Implement Gloas builder flow from beacon-APIs

[hangleang]

Specs: beacon-APIs#630, keymanager-APIs#88 (with #93, #94), builder-specs#138 (with #165, #168)

Beacon API

• POST /eth/v4/validator/blocks/{slot} takes a BuilderConfig body, requests a bid from each builder entry while the block body is built, and picks the winner by builder_boost_factor * (value + min(execution_payment, max_execution_payment)) against the local payload. It validates those bids against the block production state before selection. Returns Eth-Builder-Url when a builder API bid wins.
• POST /eth/v2/beacon/blocks forwards the signed block to the Eth-Builder-Url builder after publishing.
• POST /eth/v1/validator/builder_preferences submits each entry to its builder.

Keymanager API

• GET/POST/DELETE /eth/v1/validator/{pubkey}/builder_config. GET returns the fully resolved config, POST replaces it, DELETE resets it. Invalid configs (missing url, duplicate url + auth_data, a nonzero max_execution_payment without the opt-in) are rejected.
• Per-key configs are validated when validators.yml loads.

Built-in validator

• In the epoch before each proposal, it submits builder preferences to the key's builders and caches the signed auths to reuse during bid requests from builder APIs.
• When proposing, it requests bids from the key's builders alongside the local payload, and forwards the beacon block to the builder whose bid won.

Builder API client

• Implements client requests to builder API endpoints: getExecutionPayloadBid, submitBuilderPreferences and submitSignedBeaconBlock.
• Request bodies follow --builder-api-format. A builder that answers an SSZ body with 415 or 406 gets the request again in JSON, and JSON from then on.

Testing

Kurtosis devnet with buildoor builder_api enabled connected to a grandine node with Lodestar VC (beacon api path) and a grandine node with its built-in validator.

participants:
  - el_type: geth
    el_image: ethpandaops/geth:master
    cl_type: grandine
    cl_binary_path: "./binaries/grandine-minimal"
    cl_force_restart: true
    cl_extra_env_vars:
      GRANDINE_LOG: "http_api=debug,block_producer=debug,builder_api=debug,fork_choice_control=debug"
    vc_type: lodestar
    vc_image: chainsafe/lodestar:latest
    vc_extra_params:
      - "--builder.urls=http://buildoor-grandine-geth-1:8080,http://builder-a.invalid:18550"
  - el_type: geth
    el_image: ethpandaops/geth:master
    cl_type: lighthouse
    cl_image: ethpandaops/lighthouse:unstable
    cl_log_level: debug
  - el_type: geth
    el_image: ethpandaops/geth:master
    cl_type: grandine
    cl_binary_path: "./binaries/grandine-minimal"
    cl_force_restart: true
    cl_extra_env_vars:
      GRANDINE_LOG: "validator=debug,block_producer=debug,builder_api=debug,fork_choice_control=debug"
    cl_extra_params:
      - "--payload-builder-urls=http://buildoor-grandine-geth-1:8080,http://builder-c.invalid:18550"
      - "--allow-trusted-payments"
      - "--default-builder-max-execution-payment=50000000"
    keymanager_enabled: true

network_params:
  gloas_fork_epoch: 1
  preset: minimal

additional_services:
  - dora
  - buildoor

buildoor_params:
  image: ethpandaops/buildoor:main-latest
  epbs_builder: true
  builder_api: true
  lifecycle: true
  extra_args:
    - "--builder-api-subsidy=150000000"
    - "--builder-api-execution-payment-percent=50"

port_publisher:
  cl:
    enabled: true