Context Variables #344
Description
To communicate efficiently with the "outside-the-graph" world, we somehow need to be able to pass data to contexts (node or graph execution contexts). This can seem trivial, but it should be threadsafe, at least for the graph execution context, because more than one node may access it concurrently.
This probably means that we need a kind of an "operation queue" in the execution contexts that will apply state mutation operations in order, and one at a time.
This will allow to have graph "return values", and it may be seen as a generalization of how we manage errors (although, maybe not).