Anchor one hop: header, proof-of-work floor, txCount, caller's trust hook,
txid merkle branch. Returns what the trust hook asserted, so a caller that
needs the height bound to the header (the terminal coinbase below BIP34) can
read it; every other caller ignores it.
Anchor one hop: header, proof-of-work floor, txCount, caller's trust hook, txid merkle branch. Returns what the trust hook asserted, so a caller that needs the height bound to the header (the terminal coinbase below BIP34) can read it; every other caller ignores it.