[Feature Request] Support extended context window option for opusplan execution

Bug Description
eature Request: opusplan with 1M context option

Request: Allow combining opusplan with extended context window

• Plan Mode: Opus 4.5
• Execution: Sonnet 4.5 with 1M context

Suggested syntax: "opusplan[1m]" or similar

Use case: Complex planning with Opus quality + large codebase analysis with 1M context during execution

Environment Info

• Platform: linux
• Terminal: tmux
• Version: 2.0.76
• Feedback ID: 6768eed3-2f1b-4291-8a16-a72c7ac5b5bb

Errors

[{"error":"Error: NON-FATAL: Lock acquisition failed for /home/y_suzuki/.local/share/claude/versions/2.0.76 (expected in multi-process scenarios)\n    at W3$ (/$bunfs/root/claude:2427:2165)\n    at TTA (/$bunfs/root/claude:2427:1885)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-01-06T02:06:34.787Z"},{"error":"Error: Request was aborted.\n    at makeRequest (/$bunfs/root/claude:798:3940)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-01-06T02:15:00.602Z"}]