Fix "response position" definition; clarify sibling errors on propagation

At a glance

• Identifier: #1183
• Stage: RFC 3 / Accepted
• Champion: @benjie
• Latest activity: Spec PR merged on 2026-09-17
• Spec PR: https://github.com/graphql/graphql-spec/pull/1183

Spec PR description

If a response position resolves to {null} because of an execution error which has already been added to the {"errors"} list in the execution result, the {"errors"} list must not be further affected. That is, only one error should be added to the errors list per response position.

The response position mentioned at the beginning of this paragraph is different to the response position from which the error originated; therefore "only one error should be added to the errors list per response position" is kind of moot. Actually what we mean here is that the response path of the error (i.e. the "path" entry in the error object) should be unique.

This edit clarifies that it's the "path" of the error that matters (and should be unique), not the position that re-raised it.