message: Frozen w milestone and postable editability
diff: <WorkflowThread::Postable
  @postable={{postable}}
  @previous={{object-at milestone.visiblePostables (dec j)}}
  - @frozen={{this.frozen}}
  + @frozen={{or this.frozen (not milestone.isEditable) (not postable.isEditable)}}
  @index={{j}}
  data-test-milestone={{i}}
  />
  