Function inv_rx

tests/repro/repro_invariant_lib.h:23–25

/* ── Single-file extraction ─────────────────────────────────────── */

static inline CBMFileResult *inv_rx(const char *src, CBMLanguage lang, const char *file) {
    return cbm_extract_file(src, (int)strlen(src), lang, "t", file, 0, NULL, NULL);
}

/* INV(extract-clean): extraction returns non-NULL and does not set has_error on
 * valid input (a parser crash/abort would not return at all → subprocess-isolate