fix(mcp): mcp_tool_error events never logged — DBEventLogger.log() called without required dashboard_id/slice_id/referrer #42579

Bug

GlobalErrorHandlerMiddleware._handle_error in superset/mcp_service/middleware.py calls event_logger.log() without three arguments that DBEventLogger.log() requires:

try:
    event_logger.log(
        user_id=user_id,
        action="mcp_tool_error",
        duration_ms=duration_ms,
        curated_payload={
            "tool": tool_name,
            "error_type": type(error).__name__,
            "error_message": str(error),
            "method": context.method,
        },
    )
except Exception as log_error:
    logger.warning("Failed to log error event: %s", log_error)

DBEventLogger.log signature (confirmed via inspect.signature on 6.1.0):

(self, user_id: 'int | None', action: 'str', dashboard_id: 'int | None', duration_ms: 'int | None', slice_id: 'int | None', referrer: 'str | None', *args: 'Any', **kwargs: 'Any') -> 'None'

dashboard_id, slice_id and referrer have no defaults, so the call raises TypeError every time. The surrounding except swallows it into a WARNING, so it fails silently.

LoggingMiddleware.on_call_tool in the same file does it correctly and shows the intended call shape:

event_logger.log(
    user_id=user_id,
    action="mcp_tool_call",
    dashboard_id=dashboard_id,
    duration_ms=duration_ms,
    slice_id=slice_id,
    referrer=None,
    curated_payload={...},
)

Reproduction

Trigger any MCP tool error (e.g. call any tool with invalid arguments) on a deployment using the default DBEventLogger. Observed on every error in our logs:

WARNING:superset.mcp_service.middleware:Failed to log error event: DBEventLogger.log() missing 3 required positional arguments: 'dashboard_id', 'slice_id', and 'referrer'

Impact

No mcp_tool_error event is ever written to the logs table / Action Log UI on a default configuration. MCP tool failures are invisible to Superset's own audit and analytics surfaces — you only find them by reading container logs. This makes it impossible to monitor MCP error rates through the mechanism Superset provides for exactly that, and it defeats the stated purpose of the middleware ("proper error logging for all MCP tool calls").

It also means the one code path that fires whenever something has already gone wrong is itself broken, so failures are least observable exactly when observability matters most.

Suggested fix

Pass the three required arguments, mirroring LoggingMiddleware:

event_logger.log(
    user_id=user_id,
    action="mcp_tool_error",
    dashboard_id=None,
    duration_ms=duration_ms,
    slice_id=None,
    referrer=None,
    curated_payload={...},
)

_extract_context_info already derives dashboard_id / slice_id from the tool params, so those could be passed through instead of None to make error events as useful as call events.

Separately, logger.warning for a swallowed TypeError in the logging path is easy to miss — this bug appears to have gone unnoticed despite firing on every single MCP error. Raising or logging at error level would surface programming errors here rather than hiding them.

Environment

• Superset 6.1.0 (apache/superset:6.1.0)
• fastmcp 3.4.3
• Python 3.10.20, Linux
• Default DBEventLogger (no custom EVENT_LOGGER configured)