Function updateDesignMd

design/src/memory.ts:105–136

(
  repoRoot: string,
  extracted: ExtractedDesign,
  sourceMockup: string,
)

 * If not, creates a new one.
 */
export function updateDesignMd(
  repoRoot: string,
  extracted: ExtractedDesign,
  sourceMockup: string,
): void {
  const designPath = path.join(repoRoot, "DESIGN.md");
  const timestamp = new Date().toISOString().split("T")[0];

  const section = formatExtractedSection(extracted, sourceMockup, timestamp);

  if (fs.existsSync(designPath)) {
    // Append to existing DESIGN.md
    const existing = fs.readFileSync(designPath, "utf-8");

    // Check if there's already an extracted section, replace it
    const marker = "## Extracted Design Language";
    if (existing.includes(marker)) {
      const before = existing.split(marker)[0];
      fs.writeFileSync(designPath, before.trimEnd() + "\n\n" + section);
    } else {
      fs.writeFileSync(designPath, existing.trimEnd() + "\n\n" + section);
    }
    console.error(`Updated DESIGN.md with extracted design language`);
  } else {
    // Create new DESIGN.md
    const content = `# Design System

${section}`;
    fs.writeFileSync(designPath, content);
    console.error(`Created DESIGN.md with extracted design language`);
  }
}

function formatExtractedSection(
  extracted: ExtractedDesign,