Fix BigInt serialization in GET /api/device (500 on real hardware) (#14)

src/mesh/mesh.service.spec.ts

@@ -718,6 +718,32 @@ describe('MeshService device info', () => {
     }
   });
 
+  it('serializes proto uint64 fields as strings (JSON-safe)', async () => {
+    const bridge = await startBridge();
+    process.env.MESH_HOST = '127.0.0.1';
+    process.env.MESH_PORT = String(bridge.port);
+    const svc = new MeshService();
+    try {
+      svc.onModuleInit();
+      await waitFor(
+        () => bridge.sockets.length === 1 && svc.status().connected,
+      );
+
+      // powermonEnables is a proto uint64 — protobuf-es decodes it as native bigint
+      bridge.sockets[0].write(
+        configSectionFrame('power', { powermonEnables: 123n }),
+      );
+
+      await waitFor(() => svc.deviceInfo().localConfig.power !== undefined);
+      const info = svc.deviceInfo();
+      expect(info.localConfig.power?.powermonEnables).toBe('123'); // bigint -> decimal string
+      expect(() => JSON.stringify(info)).not.toThrow(); // no "Do not know how to serialize a BigInt"
+    } finally {
+      svc.onModuleDestroy();
+      bridge.close();
+    }
+  });
+
   it('summarizes NodeInfo snr/hopsAway/viaMqtt when present', async () => {
     const bridge = await startBridge();
     process.env.MESH_HOST = '127.0.0.1';