fix: feed repitition

internal/service/social_service.go

@@ -36,11 +36,12 @@ type PostService struct {
 	likes    *repository.LikeRepo
 	mentions *repository.MentionRepo
 	comments *repository.CommentRepo
+	feedSeen *repository.FeedRepo // per-user "already served" set for the home feed
 	notif    *NotificationService // optional; set via SetNotifier
 }
 
-func NewPostService(posts *repository.PostRepo, r2 *repository.R2, likes *repository.LikeRepo, mentions *repository.MentionRepo, comments *repository.CommentRepo) *PostService {
-	return &PostService{posts: posts, r2: r2, likes: likes, mentions: mentions, comments: comments}
+func NewPostService(posts *repository.PostRepo, r2 *repository.R2, likes *repository.LikeRepo, mentions *repository.MentionRepo, comments *repository.CommentRepo, feedSeen *repository.FeedRepo) *PostService {
+	return &PostService{posts: posts, r2: r2, likes: likes, mentions: mentions, comments: comments, feedSeen: feedSeen}
 }
 
 // SetNotifier wires the notification seam after construction (the
@@ -224,7 +225,23 @@ func (s *PostService) Feed(ctx context.Context, viewerID string, limit, offset i
 	if offset < 0 {
 		offset = 0
 	}
-	posts, err := s.posts.FeedForViewer(ctx, viewerID, limit, offset)
+
+	// Non-repetition: a per-user Redis "seen" set is the cursor. offset==0 is
+	// the start of a fresh session, so we clear it; every page then excludes
+	// already-served ids. Because the feed's tier ordering depends on viewer
+	// state (a like re-tiers a post), exclusion — not OFFSET — is what keeps
+	// pages from repeating or skipping rows. With Redis enabled we drive
+	// selection by the set alone (offset 0); without it we fall back to plain
+	// offset paging and the client de-dups the occasional drift.
+	if offset == 0 {
+		s.feedSeen.Reset(ctx, viewerID)
+	}
+	exclude := s.feedSeen.Seen(ctx, viewerID)
+	queryOffset := offset
+	if s.feedSeen.Enabled() {
+		queryOffset = 0
+	}
+	posts, err := s.posts.FeedForViewer(ctx, viewerID, limit, queryOffset, exclude)
 	if err != nil {
 		return nil, err
 	}
@@ -243,9 +260,24 @@ func (s *PostService) Feed(ctx context.Context, viewerID string, limit, offset i
 	if err := s.posts.HydrateViewerRelationships(ctx, viewerID, posts); err != nil {
 		return nil, err
 	}
+	// Record what we served so the next page skips it (no-op without Redis).
+	if len(posts) > 0 {
+		ids := make([]string, len(posts))
+		for i := range posts {
+			ids[i] = posts[i].ID
+		}
+		s.feedSeen.MarkSeen(ctx, viewerID, ids)
+	}
 	return posts, nil
 }
 
+// ResetFeed clears the viewer's home-feed seen-set — called on logout and when
+// the session ends (the page unloads / the realtime socket drops), so a stale
+// set doesn't linger in Redis past its owner. No-op without Redis.
+func (s *PostService) ResetFeed(ctx context.Context, viewerID string) {
+	s.feedSeen.Reset(ctx, viewerID)
+}
+
 // hydratePinnedSlice fills PinnedComment on a value slice.
 func (s *PostService) hydratePinnedSlice(ctx context.Context, viewerID string, posts []model.Post) error {
 	if len(posts) == 0 {