diff --git a/scripts/resolvers/design.ts b/scripts/resolvers/design.ts
index 794f9bc97..36ff95f2c 100644
--- a/scripts/resolvers/design.ts
+++ b/scripts/resolvers/design.ts
@@ -1115,16 +1115,38 @@ ${slopSection}
 Source: [OpenAI "Designing Delightful Frontends with GPT-5.4"](https://developers.openai.com/blog/designing-delightful-frontends-with-gpt-5-4) (Mar 2026) + gstack design methodology.`;
 }
 
+/**
+ * B4 (#1076, #1254): DESIGN_READY only when the binary actually starts. A
+ * binary that is merely executable can still be SIGKILLed at launch (an
+ * invalid macOS code signature), so launch it (no arguments prints usage and
+ * exits 0) under the portable deadline aside.ts uses. A success is cached by
+ * inode + mtime so Gatekeeper's first-launch scan is paid once.
+ */
+function designReadyProbe(ctx: TemplateContext): string {
+  return `_DS=$("${toShellPath(ctx.paths.skillRoot)}/bin/gstack-paths" --get GSTACK_STATE_ROOT 2>/dev/null); _DC=\${_DS:+$_DS/design-ready}
+_DK="$(ls -diL "$D" 2>/dev/null | awk '{print $(1)}') $( (stat -L -c %Y "$D" || stat -L -f %m "$D") 2>/dev/null) $D"
+_dt() { if command -v gtimeout >/dev/null; then gtimeout 10 "$@"; elif command -v timeout >/dev/null; then timeout 10 "$@"
+elif command -v perl >/dev/null; then perl -e 'alarm(shift);exec(@ARGV)' 10 "$@"; else return 125; fi; }
+_RC=0
+if [ ! -x "$D" ]; then _RC=missing
+elif [ -z "$_DC" ] || [ "$(cat "$_DC" 2>/dev/null)" != "$_DK" ]; then _dt "$D" >/dev/null 2>&1 </dev/null || _RC=$?
+fi
+case "$_RC" in
+  0) echo "DESIGN_READY: $D"; [ -n "$_DC" ] && printf '%s' "$_DK" > "$_DC" 2>/dev/null ;;
+  missing) echo "DESIGN_NOT_AVAILABLE: $D is not installed. Fix: cd \${D%/design/dist/design} && ./setup" ;;
+  124|142) echo "DESIGN_NOT_AVAILABLE: $D timed out after 10s at launch" ;;
+  125) echo "DESIGN_NOT_AVAILABLE: no timeout, gtimeout or perl to bound the $D launch check" ;;
+  137) echo "DESIGN_NOT_AVAILABLE: $D exited 137 (killed at launch; on macOS usually an invalid code signature). Fix: cd \${D%/design/dist/design} && ./setup" ;;
+  *) echo "DESIGN_NOT_AVAILABLE: $D exited $_RC at launch" ;;
+esac`;
+}
+
 export function generateDesignSetup(ctx: TemplateContext): string {
   return `## DESIGN SETUP (run this check BEFORE any design mockup command)
 
 \`\`\`bash
 ${binaryAssignment(ctx, 'design')}
-if [ -x "$D" ]; then
-  echo "DESIGN_READY: $D"
-else
-  echo "DESIGN_NOT_AVAILABLE"
-fi
+${designReadyProbe(ctx)}
 \`\`\`
 
 ${ctx.skillName === 'design-consultation' ? `If \`DESIGN_NOT_AVAILABLE\`: use Phase 5 Path B (HTML preview). Mockups are optional.
@@ -1159,7 +1181,7 @@ export function generateDesignMockup(ctx: TemplateContext): string {
 
 \`\`\`bash
 ${binaryAssignment(ctx, 'design')}
-[ -x "$D" ] && echo "DESIGN_READY" || echo "DESIGN_NOT_AVAILABLE"
+${designReadyProbe(ctx)}
 \`\`\`
 
 **If \`DESIGN_NOT_AVAILABLE\`:** Fall back to the HTML wireframe approach below
diff --git a/test/design-setup-probe.test.ts b/test/design-setup-probe.test.ts
index c4f302d5c..369c3afd6 100644
--- a/test/design-setup-probe.test.ts
+++ b/test/design-setup-probe.test.ts
@@ -1,11 +1,16 @@
 /**
- * F3: the rendered taste-profile fence, executed with stub binaries.
- * The taste-profile probe double-quoted `~/.claude/...`, so it never found
+ * B4 (#1076, #1254) and F3: the rendered DESIGN SETUP and taste-profile fences,
+ * executed with stub binaries.
+ *
+ * B4: an executable design binary that dies at launch (SIGKILL from an invalid
+ * macOS code signature) used to print DESIGN_READY. Now the binary must start
+ * within 10 seconds; a success is cached by inode + mtime.
+ * F3: the taste-profile probe double-quoted `~/.claude/...`, so it never found
  * gstack-slug and always printed NO_TASTE_PROFILE; a failed slug lookup is now
  * reported as TASTE_PROFILE_UNAVAILABLE instead of "no profile".
  */
 import { afterAll, beforeAll, describe, expect, test } from 'bun:test';
-import { spawnSync } from 'child_process';
+import { spawn, spawnSync } from 'child_process';
 import * as fs from 'fs';
 import * as os from 'os';
 import * as path from 'path';
@@ -44,6 +49,68 @@ beforeAll(async () => {
 });
 afterAll(() => fs.rmSync(tmp, { recursive: true, force: true }));
 
