Enforce merge trains

In previous versions of GitLab, you couldn't stop merges from bypassing the train. Both the option to merge immediately and the REST API could skip merge train protections without restriction. For teams running high-velocity monorepos, a single merge that skips the train can cancel and restart every in-progress pipeline, multiplying CI costs and straining infrastructure.

Now you can enforce merge train usage across the UI and API with a single project-level setting, preventing bypasses that cancel and restart in-progress pipelines. Owners and Administrators can still override the setting when needed.