nx_gramdec_lib.nx

nx_gramdec_lib.nx -- NB10 GRAMMAR-CONSTRAINED DECODE (neuro-symbolic builder lane, 2026-07-20). Makes the small maker STRUCTURALLY UNABLE to emit ungrammatical NishiLang candidates: a token is sampled, its decoded bytes are run through a NishiLang function-fragment prefix automaton, and a rejected token is LOGIT-MASKED and re-sampled (renormalized constrained decode). EOS is masked until the function is brace-complete (the model cannot stop mid-function); once complete, decode stops (accept-state). Greedy steps that the grammar accepts ride the UNCHANGED head_argmax hero path -- the mask only engages on a rejection, so an already-grammatical generation is BIT-EXACT with nsv_generate over its prefix. HONEST SCOPE (v1): a regular+counter APPROXIMATION of NishiLang for SELF-CONTAINED integer functions (the v1 judge's declared scope) -- brace/paren balance, `else` only as `} else {` (kills the else-if build-break class), NO calls in the body (ident '(' reject + known-helper denylist: kills abs()/min() undefined-fn breaks), unary minus on an identifier rejected while negative literals stay legal, charset fence. Grammar-valid != correct: the fresh compile+run grader and nx_symjudge property sweep still judge EVERY candidate (the union stays sound; the mask only shrinks the candidate space). Fail-closed: a mask deadlock stops generation (honest MISS), never lets an ungrammatical token through. license_tier: ORIGINAL No hw writes (Rule 26).