What I am looking for in the blockchain is that code was executed without error. For example, if the code that was executed is code that verified the existence of a transaction in the bitcoin blockchain, this mechanism can be used to step through the cross chain algos.
Okay - well in that case why not make your "prototype" plugin check for the existence of a Bitcoin transaction instead (that has at least x confirmations)?
The "script" will have "state" so any "plugin calls" it makes would presumably have some sort of "return value" that could be checked and/or kept in the script's state.