canonicalErrorKind
Returns the canonical error-kind string for this KpaAccessError, as used in conformance fixture JSON files.
MutateListIndexNotInteger and MutateListIndexOutOfRange intentionally map to the same string (mutate-invalid-list-index); the two exception types exist only to preserve their distinct standard-library supertypes.
Return
The canonical errorKind string for this failure.
Receiver
The adapter failure raised while resolving or mutating a document.