Commit signing fails with 400 "source: Field required

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?

Commit signing is broken. Every commit attempt fails with:

signing server returned status 400: {"type":"error","error":{"type":"invalid_request_error","message":"source: Field required"}}

The /tmp/code-sign binary returns this error when git tries to sign commits.
Request IDs: req_011CYko4MppKmzubvYukeydn, req_011CYknyPgoHjYa3oSkc1HhQ

Platform: Claude Code on the web

Every commit attempt fails. The signing server returns a 400 error, making it impossible to commit any changes in Claude Code on the web.

What Should Happen?

Commits should be signed and created successfully without errors.

Error Messages/Logs

signing server returned status 400: {"type":"error","error":{"type":"invalid_request_error","message":"source: Field required"}}

Request IDs: req_011CYko4MppKmzubvYukeydn, req_011CYknyPgoHjYa3oSkc1HhQ

Steps to Reproduce

1. Open Claude Code on the web
2. Make any change to a file in a repository
3. Ask Claude to commit the changes
4. Observe the signing error — commit fails every time

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

sonet 4.6

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

The stop hook repeatedly triggers asking to commit, but all commit attempts fail due to this signing server error. The issue appears to be on Anthropic's signing server side, not the local environment.