One post,
and you are in.
The register is the list that gets the first bloom: the opening window on every Sakura market. Post it — that is the whole thing, no wallet, no form, nothing to pay. If you want your address on the list as well, sign one message after; it costs nothing and sends nothing.
It opens X with the post written. No wallet, no connection, nothing to sign.
Optional — put the address on the list too. One signed message, and the post button starts carrying your wallet so the register can tie the two together.
A message, not a transaction: no gas, no approval, nothing moved.
Paste the link once posted and the register reads it back off X: it has to be yours and to carry your wallet.
Nothing here takes your word for anything: a signature is checked against the address, Base is read for what it knows about that wallet, and a post is read off X itself. One record per address.