Given a messages table with sender_id, recipient_id, and sent_at, write a query that returns pairs of users who have exchanged at least one message in both directions, along with the date of their first mutual exchange.

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Stay specific. One example, told well, beats three told fast. Make your decisions visible — what you chose between. End on what changed, for whom.

Given a messages table with sender_id, recipient_id, and sent_at, write a query that returns pairs of users who have exchanged at least one message in both directions, along with the date of their first mutual exchange.

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