[BUG] Mutate doesn't properly attribute commanders

I included a game log where I mutated my commander on top of a mutate pile but I was unable to cast [[Deflecting Swat]] for free. My understanding is that as long as your commander is in a mutate pile the pile is your commander. I've included the game log, but not sure how useful it will be.

[20260607_194602_Freeform Unlimited Commander_1.html](https://github.com/user-attachments/files/28696795/20260607_194602_Freeform.Unlimited.Commander_1.html)

Start with the attached 20260607_194602_Freeform Unlimited Commander_1.html game log and follow the mutate-pile commander handling involved in the reported sequence. The issue is done when a commander in a mutate pile is correctly recognized as the commander and Deflecting Swat can be cast for free.

Written by the indexing model from the issue text.