appview/db: fix stray stars from deleted repositories

appview/db/db.go

···
 		return err
 	})
 
+	// the generalize-stars-subject migration removed the foreign key constraint
+	// from stars, so deleting a repo no longer cascades to its stars.
+	// this trigger restores that behaviour at the application level.
+	orm.RunMigration(conn, logger, "add-star-cleanup-trigger", func(tx *sql.Tx) error {
+		_, err := tx.Exec(`
+			create trigger if not exists delete_stars_on_repo_delete
+			after delete on repos
+			begin
+				delete from stars where subject_at = OLD.at_uri;
+			end;
+		`)
+		return err
+	})
+
+	// purge stars that reference repos deleted before the trigger was added.
+	orm.RunMigration(conn, logger, "cleanup-orphaned-stars", func(tx *sql.Tx) error {
+		_, err := tx.Exec(`
+			delete from stars
+			where subject_at like 'at://%/sh.tangled.repo/%'
+			  and subject_at not in (select at_uri from repos);
+		`)
+		return err
+	})
+
 	return &DB{
 		db,
 		logger,