[MegaRedHand]

What

Beacon p2p now rebuilds the execution block header from a payload's own fields and REJECTs the message when keccak256(rlp(header)) is not the payload's block_hash:

• pre-gloas beacon_block gossip (bellatrix to fulu), in triage_block, after the cheap rules
• gloas execution_payload gossip, in triage_envelope
• every envelope fetched by root or range (envelope_checks::judge)

The check lives in crates/net/p2p/src/beacon/payload_hash.rs (verify_block, verify_envelope). New RejectReason::PayloadBlockHashMismatch (payload_block_hash_mismatch), counter lean_beacon_payload_block_hash_mismatch_total{kind} and a warn! with slot and root.

It sits in p2p, not in state_transition::gossip::*, so the spec-fixture gossip vectors (which carry arbitrary payload hashes) are unaffected. Header encoding is done here with ethrex-rlp's Encoder, because ethrex's BlockHeader holds base_fee_per_gas as u64. Trie roots reuse ethrex-common (withdrawals, requests hash) and ethrex-trie (transactions over raw bytes; same tag v25.0.0, already in the lockfile, no new crate).

Why

Since engine_newPayloadV2 the Engine API answers a block-hash mismatch with INVALID and a null latestValidHash, indistinguishable from an executed-invalid payload whose last valid ancestor is unknown. Upcoming work applies payloads to fork choice before the EL answers; catching the structural case here keeps those payloads from being applied.

Deviation

Stricter than the consensus-specs gossip rules. Documented in docs/spec_deviations.md ("A payload's block hash must be its header's") and docs/beacon_wire.md. Blocks fetched via beacon_blocks_by_range/root are not checked.

Header per fork

bellatrix: London fields; capella: withdrawals_root; deneb: blob_gas_used, excess_blob_gas, parent_beacon_block_root (the block's parent_root); electra/fulu: requests_hash (from the Engine API request list); gloas: block_access_list_hash (keccak of the payload's BAL bytes, EIP-7928) and slot_number (EIP-7843), parent root from the envelope. A bellatrix block with the empty default payload (pre-merge) is skipped.

Real-chain vectors (SSZ, crates/net/p2p/src/beacon/testdata/payload_hash/)

Fork	Chain	Object	Source
bellatrix	Sepolia	block, slot 500000	lodestar-sepolia.chainsafe.io
capella	Sepolia	block, slot 1900000 (carries withdrawals)	lodestar-sepolia.chainsafe.io
deneb	Hoodi	block, slot 2003	lodestar-hoodi.chainsafe.io
electra	Hoodi	block, slot 70001	lodestar-hoodi.chainsafe.io
fulu	mainnet	block, slot 15576000	ethlambda-4 beacon API
gloas	Platåberget	envelope, slot 593101	ethlambda-3 beacon API

Each vector must match, and per fork a changed field (gas_used, block_hash, withdrawal amount, excess_blob_gas, parent root, transaction byte, extra_data, an extra request, slot_number, BAL byte, base fee, ...) must be refused. A triage-level test covers the gossip reject.

Testing

make fmt, make lint, cargo test -p ethlambda-p2p --profile release-fast --lib (372 passed), cargo test -p ethlambda-state-transition --profile release-fast --lib gossip. Existing p2p tests that forwarded structurally arbitrary envelopes now seal them with a test-only seal_envelope. No leanSpec or consensus-spec fixtures were run.