feat(desktop): redirect writable data to ~/.cow for packaged app

Introduce get_data_root() driven by the COW_DATA_DIR env var so the
packaged desktop build stores config.json, run.log, user data and
WeChat credentials under ~/.cow — surviving app updates and keeping the
app bundle read-only. Source deployments leave COW_DATA_DIR unset and
fall back to the repo root, so existing behavior is unchanged.

desktop/src/main/python-manager.ts

@@ -1,9 +1,15 @@
 import { ChildProcess, spawn } from 'child_process'
 import { EventEmitter } from 'events'
 import path from 'path'
+import os from 'os'
 import fs from 'fs'
 import http from 'http'
 
+// Writable data dir for the packaged app (config.json, run.log, user data).
+// Lives in the user's home so it survives app updates and avoids writing into
+// the read-only app bundle. Source/dev runs keep using the repo CWD instead.
+const COW_DATA_DIR = path.join(os.homedir(), '.cow')
+
 export class PythonBackend extends EventEmitter {
   private process: ChildProcess | null = null
   private backendPath: string
@@ -23,6 +29,25 @@ export class PythonBackend extends EventEmitter {
     return this.status
   }
 
+  /**
+   * Locate the packaged onedir backend executable shipped with the app.
+   * Returns null when not present (e.g. during local development), so we can
+   * fall back to running app.py with a system/venv Python.
+   */
+  private findBundledBackend(): string | null {
+    const exeName = process.platform === 'win32' ? 'cowagent-backend.exe' : 'cowagent-backend'
+    const candidates = [
+      path.join(this.backendPath, 'cowagent-backend', exeName),
+      path.join(this.backendPath, exeName),
+    ]
+    for (const p of candidates) {
+      if (fs.existsSync(p)) {
+        return p
+      }
+    }
+    return null
+  }
+
   private findPython(): string {
     const venvPaths = [
       path.join(this.backendPath, '.venv', 'bin', 'python'),
@@ -40,9 +65,14 @@ export class PythonBackend extends EventEmitter {
     return process.platform === 'win32' ? 'python' : 'python3'
   }
 
-  private readPort(): number {
+  /**
+   * Resolve config.json from the given data dir to read the web port. The
+   * packaged build keeps config in COW_DATA_DIR (~/.cow); dev reads it from the
+   * repo path. Returns the default port when no config (or web_port) is found.
+   */
+  private readPort(dataDir: string): number {
     try {
-      const configPath = path.join(this.backendPath, 'config.json')
+      const configPath = path.join(dataDir, 'config.json')
       if (fs.existsSync(configPath)) {
         const config = JSON.parse(fs.readFileSync(configPath, 'utf-8'))
         if (config.web_port) {
@@ -61,7 +91,13 @@ export class PythonBackend extends EventEmitter {
     }
 
     this.status = 'starting'
-    this.port = this.readPort()
+
+    // Prefer the packaged self-contained backend (production); fall back to
+    // running app.py with a Python interpreter (local development).
+    const bundled = this.findBundledBackend()
+    // Packaged app stores writable data in ~/.cow; dev keeps it in the repo.
+    const dataDir = bundled ? COW_DATA_DIR : this.backendPath
+    this.port = this.readPort(dataDir)
 
     const alreadyRunning = await this.probeHealth()
     if (alreadyRunning) {
@@ -71,20 +107,41 @@ export class PythonBackend extends EventEmitter {
       return
     }
 
-    const pythonPath = this.findPython()
-    const appPath = path.join(this.backendPath, 'app.py')
+    let command: string
+    let args: string[]
+    let cwd: string
 
-    if (!fs.existsSync(appPath)) {
-      this.status = 'error'
-      this.emit('error', `app.py not found at ${appPath}`)
-      return
+    if (bundled) {
+      command = bundled
+      args = []
+      // The onedir bundle reads data files relative to the executable's dir.
+      cwd = path.dirname(bundled)
+      this.emit('log', `Starting bundled backend: ${bundled}`)
+    } else {
+      const pythonPath = this.findPython()
+      const appPath = path.join(this.backendPath, 'app.py')
+      if (!fs.existsSync(appPath)) {
+        this.status = 'error'
+        this.emit('error', `app.py not found at ${appPath}`)
+        return
+      }
+      command = pythonPath
+      args = [appPath]
+      cwd = this.backendPath
+      this.emit('log', `Starting Python backend: ${pythonPath} ${appPath}`)
     }
 
-    this.emit('log', `Starting Python backend: ${pythonPath} ${appPath}`)
-
-    this.process = spawn(pythonPath, [appPath], {
-      cwd: this.backendPath,
-      env: { ...process.env, PYTHONUNBUFFERED: '1' },
+    this.process = spawn(command, args, {
+      cwd,
+      // COW_DESKTOP enables the lighter desktop runtime (no plugins, no MCP).
+      // COW_DATA_DIR (packaged only) redirects writable data to ~/.cow so the
+      // app bundle stays read-only; dev runs omit it and keep using the repo.
+      env: {
+        ...process.env,
+        PYTHONUNBUFFERED: '1',
+        COW_DESKTOP: '1',
+        ...(bundled ? { COW_DATA_DIR } : {}),
+      },
       stdio: ['pipe', 'pipe', 'pipe'],
     })