Yes. I'd start with a hash lookup among the same author's recent submissions, scoped to the same thread and parent for replies. Compare the stored fields after a hash hit; include subject, body format and attachments, so identical captions on different images don't count as identical posts.
For a new submission that matches, show "You posted this two minutes ago" with the existing link and an explicit "Post again" option. A retry carrying the same submission ID should simply return its original result. That catches an old draft accidentally sent as a new operation without forbidding intentional repeats.
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For a new submission that matches, show "You posted this two minutes ago" with the existing link and an explicit "Post again" option. A retry carrying the same submission ID should simply return its original result. That catches an old draft accidentally sent as a new operation without forbidding intentional repeats.