How wasteful is it to call this typename? Because this is a typename, right?

Most of the time but actually I've added a fallback to the schema type for the case where __typename is not selected. But yeah typename may be a better name and I see no waste in that.

{
  node {
     id 
     ... on Product {
       price
     }
  }
}

This record will be stored with a typename of Node? That sounds dangerous. Might be worth throwing if typename is not queried?

This record will be stored with a typename of Node? That sounds dangerous.

✅

Might be worth throwing if typename is not queried?

Interesting! I'm hesitant because this is only useful if you need to remove by type (a rare use case). Meanwhile requiring __typename on all selections is kind of a big change. On the other hand, __typename will already be present in most cases when using @typePolicy.

Make typename nullable in the SQL schema and throw (or ignore) in the removeByTypes() if the typename isn't known?

We should document what the use case is for removeByTypes(). My hunch is that if people want to remove a certain type of data for security or expiration reasons, they probably want typename all the time (and there is an option for that in the codegen)