how do I configure paperclip/s3 for comfortable mexican sofa?

Question

not getting any results in a custom model in a comfy-enabled app. I've got a model that has a Comfortable Mexican Sofa backend, and it includes a file that is to be uploaded to AWS. There's a bucket in place, and I've configured various points:

aws.yml:

development:
  access_key_id: 'xxxxxxxxx'
  secret_access_key: 'xxxxxxxxx'

development.rb:

config.paperclip_defaults = {
  :storage => :s3,
  :bucket => 'somerton'
}

model (Drawing.rb):

has_attached_file :image

validates_attachment_content_type :image, content_type: /\Aimage\/.*\Z/

I generated the model using the paperclip generator, and a the schema is

schema.rb:

create_table "drawings", force: :cascade do |t|
  t.string   "url"
  t.string   "title"
  t.string   "description"
  t.datetime "created_at"
  t.datetime "updated_at"
  t.string   "image_file_name"
  t.string   "image_content_type"
  t.integer  "image_file_size"
  t.datetime "image_updated_at"
end

The form partial has been modified to include a file input, and is multipart:

_form.html.haml:

= form.text_field :url
= form.text_field :title
= form.text_field :description
= form.file_field :image

= form.form_group :class => 'form-actions' do
  = form.submit :class => 'btn btn-primary'

Anyone see the obvious problem I'm missing? (yes, gem is installed):

gem "paperclip", "~> 4.3" # uploads
gem 'aws-sdk' # allow use of aws for upload storage

When I update a record, I can select a file using the file input, but the columns for the related components are empty:

--- !ruby/object:Drawing
raw_attributes:
id: 1
url: blah blah
title: My new thing
description: Dog's Breakfast
created_at: '2015-10-15 20:02:03.848104'
updated_at: '2015-10-15 20:02:33.344581'
image_file_name: 
image_content_type: 
image_file_size: 
image_updated_at: 
...