[BUG] Desktop update resets model to Opus 4.6 Legacy (200k) — previously absent from picker, now silently set as default

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code

What's Wrong?

After a Desktop app auto-update on May 6, all new Code tab sessions default to claude-opus-4-6 (200k Legacy) instead of retaining the user's previous model preference. This 200k variant was not even visible in the Code tab model picker before this update — it only existed briefly in an earlier version before Opus 4.7 was released.

The user's ~/.claude/settings.json has "model": "claude-opus-4-6[1m]" set explicitly, but the Desktop app ignores this due to PROVIDER_MANAGED_BY_HOST (see #50037). There is no way to configure a persistent default model in the Desktop app.

Timeline (from session metadata)

| Date (UTC) | Model | Notes |
|---|---|---|
| Apr 30 – May 6 04:37 | claude-opus-4-6[1m] or claude-opus-4-7[1m] | All 77 sessions used 1M variants |
| May 6 ~11:05 | — | Desktop auto-update (beforeQuitForUpdate in main log) |
| May 6 14:19 – May 8 13:01 | claude-opus-4-6 | All 14 sessions switched to Legacy 200k |
| May 8 16:01 | claude-opus-4-6[1m] | Manually switched via /model |

92 sessions total: 77× 1M, 15× Legacy — the Legacy sessions begin exactly after the auto-update and continue for every new session until manual intervention.

What Should Happen

1. Desktop updates should not reset the user's model preference
2. settings.json model field should be respected (currently stripped by PROVIDER_MANAGED_BY_HOST)
3. At minimum, the picker should persist the last-selected model across sessions

Additional Context

• /stats shows Favorite Model = Opus 4.7 (by message count), yet the default was set to a model the user never actively chose

<img width="121" height="52" alt="Image" src="https://github.com/user-attachments/assets/912c8506-3ef5-46ba-971c-0a8d3cc1a639" />

• The 200k Legacy variant was not in the picker before — it appeared after the update AND became the default simultaneously

<img width="225" height="406" alt="Image" src="https://github.com/user-attachments/assets/82910c22-5188-4f9a-a957-60445054223a" />

• Related: #49689 (4.6 previously removed from picker), #50037 (env var model overrides silently stripped in Desktop)

Environment

• Claude Desktop: 1.6259.1 → 1.6608.0 (updated May 9)
• Claude Code engine: 2.1.128
• macOS (Darwin 24.6.0)
• Plan: Max