Claude Desktop (Windows, packaged/MSIX): "Launch at login" toggle does not persist

**Product**: Claude Desktop for Windows, packaged install (`Claude_1.24012.9.0_x64__pzs8sxrjxfjjc`)

**Steps to reproduce**:
1. Open Settings → enable "Launch Claude at login" (auto-start)
2. Close Settings
3. Reopen Settings → toggle shows OFF again

**Technical findings**:
- The `HKCU\Software\Microsoft\Windows\CurrentVersion\Run\Claude` value (pointing directly at the versioned `app\Claude.exe` path) disappears shortly after being set — enabling the toggle does not leave a persistent registration.
- The AppX manifest declares a `windows.startupTask` extension (`TaskId="ClaudeStartup"`, default `Enabled="false"`), but no corresponding `StartupApproved\StartupList` entry is ever created, suggesting the app isn't actually using the packaged StartupTask API and instead writes/removes a plain Run key that doesn't stick.
- Workaround: manually registering `HKCU\...\Run\Claude` = `explorer.exe shell:AppsFolder\Claude_pzs8sxrjxfjjc!Claude` restores auto-start reliably (version-independent, survives app updates).

**Expected behavior**: the toggle should remain ON and Claude should launch automatically at Windows sign-in.

Start by inspecting the packaged AppX manifest's windows.startupTask declaration and the registration behavior around HKCU\...\Run and StartupApproved\StartupList. Done means the Launch at login toggle remains enabled after reopening Settings and Claude launches automatically at Windows sign-in, including after an app update.

Written by the indexing model from the issue text.