nx_layout_box.nx

nx_layout_box.nx -- LayoutBox tree foundation for the Nishi browser. Phase 3 first primitive of docs/NISHI_BROWSER_ROADMAP.md, composes the Phase 2 CSS pipeline (nx_css_apply + value decoders) with the Phase 1 DOM tree (nx_html_tokenizer + nx_dom). This primitive owns ONLY the box-tree data structure -- no layout math here. nx_layout_block (next primitive, queued) walks this tree top-down in normal-flow order to assign concrete (x, y, w, h) pixels. nx_layout_inline (queued after that) handles line wrapping for inline boxes. LayoutBox kinds (sealed enum): BLOCK block-level box: <div>, <p>, <h1>...<h6>, <header>, etc. INLINE inline box: <span>, <a>, <em>, etc. INLINE_BLOCK inline-block: like inline externally, block internally TEXT terminal text run -- no children; content is bytes ANONYMOUS anonymous block wrapper inserted by spec when a block contains both block and inline children Tree layout (caller-owns-memory contract): The caller passes a `boxes: *LayoutBox` array + `max_boxes`. Boxes are appended in document order; parent/child/sibling links are indices into this array (-1 = none). Document root is at index 0 by convention. What this primitive does NOT do (queued for nx_layout_block): - assign x, y, w, h pixels (left as 0 until layout pass) - compute margin / padding / border from computed_style - resolve `width: auto` / `height: auto` - line-box generation for inline children - positioned-box layout (relative / absolute / fixed) - float / clear Per cardinal feedback-honest-perf-verdict-no-aspirational-claims: gap list is EXACT in this header. genealogy_id: w3c_css_box_model_module_level_3 + substrate_browser_phase_3_box_tree lineage_id: nishi_browser_layout_box_v1