Constant WORD_ASSIGN_BUILTINS 

pub const WORD_ASSIGN_BUILTINS: &[&str];

Commands that consume bareword key=value argv (Arg::WordAssign) as shell-assignment pairs and route them through tool_args.named. For every other command, key=value lands as a positional "key=value" string — matching bash (cat foo=bar opens a file named foo=bar).

Add to this list only for builtins that have a documented shell-assignment argv contract (export FOO=bar, alias greet='echo hi'). Long-flag --key=value is a separate AST node (Arg::Named) and always routes through tool_args.named regardless.