nx_chkarith_gate.nx

nx_chkarith_gate.nx -- GATE for LN1 checked integer arithmetic (lang.plan rung LN1, symbol chk_add_overflow). The rung's done-rule: i64 add and mul trap or refuse on overflow under a declared mode (--chkarith); an overflowing add TRAPS; an in-range program is byte-identical to today under the default (nothing is emitted unless the flag is on -- the equivalence net nx_cc_equiv_gate is the byte ruler for that half, this gate is the behaviour ruler). Subjects: the toolchain compiler (argv[1], default the live builder) + runtime/nx_checked_arith.nx + runtime/nx_checked_arith_const.nx. Driver = nx_ccgate_lib (the ONE compiler-gate driver, extracted from the LN3 gate): data captures in /tmp/nxchk/, RUNNABLES under _build/ (NAS /tmp is noexec), per-pid paths, phase exit codes PRINTED before the teeth. Usage: nx_chkarith_gate [compiler_elf] (CWD = the tree root, like nx_cc_equiv_gate) license_tier: ORIGINAL No hw writes (Rule 26).