Describe DM expiry reconciliation and await restarted test link

tests/test_dm_media.c

@@ -583,6 +583,7 @@ static void tick(void* arg) {
             }
 #endif
             if (value(m, "SELECT count(*) FROM dm_custody") != 0 || value(s, "SELECT count(*) FROM dm_media_jobs WHERE expired=1") != 1) break;
+            if (!instance_find_conn(s, t->ids[M])) break;
             if (snapshot(t, 3)) { failure(t, "expired body snapshot"); return; }
             uint8_t stored[24]; memcpy(stored, t->id, 16);
             uint64_t expiry = ntp_time_get_seconds(s) + 100; memcpy(stored + 16, &expiry, 8);