nx_fbx_core.nx

nx_fbx_core.nx -- shared binary-FBX FORMAT knowledge. One place that knows how a Kaydara file is laid out, so consumers differ only in WHAT THEY EXTRACT, not in how they read a node. ★WHY THIS EXISTS (seq1788). The node walk was written twice: nx_fbx_rig.nx (rig survey -- joints, skin clusters, weights, animation curves; emits nothing by design) and nx_fbx_import.nx (geometry -> fx1024). The PURPOSES are genuinely different; the FORMAT READING was one thing duplicated. Worse, the two disagreed on capability: nx_fbx_rig handles BOTH u32 and u64 node offsets, while the geometry reader refused v7500+ outright. Consolidating here means a node-format bug has ONE home and geometry extraction inherits u64 support instead of re-deriving it. ★VERSION WIDENS THE HEADER, NOT JUST THE OFFSETS. v<7500: EndOffset/NumProps/PropListLen are u32 and the record header is 13 bytes. v>=7500: all three are u64 and the header is 25. Getting this wrong does not error -- it mis-strides the whole tree and yields plausible counts over garbage, which is exactly the failure shape this lane keeps meeting. license_tier: ORIGINAL