mesh: update node batteryLevel from live NODEINFO_APP packets

battery_level was only populated during the initial sync; NodeInfo
frames streamed as NODEINFO_APP (port 4) now refresh deviceMetrics in
the node database so /api/nodes and downstream consumers see current
values between syncs. decodeNodeInfo + PORT_NODEINFO_APP added to the
codec, one branch in the existing packet-handling path.

src/mesh/mesh.service.spec.ts

@@ -44,6 +44,36 @@ function positionPacketFrame(
   );
 }
 
+// live node-info update: NODEINFO_APP packet with a serialized NodeInfo in Data.payload
+function nodeInfoPacketFrame(
+  from: number,
+  fields: {
+    user?: { id?: string; longName?: string };
+    deviceMetrics?: { batteryLevel?: number };
+  },
+): Uint8Array {
+  const data = create(P.Mesh.DataSchema, {
+    portnum: P.Portnums.PortNum.NODEINFO_APP,
+    payload: toBinary(
+      P.Mesh.NodeInfoSchema,
+      create(P.Mesh.NodeInfoSchema, { num: from, ...fields }),
+    ),
+  });
+  const pkt = create(P.Mesh.MeshPacketSchema, {
+    from,
+    id: 1,
+    payloadVariant: { case: 'decoded', value: data },
+  });
+  return frame(
+    toBinary(
+      P.Mesh.FromRadioSchema,
+      create(P.Mesh.FromRadioSchema, {
+        payloadVariant: { case: 'packet', value: pkt },
+      }),
+    ),
+  );
+}
+
 // inbound text message: TEXT_MESSAGE_APP packet with UTF-8 in Data.payload
 function textPacketFrame(
   from: number,
@@ -418,6 +448,47 @@ describe('MeshService node database', () => {
     }
   });
 
+  it('updates batteryLevel from live NODEINFO_APP packets (and stubs unknown nodes)', 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,
+      );
+
+      // sync entry with a stale battery, then a live NODEINFO_APP update
+      bridge.sockets[0].write(nodeInfoFrame(KAMIL_NUM, kamilNodeInfo()));
+      await waitFor(async () => (await svc.nodes()).length === 1);
+      expect((await svc.nodes())[0]?.batteryLevel).toBe(87);
+
+      bridge.sockets[0].write(
+        nodeInfoPacketFrame(KAMIL_NUM, { deviceMetrics: { batteryLevel: 9 } }),
+      );
+
+      await waitFor(async () => (await svc.nodes())[0]?.batteryLevel === 9);
+      // other fields of the sync entry survive the live update
+      expect(await svc.node(KAMIL_NUM)).toMatchObject({
+        longName: 'Kamil SP8MK/P',
+        shortName: 'KK',
+        batteryLevel: 9,
+      });
+
+      // unknown node: a NODEINFO_APP with deviceMetrics creates a stub entry
+      bridge.sockets[0].write(
+        nodeInfoPacketFrame(555, { deviceMetrics: { batteryLevel: 3 } }),
+      );
+
+      await waitFor(async () => (await svc.nodes()).length === 2);
+      expect((await svc.node(555))?.batteryLevel).toBe(3);
+    } finally {
+      svc.onModuleDestroy();
+      bridge.close();
+    }
+  });
+
   it('looks up nodes by exact num, numeric string, exact name and unique substring', async () => {
     const bridge = await startBridge();
     process.env.MESH_HOST = '127.0.0.1';