Contract for background execution completion events.
Emitted when Live.background() or Backtest.background() completes execution. Contains metadata about the completed execution context.
exchangeName: string
exchangeName - Name of the exchange used in execution
strategyName: string
strategyName - Name of the strategy that completed
frameName: string
frameName - Name of the frame (empty string for live mode)
backtest: boolean
backtest - True if backtest mode, false if live mode
symbol: string
symbol - Trading symbol (e.g., "BTCUSDT")