[Bug] --agents flag rejects full model names, only accepts aliases

Bug Description
Agents configured via the -–agents flag only accept model aliases, not full model names and fail silently if a full model name is used (e.g, claude-sonnet-4-5-20250929). This is contrary to official advice given on https://docs.claude.com/en/docs/about-claude/models/overview - "While aliases are useful for experimentation, we recommend using specific model versions (e.g., claude-sonnet-4-5-20250929) in production applications to ensure consistent behavior."

Environment Info

• Platform: darwin
• Terminal: Apple_Terminal
• Version: 2.0.35
• Feedback ID: c2fb25be-29a4-4c8e-a2d5-9fe298d13a86

Errors
Loading of CLI agents fail silently

Example

claude --agents '{                                                                                                                                                                                                           ⬡ 
  "code-reviewer": {
    "description": "Expert code reviewer. Use proactively after code changes.",
    "prompt": "You are a senior code reviewer. Focus on code quality, security, and best practices.",
    "tools": ["Read", "Grep", "Glob", "Bash"],
    "model": "claude-sonnet-4-5-20250929"
  },
  "debugger": {
    "description": "Debugging specialist for errors and test failures.",
    "prompt": "You are an expert debugger. Analyze errors, identify root causes, and provide fixes."
  }
}'

Expected response:

• 2 CLI agents load

Actual response

• 0 CLI agents load