Function par_subsh_wordcode_impl 

pub fn par_subsh_wordcode_impl(cmplx: &mut i32, zsh_construct: i32)

Src/parse.c:1619-1665. Handles both (...) subshell and {...} brace group (cursh) plus optional always { ... } trailing block. C uses a single function with zsh_construct=1 for {...} and 0 for (...).