nx_uxf_decode.nx

nx_uxf_decode.nx -- UXF arc R1c-2: the TOLERANT-READER decoder for canon_cid's NXR1 canonical form (ADDITIVE; canon_cid stays encode-only and untouched -- Rule 19/3). Canonical layout (from nx_canon_cid): magic "NXR1" | u32be nfields | per field: u32be klen | key | u32be vlen | value. The decoder parses EVERY field back into (key,value) pointer arrays -- it does NOT filter by a "known-key" set, so fields a consumer doesn't understand are PRESERVED, not dropped. Re-encoding the decoded fields reproduces identical canonical bytes => identical CID. That is the house-of-cards fix (Law-4): new data never breaks an old reader, because the reader round-trips unknown fields intact. Defensive at the boundary (Rule 12): malformed framing -> negative verdict, never OOB. No hardware writes (Rule 26). license_tier: ORIGINAL