TypeScript: HasManyThroughRelationContract missing throughModel?

[EmilyRagan]

I am working with @adonisjs/lucid v18.3.0, but the types that I am concerned with seem to be the same in the current code. I am using TypeScript 4.6.4. After narrowing a RelationshipContract to a HasManyThroughRelationContract using isType, I am finding that TypeScript tells me I cannot access the throughModel property that should come from BaseRelationContract. When debugging and inspecting the relationship object, throughModel does exist, and using it actually works as I hoped it would, but TypeScript yells at me about it. Why is throughModel not available on HasManyThroughRelationContract and what is the intended way to access the model for the "through" class instead?

https://github.com/adonisjs/lucid/blob/2a2bd22c2261f2548f4d794131b4b86fcdaea829/src/types/relations.ts#L146-L152
https://github.com/adonisjs/lucid/blob/2a2bd22c2261f2548f4d794131b4b86fcdaea829/src/types/relations.ts#L532-L535