[BUG] Claude code --resume is not properly resolving custom model IDs from settings.json

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When using claude --resume with a third-party provider (True Foundry) configured via the env block in ~/.claude/settings.json, the custom model IDs are not properly resolved. This results in a 403 error with a malformed model name. Starting a new session works fine.

What Should Happen?

--resume should load and apply the env block from settings.json the same way a new session does.

Error Messages/Logs

Please run /login · API Error: 403 User [REDACTED] is not
authorized to access model claude-opus-4-6/undefined or model does not
exist

Steps to Reproduce

1. Configure a third-party provider (e.g., True Foundry) using the env block in ~/.claude/settings.json with custom ANTHROPIC_DEFAULT_*_MODEL values and ANTHROPIC_BASE_URL
2. Start a new session with claude — works correctly
3. Exit the session
4. Resume with claude --resume — fails with 403 and malformed model name (claude-opus-4-6/undefined)

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.145 (Claude Code)

Platform

Other

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

_No response_