[FEATURE] Desktop (Windows): surface Check for Updates on sign-in screen and About dialog; update should work when sign-in fails on a stale client

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

An out-of-date Claude Desktop for Windows build stopped letting me sign in at all. Nothing in the app told me the client was too old, and nothing on the sign-in screen offered a way to update. The only manual update control is buried under the hamburger menu -> Help -> Check for Updates, which is not discoverable when you are stuck on a login screen, and the About dialog shows the version and date with no update action next to it.

Because the app could not authenticate, its silent background updater apparently never ran either, so the "it updates itself" design failed exactly when it was needed most. I ended up rebuilding the Windows machine before discovering the app was simply stale.

Proposed Solution

• When sign-in fails because the client is too old (or the server rejects the client version), say so explicitly and show an Update now button on the sign-in screen itself.
• Surface Check for Updates in the About dialog next to the version number, and on the sign-in screen, not only under Help.
• Have the updater run and be usable before authentication, so an unauthenticated or stale client can still pull the current build.
• Show the currently installed version and "latest available" side by side so the user can tell at a glance whether they are behind.

Alternative Solutions

Downloading a fresh installer from claude.ai/download and installing over the top works, but nothing in the app points you there. winget upgrade does not apply to the sideloaded MSIX package.

Priority

High - Significant impact on productivity

Feature Category

Other

Use Case Example

1. Launch Claude Desktop on Windows after a few weeks away.
2. Sign-in fails repeatedly with no indication that the client version is the cause.
3. With this feature, the sign-in screen would say the app is out of date and offer an Update button.
4. This would have saved a full machine rebuild that turned out to be unnecessary.

Additional Context

• Windows 11 Home 10.0.26200
• Claude Desktop installed as sideloaded MSIX (SignatureKind: Developer), now on 2.2553.1 (2026-09-18) which is current
• Related: #91482 (MSIX auto-update leaves package unlaunchable) shows the background updater is already a fragile single point of failure; a visible, pre-auth update path would mitigate both problems.