Function miniextendr_assert_utf8_locale 

#[unsafe(no_mangle)]
pub extern "C-unwind" fn miniextendr_assert_utf8_locale()

Assert that R’s locale is UTF-8.

Called once from R_init_* (package init). Errors if the R session does not use UTF-8, since charsxp_to_str assumes all CHARSXP bytes are valid UTF-8.

Uses l10n_info()[["UTF-8"]] which is public R API.

ABI: must be extern "C-unwind", not extern "C" — the failure branch raises via Rf_error, and under webR (Emscripten builds R with -sSUPPORT_LONGJMP=wasm) that longjmp is a real wasm exception that unwinds through this frame. A non-unwind extern "C" ABI makes rustc insert an abort guard at the boundary, which turns the load-gate error into an unreachable trap that kills the whole wasm runtime (observed in the tier-3 testthat pass via assert_utf8_locale_now()). On native targets longjmp never touches landing pads, which is why this only bit on wasm32.