Add an aliasing replay case

[fraware]

Add one deterministic example where two variables share an object, a nested field changes, and reverse stepping restores both references.

Done when forward and reverse states agree, repeated runs produce the same snapshot sequence, and a focused regression test passes.

A good first contribution for someone interested in debugger semantics.

[fraware]

Interested in taking this? Comment with the small program you plan to use. I’ll help keep the scenario narrow.