Is there an option for radio buttons with Facet API + Search API (database)? I am using several check box facets.  Some of the facets allow me to use check boxes for multiple values.  There is one facet, however, of taxonomy terms for which I want to only allow a single choice; and per the client's spec, it must be a radio button.

I can't seem to figure out how to do that.  I installed the Facet API Select sandbox module, but that just gives me a drop-down box (and what sucks is when I make a selection, I stay locked on that one and don't get the other choices back).  I installed Facet Bonus pack, but the select option from that keeps giving me a PHP error.

I am using Views on top of Search API database.  It may be that I am missing something conceptually, as I am still getting my arms around Facets.

If there isn't an option for radio buttons, then I will contribute a patch to the Facet API Select sandbox module (if it is feasible).  This is for a paid client, so this is happening.

EDIT:  I need to clarify my biz case of what I'm trying to do.  I have 3 facets with check boxes of multiple items to filter down.  On a fourth facet, I provide a list of filters, but need to allow one item to be selected.  So, my choices look like:

Facet 1:  Type of product
   - phone
   - tablet
   - tv

This would filter down the main product category, i.e., single select option the client wants a radio button for.

Facet 2:  Color
   - red
   - blue
   - green
   - black

Facet 3, Facet 4, etc., would be like Facet 2, where the user can select multiple check boxes for the various sub categories.

These facet categories are taxonomy terms, if that matters.
There is a patch for the Facet API Bonus module that adds a radio buttons widget.

The issue with the patch is https://drupal.org/node/2034777

With this patch you also need to use the Facet API module patch mentioned by RajeevK in the comments of your question, which can be found at https://drupal.org/node/1393928

If you try those patches and comment back in those issues with how it worked out for you it will also help progress those issues so that the patches can be committed and you no longer have to use patched modules - a win for all.