/model command: invalid 256-character error on valid aliases

Bug Report

Steps to reproduce

1. In an active Claude Code interactive session, run /model haiku
2. Observe the error response

Actual behavior

API error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"model: String should have at most 256 characters"},"request_id":"req_011CYjfCvfoLGpsvsZSNgzeb"}

Expected behavior

Model switches to Haiku 4.5 (as it does when using /model claude-haiku-4-5)

The problem

The error message is nonsensical:

• haiku is 5 characters — nowhere near 256
• The same alias works fine when spelled out as the full model ID: claude-haiku-4-5
• This suggests either:
• The validation logic is broken (rejecting valid aliases)
• The error reporting is broken (lying about why it failed)

Workaround

Use the full model ID: /model claude-haiku-4-5 (works)

Impact

Users trying to use convenient aliases get a confusing, inaccurate error message that wastes time debugging.