[Bug] Plan mode triggers 'Auto mode is unavailable for your plan' on Max subscription

Description

On Claude Max plan, attempting to enter Plan mode via Shift+Tab or /plan command triggers the error: "Auto mode is unavailable for your plan"

Plan mode should not require Auto mode permissions, but the mode switching logic appears to check Auto mode eligibility even when Plan mode is selected.

Steps to Reproduce

1. Log in with a Claude Max account
2. Start a session: claude
3. Try either:

• Press Shift+Tab to cycle to Plan mode → Error appears
• Type /plan <any prompt> → Same error

Expected Behavior

Plan mode should activate without Auto mode restrictions, as it is a read-only mode.

Actual Behavior

Error message: "Auto mode is unavailable for your plan"

Workaround

Starting the session with the CLI flag works correctly:

claude --permission-mode plan

Environment

• Claude Code version: 2.1.92
• Subscription: Claude Max
• Model: claude-opus-4-6
• Platform: macOS (Darwin 25.3.0)
• Tested in: CLI and VS Code extension (both reproduce)