Function source 

pub fn source(s: &str) -> i32

Port of mod_export enum source_return source(char *s) from Src/init.c:1551.

Body dispatches through with_executor to the fusevm bytecode pipeline (execute_script_zsh_pipeline), matching the path bins/zshrs.rs::source_from_memory takes. scriptname / scriptfilename / sourcelevel are saved+restored around the nested execution per the C save/restore at c:1572-1670.