Rack request['param']= not being honored?

[Neil <neil.matatall@gmail.com>]

Based on the docs and https://groups.google.com/group/rack-devel/browse_thread/thread/7a06ab0518ac54c1
this code should set a request parameter available to the controller.

          request['blog_post_id'] = 'test'
          Rails.logger.info("Routing website request
#{request.path_info} | #{request.params}")
          env = request.env
          return @app.call(env)

The logging statement produces:
Routing website request parent/1/nested/1 | {"blog_post_id"=>"test"},

So it is being set, and passed into @app.call, but when my Rails
action starts, the blog_post_id is curiously missing:

Started GET "/parent/1/nested/1" for 127.0.0.1 at 2011-08-08 15:12:03
-0700
  Processing by Controller#show as HTML
  Parameters: {"parent"=>"1", "id"=>"1"}

The blog_post_id is missing from my params hash.  I think this was
working at some point, any idea why my param is disappearing?

Rails 3.1, rack 1.3.2