Add persistent device traffic history charts

test/server/device-inventory.test.js

@@ -273,6 +273,51 @@ test('device traffic totals persist exact deltas across polls and process epochs
   assert.equal(snapshot.source.traffic.error, 'traffic unavailable');
 });
 
+test('device traffic history stays in bounded service memory and survives client snapshots', async (t) => {
+  const directory = fs.mkdtempSync(path.join(os.tmpdir(), 'harbor-device-history-'));
+  t.after(() => fs.rmSync(directory, { recursive: true, force: true }));
+  const filePath = path.join(directory, 'devices.json');
+  const store = createJsonStore({ filePath, defaultValue: {}, migrate: migrateDeviceInventoryState });
+  const mac = '00:11:22:33:44:55';
+  let observedAt = '2026-08-07T12:00:00.000Z';
+  let uploadBytes = '100';
+  let proxyDownloadBytes = '20';
+  const createService = () => createDeviceInventoryService({
+    store,
+    observe: () => ({
+      observedAt,
+      error: null,
+      observations: [{ ip: '192.168.50.7', mac, interface: 'eth0', observedAt, active: true }],
+    }),
+    observeTraffic: () => ({
+      epoch: 'epoch-a',
+      generation: 'rules-a',
+      observedAt,
+      source: { error: null },
+      devices: [{
+        ip: '192.168.50.7', mac, interface: 'eth0', uploadBytes, downloadBytes: '0',
+        proxyUploadBytes: '0', proxyDownloadBytes,
+      }],
+    }),
+  });
+  const service = createService();
+  assert.deepEqual((await service.refresh()).devices[0].trafficHistory, []);
+
+  observedAt = '2026-08-07T12:00:15.000Z';
+  uploadBytes = '130';
+  proxyDownloadBytes = '25';
+  const snapshot = await service.refresh();
+  assert.equal(snapshot.trafficHistoryCapacity, 120);
+  assert.deepEqual(snapshot.devices[0].trafficHistory, [{
+    observedAt,
+    gatewayBytes: '30',
+    proxyBytes: '5',
+  }]);
+  assert.deepEqual(service.snapshot().devices[0].trafficHistory, snapshot.devices[0].trafficHistory);
+  assert.doesNotMatch(fs.readFileSync(filePath, 'utf8'), /trafficHistory/);
+  assert.deepEqual(createService().snapshot().devices[0].trafficHistory, []);
+});
+
 test('legacy dataplane samples preserve saved proxy totals while Gateway totals keep advancing', async (t) => {
   const directory = fs.mkdtempSync(path.join(os.tmpdir(), 'harbor-device-proxy-legacy-'));
   t.after(() => fs.rmSync(directory, { recursive: true, force: true }));