Build a SuperDoc custom action

A custom action is a named, namespaced verb (superdoc.<verb>, e.g. superdoc.add_footnote) that a customer authors once and exposes to an LLM through superdoc_perform_action, alongside the 40 built-in core actions. An action is deterministic application code, not a prompt.

Your job when this skill is active: turn a plain-language request into a correct, registered, live-verified ActionSpec, plus a test. Never hand back an action you haven't executed against a real document.

1. The canonical ActionSpec — two execution tiers