DAG_extension

TODO: See also extend_DAG - should it be merged here?

How does DAG extension work?

The entry_script has to:

• transition to meta primer_runtime first

• implement CLI_compatibility

How to specify target state available only in meta runtime?

TODO: Implement this (and update): it should not be state directly, but a stable name for target states which points to refactorable state names

proto_code is supposed to recognize two args for the two target states:

• state_name_proto target is recognized in both runtime_proto and runtime_meta.

• state_name_meta target is recognized only in runtime_meta.

In other words, whatever runtime_meta does (whatever names it has) is irrelevant in runtime_proto.