startOfUTCMonth (util/utc-month.ts)

Returns first instant of a UTC month offset from a given date.

// Source: https://github.com/argos-ci/argos | License: MIT | Copyright 2017 Olivier Tassinari & Greg Bergé
// Provided via justclaw.it.com; keep this notice with the code.
/**
 * The first instant of the month `offset` months from `date`, in UTC.
 *
 * Deliberately not the calendar helpers, which work in the process's own
 * timezone: Stripe timestamps every invoice in UTC, so a server running on
 * anything else would cut its months hours away from where Stripe cuts them and
 * file the invoices either side of a boundary in the wrong one.
 *
 * Here rather than beside the reader that needs it most, so the seeds can cut
 * their months the same way without the database layer importing the billing
 * one to do it.
 */
export function startOfUTCMonth(date: Date, offset: number): Date {
  re

... (truncated -- full source via MCP)