Stable AppId via ComputeAppId()

I was wondering if it's possible to somehow generate stable AppIds or override the AppId to something stable (for unpackaged apps)?

My Scenario:

Single Instance App, works perfectly fine when installed on machine, problem occurs when I try to run a portable version of my app for example (or launching from Visual Studio when the machine version is installed and running). Since the app exes are in separate locations, they gain separate AppIds, and instance redirecting no longer works.

This has caught us out a few times when debugging things internally, and we've also observed in the wild users with multiple instances of our app running at the same time (usually by doing weird things to their machine - but it would be nice to handle this regardless).

Start by tracing how AppIds are generated for unpackaged apps and how single-instance redirection uses them. Compare installed, portable, and Visual Studio launch scenarios described in the issue. Done means the required API or behavior for a stable AppId is clearly defined and the separate launch locations can redirect to the same instance.

Written by the indexing model from the issue text.