Item.GlueItem

Item.BoxItem, Item.GlueItem, and Item.PenaltyItem preserve their record payloads. Constructing these records and variants does not plan a paragraph or validate its measurements.

BoxItem and GlueItem contribute one measured unit each in their encounter order. Their unitIndex fields must be exactly zero through the unit count minus one. PenaltyItem contributes a boundary without consuming a unit index.

Box.text and Glue.text retain the supplied string, including empty text and multiple Unicode scalars. A measured unit remains indivisible. Unit indices count these records rather than bytes, scalars, or grapheme clusters.

Box.width and Glue.width include trackingAfter. Width and width minus trackingAfter must both be nonnegative. Tracking may be positive, zero, or negative while those two conditions hold.

Each width, tracking amount, stretch, and shrink is a Length<Pt>. Paragraph planning quantizes it through the selected grid. A line span sums its unit widths and removes the final unit's trackingAfter.

Glue.stretch and Glue.shrink are nonnegative adjustment capacities. A box supplies zero capacity. The selected cost and justification policies determine how capacities participate in planning.

Positive capacity does not itself insert text or change the input records. Unjustified planning performs no distributed adjustment. Text trimming and model-specific glue treatment follow the PlanLine and paragraph contracts.

breakParagraph returns InvalidInput for a noncontiguous unitIndex, a negative width or capacity, or a negative width before tracking. Validation applies even when a later candidate would discard that unit.

The function uses the supplied measurements without shaping the text again. It does not reorder or mutate the caller's item array or its records.