diff --git a/src/db/migrations/index.ts b/src/db/migrations/index.ts
index 9b51b87..c182899 100644
--- a/src/db/migrations/index.ts
+++ b/src/db/migrations/index.ts
@@ -375,5 +375,19 @@ export const migrations: Migration[] = [
         }
       } catch {}
     }
+  },
+  {
+    version: 13,
+    name: 'groups-onboarding-prompted-at',
+    checksum: 'v13-groups-onboarding-2025-10-17',
+    up: (db: Database) => {
+      try {
+        const cols = db.query(`PRAGMA table_info(groups)`).all() as any[];
+        const hasCol = Array.isArray(cols) && cols.some((c: any) => String(c.name) === 'onboarding_prompted_at');
+        if (!hasCol) {
+          db.exec(`ALTER TABLE groups ADD COLUMN onboarding_prompted_at TEXT NULL;`);
+        }
+      } catch {}
+    }
   }
 ];
diff --git a/tests/unit/services/group-sync.onboarding.test.ts b/tests/unit/services/group-sync.onboarding.test.ts
new file mode 100644
index 0000000..4b38a5b
--- /dev/null
+++ b/tests/unit/services/group-sync.onboarding.test.ts
@@ -0,0 +1,83 @@
+import { describe, it, beforeEach, afterEach, expect } from 'bun:test';
+import Database from 'bun:sqlite';
+import { initializeDatabase } from '../../../src/db';
+import { GroupSyncService } from '../../../src/services/group-sync';
+import { AllowedGroups } from '../../../src/services/allowed-groups';
+
+const envBackup = { ...process.env } as NodeJS.ProcessEnv;
+
+describe('GroupSyncService - onboarding A3', () => {
+  let memdb: Database;
+
+  beforeEach(() => {
+    process.env = {
+      ...envBackup,
+      NODE_ENV: 'test',
+      ONBOARDING_ENABLE_IN_TEST: 'true',
+      ONBOARDING_PROMPTS_ENABLED: 'true',
+      ONBOARDING_GRACE_SECONDS: '0',
+      ONBOARDING_COOLDOWN_DAYS: '7',
+      ONBOARDING_COVERAGE_THRESHOLD: '1',
+      CHATBOT_PHONE_NUMBER: '555111222'
+    };
+    memdb = new Database(':memory:');
+    initializeDatabase(memdb);
+    (GroupSyncService as any).dbInstance = memdb;
+    (AllowedGroups as any).dbInstance = memdb;
+
+    // Sembrar grupo activo
+    memdb.prepare(`INSERT INTO groups (id, community_id, name, active, last_verified) VALUES (?,?,?,?, strftime('%Y-%m-%d %H:%M:%f','now'))`)
+      .run('g1@g.us', 'comm-1', 'Grupo 1', 1);
+  });
+
+  afterEach(() => {
+    memdb.close();
+    process.env = envBackup;
+  });
+
+  it('publica prompt cuando coverage < 100, grace cumplido y sin cooldown', () => {
+    // snapshot con un resoluble (dígitos) y uno no resoluble (alias sin mapeo)
+    const res = GroupSyncService.reconcileGroupMembers('g1@g.us', [
+      { userId: '111', isAdmin: false },
+      { userId: 'alias_lid', isAdmin: false }
+    ], '2025-01-01 00:00:00.000');
+
+    expect(res).toEqual(expect.objectContaining({ added: 2 }));
+    const row = memdb.query(`SELECT recipient, message, status FROM response_queue ORDER BY id DESC LIMIT 1`).get() as any;
+    expect(row).toBeTruthy();
+    expect(row.recipient).toBe('g1@g.us');
+    expect(String(row.message)).toContain('https://wa.me/555111222');
+
+    const g = memdb.query(`SELECT onboarding_prompted_at FROM groups WHERE id = 'g1@g.us'`).get() as any;
+    expect(g).toBeTruthy();
+    expect(g.onboarding_prompted_at).toBeTruthy();
+  });
+
+  it('omite prompt cuando coverage = 100', () => {
+    // Previo: no debe existir prompt para este grupo
+    const before = memdb.query(`SELECT COUNT(*) AS c FROM response_queue`).get() as any;
+    expect(Number(before.c)).toBe(0);
+
+    // snapshot totalmente resoluble (dos dígitos)
+    GroupSyncService.reconcileGroupMembers('g1@g.us', [
+      { userId: '111', isAdmin: false },
+      { userId: '222', isAdmin: false }
+    ], '2025-01-01 00:00:00.000');
+
+    const after = memdb.query(`SELECT COUNT(*) AS c FROM response_queue`).get() as any;
+    expect(Number(after.c)).toBe(0);
+  });
+
+  it('omite prompt en modo enforce si el grupo no está allowed', () => {
+    process.env.GROUP_GATING_MODE = 'enforce';
+    AllowedGroups.setStatus('g1@g.us', 'blocked');
+
+    GroupSyncService.reconcileGroupMembers('g1@g.us', [
+      { userId: '111', isAdmin: false },
+      { userId: 'alias_lid', isAdmin: false }
+    ], '2025-01-01 00:00:00.000');
+
+    const count = memdb.query(`SELECT COUNT(*) AS c FROM response_queue`).get() as any;
+    expect(Number(count.c)).toBe(0);
+  });
+});