Your streak counts consecutive days you completed at least one quest. Any quest counts, of any of the four types.
Streak freezes. This is the part most people miss. Complete two or more quests in a day and you earn a freeze. You can hold up to two at a time.
When you miss a day, a freeze is spent automatically to bridge it. Your streak survives, but the skipped day doesn't add to it.
Today doesn't count against you until it's over. A streak isn't broken at 9am because you haven't done anything yet.
A strong week buys you insurance for a bad one. That is the intended behaviour, not a loophole.