Whoops, sorry about that. Wasn't thinking.
Relevant line in the 1.22-ctest18 file:
[main/DEBUG] [FastCraft/]: Mod detection results: {Bukkit=false, ColoredLights=false, OptiFine=false, ShadersMod=false, DynamicLights=false, NotEnoughIds=false}
Relevant line in the 1.23 file:
[main/DEBUG] [FastCraft/]: Mod detection results: {AsRuins=false, Bukkit=false, ColoredLights=false, OptiFine=false, ShadersMod=false, DynamicLights=false, NotEnoughIds=false}
I guess it's just not picking up that Ruins is active.