Can you post some links for how the smart contract works, conditions of start, end smart contart, deposit and withdrawal and how it will correspond to all the difference between the types of Blockchain without hard fork or soft fork.

The best solution I can think of is to create a second layer to make payments similar to the lightning network, but it supports more than one crypto currency, and therefore you can close a certain number of Bitcoin to get the amount in USDT, and then you can get stable liquidity.

you can do it with some eth tokens