feat: add post mention

internal/service/notification_service.go

@@ -32,6 +32,7 @@ const (
 	NotifFollowRequest  = "follow_request"
 	NotifFollowAccepted = "follow_accepted"
 	NotifPostLike       = "post_like"
+	NotifPostMention    = "post_mention"
 
 	// Reminder kinds are delivered live (email + push + a websocket toast)
 	// but NOT persisted — they're ephemeral nudges, not history.
@@ -192,6 +193,38 @@ func (s *NotificationService) NotifyPostLike(ctx context.Context, postID, author
 // single post — a burst of likes within the window produces one email.
 const likeEmailThrottle = 6 * time.Hour
 
+// NotifyPostMention tells `mentionedID` that `actorID` (the post author)
+// tagged them in a post. Persisted row + realtime + Web Push; no email
+// (push/in-app is enough, and a post can tag many people). Skips self-tags.
+func (s *NotificationService) NotifyPostMention(ctx context.Context, mentionedID, actorID, postID string) {
+	if mentionedID == "" || actorID == "" || mentionedID == actorID {
+		return
+	}
+	if err := s.notifs.CreateMention(ctx, mentionedID, actorID, postID); err != nil {
+		s.logger.Warn("persist mention notification failed",
+			zap.String("recipient", mentionedID), zap.Error(err))
+	}
+	actorUser, _ := s.users.FindByID(ctx, actorID)
+	s.publishRealtime(ctx, mentionedID, NotifPostMention, actorUser)
+
+	if s.push == nil {
+		return
+	}
+	who := "Someone"
+	url := s.frontendURL + "/notifications"
+	if actorUser != nil {
+		who = actorDisplay(actorUser)
+		url = s.frontendURL + "/u/" + actorUser.Handle + "/posts#post-" + postID
+	}
+	s.push.SendToUser(ctx, mentionedID, PushPayload{
+		Title: "You were mentioned",
+		Body:  who + " mentioned you in a post",
+		URL:   url,
+		Icon:  s.iconURL(),
+		Tag:   NotifPostMention + ":" + postID,
+	})
+}
+
 // likeMessage renders the aggregated like text: "X liked your post" or
 // "X and N others liked your post".
 func likeMessage(who string, count int) string {