## Summary This issue tracks the rollout of the `merge_train_api_auto_merge_fallback` feature flag. Related merge request: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/226033 ## What does this feature flag do? When enabled, the merge train API endpoint `POST /projects/:id/merge_trains/merge_requests/:iid?auto_merge=true` will fall back to the `merge_train` strategy when the `add_to_merge_train_when_checks_pass` strategy is unavailable (i.e., when all merge preconditions are already fulfilled). Without this flag, the API returns a 400 Bad Request when `auto_merge=true` is passed and the pipeline has already succeeded, because it hardcodes the `add_to_merge_train_when_checks_pass` strategy which reports itself as unavailable when there are no checks to wait for. ## Owners - Team: `group::code review` - Feature flag name: `merge_train_api_auto_merge_fallback` - Type: `gitlab_com_derisk` ## Rollout plan ### Rollout Steps - [ ] Enable on staging (`/chatops run feature set merge_train_api_auto_merge_fallback true --staging`) - [ ] Test on staging - [ ] Enable on GitLab.com for a percentage of actors - [ ] 25% (`/chatops run feature set merge_train_api_auto_merge_fallback 25 --actors`) - [ ] 50% (`/chatops run feature set merge_train_api_auto_merge_fallback 50 --actors`) - [ ] 100% (`/chatops run feature set merge_train_api_auto_merge_fallback 100 --actors`) - [ ] Monitor for errors/regressions - [ ] Enable by default (set `default_enabled: true` in YAML) - [ ] Remove the feature flag and legacy code path