Further refine the availability filter to work for Overdrive titles
The availability filter is more helpful now that it can filter out titles which have no physical items available. Checking "at library" does indeed find only titles that have an item available on the shelf. Thank you! But if you check "online" for availability, it just shows everything from Overdrive - it doesn't actually filter out the unavailable Overdrive titles.
This cannot be done for OverDrive and other econtent. Vega has to ping the econtent vendor API for each individual title separately in order to get 'availability' status. It's impossible to do this for all search results rather than just the displayed page of results and return correct availability on the fly for a facet.