feat(desktop): enable Electron migration path

Introduce the Electron desktop shell alongside the existing React renderer and local Bun server boundary. The migration keeps the DesktopHost contract explicit across Tauri, Electron, and browser runtimes while adding Electron main/preload services for dialogs, shell, notifications, updates, tray/window lifecycle, terminal, preview WebContentsView, app mode, and release/package validation.

The commit also carries the latest local main desktop command updates, including agent slash entries and hidden-by-default markdown thinking details, so the packaged Electron build matches the current main UX surface.

Constraint: React renderer, local Bun server, REST/WebSocket, and sidecar boundaries must remain reusable during the migration
Constraint: macOS dev packages are ad-hoc signed and cannot prove Developer ID notarization or Gatekeeper release launch
Rejected: Browser-only smoke validation | it cannot exercise native dialogs, keychain prompts, notification behavior, or packaged app startup
Confidence: medium
Scope-risk: broad
Directive: Do not remove Tauri host support until signed Electron release artifacts pass native OS smoke on macOS, Windows, and Linux
Tested: bun run check:desktop
Tested: cd desktop && bun run check:electron
Tested: CSC_IDENTITY_AUTO_DISCOVERY=false bun run electron:package:dir
Tested: bun run test:package-smoke --platform macos --package-kind dir --artifacts-dir desktop/build-artifacts/electron
Tested: Computer Use read packaged Electron app window at desktop/build-artifacts/electron/mac-arm64/Claude Code Haha.app
Not-tested: Developer ID signed/notarized Gatekeeper launch
Not-tested: Real OS notification click-to-session action
Not-tested: Windows and Linux packaged app smoke on real hosts

desktop/src/stores/updateStore.ts

@@ -1,6 +1,6 @@
 import { create } from 'zustand'
-import type { Update } from '@tauri-apps/plugin-updater'
-import { isTauriRuntime } from '../lib/desktopRuntime'
+import { getDesktopHost } from '../lib/desktopHost'
+import type { DesktopHost, DesktopUpdate } from '../lib/desktopHost'
 import type { UpdateProxySettings } from '../types/settings'
 import { useSettingsStore } from './settingsStore'
 
@@ -33,13 +33,13 @@ type UpdateStore = {
   checkedAt: number | null
   shouldPrompt: boolean
   initialize: () => Promise<void>
-  checkForUpdates: (options?: CheckOptions) => Promise<Update | null>
+  checkForUpdates: (options?: CheckOptions) => Promise<DesktopUpdate | null>
   downloadUpdate: () => Promise<void>
   installUpdate: () => Promise<void>
   dismissPrompt: () => void
 }
 
-let pendingUpdate: Update | null = null
+let pendingUpdate: DesktopUpdate | null = null
 let pendingUpdateProxyKey: string | null = null
 let pendingUpdateDownloaded = false
 let downloadPromise: Promise<void> | null = null
@@ -86,7 +86,12 @@ function getUpdateCheckOptions() {
   return proxy ? { proxy } : undefined
 }
 
-async function setPendingUpdate(next: Update | null, proxyKey: string | null) {
+function getUpdateHost(): DesktopHost | null {
+  const host = getDesktopHost()
+  return host.capabilities.updates ? host : null
+}
+
+async function setPendingUpdate(next: DesktopUpdate | null, proxyKey: string | null) {
   const previous = pendingUpdate
   pendingUpdate = next
   pendingUpdateProxyKey = next ? proxyKey : null
@@ -124,7 +129,7 @@ export const useUpdateStore = create<UpdateStore>((set, get) => ({
   shouldPrompt: false,
 
   initialize: async () => {
-    if (!isTauriRuntime()) return
+    if (!getUpdateHost()) return
     if (!startupCheckPromise) {
       startupCheckPromise = (async () => {
         await new Promise((resolve) => setTimeout(resolve, 5000))
@@ -138,7 +143,8 @@ export const useUpdateStore = create<UpdateStore>((set, get) => ({
   },
 
   checkForUpdates: async ({ silent = false, autoDownload = true } = {}) => {
-    if (!isTauriRuntime()) return null
+    const host = getUpdateHost()
+    if (!host) return null
     if (downloadPromise && get().status === 'downloading' && pendingUpdate) return pendingUpdate
 
     set((state) => ({
@@ -148,9 +154,8 @@ export const useUpdateStore = create<UpdateStore>((set, get) => ({
     }))
 
     try {
-      const { check } = await import('@tauri-apps/plugin-updater')
       const updateProxyKey = getUpdateProxyKey()
-      const update = await check(getUpdateCheckOptions())
+      const update = await host.updates.check(getUpdateCheckOptions())
       await setPendingUpdate(update, updateProxyKey)
 
       const checkedAt = Date.now()
@@ -214,7 +219,7 @@ export const useUpdateStore = create<UpdateStore>((set, get) => ({
   },
 
   downloadUpdate: async () => {
-    if (!isTauriRuntime()) return
+    if (!getUpdateHost()) return
 
     let update = pendingUpdate
     if (update && pendingUpdateProxyKey !== getUpdateProxyKey()) {
@@ -332,7 +337,8 @@ export const useUpdateStore = create<UpdateStore>((set, get) => ({
   },
 
   installUpdate: async () => {
-    if (!isTauriRuntime()) return
+    const host = getUpdateHost()
+    if (!host) return
 
     let update = pendingUpdate
     if (update && pendingUpdateProxyKey !== getUpdateProxyKey()) {
@@ -352,9 +358,6 @@ export const useUpdateStore = create<UpdateStore>((set, get) => ({
       }
       if (!pendingUpdateDownloaded) return
 
-      const { invoke } = await import('@tauri-apps/api/core')
-      const { relaunch } = await import('@tauri-apps/plugin-process')
-
       set((state) => ({
         ...state,
         status: 'installing',
@@ -364,7 +367,7 @@ export const useUpdateStore = create<UpdateStore>((set, get) => ({
       }))
 
       prepareInstallAttempted = true
-      await invoke('prepare_for_update_install')
+      await host.updates.prepareInstall()
       await update.install()
 
       set((state) => ({
@@ -373,12 +376,11 @@ export const useUpdateStore = create<UpdateStore>((set, get) => ({
         progressPercent: 100,
       }))
 
-      await relaunch()
+      await host.updates.relaunch()
     } catch (error) {
       if (prepareInstallAttempted) {
         try {
-          const { invoke } = await import('@tauri-apps/api/core')
-          await invoke('cancel_update_install')
+          await host.updates.cancelInstall()
         } catch {
           // Best effort: keep the update prompt recoverable even if native reset fails.
         }