Progress is flickering

[fw2568]

When progress is shown in compute client (e.g. new-Catlet) the progress is flickering, see this gif:

AB#686

[ChristopherMann]

After some investigation, I have not found any good solution to prevent the flickering. Some general notes:

• Powershell 7 supports two rendering modes: Classic and Minimal:
  • Minimal is the default and shows one-line progress at the bottom
  • Classic has the same behavior as Powershell 5 and shows an overlay at the top
• For performance reasons, Powershell renders progress updates only when a timer expires or an activity is completed. See https://github.com/PowerShell/PowerShell/blob/b428e1a393242ce15e54f24c6fcd9d8bae97ada2/src/Microsoft.PowerShell.ConsoleHost/host/msh/ConsoleHostUserInterfaceProgress.cs#L99. Hence, the amount and timing of render updates is hard to predict.
• The Classic mode flickers in both Powershell 5 and 7 when using the new Windows Terminal (checked with version 1.21). I was able to reproduce the flickering with a minimal example which just starts and completes child activities in a loop.

The Windows Terminal currently has quite few open issues related to flickering and other rendering issues. We should postpone this issue for now as the root cause is most likely the rendering of Windows Terminal.