maybe we should bitcoin+nostr+mcp this hashcash thing https://github.com/TecharoHQ/anubis but make it so that the challenge string (provided by a spam-deterring site operator) is actually the components of a prospective bitcoin block header.

If the operator is too lazy to run their own bitcoin node to construct the block template, then they can grab one from a service like mempool.space

From the visitor's perspective it is the same (they must complete the pow challenge), but at least this way every website operator can also be a solo miner.