Why local class can access const local variables of enclosing function?

I recently discovered that local class cannot access Auto variables of enclosing function as they might contain invalid reference to local variable. For Example

struct Helper {
    virtual int getLocal() = 0;
};

Helper* nutshell(){
    int local = 123;
    struct Internal : public Helper {
        int i = INT16_MAX; // Unnecessary
        int getLocal(){ return local; }
    };
    return new Internal();
};

The above code is disaster because getLocal has invalid reference to local. A solution for this could be making local static or enum, But what's interesting for me is that making it a const is also a possible way.

struct Helper {
    virtual int getLocal() = 0;
};

Helper* nutshell(){
    const int local = 123;
    struct Internal : public Helper {
        int i = INT16_MAX; // Unnecessary
        int getLocal(){ return local; }
    };
    return new Internal();
};

My question is why is that, Why local class can access const variable?

Isn't a const qualified variable a Auto variable?