Desktop Code tab uses 200k context instead of 1M on Max plan (Windows)

Bug Description

The Claude Desktop Code tab does not activate the 1M context window for Opus 4.6 on a Max plan. It shows claude-opus-4-6 with 200k context, while the terminal CLI on the same machine correctly shows claude-opus-4-6[1m] with 1M context.

Steps to Reproduce

1. Open Claude Desktop (Windows) → Code tab
2. Send a message, then run /context
3. Observe: claude-opus-4-6 · 200k tokens
4. Open a terminal, run claude, then /context
5. Observe: claude-opus-4-6[1m] · 1000k tokens

Expected Behavior

The Desktop Code tab should use claude-opus-4-6[1m] with 1M context on Max plans, matching the terminal CLI behavior.

Environment

• Platform: Windows 11 Pro (10.0.26200)
• Claude Desktop version: Latest (Code tab)
• Claude CLI version: 2.1.78
• Plan: Claude Max
• Model shown in Desktop Code tab: claude-opus-4-6 (200k)
• Model shown in terminal CLI: claude-opus-4-6[1m] (1M)

Troubleshooting Attempted

• Cleared Desktop app cache and session storage → no change
• Restarted Desktop app → no change
• Removed ANTHROPIC_DEFAULT_OPUS_MODEL env override from settings.json → no change
• Terminal CLI works correctly with 1M — issue is isolated to the Desktop Code tab

Additional Context

The model dropdown at the bottom of the Desktop Code tab shows "Opus 4.6" with no option for the 1M variant. On Max plans, 1M should be the default automatically.