The parent-child pipeline MVC was implemented in https://gitlab.com/gitlab-org/gitlab/issues/16094, which allowed a parent (originating) pipeline to trigger child pipelines that could run concurrently. The MVC issue (https://gitlab.com/gitlab-org/gitlab/issues/16094) was a minimal iteration as a starting point. This epic is intended to capture the additional follow-up issues to make the feature better, such as but not limited to: * when canceling/deleting a parent pipeline this should cascade to child pipelines * enable errors on downstream pipelines to be visible to upstream pipelines (known issue that is more obvious with parent-child pipelines) * visibility of child pipelines and trigger jobs via API