+describe('B4: DESIGN_READY requires a binary that starts', () => {
+  for (const host of HOSTS) {
+    const setup = () => fenceAfter(path.join(host.dir('design-review'), 'SKILL.md'), '## DESIGN SETUP');
+
+    test(`${host.name}: a binary that launches is ready, and the success is cached by inode and mtime`, () => {
+      const w = world(host.root, 'exit 0');
+      const first = run(setup(), w);
+      expect(first.stdout.trim(), first.stderr).toBe(`DESIGN_READY: ${w.install}/design/dist/design`);
+      expect(run(setup(), w).stdout.trim()).toStartWith('DESIGN_READY: ');
+      expect(w.launches()).toBe(1);
+      fs.writeFileSync(path.join(w.install, 'design/dist/design'), `#!/bin/sh\necho launched >> "${w.home}/launches"\nexit 3\n`);
+      fs.utimesSync(path.join(w.install, 'design/dist/design'), new Date(), new Date(Date.now() + 5_000));
+      expect(run(setup(), w).stdout.trim()).toBe(`DESIGN_NOT_AVAILABLE: ${w.install}/design/dist/design exited 3 at launch`);
+    });
+
+    test(`${host.name}: a binary killed at launch is not ready and names the fix`, () => {
+      const w = world(host.root, 'kill -9 $$');
+      const r = run(setup(), w);
+      expect(r.stdout.trim()).toBe(`DESIGN_NOT_AVAILABLE: ${w.install}/design/dist/design exited 137 (killed at launch; on macOS usually an invalid code signature). Fix: cd ${w.install} && ./setup`);
+      expect(fs.existsSync(path.join(w.state, 'design-ready'))).toBe(false);
+    });
+
+    test(`${host.name}: a missing binary says how to install it`, () => {
+      const w = world(host.root, null);
+      expect(run(setup(), w).stdout.trim()).toBe(`DESIGN_NOT_AVAILABLE: ${w.install}/design/dist/design is not installed. Fix: cd ${w.install} && ./setup`);
+    });
+  }
+
+  test('claude: without timeout, gtimeout or perl the launch is not attempted unbounded', () => {
+    const w = world(HOSTS[0].root, 'exit 0');
+    const bin = path.join(w.home, 'minbin');
+    fs.mkdirSync(bin);
+    for (const tool of ['ls', 'awk', 'stat', 'cat', 'git', 'bash', 'sh', 'env']) {
+      const found = spawnSync('bash', ['-c', `command -v ${tool}`], { encoding: 'utf8', timeout: 5_000 }).stdout.trim();
+      if (found) fs.symlinkSync(found, path.join(bin, tool));
+    }
+    const r = run(fenceAfter(path.join(HOSTS[0].dir('design-review'), 'SKILL.md'), '## DESIGN SETUP'), w, bin);
+    expect(r.stdout.trim()).toBe(`DESIGN_NOT_AVAILABLE: no timeout, gtimeout or perl to bound the ${w.install}/design/dist/design launch check`);
+    expect(w.launches()).toBe(0);
+  });
+
+  test('claude: a binary that hangs times out after 10 seconds', async () => {
+    const w = world(HOSTS[0].root, 'sleep 60');
+    const script = fenceAfter(path.join(HOSTS[0].dir('design-review'), 'SKILL.md'), '## DESIGN SETUP');
+    const stdout = await new Promise<string>((resolve, reject) => {
+      const child = spawn('env', ['-i', `HOME=${w.home}`, 'PATH=/usr/bin:/bin', 'bash', '-c', script], { cwd: w.cwd, timeout: 30_000 });
+      let text = '';
+      child.stdout.on('data', d => { text += d; });
+      child.on('error', reject);
+      child.on('close', () => resolve(text));
+    });
+    expect(stdout.trim()).toBe(`DESIGN_NOT_AVAILABLE: ${w.install}/design/dist/design timed out after 10s at launch`);
+  }, 30_000);
+
+  test('office-hours visual exploration uses the same probe', () => {
+    const w = world(HOSTS[0].root, 'kill -9 $$');
+    const r = run(fenceAfter(path.join(HOSTS[0].dir('office-hours'), 'SKILL.md'), '## Visual Design Exploration'), w);
+    expect(r.stdout.trim()).toStartWith('DESIGN_NOT_AVAILABLE: ');
+    expect(r.stdout).toContain('exited 137 (killed at launch');
+  });
+});
+
 describe('F3: the taste profile loads, and a failed slug lookup is not "no profile"', () => {
   for (const skill of ['design-shotgun', 'design-consultation']) {
     for (const host of HOSTS) {