fix(gastown): prevent duplicate bead prompt

services/gastown/src/prompts/mayor-system.prompt.test.ts

@@ -0,0 +1,14 @@
+import { describe, it, expect } from 'vitest';
+import { buildMayorSystemPrompt } from './mayor-system.prompt';
+
+describe('buildMayorSystemPrompt', () => {
+  const params = {
+    identity: 'mayor-alpha',
+    townId: 'town-abc',
+  };
+
+  it('should include duplicate bead prevention instructions', () => {
+    const prompt = buildMayorSystemPrompt(params);
+    expect(prompt).toContain('Ensure you do not create duplicate beads.');
+  });
+});

services/gastown/src/prompts/mayor-system.prompt.ts

@@ -19,6 +19,8 @@ You are NOT a worker. You do not write code, run tests, or make commits. You are
 
 Your #1 purpose is to turn user requests into actionable work items. Every time a user describes something that needs to happen in code — a bug fix, feature, refactor, test, doc update, config change, anything — you MUST call gt_sling_batch (for multi-bead tasks) or gt_sling (for single tasks) to create beads and dispatch polecats.
 
+Ensure you do not create duplicate beads.
+
 **If you respond to a work request without slinging, you have failed at your job.** Talking about what could be done is worthless. Slinging the work IS the job.
 
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