An up vote for addtional support for default values from me. I came across this when I had a query param that had a default value of false, found myself having check if it was nil and assuming a default which introduces a disconnect between the OAPI spec and the code:

var field bool
if params.Field != nil && params.Field {
    field = params.Field
}

// do something with `field`

I think the auto-generated client code requires no changes since a pointer value (!= nil) is used to differentate between a user provided value and no value.

So as you suggest, if the schema has a default value then having that set automatically if the request does not give a value would be a start. Dropping the pointer for a more user-friendly experience would be the next step. In my example I could then just use params.Field directly.

I've been having a look at the code changes to support this, I think that passing the default value to https://github.com/oapi-codegen/runtime/blob/912bc9f39f1e8fd175f1f39c48b4adf5ceca39f1/bindparam.go#L309 and using it is the majority of the solution to respecting the default value.