[BUG] >=2.1.154 breaks `--resume` with `ANTHROPIC_CUSTOM_HEADERS` set in settings.

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?

In 2.1.153 I can run claude and then claude --resume In 2.1.154, upon --resume, completion requests return:

API Error: 400 Either x-portkey-config or x-portkey-provider header is required                                                                                          

I'm using the follwing in $HOME/.claude/settings.json:

{                                                                                                                                                                        
  "env": {                                                                                                                                                               
    "ANTHROPIC_BASE_URL": "https://portkeygateway.example.com",                                                                                                          
    "ANTHROPIC_CUSTOM_HEADERS": "x-portkey-metadata: {\\"_user\\":\\"me@company.com\\",\\"tool\\":\\"claude\\"}"
  },
  "model": "@org-gcp-general-multius/anthropic.claude-opus-4-8",
  "modelOverrides": {
    "claude-haiku-4-5-20251001": "@bedrock-1/us.anthropic.claude-haiku-4-5-20251001-v1:0",
    "Opus 4.7": "@org-gcp-general-multius/anthropic.claude-opus-4-7",
    "Opus 4.8": "@org-gcp-general-multius/anthropic.claude-opus-4-8"
  },
  "alwaysThinkingEnabled": false,
  "effortLevel": "low",
  "skipDangerousModePermissionPrompt": true,
  "permissions": {
    "blockReadsOutsideWorkingDirectories": true
  }
}

What Should Happen?

--resume should work.

Error Messages/Logs

API Error: 400 Either x-portkey-config or x-portkey-provider header is required

Steps to Reproduce

1. run claude
2. type hello
3. quit
4. run claude --resume {id}
5. type hello

Claude Model

Not sure / Multiple models

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.153

Claude Code Version

2.1.282

Platform

AWS Bedrock

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Xterm

Additional Information

_No response_