feat(desktop): add Electron desktop shell over the web profile

Spawn the real dsh CLI running the web profile on loopback (OS-assigned
port), parse the printed readiness URL, and open a native window at it.
The harness and its native addons stay on the system Node ABI; the main
imports only electron and node builtins.

Co-Authored-By: Claude <noreply@anthropic.com>

apps/desktop/src/main.ts

@@ -0,0 +1,125 @@
+/**
+ * DeepSeek Harness desktop shell. The Electron main process is deliberately a
+ * thin wrapper: it spawns the real `dsh` CLI running the `web` profile on
+ * loopback (an OS-assigned port), parses the readiness URL line the profile
+ * prints, and opens a native window at that address. The harness — its Cordis
+ * plugins, webserver, static frontend dist, and WebSocket transport — is
+ * untouched and runs exactly as `dsh web` would, as a separate Node process.
+ *
+ * Keeping the harness in its own system-Node child also keeps native addons
+ * (e.g. the PTY used by the terminal capability) on the system Node ABI; the
+ * Electron main and renderer never load them.
+ * @module @deepseek-ai/dsh-desktop/main
+ */
+
+import { spawn, type ChildProcess } from 'node:child_process'
+import { createRequire } from 'node:module'
+import { resolve } from 'node:path'
+import { app, dialog, BrowserWindow } from 'electron'
+
+import { LOOPBACK_HOST, parseReadyPort } from './ready-port.ts'
+
+const require = createRequire(import.meta.url)
+
+/** Spawn's node executable: a bundled one when the app is packaged, else PATH. */
+function nodeExecutable(): string {
+  if (process.env.DSH_NODE) return resolve(process.env.DSH_NODE)
+  return 'node'
+}
+
+/** The dsh CLI entry to spawn: an explicit dev override, else the built bin. */
+function dshEntry(): string {
+  if (process.env.DSH_ENTRY) return resolve(process.env.DSH_ENTRY)
+  return require.resolve('@deepseek-ai/dsh/lib/bin.js')
+}
+
+/** Open the harness window, wired to a live loopback port. */
+function openWindow(url: string): BrowserWindow {
+  const win = new BrowserWindow({
+    width: 1280,
+    height: 840,
+    title: 'DeepSeek Harness',
+    webPreferences: {
+      // The UI is a remote SPA served by the harness; keep Node out of it.
+      nodeIntegration: false,
+      contextIsolation: true,
+      sandbox: true,
+    },
+  })
+  void win.loadURL(url)
+  return win
+}
+
+/** A spawned harness and the window bound to it. */
+interface Session {
+  child: ChildProcess
+  url: string
+  window: BrowserWindow
+}
+
+let session: Session | undefined
+
+/** Fail loudly in the shell when the harness cannot start. */
+function reportFatal(error: unknown): void {
+  void dialog.showErrorBox('DeepSeek Harness failed to start', String(error))
+  app.exit(1)
+}
+
+/** Spawn the web profile and open a window once its URL is known. */
+function startSession(): void {
+  const entry = dshEntry()
+  const child = spawn(nodeExecutable(), [entry, '--profile', 'web', '--host', LOOPBACK_HOST, '--port', '0'], {
+    stdio: ['ignore', 'pipe', 'inherit'],
+    env: { ...process.env, DSH_TELEMETRY_DISABLED: '1' },
+  })
+  let settled = false
+  let buffered = ''
+  child.stdout.setEncoding('utf8')
+  child.stdout.on('data', (chunk: string) => {
+    buffered += chunk
+    // Only a COMPLETE line is trustworthy: the readiness port is not matched
+    // until its newline arrives, so a chunk ending mid-number cannot open a
+    // window at a truncated port.
+    let newline: number
+    while ((newline = buffered.indexOf('\n')) !== -1) {
+      const line = buffered.slice(0, newline).trimEnd()
+      buffered = buffered.slice(newline + 1)
+      if (settled) return
+      const port = parseReadyPort(line)
+      if (port === undefined) continue
+      settled = true
+      const url = `http://${LOOPBACK_HOST}:${String(port)}`
+      session = { child, url, window: openWindow(url) }
+      return
+    }
+  })
+  child.on('error', (error) => {
+    if (!settled) reportFatal(`Could not start the harness:\n${error.message}`)
+  })
+  child.on('exit', (code) => {
+    if (!settled) {
+      settled = true
+      reportFatal(`The harness exited before serving (code ${String(code)}). Is the frontend dist built?`)
+    } else if (app.isReady()) {
+      app.quit()
+    }
+  })
+}
+
+app.whenReady().then(() => {
+  startSession()
+  app.on('activate', () => {
+    if (BrowserWindow.getAllWindows().length === 0 && session !== undefined) {
+      session.window = openWindow(session.url)
+    }
+  })
+})
+
+app.on('window-all-closed', () => {
+  // The harness owns the window lifecycle; on macOS keep the app until the
+  // user quits, elsewhere exit when every window is gone.
+  if (process.platform !== 'darwin') {
+    session?.child.kill()
+    app.quit()
+  }
+})