Single instance activities

[Ethan]

I'm new to cornerstone and just started looking at its code and
wondering how single instance activities are handled across panels?

Something like Activity A (single instance) running in Panel 1 and
Activity B (standard) running in Panel 2 and has a button to launch
Activity A.

Now, if the user clicks the button on Activity B to launch Activity
A, how does cornerstone handle it?

If i remember, in case of default stack of am, the task affinity of
activity A is changed.

[onhsnm]

This is handled in the ActivityManagerService, you can search for the cornerstone specific code and see the logic that restricts this case you describe from happening.