What is the Typescript type of a AWS Lambda event coming from a Step Function

@types/aws-lambda lists the Event type for 34 different sources, from ALB to SQS, but SFN or StepFunctions is not on the list.

I just want to be able to (confidently) write

export const hander:Handler<SFNEvent> = (event) => {

Anybody know where this is?

Step Functions does not impose any restrictions on the type of the “event”, which Step Functions calls the “payload”, except I suppose that it must be expressible in JSON. Consider the following state-machine:

{
  "StartAt": "InvokeVendor",
  "States": {
    "InvokeVendor": {
      "Type": "Task",
      "InputPath": "$",
      "ResultPath": "$.vendorResult",
      "Resource": "arn:aws:states:::lambda:invoke-vendor",
      "Parameters": {
        "FunctionName": "arn:aws:lambda:us-east-1:011668294191:function:vendor-webhook",
        "Payload": {
          "path": "process-webhook"
        }
      }
    }
  }
}

The handler for this could be written as:

export const handler: Handler<{ path: string }> = async (event, context, callback) => {
  const route = routes[event.path];
  if (!route) {
    throw new Error(`Path ${event.path} not understood`);
  }
  return route(event, context, callback);
};

(Note the pattern used here, of passing in a path and then using that to dispatch to a function that does the actual work, is by no means necessary, but is a handy way to reduce the number of separate Lambdas a complex project will require.)

Thanks to @STerliakov for explaining this to me.