ActionView::Template::Error ( isn't precompiled): on heroku cedar
===

I've a number of SO questions about this issue of heroku cedar and the Rails asset pipeline, and I've tried a number of solutions, but none of them works, and it's probably because the issue I'm having has a wrinkle that I've not seen anywhere else.

My app uses Rails 3.2.6 and I've deployed it on Heroku's cedar stack. It's a basic search app that searches an attached postgres db via websolr, so when you load the index (index#index) without params[:q].present? you get a search box, and this works fine. But when I put something in the search box and hit submit, and index#index loads again but this time tries to display the results, I get:

    app[web.1]: Completed 500 Internal Server Error in 440ms
    app[web.1]: 
    app[web.1]: ActionView::Template::Error ( isn't precompiled):
    app[web.1]:     12:         - @results.each do |result|
    app[web.1]:     13:           %li
    app[web.1]:     14:             %div
    app[web.1]:     15:               = image_tag result.image
    app[web.1]:     16:             %div
    app[web.1]:     17:               = result.title
    app[web.1]:     18:             %div
    app[web.1]:   app/views/index/index.html.haml:15:in `block in _app_views_index_index_html_haml___4350601325072829986_32734540'
    app[web.1]:   app/views/index/index.html.haml:12:in   _app_views_index_index_html_haml___4350601325072829986_32734540'

What's bizarre about my particular case vs. others I've seen is the following line:

    ActionView::Template::Error ( isn't precompiled):
With all of the other questions like this I've seen, there's a css file in the parenthesis, i.e. ("foo.css" isn't precompiled), or in my case it seems like it should be ("index.css" isn't precompiled). But here it's just blank!

This is my staging deploy that I'm trying to get to work, so I've tried running
   RAILS_ENV=staging rake assets:precompile (then committing the results, of course), but that doesn't fix it. I even tried stripping out the in the view (notice the lack of any actual styling there). Nothing works, and I'm at a loss. Any help would be greatly appreciated.

For reference, here is my gemfile:

    source 'https://rubygems.org'

    gem 'rails', '3.2.6'
    gem 'pg'
    gem 'haml-rails'
    gem 'mongoid'
    gem 'sunspot_rails', '~> 1.3.0'
    gem 'sunspot_solr'


    # Gems used only for assets and not required
    # in production environments by default.
    group :assets do
      gem 'sass-rails',   '~> 3.2.3'
      gem 'coffee-rails', '~> 3.2.1'
      gem 'uglifier', '>= 1.0.3'
    end

    gem 'jquery-rails'

    group :development do
      gem 'heroku_san'
      gem 'annotate'
      gem 'awesome_print'
    end

    group :development, :test do
      gem 'rspec-rails'
    end

    group :test do
      gem 'cucumber-rails', :require => false
      gem 'capybara'
      gem 'database_cleaner'
      gem 'spork'
      gem 'launchy'
    end

    group :staging, :production do
      gem 'thin'
    end

Here are the config options in my config/application.rb file:

    config.encoding = "utf-8"
    config.filter_parameters += [:password]
    config.active_support.escape_html_entities_in_json = true
    config.active_record.whitelist_attributes = true
    config.assets.enabled = true
    config.assets.version = '1.0'
    config.assets.compile = true

And here are the config options in my environments/staging.rb file:

    config.cache_classes = true
    config.consider_all_requests_local       = false
    config.action_controller.perform_caching = true
    config.serve_static_assets = false
    config.assets.compress = true
    config.assets.compile = true
    config.assets.precompile += ['index.css.scss']
    config.assets.digest = true
    config.i18n.fallbacks = true
    config.active_support.deprecation = :notify
