Should ignore query-terms on ext.selected

When the Codex Search UI module sends mod-codex-mux the query:

title="a*" sortby title

It gets back records from both the KB (mod-codex-ekb) and the local inventory (mod-codex-inventory), which is as it should be. However, when I enable the Holding Status: Available online filter, and consequently send the query:

(title="a*") and ext.selected="true" sortby title

The results contain no records from the inventory.

I assume this is because mod-codex-inventory is blindly looking for records whose selected field contains the string true. But in fact there is no notion of "selected" in local inventory, so the ext.selected index should be treated as unsupported; and because it's in the ext set, the query should be exactly equivalent to the simple initial query above.

The POs want Holding Status: Available online to be on by default (see UISE-59), but I can't do that at the moment without omitting all inventory records.

I've P2'd this because kgambrell keeps asking me on Slack when UISE-59 will be done, so it's evidently of imminent interest to the SMEs.