Runtime variable changes aren't reset

When a graph is executed, any variable/set changes alter the JSON format with the new value; that value doesn't reset when the graph is run again, or changes are made, etc. This took me a day to realize and I feel that this could either be communicated more clearly, or, when the graph is changed or play is pressed again, the variable is reset to the initial value.

No files, tests, or entry points are named in the issue. Reproduce the behavior by executing a graph, changing a variable, and executing or editing it again; then trace where runtime variable changes are retained. Done means the expected reset or clearer behavior is defined and verified for repeated graph execution.

Written by the indexing model from the issue text.