Function trait_call 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn trait_call(
    json_ptr: *const u8,
    json_len: usize,
    out_len: *mut usize,
) -> *mut u8

C ABI entry point: receives JSON args, calls trait function, returns JSON result.

Safety

• json_ptr must point to json_len valid bytes of JSON
• out_len must be a valid pointer to write the result length
• Caller must free the returned buffer via trait_free