feat: disciple link

internal/repository/social_graph_repo.go

@@ -334,6 +334,62 @@ func (r *NotificationRepo) CreateAdminMessage(ctx context.Context, userID, body
 	return nil
 }
 
+// BroadcastToAllUsers writes one notification of `kind` to every active user
+// except `actorID`, in a single INSERT…SELECT. One round trip regardless of
+// audience size — the alternative (a row per user from Go) would be hundreds
+// of round trips on the request path.
+//
+// Deliberately does NOT filter on notification_prefs: ListByUser already
+// excludes kinds the reader has disabled for the in_app channel at read time,
+// so writing the rows unconditionally keeps a re-enabled preference able to
+// surface history — exactly how the existing kinds behave.
+//
+// Banned accounts are skipped; they can't sign in to read it anyway.
+func (r *NotificationRepo) BroadcastToAllUsers(ctx context.Context, kind, actorID string) (int64, error) {
+	tag, err := r.pg.Pool.Exec(ctx, `
+		INSERT INTO notifications (user_id, actor_id, kind)
+		SELECT u.id, $2, $1
+		FROM users u
+		WHERE u.id <> $2 AND u.banned_at IS NULL`, kind, actorID)
+	if err != nil {
+		return 0, fmt.Errorf("broadcast notification: %w", err)
+	}
+	return tag.RowsAffected(), nil
+}
+
+// PushRecipientsForKind lists the ids of users who should receive a *push* for
+// `kind` — everyone except the actor, minus banned accounts, minus anyone who
+// turned this kind off for the push channel, and minus anyone with no push
+// subscription registered at all.
+//
+// That last filter is what keeps a broadcast cheap: only devotees who actually
+// enabled web push are worth iterating, which is typically a small fraction of
+// the user base.
+func (r *NotificationRepo) PushRecipientsForKind(ctx context.Context, kind, actorID string) ([]string, error) {
+	rows, err := r.pg.Pool.Query(ctx, `
+		SELECT DISTINCT u.id
+		FROM users u
+		JOIN push_subscriptions ps ON ps.user_id = u.id
+		WHERE u.id <> $2 AND u.banned_at IS NULL
+		  AND NOT EXISTS (
+		      SELECT 1 FROM notification_prefs np
+		      WHERE np.user_id = u.id AND np.kind = $1
+		        AND np.channel = 'push' AND np.enabled = FALSE)`, kind, actorID)
+	if err != nil {
+		return nil, fmt.Errorf("list push recipients: %w", err)
+	}
+	defer rows.Close()
+	out := []string{}
+	for rows.Next() {
+		var id string
+		if err := rows.Scan(&id); err != nil {
+			return nil, fmt.Errorf("scan push recipient: %w", err)
+		}
+		out = append(out, id)
+	}
+	return out, rows.Err()
+}
+
 // ListByUser returns a recipient's notifications, newest first, with the
 // actor's display fields joined in for rendering (nil for system
 // notifications or since-deleted actors). Kinds the user has turned off for