[ThomasMayerl]

The PCG would relabel delegation edges after writing to the underlying value. Therefore, writing to the underlying value (e.g., through a mutef) would decouple the mutref from a derived raw pointer. Afterwards, the PCG might convert the mutef to a generic type even though we are still accessing the rawptr. The following snippet shows this issue:

fn main() {
    let mut x = 3;
    let r_x = &mut x;
    let p_x = r_x as *mut i32;
    *r_x = *r_x + 1;
    unsafe { *p_x = *p_x + 1 };
    *r_x = *r_x + 1;
    assert!(x == 6);
}

This PR fixes this issue by preventing delegation edges from being relabelled after writing to a place.

Disclaimer: This PR was written using Claude Code.