/model opusplan does not use Opus 4.6 for planning phase

Description

The /model opusplan setting is expected to use claude-opus-4-6 for planning and claude-sonnet-4-6 for execution. However, it currently maps entirely to claude-sonnet-4-6 for both phases.

Expected behavior

• Planning phase → claude-opus-4-6
• Execution phase → claude-sonnet-4-6

Actual behavior

• Both phases → claude-sonnet-4-6

Steps to reproduce

1. Run /model opusplan
2. Observe output: Set model to opusplan (claude-sonnet-4-6)
3. Enter /plan mode — still uses Sonnet 4.6, not Opus 4.6

Environment

• Platform: macOS (Darwin 25.3.0)
• Claude Code CLI