With 'initial move' I did not mean just the first time the piece was moved, but a move that would only be allowed when the piece is still virgin (XBetza i). Pawns can definitely not be e.p. captured on their starting square, after their double push, so I treated this more as a property of castling than as a consequence of the virgin-only requirement. But if other royal initial moves (such as the Knight jump in Chaturanga or Ouk, or the Alibaba move in Grant Acedrex) are forbidden when in check, I could make it the default behavior for all i moves of a royal.
If it is not universal, it would have to be configurable, and there are several aspects to that: Interactive Diagram (AI), Play-Test Applet (interface), GAME code. Or we could introduce a special XBetza notation for virgin moves that cannot be played when in check.
Metamachy is a bit exceptional anyway: the ban on the King's virgin moves there cannot be explained in terms of e.p. capture, as you are also not allowed to jump over protected enemy pieces with them. And the jumped-over piece would then block its protector from moving to the e.p. square to make the capture.
With 'initial move' I did not mean just the first time the piece was moved, but a move that would only be allowed when the piece is still virgin (XBetza i). Pawns can definitely not be e.p. captured on their starting square, after their double push, so I treated this more as a property of castling than as a consequence of the virgin-only requirement. But if other royal initial moves (such as the Knight jump in Chaturanga or Ouk, or the Alibaba move in Grant Acedrex) are forbidden when in check, I could make it the default behavior for all i moves of a royal.
If it is not universal, it would have to be configurable, and there are several aspects to that: Interactive Diagram (AI), Play-Test Applet (interface), GAME code. Or we could introduce a special XBetza notation for virgin moves that cannot be played when in check.
Metamachy is a bit exceptional anyway: the ban on the King's virgin moves there cannot be explained in terms of e.p. capture, as you are also not allowed to jump over protected enemy pieces with them. And the jumped-over piece would then block its protector from moving to the e.p. square to make the capture.