Release v1.8.12

• A backtest skips a market that has not resolved yet as "market not resolved yet" instead of "export pending", since history files are built only after a market resolves (usually within 2 hours). "export pending" now means a resolved market whose file is still being built.
• ExportNotReadyError.last_error is set only when the export failed. The server's message now explains why a file is not ready, and that explanation used to land in last_error as if it were an error.
• The MCP backtest hint for ExportNotReadyError says that markets have no history file until they resolve, instead of describing exports as building out of order.