is believed to be applying it, and the size of the largest entity that could be hoarding votes.
3. The current canonical head arrived after the attestation deadline from our perspective. This condition was only added to support suppression of forkchoiceUpdated messages, but makes intuitive sense.
4. The block is being proposed in the first 2 seconds of the slot. This gives it time to propagate and receive the proposer boost.
## Additional Info
For the initial idea and background, see: https://github.com/ethereum/consensus-specs/pull/2353#issuecomment-950238004
There is also a specification for this feature here: https://github.com/ethereum/consensus-specs/pull/3034
Co-authored-by: Michael Sproul <micsproul@gmail.com>
Co-authored-by: pawan <pawandhananjay@gmail.com>
## Issue Addressed
our bootnodes as of now support only ipv4. this makes it so that they support ipv6
## Proposed Changes
- Adds code necessary to update the bootnodes to run on dual stack nodes and therefore contact and store ipv6 nodes.
- Adds some metrics about connectivity type of stored peers. It might have been nice to see some metrics over the sessions but that feels out of scope right now.
## Additional Info
- some code quality improvements sneaked in since the changes seemed small
- I think it depends on the OS, but enabling mapped addresses on an ipv6 node without dual stack support enabled could fail silently, making these nodes effectively ipv6 only. In the future I'll probably change this to use two sockets, which should fail loudly
## Issue Addressed
#3723
## Proposed Changes
Adds a new CLI flag `--gui` which enables all the various flags required for the gui to function properly.
Currently enables the `--http` and `--validator-monitor-auto` flags.
## Issue Addressed
Partially addresses #3651
## Proposed Changes
Adds server-side support for light_client_bootstrap_v1 topic
## Additional Info
This PR, creates each time a bootstrap without using cache, I do not know how necessary a cache is in this case as this topic is not supposed to be called frequently and IMHO we can just prevent abuse by using the limiter, but let me know what you think or if there is any caveat to this, or if it is necessary only for the sake of good practice.
Co-authored-by: Pawan Dhananjay <pawandhananjay@gmail.com>
This PR adds some health endpoints for the beacon node and the validator client.
Specifically it adds the endpoint:
`/lighthouse/ui/health`
These are not entirely stable yet. But provide a base for modification for our UI.
These also may have issues with various platforms and may need modification.
## Issue Addressed
Part of https://github.com/sigp/lighthouse/issues/3651.
## Proposed Changes
Add a flag for enabling the light client server, which should be checked before gossip/RPC traffic is processed (e.g. https://github.com/sigp/lighthouse/pull/3693, https://github.com/sigp/lighthouse/pull/3711). The flag is available at runtime from `beacon_chain.config.enable_light_client_server`.
Additionally, a new method `BeaconChain::with_mutable_state_for_block` is added which I envisage being used for computing light client updates. Unfortunately its performance will be quite poor on average because it will only run quickly with access to the tree hash cache. Each slot the tree hash cache is only available for a brief window of time between the head block being processed and the state advance at 9s in the slot. When the state advance happens the cache is moved and mutated to get ready for the next slot, which makes it no longer useful for merkle proofs related to the head block. Rather than spend more time trying to optimise this I think we should continue prototyping with this code, and I'll make sure `tree-states` is ready to ship before we enable the light client server in prod (cf. https://github.com/sigp/lighthouse/pull/3206).
## Additional Info
I also fixed a bug in the implementation of `BeaconState::compute_merkle_proof` whereby the tree hash cache was moved with `.take()` but never put back with `.restore()`.
## Issue Addressed
#3702
Which issue # does this PR address?
#3702
## Proposed Changes
Added checkpoint-sync-url-timeout flag to cli. Added timeout field to ClientGenesis::CheckpointSyncUrl to utilize timeout set
## Additional Info
Please provide any additional information. For example, future considerations
or information useful for reviewers.
