Improvement to board editor

[yafred]

When castling is not possible:
1/ the corresponding letter is removed from the FEN (what we expect)
2/ the corresponding seems usable although it is not

The checkbox should be unchecked and disabled

[hb20007]

The board editor can also be used to set up Chess960 positions, so it should check whether there is a rook anywhere to the left or right of the king on any square on the first rank.

[yafred]

I am reading the code and testing the feature at the moment:
1/ You can paste a chess960 initial position in the FEN input and the position of the rooks and kings will be remembered to handle castling rights
2/ If you start with a position (let's say standard position) and move the pieces to obtain a valid chess960 initial position, you don't have castling rights

If have not found the explanation in the lila code yet ... my feeling is that all the magic comes from chessground

So, at the moment, the board editor module in lila does not know about castling.
The castling checkboxes are just meaningful if the kings and rooks are on their initial square (valid for chess960 too)

[hb20007]

Regarding your point 2/, are you talking about moving the pieces in the board editor? If so, I don't agree with the statement, since I've tried it and castling rights are there since all the checkboxes are checked by default. Basically, if the checkboxes are checked, the FEN will have KQkq at the end. The problem is that, currently, this could be the case even when castling is illegal, even when including Ches960.

[yafred]

That is exactly the point of this issue: the checkboxes are not the reference ... the field is the FEN is

Look at the screenshot:
Qkq is correct (white cannot rook king side)
The checkboxes may let you think that all castling rights are there

[hb20007]

I see. You were talking about the FEN, and not the checkboxes. Basically, what I'm trying to say is: If the position is a valid Chess960 position, then the checkbox should be unchecked to reflect the FEN; if not, it should be disabled.

Checking what happens when pasting in FEN might be useful in finding how it works, because, in that case, the checkboxes are updated to reflect the FEN.

[yafred]

2026-01-10.11-44-37.mp4

I agree with your last point: if you paste a random position, the checkbox reflect the castling rights (but you can still check them again ... which is also part of the issue I'd like to fix)