toExactPointer

The exact pointer this value names, when it names exactly one — A12's toDocumentPointer().

Two things have to be true, and each has its own reason.

1. Every level resolves to one row. The final level may additionally hold WILDCARD, because on an exact pointer that digit is not a wildcard at all but the RepetitionsV2 slot; above the last level a zero really is a wildcard. An unresolved level (UNKNOWN) or a wildcard above the last one names a set or a level that matched no row.

2. Every level can be named. An exact pointer is a list of parts, and a part needs a non-empty name, so an empty level — the interior of /Order//Items — has no part to become. That name is legal on this type (the message factory validates splitting only), which is exactly why the case is reachable.

Either way the answer is null, and null is an answer rather than a failure — A12 reports both as an absent Optional. (For the empty level that is A12's PRODUCTION behaviour; its conversion catches the part rejection and returns empty, guarded by a bare assert that additionally raises under -ea. We match what runs in production, and A12PointerKernelDomainDiffTest measures both assertion modes so the difference is recorded rather than absorbed.)

The root reports differently, and that is measured behaviour rather than a choice. A12's own conversion cannot answer for a zero-length pointer: it raises instead of returning an absent result (IllegalArgumentException, kernel 30.8.1, in both assertion modes because the failure happens before its own guard). Returning the root exact pointer here would be repairing an edge while claiming to be the counterpart of the thing being repaired.