Co-authored-by: GeemoCandama <104614073+GeemoCandama@users.noreply.github.com>
Co-authored-by: Michael Sproul <micsproul@gmail.com>
## Issue Addressed
New lints for rust 1.65
## Proposed Changes
Notable change is the identification or parameters that are only used in recursion
## Additional Info
na
Overrides any previous option that enables the eth1 service.
Useful for operating a `light` beacon node.
Co-authored-by: Michael Sproul <micsproul@gmail.com>
## Issue Addressed
Add flag to lengthen execution layer timeouts
Which issue # does this PR address?
#3607
## Proposed Changes
Added execution-timeout-multiplier flag and a cli test to ensure the execution layer config has the multiplier set correctly.
Please list or describe the changes introduced by this PR.
Add execution_timeout_multiplier to the execution layer config as Option<u32> and pass the u32 to HttpJsonRpc.
## Additional Info
Not certain that this is the best way to implement it so I'd appreciate any feedback.
Please provide any additional information. For example, future considerations
or information useful for reviewers.
## Proposed Changes
In this change I've added a new beacon_node cli flag `--execution-jwt-secret-key` for passing the JWT secret directly as string.
Without this flag, it was non-trivial to pass a secrets file containing a JWT secret key without compromising its contents into some management repo or fiddling around with manual file mounts for cloud-based deployments.
When used in combination with environment variables, the secret can be injected into container-based systems like docker & friends quite easily.
It's both possible to either specify the file_path to the JWT secret or pass the JWT secret directly.
I've modified the docs and attached a test as well.
## Additional Info
The logic has been adapted a bit so that either one of `--execution-jwt` or `--execution-jwt-secret-key` must be set when specifying `--execution-endpoint` so that it's still compatible with the semantics before this change and there's at least one secret provided.
## Issue Addressed
N/A
## Proposed Changes
With https://github.com/sigp/lighthouse/pull/3214 we made it such that you can either have 1 auth endpoint or multiple non auth endpoints. Now that we are post merge on all networks (testnets and mainnet), we cannot progress a chain without a dedicated auth execution layer connection so there is no point in having a non-auth eth1-endpoint for syncing deposit cache.
This code removes all fallback related code in the eth1 service. We still keep the single non-auth endpoint since it's useful for testing.
## Additional Info
This removes all eth1 fallback related metrics that were relevant for the monitoring service, so we might need to change the api upstream.
## 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
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.
## Issue Addressed
Closes#3514
## Proposed Changes
- Change default monitoring endpoint frequency to 120 seconds to fit with 30k requests/month limit.
- Allow configuration of the monitoring endpoint frequency using `--monitoring-endpoint-frequency N` where `N` is a value in seconds.
## Issue Addressed
Resolves https://github.com/sigp/lighthouse/issues/3517
## Proposed Changes
Adds a `--builder-profit-threshold <wei value>` flag to the BN. If an external payload's value field is less than this value, the local payload will be used. The value of the local payload will not be checked (it can't really be checked until the engine API is updated to support this).
Co-authored-by: realbigsean <sean@sigmaprime.io>
## Issue Addressed
Add a flag that can increase count unrealized strictness, defaults to false
## Proposed Changes
Please list or describe the changes introduced by this PR.
## Additional Info
Please provide any additional information. For example, future considerations
or information useful for reviewers.
Co-authored-by: realbigsean <seananderson33@gmail.com>
Co-authored-by: sean <seananderson33@gmail.com>
## Issue Addressed
NA
## Proposed Changes
This PR is motivated by a recent consensus failure in Geth where it returned `INVALID` for an `VALID` block. Without this PR, the only way to recover is by re-syncing Lighthouse. Whilst ELs "shouldn't have consensus failures", in reality it's something that we can expect from time to time due to the complex nature of Ethereum. Being able to recover easily will help the network recover and EL devs to troubleshoot.
The risk introduced with this PR is that genuinely INVALID payloads get a "second chance" at being imported. I believe the DoS risk here is negligible since LH needs to be restarted in order to re-process the payload. Furthermore, there's no reason to think that a well-performing EL will accept a truly invalid payload the second-time-around.
