It turns out that using the JSON CloudFormation format as the internal state for @StackToolbox was a mistake. I didn't pick it up until I made two keys the same while editing the name for one.
I've been working on @StackToolbox over the Easter long weekend.
The form editor is progressing nicely now I have a solution to the UX issue that was making it difficult to support all CloudFormation resources without building custom screens for each one.
Today I made the classic startup mistake of wasting time on something that makes @StackToolbox look prettier and future proofing it instead of focusing on work that would help me get it in front of customers.
Luckily I caught myself after a few hours and stopped.