[Bug] `CLAUDE_CODE_SUBAGENT_MODEL` env variable causes plugin agent return 404 errors

Bug Description

When CLAUDE_CODE_SUBAGENT_MODEL env is set in the user's settings, it causes plugin agents to return 404 errors.

Response:
       API Error: 404 {"type":"error","error":{"type":"not_found_error","message":"model: sonnet"},"request_id":"req_011CU8sqmcG1yPDdCE2HBtXg"}

Environment Info

• Platform: darwin
• Terminal: xterm-256color
• Version: 2.0.15
• Feedback ID: fdd70d8e-c582-4f67-a6c0-f0642b1684fa