## Additional Info
This implementation has the following intricacies:
1. Instead of just resetting *invalid* payloads to optimistic, we'll also reset *valid* payloads. This is an artifact of our existing implementation.
1. We will only reset payload statuses when we detect an invalid payload present in `proto_array`
- This helps save us from forgetting that all our blocks are valid in the "best case scenario" where there are no invalid blocks.
1. If we fail to revert the payload statuses we'll log a `CRIT` and just continue with a `proto_array` that *does not* have reverted payload statuses.
- The code to revert statuses needs to deal with balances and proposer-boost, so it's a failure point. This is a defensive measure to avoid introducing new show-stopping bugs to LH.
## Proposed Changes
This PR has two aims: to speed up attestation packing in the op pool, and to fix bugs in the verification of attester slashings, proposer slashings and voluntary exits. The changes are bundled into a single database schema upgrade (v12).
Attestation packing is sped up by removing several inefficiencies:
- No more recalculation of `attesting_indices` during packing.
- No (unnecessary) examination of the `ParticipationFlags`: a bitfield suffices. See `RewardCache`.
- No re-checking of attestation validity during packing: the `AttestationMap` provides attestations which are "correct by construction" (I have checked this using Hydra).
- No SSZ re-serialization for the clunky `AttestationId` type (it can be removed in a future release).
So far the speed-up seems to be roughly 2-10x, from 500ms down to 50-100ms.
Verification of attester slashings, proposer slashings and voluntary exits is fixed by:
- Tracking the `ForkVersion`s that were used to verify each message inside the `SigVerifiedOp`. This allows us to quickly re-verify that they match the head state's opinion of what the `ForkVersion` should be at the epoch(s) relevant to the message.
- Storing the `SigVerifiedOp` on disk rather than the raw operation. This allows us to continue track the fork versions after a reboot.
This is mostly contained in this commit 52bb1840ae5c4356a8fc3a51e5df23ed65ed2c7f.
## Additional Info
The schema upgrade uses the justified state to re-verify attestations and compute `attesting_indices` for them. It will drop any attestations that fail to verify, by the logic that attestations are most valuable in the few slots after they're observed, and are probably stale and useless by the time a node restarts. Exits and proposer slashings and similarly re-verified to obtain `SigVerifiedOp`s.
This PR contains a runtime killswitch `--paranoid-block-proposal` which opts out of all the optimisations in favour of closely verifying every included message. Although I'm quite sure that the optimisations are correct this flag could be useful in the event of an unforeseen emergency.
Finally, you might notice that the `RewardCache` appears quite useless in its current form because it is only updated on the hot-path immediately before proposal. My hope is that in future we can shift calls to `RewardCache::update` into the background, e.g. while performing the state advance. It is also forward-looking to `tree-states` compatibility, where iterating and indexing `state.{previous,current}_epoch_participation` is expensive and needs to be minimised.
## Proposed Changes
Update the merge migration docs to encourage updating mainnet configs _now_!
The docs are also updated to recommend _against_ `--suggested-fee-recipient` on the beacon node (https://github.com/sigp/lighthouse/issues/3432).
Additionally the `--help` for the CLI is updated to match with a few small semantic changes:
- `--execution-jwt` is no longer allowed without `--execution-endpoint`. We've ended up without a default for `--execution-endpoint`, so I think that's fine.
- The flags related to the JWT are only allowed if `--execution-jwt` is provided.
## Proposed Changes
Enable multiple database backends for the slasher, either MDBX (default) or LMDB. The backend can be selected using `--slasher-backend={lmdb,mdbx}`.
## Additional Info
In order to abstract over the two library's different handling of database lifetimes I've used `Box::leak` to give the `Environment` type a `'static` lifetime. This was the only way I could think of using 100% safe code to construct a self-referential struct `SlasherDB`, where the `OpenDatabases` refers to the `Environment`. I think this is OK, as the `Environment` is expected to live for the life of the program, and both database engines leave the database in a consistent state after each write. The memory claimed for memory-mapping will be freed by the OS and appropriately flushed regardless of whether the `Environment` is actually dropped.
