Use the Solr Group By feature to group the description item id.

Since items are indexed per-description, we have a mismatch between
the search results and logical items within the system. This is
confusing and it makes the search functionality harder to reuse in
other places (like item lists.)

By grouping descriptions by logical item id we can make the search
results behave like logical item listing. Faceting etc still appears
to work okay, but this still needs more testing.