[BUG] Cowork VM: recurring auth 500 on macOS — requires rm -rf vm_bundles to recover (~20 occurrences)

Description

Cowork VM repeatedly fails to start with authentication server error 500. The "Try again" button never works. The only recovery is:

rm -rf ~/Library/Application\ Support/Claude/vm_bundles/claudevm.bundle/

...followed by fully quitting and relaunching Claude Desktop. This forces a re-download of the ~11GB VM bundle image. The fix works for one session, then the error recurs on the next Cowork session start.

This has happened approximately 20 times over the past several weeks.

Error Message

Something went wrong Unable to start session. The authentication server returned an error (500). You can try again. You can restart the conversation from an earlier message.

Environment

• Platform: macOS (Apple Silicon M4 Pro)
• Claude Desktop: Max plan
• Claude Code version: 2.1.78+
• macOS version: Darwin 25.3.0

Steps to Reproduce

1. Open Claude Desktop
2. Switch to Cowork tab
3. Start a new task or select an existing one
4. Error dialog appears: "Unable to start session. The authentication server returned an error (500)."
5. Click "Try again" — same error every time
6. Only recovery: quit app → rm -rf ~/Library/Application Support/Claude/vm_bundles/claudevm.bundle/ → relaunch

Expected Behavior

Cowork VM should start reliably, or at minimum the "Try again" button should work without requiring manual bundle deletion.

Observations

• Chat and Code modes work fine — only Cowork is affected (consistent with #33216 which noted separate OAuth client IDs for Cowork vs Chat/Code)
• The error is identical to closed issue #33216 (Windows), but this is macOS and the issue persists/recurs
• The claudevm.bundle/ directory contains an 11GB rootfs.img + 6.6GB sessiondata.img — forcing users to re-download ~20GB per recovery is expensive
• The bundle's efivars.fd and sessiondata.img update on every session, suggesting stale session state may trigger the auth failure
• Frequency: nearly every time Cowork is used after the machine has been idle or after a previous Cowork session ends

Workaround

Shell function that automates the recovery:

fix-cowork() {
  osascript -e 'tell application "Claude" to quit' 2>/dev/null
  sleep 2
  rm -rf ~/Library/Application\ Support/Claude/vm_bundles/claudevm.bundle/
  open -a Claude
}

Related Issues

• #33216 — Same auth 500 error on Windows (closed)
• #42614 — "Cannot Start for a Month" (open, Windows)