canonicalErrorCode
Returns the canonical conformance error code for this KpaAccessError, as used in conformance fixture JSON files.
MutateListIndexNotInteger and MutateListIndexOutOfRange intentionally map to the same code (KP-4004); the two exception types exist only to preserve their distinct standard-library supertypes.
Return
The canonical errorCode string (e.g. "KP-3001") for this failure.
Receiver
The adapter failure raised while resolving or mutating a document.