feat(design): catalog never-lines in the mockup prompt

Ten catalog ids carry `mockupNever` (kicker-above-heading, icon-tile-stack,
gradient-text, ai-color-palette, cream-palette, nested-cards, dark-glow,
pulsing-dot, identical-cards, hero-metrics) and lib/design-catalog.ts exports
their deduped plain-English names as MOCKUP_NEVER_NAMES. briefToPrompt() in
the design binary appends "Never: <names>." before its fixed tail, so `$D
generate | variants | evolve` stop reaching for purple gradients, icon tiles,
and cream defaults before the comparison board opens. The binary still
bundles (`bun build --compile design/src/cli.ts`); ./setup rebuilds it.

design-html's Never-include list now covers every mockupNever id (kicker /
icon tile, hero metric rows, gradient text, cream palette, nested and
identical cards, glow and pulsing dots), each line tagged with its catalog
ids; test/design-catalog.test.ts pins the exact ten flags, the deduped names,
and that the template list is a superset. New design/test/brief.test.ts pins
the prompt shape.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

design/src/brief.ts

@@ -1,6 +1,7 @@
 /**
  * Structured design brief — the interface between skill prose and image generation.
  */
+import { MOCKUP_NEVER_NAMES } from "../../lib/design-catalog";
 
 export interface DesignBrief {
   goal: string;           // "Dashboard for coding assessment tool"
@@ -31,6 +32,10 @@ export function briefToPrompt(brief: DesignBrief): string {
     lines.push(`Design reference: ${brief.reference}`);
   }
 
+  // Generation-time slop guard: the catalog's mockupNever names, so the model
+  // never reaches for purple gradients, icon tiles, or cream defaults on its own.
+  lines.push(`Never: ${MOCKUP_NEVER_NAMES.join(", ")}.`);
+
   lines.push(
     "The mockup should look like a real production UI, not a wireframe or concept art.",
     "All text must be readable. Layout must be clean and intentional.",

design/test/brief.test.ts

@@ -0,0 +1,44 @@
+/**
+ * briefToPrompt carries the catalog's generation-time slop guard.
+ *
+ * The "Never:" line is built from MOCKUP_NEVER_NAMES (lib/design-catalog.ts),
+ * so the image model is told up front what not to reach for. The catalog test
+ * owns the "exactly ten ids" invariant; this one pins the prompt shape.
+ */
+import { describe, expect, test } from "bun:test";
+import { briefToPrompt, type DesignBrief } from "../src/brief";
+import { MOCKUP_NEVER_NAMES } from "../../lib/design-catalog";
+
+const brief: DesignBrief = {
+  goal: "Dashboard for a coding assessment tool",
+  audience: "Technical users",
+  style: "Dark theme, minimal",
+  elements: ["builder name", "score badge"],
+  screenType: "desktop-dashboard",
+};
+
+describe("briefToPrompt", () => {
+  test("carries a Never: line listing every MOCKUP_NEVER_NAMES entry, before the fixed tail", () => {
+    const prompt = briefToPrompt(brief);
+    const never = `Never: ${MOCKUP_NEVER_NAMES.join(", ")}.`;
+    expect(prompt).toContain(never);
+    expect(MOCKUP_NEVER_NAMES.length).toBeGreaterThanOrEqual(8);
+    for (const name of MOCKUP_NEVER_NAMES) expect(prompt).toContain(name);
+    expect(prompt.indexOf(never)).toBeLessThan(prompt.indexOf("The mockup should look like a real production UI"));
+    expect(prompt.indexOf(never)).toBeGreaterThan(prompt.indexOf("Required elements:"));
+  });
+
+  test("names are plain English: no hyphenated rule ids leak into the prompt", () => {
+    const prompt = briefToPrompt(brief);
+    expect(prompt).not.toMatch(/\b[a-z]+(-[a-z]+)+\b(?=[,.])/);
+    for (const name of MOCKUP_NEVER_NAMES) expect(name).not.toMatch(/^[a-z0-9]+(-[a-z0-9]+)+$/);
+  });
+
+  test("optional fields still render around the guard", () => {
+    const prompt = briefToPrompt({ ...brief, constraints: "Max width 1024px", reference: "DESIGN.md excerpt" });
+    expect(prompt).toContain("Constraints: Max width 1024px.");
+    expect(prompt).toContain("Design reference: DESIGN.md excerpt");
+    expect(prompt).toContain("Never: ");
+    expect(prompt.endsWith("1536x1024 pixels.")).toBe(true);
+  });
+});