Constant MIGRATION_004 

const MIGRATION_004: &str = r#"
-- Add priority column for queue ordering
ALTER TABLE downloads ADD COLUMN priority INTEGER DEFAULT 0;

-- Add bytes_downloaded for resume support
ALTER TABLE downloads ADD COLUMN bytes_downloaded INTEGER DEFAULT 0;

-- Create index for efficient queue processing (priority DESC, FIFO within same priority)
CREATE INDEX IF NOT EXISTS idx_downloads_queue
  ON downloads(status, priority DESC, queued_at ASC)
  WHERE status IN ('pending', 'downloading');
"#;

Migration to enhance downloads table with priority and bytes_downloaded