Framelink MCP (https://github.com/GLips/Figma-Context-MCP)
Playwright MCP (https://github.com/microsoft/playwright-mcp)
Pull down designs via Framelink, optionally enrich with PNG exports of nodes added as image uploads to the prompt, write out the components, test/verify via Playwright MCP.
Gemini has a 1M context size now, so this applies to large mature codebases as well as greenfield. The key thing here is the coding agent being really clever about maintaining its' context; you don't need to fit an entire codebase into a single prompt in the same way that you don't need to fit the entire codebase into your head to make a change, you just need enough context on the structure and form to maintain the correct patterns.
Indeed, in fact design has become the bottleneck now. Figma has really dropped the ball here WRT building out AI assisted (not driven) tooling for designers.