fix(lidarrquarantine): translate FK violation to ErrTrackNotFound + drop unneeded *string AlbumTitle

- Flag now detects Postgres SQLSTATE 23503 (foreign_key_violation) on
  UpsertQuarantine and surfaces ErrTrackNotFound instead of a wrapped
  generic. T8's handler can now return 404 track_not_found cleanly.
  Constraint-name guard ('track' substring) keeps a future user_id FK from
  mis-mapping to the same error.
- AdminQueueRow.AlbumTitle is now string (not *string). albums.title is
  NOT NULL upstream; the empty-string-to-nil dance was answering a
  nullability question that doesn't exist in the schema.
- Add TestFlag_NonexistentTrackReturnsErrTrackNotFound covering the new
  branch.

internal/lidarrquarantine/service.go

@@ -9,8 +9,10 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"strings"
 
 	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgconn"
 	"github.com/jackc/pgx/v5/pgtype"
 	"github.com/jackc/pgx/v5/pgxpool"
 
@@ -64,10 +66,15 @@ func (s *Service) Flag(ctx context.Context, userID, trackID pgtype.UUID, reason
 		Notes:   notesPtr,
 	})
 	if err != nil {
-		// FK violation on track_id surfaces here as a postgres error;
-		// callers can treat any error as "track doesn't exist or DB issue."
-		// Distinguishing FK violation specifically isn't worth the extra
-		// dependency on pgconn just for one branch.
+		// FK violation on track_id (no such track) → ErrTrackNotFound so the
+		// handler can return 404 instead of a generic 500. Code 23503 is the
+		// Postgres SQLSTATE for foreign_key_violation; the constraint check
+		// guards against future FKs (e.g. user_id) firing the same code.
+		var pgErr *pgconn.PgError
+		if errors.As(err, &pgErr) && pgErr.Code == "23503" &&
+			(pgErr.ConstraintName == "" || strings.Contains(pgErr.ConstraintName, "track")) {
+			return dbq.LidarrQuarantine{}, ErrTrackNotFound
+		}
 		return dbq.LidarrQuarantine{}, fmt.Errorf("upsert: %w", err)
 	}
 	return row, nil
@@ -102,7 +109,7 @@ type AdminQueueRow struct {
 	TrackID         pgtype.UUID
 	TrackTitle      string
 	ArtistName      string
-	AlbumTitle      *string
+	AlbumTitle      string
 	AlbumID         pgtype.UUID
 	LidarrAlbumMBID *string
 	ReportCount     int32
@@ -149,16 +156,11 @@ func (s *Service) ListAdminQueue(ctx context.Context) ([]AdminQueueRow, error) {
 				CreatedAt: rep.CreatedAt,
 			})
 		}
-		var albumTitle *string
-		if r.AlbumTitle != "" {
-			t := r.AlbumTitle
-			albumTitle = &t
-		}
 		out = append(out, AdminQueueRow{
 			TrackID:         r.TrackID,
 			TrackTitle:      r.TrackTitle,
 			ArtistName:      r.ArtistName,
-			AlbumTitle:      albumTitle,
+			AlbumTitle:      r.AlbumTitle,
 			AlbumID:         r.AlbumID,
 			LidarrAlbumMBID: r.LidarrAlbumMbid,
 			ReportCount:     r.ReportCount,

internal/lidarrquarantine/service_test.go

@@ -9,6 +9,7 @@ import (
 	"path/filepath"
 	"testing"
 
+	"github.com/jackc/pgx/v5/pgtype"
 	"github.com/jackc/pgx/v5/pgxpool"
 
 	"git.fabledsword.com/bvandeusen/minstrel/internal/db"
@@ -117,6 +118,21 @@ func TestFlag_UpsertOnSecondFlag(t *testing.T) {
 	}
 }
 
+func TestFlag_NonexistentTrackReturnsErrTrackNotFound(t *testing.T) {
+	pool := newPool(t)
+	user := seedUser(t, pool, "alice")
+
+	var bogus pgtype.UUID
+	bogus.Bytes = [16]byte{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16}
+	bogus.Valid = true
+
+	svc := NewService(pool, lidarrconfig.New(pool), nil)
+	_, err := svc.Flag(context.Background(), user.ID, bogus, "bad_rip", "")
+	if !errors.Is(err, ErrTrackNotFound) {
+		t.Errorf("err = %v, want ErrTrackNotFound", err)
+	}
+}
+
 func TestFlag_BadReasonRejected(t *testing.T) {
 	pool := newPool(t)
 	user := seedUser(t, pool, "alice")