[ADD] missing @model decorator breaking switch between new and old API methods
[FIX] copy model before altering it in place

New API uses immutable dicts for contexts, methods which want to play around
with altering context have to copy it to a "real" dict.
[FIX] remove id: key in !python yaml directives

!python {id:} did nothing in the old API (was noise/cargo cultism), in new API
 it's used to browse the model for the API before applying the code block (->
 the execution context is the record's model, not just the model) so old {id:}
 may break everything.