[BUG] Commit signing fails with 400 "missing source" in remote planning sessions, breaking PR handoff

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 Code on the web (remote planning session), the implementation phase fails to commit because the commit signing server returns a 400 missing source error. This breaks the intended plan → implement → PR workflow, leaving changes stranded in the remote environment with no automated way to get them back to the local terminal.

What Should Happen?

When using Claude Code on the web (remote planning session), the implementation phase fails to commit because the commit signing server returns a 400 missing source error. This breaks the intended plan → implement → PR workflow, leaving changes stranded in the remote environment with no automated way to get them back to the local terminal.

Steps to reproduce:

From a local Claude Code terminal session, trigger a remote planning session (Claude Code on the web)
Approve the plan
Claude attempts to implement the changes and commit them in the remote environment
Commit fails at the signing step
Expected behavior:
Changes are committed, pushed to a branch, and a PR is opened — which the user can then pull locally.

Actual behavior:

error: Debug: Namespace set to "git" (ignored)
Debug: Key file set to "/home/claude/.ssh/commit_signing_key.pub" (ignored, using server key)
Error: signing failed: Signing failed: signing operation failed: signing server returned status 400: {"error":{"message":"missing source","reason":"","type":"invalid_request_error"},"request_id":"req_011CaTYLjtCGS8inqudzDPkS","type":"error"}
fatal: failed to write commit object
Request ID (for server-side tracing): req_011CaTYLjtCGS8inqudzDPkS

Impact:
The entire PR handoff is blocked. Changes implemented in the remote session cannot be automatically returned to the local terminal, requiring manual workarounds (patch files, base64-encoded scripts, etc.).

Environment:

Claude Code on the web (remote planning session)
Local terminal: zsh on macOS
Repo: private GitHub repository

Error Messages/Logs

error: Debug: Namespace set to "git" (ignored)
Debug: Key file set to "/home/claude/.ssh/commit_signing_key.pub" (ignored, using server key)
Error: signing failed: Signing failed: signing operation failed: signing server returned status 400: {"error":{"message":"missing source","reason":"","type":"invalid_request_error"},"request_id":"req_011CaTYLjtCGS8inqudzDPkS","type":"error"}
fatal: failed to write commit object

Steps to Reproduce

Steps to reproduce:

From a local Claude Code terminal session, trigger a remote planning session (Claude Code on the web)
Approve the plan
Claude attempts to implement the changes and commit them in the remote environment
Commit fails at the signing step

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.119 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_