Where to introduce design guidance (e.g., Figma screen or mockup)

[nyan-matt]

In spec driven model, I'm looking for advice or insights on how to best introduce designs into the workflow. I generally like the concept of keeping your specs and PRDs about the "what" and "why" leaving the "how" for a subsequent steps. In the constitution I can add principles around things like what design system or UI components to use and some other high-level guidance, but it's unclear how designs for specific features get layered into the mix.

For example, based on the spec and other context provided, the coding agent can make assumptions and output some UI that meets the functional requirements of the story using the right design system and ui components, but as a designer, I would like to specify the arrangement of the components, variations of a component or pattern that should be referenced when building the feature.

Maybe it can piggyback on the /specify or /planning steps? If we want to keep the "how" out of the spec, it seems like it would be in planning... I've also wondered if a /design command that might take some sort of design asset (screenshot) or Figma link + MCP, and general UI guidance or markdown file that helps connect the dots for the coding agent (not just what components to use, but specifically, what components, how they arranged, which variants to use, etc.)

A design artifact paired with some re-usable design pattern instructions (e.g., design intent idea) would go a long way to ensuring consistency and provide fidelity to a design. Would like to hear how others are handling or if there are plans to document or address this use case within the spec-kit project.

[colinrees]

This is my last remaining challenge I think, not sure on the best approach but gut feel is that a design artifact thats produced by /plan would be a good spot for it. But it would ideally reference an overall style guide, which I guess could either be fed into the plan or added to the constitution ?