We are depending on two `sigp` forks of `libmdbx-rs` and `lmdb-rs`, to give us greater control over MDBX OS support and LMDB's version.
## Issue Addressed
Resolves#3388Resolves#2638
## Proposed Changes
- Return the `BellatrixPreset` on `/eth/v1/config/spec` by default.
- Allow users to opt out of this by providing `--http-spec-fork=altair` (unless there's a Bellatrix fork epoch set).
- Add the Altair constants from #2638 and make serving the constants non-optional (the `http-disable-legacy-spec` flag is deprecated).
- Modify the VC to only read the `Config` and not to log extra fields. This prevents it from having to muck around parsing the `ConfigAndPreset` fields it doesn't need.
## Additional Info
This change is backwards-compatible for the VC and the BN, but is marked as a breaking change for the removal of `--http-disable-legacy-spec`.
I tried making `Config` a `superstruct` too, but getting the automatic decoding to work was a huge pain and was going to require a lot of hacks, so I gave up in favour of keeping the default-based approach we have now.
## Issue Addressed
Enable https://github.com/sigp/lighthouse/pull/3322 by default on all networks.
The feature can be opted out of using `--count-unrealized=false` (the CLI flag is updated to take a parameter).
## Issue Addressed
https://github.com/sigp/lighthouse/issues/3091
Extends https://github.com/sigp/lighthouse/pull/3062, adding pre-bellatrix block support on blinded endpoints and allowing the normal proposal flow (local payload construction) on blinded endpoints. This resulted in better fallback logic because the VC will not have to switch endpoints on failure in the BN <> Builder API, the BN can just fallback immediately and without repeating block processing that it shouldn't need to. We can also keep VC fallback from the VC<>BN API's blinded endpoint to full endpoint.
## Proposed Changes
- Pre-bellatrix blocks on blinded endpoints
- Add a new `PayloadCache` to the execution layer
- Better fallback-from-builder logic
## Todos
- [x] Remove VC transition logic
- [x] Add logic to only enable builder flow after Merge transition finalization
- [x] Tests
- [x] Fix metrics
- [x] Rustdocs
Co-authored-by: Mac L <mjladson@pm.me>
Co-authored-by: realbigsean <sean@sigmaprime.io>
## Issue Addressed
Add a flag that optionally enables unrealized vote tracking. Would like to test out on testnets and benchmark differences in methods of vote tracking. This PR includes a DB schema upgrade to enable to new vote tracking style.
Co-authored-by: realbigsean <sean@sigmaprime.io>
Co-authored-by: Paul Hauner <paul@paulhauner.com>
Co-authored-by: sean <seananderson33@gmail.com>
Co-authored-by: Mac L <mjladson@pm.me>
## Issue Addressed
This PR is a subset of the changes in #3134. Unstable will still not function correctly with the new builder spec once this is merged, #3134 should be used on testnets
## Proposed Changes
- Removes redundancy in "builders" (servers implementing the builder spec)
- Renames `payload-builder` flag to `builder`
- Moves from old builder RPC API to new HTTP API, but does not implement the validator registration API (implemented in https://github.com/sigp/lighthouse/pull/3194)
Co-authored-by: sean <seananderson33@gmail.com>
Co-authored-by: realbigsean <sean@sigmaprime.io>
## Issue Addressed
Resolves#3069
## Proposed Changes
Unify the `eth1-endpoints` and `execution-endpoints` flags in a backwards compatible way as described in https://github.com/sigp/lighthouse/issues/3069#issuecomment-1134219221
Users have 2 options:
1. Use multiple non auth execution endpoints for deposit processing pre-merge
2. Use a single jwt authenticated execution endpoint for both execution layer and deposit processing post merge
Related https://github.com/sigp/lighthouse/issues/3118
To enable jwt authenticated deposit processing, this PR removes the calls to `net_version` as the `net` namespace is not exposed in the auth server in execution clients.
