_mulcse_minrepro.nx

_mulcse_minrepro.nx -- COMPILER DEFECT min-repro (2026-06-10, found by nx_worldgen_tuner_test KAT4 + _ts_diag): in a function whose first statement builds a chained multiply from a PARAM (`grade * lw * lw`), a later `s = s + <call>() * lw` emits <call>*lw*lw -- the doubled multiply chain is wrongly reused (CSE/opt suspected). The all-literal local form does NOT reproduce (T1); the param+call form does (T2). Workaround that compiles right: hoist lw2 = lw*lw and each product into its own `let` (see tl_score in nx_worldgen_tunelib.nx). Exit 0 = compiler correct; exit 1 = T2 miscompile; exit 2 = T1 (new).