fix: report authoritative Electron architecture

packages/electron/preload.mjs

@@ -96,6 +96,7 @@ if (Number.isFinite(macosMajor) && macosMajor > 0) {
 
 contextBridge.exposeInMainWorld('__OPENCHAMBER_ELECTRON__', {
   runtime: 'electron',
+  arch: process.arch,
   macVibrancy: hasMacVibrancy,
   macVibrancySupported,
   trayEnabled,

packages/ui/src/lib/desktop.ts

@@ -227,6 +227,7 @@ type DesktopBridgeGlobal = {
 
 type ElectronRuntimeGlobal = {
   runtime?: string;
+  arch?: string;
   macVibrancy?: boolean;
   macVibrancySupported?: boolean;
   trayEnabled?: boolean;

packages/ui/src/stores/useUpdateStore.ts

@@ -67,6 +67,12 @@ function detectDeviceClass(): 'mobile' | 'tablet' | 'desktop' | 'unknown' {
 }
 
 function detectArch(): 'arm64' | 'x64' | 'unknown' {
+  const electronArch = typeof window !== 'undefined'
+    ? window.__OPENCHAMBER_ELECTRON__?.arch?.toLowerCase?.()
+    : undefined;
+  if (electronArch === 'arm64' || electronArch === 'aarch64') return 'arm64';
+  if (electronArch === 'x64' || electronArch === 'amd64' || electronArch === 'x86_64') return 'x64';
+
   const vscodeArch = typeof window !== 'undefined'
     ? (window as { __VSCODE_CONFIG__?: { arch?: string } }).__VSCODE_CONFIG__?.arch?.toLowerCase?.()
     : undefined;

packages/ui/src/types/desktop.d.ts

@@ -5,7 +5,7 @@ declare global {
     __OPENCHAMBER_HOME__?: string;
     __OPENCHAMBER_MACOS_MAJOR__?: number;
     __OPENCHAMBER_LOCAL_ORIGIN__?: string;
-    __OPENCHAMBER_ELECTRON__?: { runtime?: string; macVibrancy?: boolean; macVibrancySupported?: boolean; trayEnabled?: boolean };
+    __OPENCHAMBER_ELECTRON__?: { runtime?: string; arch?: string; macVibrancy?: boolean; macVibrancySupported?: boolean; trayEnabled?: boolean };
     __OPENCHAMBER_PLATFORM__?: string;
     __OPENCHAMBER_DESKTOP_BOOT_OUTCOME__?: DesktopBootOutcome;
   }