refactor(server): final writeErr migration + ErrNotFound aliases (T3c)

internal/playlists/service.go

@@ -24,13 +24,18 @@ import (
 	"github.com/jackc/pgx/v5/pgtype"
 	"github.com/jackc/pgx/v5/pgxpool"
 
+	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
 )
 
 // Typed errors. The API layer maps each to its wire status code; tests
 // use errors.Is to assert the right path was taken.
+//
+// ErrNotFound aliases apierror.ErrNotFound so handlers can errors.Is
+// against the shared sentinel; existing playlists.ErrNotFound callsites
+// still resolve to the same pointer.
 var (
-	ErrNotFound               = errors.New("playlists: playlist not found")
+	ErrNotFound               = apierror.ErrNotFound
 	ErrForbidden              = errors.New("playlists: forbidden")
 	ErrInvalidInput           = errors.New("playlists: invalid input")
 	ErrTrackNotFound          = errors.New("playlists: track not found")