gistfile1.txt

Existing Rules ContextInterface -> Merge into Drupal\Core\Plugin\Context
Determine if ContextDefinitionInterface is still necessary (instead of DataDefinitionInterface) (hopefully not neccessary).
Form Widget Definitions are not part of Context, Fago will make a separate method for when he needs this at the plugin level.
Allowed values are part of contexts, Kris would prefer a addConstraint() approach to this usage.
Context validation will not happen on setContextValue().
Static methods for plugin context definitions is an implementation detail, Kris doesn't like it but w/e.
Fago wants a ContextException to actually get used & documented.
Fago wants getContext() to return Context objects even if a value has not been set for that context. Kris agrees in principle.
Fago & Kris both support a ContextDefinition Annotation class.