Model picker doesn't show all available models for Max plan

Bug Description

The /model picker in Claude Code does not display all available models for the user's subscription plan. Specifically, Sonnet 4.6 (claude-sonnet-4-6) was missing from the picker despite being available on a Max plan.

Steps to Reproduce

1. Authenticate with a Max plan account (claude auth status confirms subscriptionType: "max")
2. Run /model to open the model picker
3. Only Opus 4.6 is listed — Sonnet 4.6 and Haiku 4.5 are not shown

Expected Behavior

The model picker should automatically detect and display all models available for the user's subscription plan without manual configuration.

Workaround

Adding availableModels to ~/.claude/settings.json forces the models to appear:

"availableModels": [
  "claude-opus-4-6",
  "claude-sonnet-4-6",
  "claude-haiku-4-5-20251001"
]

This works but shouldn't be necessary — the picker should resolve available models from the user's plan automatically.

Environment

• Claude Code version: 2.1.80
• Auth method: claude.ai (OAuth)
• Subscription: Max
• OS: macOS (Darwin 25.3.0)