Function param_enabled 

pub fn param_enabled() -> bool

PARAMETRIC rectangular-opening fast path (placement-frame, ground-truth-exact cut). DEFAULT ON – opt out with IFC_LITE_RECT_PARAM=0 (parametric path only), IFC_LITE_RECT_FAST=0 (the GLOBAL rect-fast kill switch: disables this path AND the legacy enabled path, preserving the documented single-flag parity/bisection hatch), or param_set_enabled_override. Gated separately from enabled because it is a deliberate behaviour change: it emits the analytic box-minus-boxes solid, which is MORE correct than the exact kernel on engulfing-opening walls. Corpus-validated ON (tests/rect_param_validate.rs A/B over 5 real models): every non-firing element byte-identical ON vs OFF, every firing host watertight and matching the analytic ground truth. wasm has no env, so std::env::var errs there and the default is ON on both targets – native==wasm stays in lockstep; the wasm-side setRectParamFastPath override remains the programmatic escape hatch (and, being an explicit per-process call, takes precedence over both env flags).