I couldn't find a solution. It seems like the .as file extension is registered in the system as "AppleSingle Archive". In iCloud Drive on OS X it has a file icon that is similar to a .zip file.

So it looks like iCloud Drive treats it as a file archive and doesn't allow it to be opened as a text file.

You can enable this feature in system preferences. See http://www.textasticapp.com/mac/manual/lessons/Why_aren_t_documents_and_windows_restored_when_I_re-open_Textastic.html

I see. I'll consider it.

When editing a file in Textastic on iPhone, only a transparent status bar is shown. This allows you to scroll to the top with one tap on the status bar and to the bottom of the file with a second tap.

Is this status bar already too much?

This seems to be a global setting that cannot be disabled per app. Also, some users may want to have it, for example if editing comments or Markdown documentation.

You can change this by disabling the following setting in your device's settings:

General -> Keyboard -> "." Shortcut

Here is a screenshot: