Impossible to produce blocks with forkchoiceUpdated

[tersec]

master and #2423 have the same issue

If it already knows about the block:

nimbus-eth1/nimbus/beacon/api_handler/api_forkchoice.nim

Lines 154 to 163 in 0723464

	# If the head block is already in our canonical chain, the beacon client is
	# probably resyncing. Ignore the update.
	# See point 2 of fCUV1 specification
	# https://github.com/ethereum/execution-apis/blob/v1.0.0-beta.4/src/engine/paris.md#specification-1
	var canonHash: common.Hash256
	if db.getBlockHash(header.number, canonHash) and canonHash == blockHash:
	notice "Ignoring beacon update to old head",
	blockHash=blockHash.short,
	blockNumber=header.number
	return validFCU(Opt.none(PayloadID), blockHash)

then it returns and never processes the payload attributes to trigger payload generation later on in that function:

nimbus-eth1/nimbus/beacon/api_handler/api_forkchoice.nim

Lines 189 to 210 in 0723464

	# If payload generation was requested, create a new block to be potentially
	# sealed by the beacon client. The payload will be requested later, and we
	# might replace it arbitrarilly many times in between.
	if attrsOpt.isSome:
	let attrs = attrsOpt.get()
	validateVersion(attrs, com, apiVersion)
	let bundle = ben.generatePayload(attrs).valueOr:
	error "Failed to create sealing payload", err = error
	raise invalidAttr(error)
	let id = computePayloadId(blockHash, attrs)
	ben.put(id, bundle.blockValue, bundle.executionPayload, bundle.blobsBundle)
	info "Created payload for sealing",
	id = id.toHex,
	hash = bundle.executionPayload.blockHash.short,
	number = bundle.executionPayload.blockNumber
	return validFCU(Opt.some(id), blockHash)
	return validFCU(Opt.none(PayloadID), blockHash)

[jangko]

Client software MAY skip an update of the forkchoice state and MUST NOT begin a payload build process if forkchoiceState.headBlockHash references a VALID ancestor of the head of canonical chain, i.e. the ancestor passed payload validation process and deemed VALID. In the case of such an event, client software MUST return {payloadStatus: {status: VALID, latestValidHash: forkchoiceState.headBlockHash, validationError: null}, payloadId: null}.

This is what the spec says.