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A per-user ShotCommentRead marker records how far each person has read a shot's comments. Comments and replies from others after the marker put an orange "!" beside the shot code; its popover lists them and only "Mark read" clears it. A chip filters the board to flagged shots and marks all read. The migration marks existing comments as read so the board starts clean. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>