Should lighthouse sync blocks outside da window?

[dapplion]

The Deneb p2p makes it impossible for nodes to download blobs outside the data availability (da) window (approx 18 days from the clock slot).

During forward sync, Lighthouse currently imports these blocks outside the data availability (DA) retention window regardless of whether they were available.

Consider the following chain. Should a Lighthouse full node attest to this head?

And this one?

IMO it should not. A full node must independently check that blocks are valid and available, without relying on any majority. A finalized un-available block is still an un-available block that must be rejected.

Therefore LH should reject blocks from outside the DA window that it can't independently verify to be available. If a node runner has a node that has been stopped for more than 18 days, it should do one of the following:

• Checkpoint sync into a finalized checkpoint inside the retention window
• Run the node with a flag like --unsafe-da-sync
• Manually tell the node that some block hash and its ancestors are available