Users may want to retry a build in both Swarmbucket and Buildbot lands. Buildbucket has retry API that will work for both.
https://apis-explorer.appspot.com/apis-explorer/?base=https://cr-buildbucket.appspot.com/_ah/api#p/buildbucket/v1/buildbucket.retry

Please add a button to a build page (both Swarmbucket and Buildbot modes) that calls the API.
 

Users may want to retry a build in both Swarmbucket and Buildbot lands. Buildbucket has retry API that will work for both.
https://apis-explorer.appspot.com/apis-explorer/?base=https://cr-buildbucket.appspot.com/_ah/api#p/buildbucket/v1/buildbucket.retry

Please add a retry button to a build page (both Swarmbucket and Buildbot modes) and retry last to builder page.