A segment as emitted by a concrete segmenter's SegmentCore, before the base
class normalizes it (assigns Sequence/Depth/TokenEstimate, enforces the
token ceiling, and resolves parent links).
ParentIndex refers to the index within the raw array returned by
SegmentCore; the base class remaps it to a real Sequence afterwards, which
keeps subclasses from having to reason about post-split numbering.
A segment as emitted by a concrete segmenter's
SegmentCore, before the base class normalizes it (assignsSequence/Depth/TokenEstimate, enforces the token ceiling, and resolves parent links).ParentIndexrefers to the index within the raw array returned bySegmentCore; the base class remaps it to a realSequenceafterwards, which keeps subclasses from having to reason about post-split numbering.