diff --git a/packages/diagnostics-client/src/device.ts b/packages/diagnostics-client/src/device.ts
index 993cef2e..efe43b77 100644
--- a/packages/diagnostics-client/src/device.ts
+++ b/packages/diagnostics-client/src/device.ts
@@ -7,24 +7,19 @@
 import type { DeviceState } from './types.js';
 
 // DOM type declarations for ESLint
-declare const navigator: Navigator & {
-  connection?: NetworkInformation;
-  getBattery?: () => Promise<BatteryManager>;
+type Navigator = {
+  onLine: boolean;
+  connection?: { effectiveType?: string };
+  getBattery?: () => Promise<{ charging: boolean; level: number }>;
   storage?: { estimate(): Promise<{ usage?: number }> };
 };
-declare const performance: Performance & { memory?: { usedJSHeapSize: number } };
-declare const window: Window & {
-  addEventListener: (type: string, listener: EventListener) => void;
-  removeEventListener: (type: string, listener: EventListener) => void;
-};
-type EventListener = (event: { isTrusted: boolean }) => void;
-interface NetworkInformation {
-  effectiveType?: string;
-}
-interface BatteryManager {
-  charging: boolean;
-  level: number;
+declare const navigator: Navigator;
+declare const performance: { memory?: { usedJSHeapSize: number } };
+interface Window {
+  addEventListener: (type: string, listener: () => void) => void;
+  removeEventListener: (type: string, listener: () => void) => void;
 }
+declare const window: Window;
 
 /**
  * Collect current device state
@@ -36,34 +31,39 @@ export function collectDeviceState(): DeviceState {
   };
 
   // Network type (experimental API)
-  const connection = (navigator as Navigator & { connection?: NetworkInformation }).connection;
+  const connection = (navigator as { connection?: { effectiveType?: string } }).connection;
   if (connection) {
     state.networkType = connection.effectiveType ?? 'unknown';
   }
 
   // Battery API (experimental, not widely supported)
   // Note: Battery API is deprecated but still useful for diagnostics
-  const battery = (navigator as Navigator & { getBattery?: () => Promise<BatteryManager> }).getBattery;
+  const battery = (
+    navigator as { getBattery?: () => Promise<{ charging: boolean; level: number }> }
+  ).getBattery;
   if (battery) {
     // We'll return a promise, but sync API can't wait
     // Store last known value if available
   }
 
   // Memory (Chrome-only experimental)
-  const memory = (performance as Performance & { memory?: { usedJSHeapSize: number } }).memory;
+  const memory = (performance as { memory?: { usedJSHeapSize: number } }).memory;
   if (memory) {
     state.memoryMB = Math.round(memory.usedJSHeapSize / 1024 / 1024);
   }
 
   // Storage (async, but we'll fire-and-forget)
   if (navigator.storage && navigator.storage.estimate) {
-    navigator.storage.estimate().then(estimate => {
-      if (estimate.usage !== undefined) {
-        state.storageMB = Math.round(estimate.usage / 1024 / 1024);
-      }
-    }).catch(() => {
-      // Ignore errors
-    });
+    navigator.storage
+      .estimate()
+      .then(estimate => {
+        if (estimate.usage !== undefined) {
+          state.storageMB = Math.round(estimate.usage / 1024 / 1024);
+        }
+      })
+      .catch(() => {
+        // Ignore errors
+      });
   }
 
   return state;
@@ -72,9 +72,7 @@ export function collectDeviceState(): DeviceState {
 /**
  * Subscribe to online/offline events
  */
-export function subscribeToConnectivity(
-  callback: (isOnline: boolean) => void
-): () => void {
+export function subscribeToConnectivity(callback: (isOnline: boolean) => void): () => void {
   const handleOnline = () => callback(true);
   const handleOffline = () => callback(false);
 
@@ -86,25 +84,3 @@ export function subscribeToConnectivity(
     window.removeEventListener('offline', handleOffline);
   };
 }
-
-/**
- * Network Information interface (experimental)
- */
-interface NetworkInformation {
-  effectiveType?: string;
-  downlink?: number;
-  rtt?: number;
-  saveData?: boolean;
-}
-
-/**
- * Battery Manager interface (experimental)
- */
-interface BatteryManager {
-  charging: boolean;
-  level: number;
-  chargingTime: number;
-  dischargingTime: number;
-  addEventListener: (type: string, listener: EventListener) => void;
-  removeEventListener: (type: string, listener: EventListener) => void;
-}