Too high cost emitted for @OneOf-InputTypes

Product

Hot Chocolate

Version

16.0.0.rc.1.30

Link to minimal reproduction

See sample below

Steps to reproduce

Currently cost calculation does not take @oneOf semantics into account.

Consider the following schema:

type Mutation {  
  setField(input: OneOfSampleInput): String!  
}  

input OneOfSampleInput @oneOf {  
  fieldOne: String! @cost(weight: "900")  
  fieldTwo: String! @cost(weight: "400")  
}  

For the mutation:

mutation ($input: OneOfSampleInput) {  
  setField(input: $input)  
}  

The result is:

{  
  "errors": [  
    {  
      "message": "The maximum allowed field cost was exceeded.",  
      "extensions": {  
        "code": "HC0047",  
        "fieldCost": 1301,  
        "maxFieldCost": 1000  
      }  
    }  
  ]  
}  

This result is incorrect / way too high.
Since OneOfSampleInput is annotated with @oneOf, exactly one field must be provided. Therefore, the cost must not be computed as the sum of all fields. Instead, it must be the maximum cost of all fields, since only one field may have a value.

Background: I am having kind of a "God"-muation, with one huge OneOf-Input. Each field of that OneOf-type is fine regarding cost on its own, but when they a summed up, cost validation is violated by a huge amout.

mutation {  
  createObject(input: ObjectInput)  
}  
input ObjectInput @oneOf {  
  typeA: TypeAInput  
  typeB: TypeBInput  
  typeC: TypeCInput
  ...
   # maaaany more types  
  typeZ: TypeZInput
}  

This forces me to disable cost validation, even though this shouldn't be required.

What is expected?

cost(oneOf { f1, f2, ..., fn }) = max(cost(f1), cost(f2), ..., cost(fn))

What is actually happening?

cost(oneOf { f1, f2, ..., fn }) = cost(f1) + cost(f2) + ... + cost(fn))

Relevant log output

Additional context

No response

Start by reproducing the reported schema and mutation with the @oneOf input and weighted fields, then trace the cost calculation for OneOf input types. Done means the calculated cost uses the maximum field cost rather than summing all fields, while preserving the reported limit validation behavior.