@Carlton
> they're all state-update transactions, and they're all valid on-chain. That's the whole point, it wouldn't work otherwise.

All the state update transactions are valid on-chain, yes that's true. *Until* any one of them is confirmed on chain. Then none valid. However, the refund (anti-cheating) transaction becomes valid if the confirmed transaction is an out of date state. Once the refund transaction goes through, there are no more presigned transactions that are valid - both parties have their final money from the channel and its fully closed.

> permits any updates in any order, on-chain

I don't believe that's true. You can't spend the same output twice, and all these are pre-signed transctions. What mechanism do you think is being used to allow these update transactions to be spent in "any order"? I don't think such a mechanism exists. What am I missing Carlton?