queue.register { step: 'postproc' },
  # attributes that comprise the job ID; requests with identical IDs are merged into a single job
  id: ['project', 'step']

  # merge oldRequest into newRequest; by default, all array attributes are merged;
  # ID attributes are guaranteed to be equal
  merge: (newRequest, oldRequest) ->

  execute: (request, emit) ->
    @add type: 'warning', file: '/foo'
    @done null

queue.add { project: @project.id, step: 'postproc', paths: paths }

# value triggering (remove existing jobs with this scope, then add new ones)
queue.update { project: @project.id, step: 'postproc' }, { paths: [paths] }
queue.update { project: @project.id, step: 'compile' }, [{src: '/path/to/src'}, {src: '/another/src'}]

queue.cancel { project: @project.id }