Update getVar to check locals first, then globals:

fn getVar(name: []const u8) i64 {
    // Check locals first (innermost scope wins)
    var i: usize = num_vars;
    while (i > 0) {
        i -= 1;
        if (streq(var_names[i], name)) {
            return var_values[i];
        }
    }
    // Then globals
    return getGlobal(name);
}

Update setVar the same way -- check locals, then globals, then create a new local:

fn setVar(name: []const u8, val: i64) void {
    // Check locals first
    for (0..num_vars) |i| {
        if (streq(var_names[i], name)) {
            var_values[i] = val;
            return;
        }
    }
    // Check globals
    for (0..num_globals) |i| {
        if (streq(global_names[i], name)) {
            global_values[i] = val;
            return;
        }
    }
    // Create new local
    var_names[num_vars] = name;
    var_values[num_vars] = val;
    num_vars += 1;
}

Now setVar finds existing variables in either scope. If x is a global, assigning x = 99 inside a function updates the global. If y is a local, it updates the local. If neither exists, it creates a new local.