Re index: depending on the frequency of deletion, even if there wasn't an index, we're talking about skipping approx one (or five, or seven) record(s) in 180, so it doesn't matter too much where the pruning happens!

My concern about OOM etc.: `deleteEventsBefore` is going to allocate objects, and it has other ways of failing (some memory-related, such as paging in indices, and some just Java).

If our pruning fails for any reason, we'll never submit a document. (And even with a `try..catch`, we can end up in a situation where the upload fails; segfaults, for example.)

So this is a case of prioritization: if submission succeeds today but pruning fails, great; pruning will probably succeed tomorrow. If pruning fails and we don't submit, then sadface.

Yes, we should log, and eventually dump into the FHR error collector itself.