The node embeds the reward preimage verbatim in the PreRuntime digest of
every block it authors (client/consensus/qpow/src/lib.rs:726), and the
mining-rewards pallet reads that digest back to derive the payout
address on-chain. It is public from the first mined block.
So the Gitea secret, the 0640 handling and the ps-visibility caveat were
all theatre over a value published on a blockchain. It moves to the
workflow env: block with the rest of the infra truth, and
infra-setup.sh loses --mint-reward-key entirely along with its pass and
Gitea-API dependencies.
This also answers why the node takes a preimage and not an address: the
runtime does the derivation, which is what proves the payout target is a
canonical wormhole address rather than an arbitrary account. An address
would give it nothing to verify.