Using OpenAPI overlays, when an update applies to several targets the update object/source is applied by reference to all targets.

This means that if you subsequently try to make a further update to only one of these targets, this update will be applied to all of the previously applied targets (via the reference)

This PR adds a structuredClone to the update object which makes a deep copy/clone of it before applying, which I think is the correct fix for the issue. (Note: structuredClone is available from node 17)

I've included a rough reproduction which is the easiest way to see the problem. If you revert the fix I've applied here you will see that the output of the overlay produces something like the following i.e. the second update is applied three times.

...
a:
  type: object
  oneOf:
    - type: object
      properties:
        type:
          const: c
        c:
          type: object
    - type: object
      properties:
        type:
          const: c
        c:
          type: object
    - type: object
      properties:
        type:
          const: c
        c:
          type: object
...

I've also added some comments in the reproduction to help understand the issue, I'd be happy to remove these before merge if you don't want these to stay in there.

Let me know if you have any questions on the above 👍