feat(test-consume): add engine-witness simulator for witness verification

[spencer-tb]

🗒️ Description

Fully vibe coded experimental.

Adds a new consume engine-witness Hive simulator that drives Amsterdam blockchain-engine fixtures through a witness-emitting Engine API endpoint and verifies the client-generated ExecutionWitness against the
fixture's expected witness.

Supports two transports on a single simulator:

Mode	Endpoint	Witness encoding	Clients today
Default (no flag)	JSON-RPC engine_newPayloadWithWitnessVX	RLP	go-ethereum
--ssz	REST POST /new-payload-with-witness	SSZ	Ethrex feat/zkengine-http prototype only

Both paths converge on a shared NewPayloadWithWitnessResponse dataclass and the same assert_witness_matches helper. Clients that do not implement the chosen transport skip cleanly:

• REST: HTTP 404 / 405 raises EngineWitnessEndpointNotImplementedError
• JSON-RPC: -32601 Method not found is caught and turned into pytest.skip

The simulator also skips whole fixtures with no executionWitness on any payload (i.e. pre-Amsterdam forks).

Usage

Still to test!

# Fill witness-bearing fixtures
uv run fill tests/amsterdam/ --fork=Amsterdam --output=fixtures_witness

# Hive in dev mode (separate shell)
./hive --dev --client go-ethereum
export HIVE_SIMULATOR=http://127.0.0.1:3000

# Default: JSON-RPC + RLP (Geth)
uv run consume engine-witness --input=fixtures_witness

# Alternative: REST + SSZ (Ethrex zkengine-http branch)
uv run consume engine-witness --input=fixtures_witness --ssz

🔗 Related Issues or PRs

• Consumes fixture infrastructure from feat(zkevm): add execution witness support to other fixture formats #2667 (jsign-support-blockchain-test-engine), already merged on projects/zkevm.
• REST+SSZ endpoint spec: execution-apis#773.
• JSON-RPC endpoint it targets by default: go-ethereum#30069.

✅ Checklist

• All: Ran fast static checks to avoid unnecessary CI fails, see also Code Standards and Enabling Pre-commit Checks:

  just static

• All: PR title adheres to the repo standard - it will be used as the squash commit message and should start type(scope):.
• All: Considered updating the online docs in the ./docs/ directory.
• All: Set appropriate labels for the changes (only maintainers can apply labels).

[jsign]

Should this new name be added to

execution-specs/packages/testing/src/execution_testing/cli/pytest_commands/plugins/consume/simulators/base.py

Lines 28 to 42 in 560d632

	@pytest.fixture(scope="function")
	def check_live_port(test_suite_name: str) -> Literal[8545, 8551]:
	"""Port used by hive to check for liveness of the client."""
	if test_suite_name == "eels/consume-rlp":
	return 8545
	elif test_suite_name in {
	"eels/consume-engine",
	"eels/consume-enginex",
	"eels/consume-sync",
	}:
	return 8551
	raise ValueError(
	f"Unexpected test suite name '{test_suite_name}' while setting "
	"HIVE_CHECK_LIVE_PORT."
	)

?

[jsign]

Is this missing an else and some check payload.validation_error?