feat(engine/metrics): add latest valid fcu

[figtracer]

#20621

[Rjected]

Should have specified this better in the issue, but I don't think it's useful to have the hash bits as a gauge. We should instead have a number for the latest valid fcu head / safe / finalized

[figtracer]

Should have specified this better in the issue, but I don't think it's useful to have the hash bits as a gauge. We should instead have a number for the latest valid fcu head / safe / finalized

on it

[figtracer]

this will run if fcu is invalid as well, but ig it's not that relevant

[mattsse]

not perfectly clear to me what the use case for this is

We should track these in metrics, so that we can see what the latest valid state is without logs

the last valid tags would track:

reth/crates/chain-state/src/chain_info.rs

Lines 154 to 161 in dea27a5

	/// Tracks the number of the `canonical_head`.
	canonical_head_number: AtomicU64,
	/// The canonical head of the chain.
	canonical_head: RwLock<SealedHeader<N::BlockHeader>>,
	/// The block that the beacon node considers safe.
	safe_block: watch::Sender<Option<SealedHeader<N::BlockHeader>>>,
	/// The block that the beacon node considers finalized.
	finalized_block: watch::Sender<Option<SealedHeader<N::BlockHeader>>>,

so perhaps we add the metrics there instead?

[mattsse]

his now most likely always goes to disk for the finalized/safe block, before we send the respond

we need to avoid this

we already track the finalized/safe/head block, unsure what the use case for these metrics are here

is this just for tracking what we receive as fcu or what we actually have as finalized/safe/head @Rjected ?

because we already have:

reth/crates/chain-state/src/chain_info.rs

Lines 100 to 131 in dea27a5

	/// Sets the canonical head of the chain.
	pub fn set_canonical_head(&self, header: SealedHeader<N::BlockHeader>) {
	let number = header.number();
	*self.inner.canonical_head.write() = header;
	// also update the atomic number.
	self.inner.canonical_head_number.store(number, Ordering::Relaxed);
	}
	/// Sets the safe header of the chain.
	pub fn set_safe(&self, header: SealedHeader<N::BlockHeader>) {
	self.inner.safe_block.send_if_modified(|current_header| {
	if current_header.as_ref().map(SealedHeader::hash) != Some(header.hash()) {
	let _ = current_header.replace(header);
	return true
	}
	false
	});
	}
	/// Sets the finalized header of the chain.
	pub fn set_finalized(&self, header: SealedHeader<N::BlockHeader>) {
	self.inner.finalized_block.send_if_modified(|current_header| {
	if current_header.as_ref().map(SealedHeader::hash) != Some(header.hash()) {
	let _ = current_header.replace(header);
	return true
	}
	false
	});
	}