Nightshift
You sleep eight hours. The chain does not. Leave the rules of the shift and somebody sits at the desk from 23:00 to 07:00, watches every coin you hold, and pulls you out of the ones that break a rule. In the morning the log says whether he had to.
THE WALL
connect a wallet and every coin gets a screenORDERS FOR THE SHIFT
Standing rules. The guard may do these and nothing else.
WHAT THE GUARD MAY DO
Sell a coin you already hold, on its own curve, back into ETH that lands in your wallet. Nothing else.
It cannot buy, cannot move a coin to another address, and cannot touch anything you did not list.
Permission is an allowance you sign per coin and can revoke at any second.
The rules live on the desk contract, so what the guard did can be checked against what you asked for.
1% of what a sale returns is the desk's fee, and only on a sale. A quiet night costs nothing.