[BUG] Cowork (macOS): Max→Pro downgrade wiped ALL session history from the UI — data loss of paid work, again

Preflight Checklist

• [x] I have searched existing issues 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?

Max→Pro downgrade wiped ALL session history from the UI — data loss of paid work, again.

This is the third data-loss report of this kind (#45076, #38055) and it's still happening. This needs to be treated as a critical bug, not a stale issue.

What Should Happen?

I'm a solo developer. I used Cowork on macOS daily on the Max plan ($88+/month) for weeks of business-critical work: Apple Search Ads campaign setup, paid marketing strategy, SEO, pricing and paywall strategy for my apps.

On July 19 my scheduled downgrade from Max to Pro took effect. When I opened Cowork, my ENTIRE session history was gone from the sidebar. No warning. No error. No migration. Just gone.

What filesystem inspection shows

• Session metadata files (titles, timestamps, session IDs) still exist under ~/Library/Application Support/Claude/local-agent-mode-sessions/{vm-uuid}/{org-id}/local_*/. The UI simply no longer shows them.
• Transcript .jsonl files exist in hidden .claude/projects/ folders inside the per-session VM storage — but it is unclear whether they are complete or whether data was lost. I have no way to verify integrity, and no supported way to restore any of it into the app.
• This matches the VM re-provisioning behavior described in #38055: the app appears to abandon existing session storage instead of migrating it.

Error Messages/Logs

Steps to Reproduce

1. Use Cowork on macOS on a Max plan, accumulate sessions
2. Downgrade to Pro, let it take effect
3. Open Cowork → sidebar is empty, sessions orphaned on disk

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.148

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

1. I PAID for this work. Every one of those sessions cost Max-plan usage, and the output vanished from the product I paid for.
2. Finding out the data even partially exists required grep/find archaeology through hidden VM directories that no normal user would ever attempt. A non-technical user would simply believe everything is gone (see #55084 — they did).
3. There is no export, no backup option, and no warning before a plan change or update orphans local sessions.