Gitea 1.27's MergePullRequestOption has merge_title_field, not merge_message_title; an unknown field is dropped without an error, so a custom merge title never took effect. The tool's argument keeps its name. The new test checks the field name on the wire (the existing fake never did). Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01SZkhi49hfeSqBp5aZJNXsM