To solve this CTF puzzle, let's break down the critical parts of the text:
The child’s birth and prophecy: The prophecy speaks of a child born beneath a sky with no shadow, which ties into the number 13 (as mentioned with the bells ringing 13 times and the number XIII). The child is important, but there is something related to time—ten days that never arrived, stolen or forgotten. These lost ten days seem to be crucial in this puzzle.
The Thirteenth (XIII): The man cloaked in violet, known only as the Thirteenth, mentions that "the wound cannot be undone. But it can be explained — and remembered." This suggests a reversal or a time-related puzzle.
The chapel stone inscription: The line “Mark the last day the world stood whole — for the child took the rest" is a clue. It could suggest the last day before the "child" or some event marked a significant change in time.
Date calculation: The key seems to be related to the child’s birth and the phrase about the world standing "whole." The statement about the child taking the rest of the time may refer to the Gregorian calendar change, which was introduced after the "Julian Calendar" was dropped. Specifically, ten days were lost during the switch from the Julian calendar to the Gregorian calendar.
Historical Context
The Gregorian calendar was adopted by most countries in 1582, and this caused a shift of 10 days. The 4th of October, 1582, was directly followed by the 15th of October, 1582.
Final Answer
Since the CTF is asking for the child's date of birth and the key clue is tied to the 10-day shift in the calendar, we infer that the child’s birth is related to this significant calendar event.
Thus, the date of birth for the child (according to the puzzle) is October 4, 1582, the last day before the calendar change.