fix(design/variants): guard --count against NaN/zero/negative input

`design variants --count <bad value>` silently produced zero variants
because the generation loop only clamped the upper bound. `--count` arrives
via `parseInt`, which yields NaN for non-numeric input ("abc") and passes
zero/negative values straight through. `Math.min(NaN, 7)` is NaN, so the
`for (i = 0; i < NaN; i++)` loop never ran and the JSON result emitted
`"count": null` — a confusing success-with-nothing for any caller parsing it.

Add an exported `normalizeVariantCount` helper that clamps to the supported
[1, 7] range and falls back to the default of 3 for non-finite input, then
use it where the bare upper-bound cap was. Pure and unit-tested so the
behavior is pinned without an API key.

Fixes #2032

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

design/src/variants.ts

@@ -19,6 +19,23 @@ export interface VariantsOptions {
   viewports?: string; // "desktop,tablet,mobile" — generates at multiple sizes
 }
 
+/**
+ * Normalize a requested variant count to the supported range.
+ *
+ * `--count` reaches us via `parseInt`, which yields `NaN` for non-numeric
+ * input and happily passes zero/negative values through. The generation loop
+ * only capped the upper bound, so any of those silently produced zero variants
+ * and emitted `"count": null`/`0`/negative in the JSON result. Clamp to the
+ * supported `[1, 7]` range; fall back to the default of 3 when the value is not
+ * a finite number (an unparseable flag, not an explicit out-of-range request).
+ *
+ * Exported for direct unit testing.
+ */
+export function normalizeVariantCount(count: number): number {
+  if (!Number.isFinite(count)) return 3;
+  return Math.max(1, Math.min(Math.trunc(count), 7));
+}
+
 const STYLE_VARIATIONS = [
   "", // First variant uses the brief as-is
   "Use a bolder, more dramatic visual style with stronger contrast and larger typography.",
@@ -153,7 +170,7 @@ export async function variants(options: VariantsOptions): Promise<void> {
     return;
   }
 
-  const count = Math.min(options.count, 7); // Cap at 7 style variations
+  const count = normalizeVariantCount(options.count); // Clamp to [1, 7] style variations
   const size = options.size || "1536x1024";
 
   console.error(`Generating ${count} variants...`);

design/test/variants-retry-after.test.ts

@@ -2,7 +2,7 @@ import { describe, test, expect, beforeEach, afterEach } from "bun:test";
 import fs from "fs";
 import os from "os";
 import path from "path";
-import { generateVariant } from "../src/variants";
+import { generateVariant, normalizeVariantCount } from "../src/variants";
 
 // 1x1 transparent PNG, base64 — valid bytes that fs.writeFileSync can write.
 const TINY_PNG_BASE64 =
@@ -131,3 +131,35 @@ describe("generateVariant Retry-After handling", () => {
     expect(gap).toBeLessThan(500);
   });
 });
+
+describe("normalizeVariantCount", () => {
+  test("non-numeric (NaN) falls back to the default of 3", () => {
+    // Regression: `--count abc` -> parseInt -> NaN -> Math.min(NaN, 7) -> NaN,
+    // so the loop ran zero times and the JSON result emitted `"count": null`.
+    expect(normalizeVariantCount(NaN)).toBe(3);
+    expect(normalizeVariantCount(Number.parseInt("abc", 10))).toBe(3);
+  });
+
+  test("zero and negative counts clamp up to the minimum of 1", () => {
+    // Regression: `--count 0` / `--count -2` produced zero variants.
+    expect(normalizeVariantCount(0)).toBe(1);
+    expect(normalizeVariantCount(-2)).toBe(1);
+  });
+
+  test("counts above the cap clamp down to 7", () => {
+    expect(normalizeVariantCount(10)).toBe(7);
+    expect(normalizeVariantCount(7)).toBe(7);
+  });
+
+  test("in-range counts pass through unchanged", () => {
+    expect(normalizeVariantCount(1)).toBe(1);
+    expect(normalizeVariantCount(3)).toBe(3);
+    expect(normalizeVariantCount(6)).toBe(6);
+  });
+
+  test("fractional counts truncate toward zero before clamping", () => {
+    expect(normalizeVariantCount(2.9)).toBe(2);
+    expect(normalizeVariantCount(0.5)).toBe(1);
+    expect(normalizeVariantCount(Infinity)).toBe(3);
+  });
+});