I have had Context enabled on a site for quite a while. Today I enabled Delta API and Delta UI, and created a delta snapshot that I wanted to use for the home page for the site. Very straightforward -- so far, so good -- great module -- thanks!

Next I went to Context, found the context I wanted, and clicked Edit. In the Reactions section, there was no option to select "Delta" as a reaction. Huh?

So I searched issues for Delta and found another one that suggested clearing the cache. That worked -- the Delta reaction is now available.

But... The user should not have to clear the cache manually (or at least they should be warned that it is necessary). When you save your first Delta snapshot, the module should automatically clear the cache, for good usability.

Probably all it needs to do is something like this:

if (module_exists('context')) {
   context_invalidate_cache();
}

Or it could just do

drupal_flush_all_caches()

although that is more extreme and I don't know if it's necessary for Delta to clear page, menu router, theme, and other caches when a snapshot is saved? Possibly, since the theme cache might be invalid at that point.