## Issue Addressed
NA
## Proposed Changes
Registers validators with the doppelganger service at the earliest possible point.
This avoids the following (non-harmful, but scary) log when pruning the slashing DB on startup:
```
CRIT Validator unknown to doppelganger service, pubkey: 0xabc..., msg: preventing validator from performing duties, service: doppelganger
```
## Additional Info
NA
## Issue Addressed
N/A
## Proposed Changes
This is just a cosmetic change to print only the unique list of violaters. We could repeat violaters in the list if an attestation and aggregation both were detected from the same validator.
## Issue Addressed
NA
## Proposed Changes
Fixes a bug in Doppelganger Protection which would cause false-positives when a VC is restarted in the same epoch where it has already produced a signed message.
It could also cause a false-negative in the scenario where time skips forward (perhaps due to host suspend/wake). The new `time_skips_forward_with_doppelgangers` test covers this case.
This was a simple (and embarrassing, on my behalf) `>=` instead of `<=` bug that was missed by my tests but detected during manual testing by @michaelsproul (🙏). Regression tests have been added.
## Additional Info
NA
## TODO
- [x] Add test for doppelganger in epoch > next_check_epoch
## Issue Addressed
Resolves#2069
## Proposed Changes
- Adds a `--doppelganger-detection` flag
- Adds a `lighthouse/seen_validators` endpoint, which will make it so the lighthouse VC is not interopable with other client beacon nodes if the `--doppelganger-detection` flag is used, but hopefully this will become standardized. Relevant Eth2 API repo issue: https://github.com/ethereum/eth2.0-APIs/issues/64
- If the `--doppelganger-detection` flag is used, the VC will wait until the beacon node is synced, and then wait an additional 2 epochs. The reason for this is to make sure the beacon node is able to subscribe to the subnets our validators should be attesting on. I think an alternative would be to have the beacon node subscribe to all subnets for 2+ epochs on startup by default.
## Additional Info
I'd like to add tests and would appreciate feedback.
TODO: handle validators started via the API, potentially make this default behavior
Co-authored-by: realbigsean <seananderson33@gmail.com>
Co-authored-by: Michael Sproul <michael@sigmaprime.io>
Co-authored-by: Paul Hauner <paul@paulhauner.com>
