`t.run_action` causes the provider to run immediately, rather than "in order" on the resource stack.  This ensures that the template is created and `supervisorctl update` is called prior to the next resource on the stack.  In my case, if I have a:
`supervisor_service 'my service' do
  action [:enable, :start]
end`

The `enable` action was running and creating the template resource, but not running it.  Then the `start` action would kick off and fail because the file was not yet there (since the template hadn't run yet).  I *thought* that all resources created within a provider were inserted directly into the resource stack (rather than added to the end), but that does not appear to be what is happening here.