Moving away from using `networkId` is a good step in my opinion as it doesn't provide us with any added guarantees over `chainId`. See https://github.com/ethereum/consensus-specs/issues/2163 and https://github.com/sigp/lighthouse/issues/2115
Co-authored-by: Paul Hauner <paul@paulhauner.com>
## Issue Addressed
Fix for the eth1 cache sync issue observed on Ropsten.
## Proposed Changes
Ropsten blocks are so infrequent that they broke our algorithm for downloading eth1 blocks. We currently try to download forwards from the last block in our cache to the block with block number [`remote_highest_block - FOLLOW_DISTANCE + FOLLOW_DISTANCE / ETH1_BLOCK_TIME_TOLERANCE_FACTOR`](6f732986f1/beacon_node/eth1/src/service.rs (L489-L492)). With the tolerance set to 4 this is insufficient because we lag by 1536 blocks, which is more like ~14 hours on Ropsten. This results in us having an incomplete eth1 cache, because we should cache all blocks between -16h and -8h. Even if we were to set the tolerance to 2 for the largest allowance, we would only look back 1024 blocks which is still more than 8 hours.
For example consider this block https://ropsten.etherscan.io/block/12321390. The block from 1536 blocks earlier is 14 hours and 20 minutes before it: https://ropsten.etherscan.io/block/12319854. The block from 1024 blocks earlier is https://ropsten.etherscan.io/block/12320366, 8 hours and 48 minutes before.
- This PR introduces a new CLI flag called `--eth1-cache-follow-distance` which can be used to set the distance manually.
- A new dynamic catchup mechanism is added which detects when the cache is lagging the true eth1 chain and tries to download more blocks within the follow distance in order to catch up.
## Issue Addressed
Upcoming spec change https://github.com/ethereum/consensus-specs/pull/2878
## Proposed Changes
1. Run fork choice at the start of every slot, and wait for this run to complete before proposing a block.
2. As an optimisation, also run fork choice 3/4 of the way through the slot (at 9s), _dequeueing attestations for the next slot_.
3. Remove the fork choice run from the state advance timer that occurred before advancing the state.
## Additional Info
### Block Proposal Accuracy
This change makes us more likely to propose on top of the correct head in the presence of re-orgs with proposer boost in play. The main scenario that this change is designed to address is described in the linked spec issue.
### Attestation Accuracy
This change _also_ makes us more likely to attest to the correct head. Currently in the case of a skipped slot at `slot` we only run fork choice 9s into `slot - 1`. This means the attestations from `slot - 1` aren't taken into consideration, and any boost applied to the block from `slot - 1` is not removed (it should be). In the language of the linked spec issue, this means we are liable to attest to C, even when the majority voting weight has already caused a re-org to B.
### Why remove the call before the state advance?
If we've run fork choice at the start of the slot then it has already dequeued all the attestations from the previous slot, which are the only ones eligible to influence the head in the current slot. Running fork choice again is unnecessary (unless we run it for the next slot and try to pre-empt a re-org, but I don't currently think this is a great idea).
### Performance
Based on Prater testing this adds about 5-25ms of runtime to block proposal times, which are 500-1000ms on average (and spike to 5s+ sometimes due to state handling issues 😢 ). I believe this is a small enough penalty to enable it by default, with the option to disable it via the new flag `--fork-choice-before-proposal-timeout 0`. Upcoming work on block packing and state representation will also reduce block production times in general, while removing the spikes.
### Implementation
Fork choice gets invoked at the start of the slot via the `per_slot_task` function called from the slot timer. It then uses a condition variable to signal to block production that fork choice has been updated. This is a bit funky, but it seems to work. One downside of the timer-based approach is that it doesn't happen automatically in most of the tests. The test added by this PR has to trigger the run manually.
