Selective isolation

Having a mix of calls to `start()` where some have the isolation level set and some not will make it difficult to debug.

If on the other hand you can explicitly and uniquely set the isolation level without the possibility of something else changing it, it would be better/cleaner.

Maybe the decorator is not the right approach given that you can't anticipate it early enough? 

The hooks have access to all Pecan's internals, including the requests, so you could potentially set the isolation levels on URLs rather than on specific controller methods