Problem

Prompts chain of Start/End dates, End date should not be before Start date.

const responses = await prompts([
  {
    type: 'date',
    name: 'startDate',
    message: 'Start Date',
    initial: new Date(),
  },
  {
    type: 'date',
    name: 'endDate',
    message: 'End Date',
    initial: new Date(),
    validate(date) {
      // `endDate` should not be before `startDate`
    },
  },
]);

Solution

  {
    type: 'date',
    name: 'endDate',
    message: 'End Date',
    initial: new Date(),
    validate(date, values) {
      return date >= values.startDate || 'End Date should not be before Start Date';
    },
  },

Describe alternatives you've considered

Multiple prompts or onSubmit hacks as mentioned in #2.
If we already have validate, makes sense to allow access to previous answers.

I was also thinking about min and max values that could make sense (additionally)...
e.g. Once startDate is selected, endDate could have min: (prev, values) => values.startDate and then the user can't select a date before that date.

Additional context

Maybe it makes sense, for consistency, to add prompt as the 3rd argument, just like some of the other props https://github.com/terkelg/prompts#-prompt-objects. Though I'm not sure what would be the use case for that.
Btw, format doesn't get prompt as a 3rd argument but the docs in the same section say:

The function signature is (prev, values, prompt)