Indeed, the counterstrike should be forbidden here.
The Interactive Diagram does implement the counterstrike rule: when you place both Lions in front of an enemy GB, switch on the AI, and play GBxLn, it will not capture the Lion. In the highlighting you won't see it, though, as the I.D. does pseudo-legal highlighting. Moves that expose you to check will also be highlighted. (If it is the King making such moves these are highlighted in grey, but betzaNew.js doesn't even do that anymore. Perhaps one of these days I will subject the highlighted moves to a legality test, and use another highlight symbol for the illegal ones.)
The same test appears to work in Jocly, though. And then it doesn't even highlight the counterstrike GBxLn.
Indeed, the counterstrike should be forbidden here.
The Interactive Diagram does implement the counterstrike rule: when you place both Lions in front of an enemy GB, switch on the AI, and play GBxLn, it will not capture the Lion. In the highlighting you won't see it, though, as the I.D. does pseudo-legal highlighting. Moves that expose you to check will also be highlighted. (If it is the King making such moves these are highlighted in grey, but betzaNew.js doesn't even do that anymore. Perhaps one of these days I will subject the highlighted moves to a legality test, and use another highlight symbol for the illegal ones.)
The same test appears to work in Jocly, though. And then it doesn't even highlight the counterstrike GBxLn.