Allow configuring different models for plan mode vs execution mode

Problem

Users on Max/Team Premium plans want to conserve their Opus budget by using it for high-value tasks (planning, architecture, complex debugging) while using Sonnet for straightforward execution (writing code, editing files, running commands).

Currently there's no way to configure this — you must manually run /model to switch between phases of work, which is easy to forget and breaks flow.

Proposed solution

Allow users to configure separate model preferences for different modes:

{
  "planModel": "opus",
  "executeModel": "sonnet"
}

When entering plan mode (via /plan or Shift+Tab), Claude Code would automatically use the planModel. When exiting plan mode and executing, it would switch to executeModel.

Alternatives considered

• Manual /model switching — works but relies on user discipline and breaks flow
• CLAUDE.md reminders — fragile, can't actually switch models
• Running two sessions — awkward and loses shared context

Impact

This would help users get the most value from their weekly Opus budget by automatically routing high-reasoning tasks to Opus and routine execution to Sonnet, without any manual intervention.

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