Self-contained setup for a dedicated design session: product goal and
audience, the inherited visual language from the Python prototype,
what exists today (including the API's missing graph-topology
endpoint, a known gap), the locked decisions the spec must respect,
the questions it must answer (accessibility criteria among them, still
undefined), and the required shape of the deliverable, docs/ui-spec.md.
Design before build; the implementation session executes the spec.
