Save the app's meeting records, each by its key: a new key is a new record, a known one is rewritten.

The backend links each to the call coached in it (the caller's call with the same meeting_key) and keeps it until 90 days after the meeting ends, or as long as a call in it is kept; the app never sets either. A meeting that ended more than 90 days ago is not stored, so saved can be less than what was sent. The same key twice: the later one is saved. A save keeps what another of the user's Macs saw of the offer (see the repository's upsert).