[BUG] can no longer sync to claude code sessions via mobile

### Preflight Checklist

- [x] I have searched [existing issues](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20state%3Aopen%20label%3Abug) and this hasn't been reported yet
- [x] This is a single bug report (please file separate reports for different bugs)
- [x] I am using the latest version of Claude Code

### What's Wrong?

Sync broke for sessions created after ~2:29 AM on 2026-09-15 (Eastern) — everything before that syncs fine, everything since (8+ sessions) does not appear on mobile.
All previously-synced sessions now show as "disconnected" in the mobile app.
Tried: full desktop app quit/relaunch, mobile sign-out/sign-in, no VPN. None restored sync.
Desktop app has an update staged (Claude 2.110.0) that is not installing even after relaunch — same stagedAt timestamp before and after restart, and no new CLI binary was pulled down (still on 2.1.270 from 2026-09-14).

### What Should Happen?

I should be able to sync to the sessions remotely like I had previously been doing.
New Claude Code sessions created on desktop should sync to the Claude mobile app within a short time of being created, and sessions that were previously syncing should remain connected and viewable on mobile — not silently stop appearing or flip to "disconnected."

### Error Messages/Logs

```shell

```

### Steps to Reproduce

Steps to Reproduce:

Use Claude Code normally across multiple sessions on desktop (Windows) — sessions sync to the Claude mobile app as expected.
At some point between 2:29 AM and 8:13 AM ET on 2026-09-15, new sessions stop appearing on the mobile app.
Continue creating new Claude Code sessions on desktop as normal (8 created since the cutoff).
Open the Claude mobile app — none of the sessions from step 3 appear. All previously-synced sessions now show as "disconnected."
Attempted fixes, none resolved it:
Fully quit and relaunch the desktop app
Sign out and back into the mobile app
Uninstall/reinstall the mobile app
Confirmed same account on both, no VPN involved

### Claude Model

Sonnet (default)

### Is this a regression?

Yes, this worked in a previous version

### Last Working Version

Claude Code CLI version 2.1.270

### Claude Code Version

Claude Code CLI version 2.1.270

### Platform

Anthropic API

### Operating System

Windows

### Terminal/Shell

Other

### Additional Information

all of this is occurring in the claude desktop app for windows.

No files, tests, or code entry points are named. Start by reproducing the Windows desktop-to-mobile sync failure with Claude Code CLI 2.1.270, comparing sessions created before and after the reported 2:29 AM ET cutoff. Done means new sessions appear on mobile and previously synced sessions no longer show as disconnected.

Written by the indexing model from the issue text.