Fix: Prevent Enter key leaking to terminal during Command Palette actions

[nicolasalarconrapela]

Summary of the Pull Request

This PR addresses the issue reported in #20188, where triggering the "Export Text" action from the Command Palette would result in a phantom Enter key press being sent to the active terminal session.

The original implementation marked the event as handled (args.Handled(true)) only after invoking the _ExportTab function. When no predefined file path is provided (the default behavior in the Command Palette), _ExportTab triggers a modal Windows dialog (FileSavePicker). This system dialog captures the UI focus immediately.

The Problem

Because the focus shifted before the event was marked as handled, the WinUI event routing system allowed the residual Enter keystroke to "leak" into the terminal control that regained focus in the background.

This behavior might stem from an early design focus on single-window control architectures, as seen in previous discussions like: #6635

Solution

1. Early Neutralization: Moved args.Handled(true); to the very beginning of the _HandleExportBuffer method. This ensures the Enter event is consumed by the Command Palette while it still holds focus, preventing any further propagation.

2. Flow Refactoring: Refactored the method to utilize a single execution path for _ExportTab. The method now prepares the path string and executes the call once, improving code readability and ensuring consistent behavior regardless of whether a path argument is provided.

Validation Steps Performed

Before

After

PR Checklist

• Closes "Export text" action invoked from cmd paletter forwards Enter key #20188
• Tests passed (Manual validation and successful compilation)
• Documentation updated
• Schema updated (if necessary)

[nicolasalarconrapela]

@microsoft-github-policy-service agree

[carlos-zamora]

Thanks for the contribution! Sorry for the delay in reviewing this.

I've verified that this does fix the issue. However, I think this change can be simplified a bit. Rather than detecting if it's an export buffer action in the command palette, we can add co_await wil::resume_foreground(Dispatcher()); to _ExportTab() directly. I'm going ahead and opening a separate PR for this. Thanks again for looking into this!

[carlos-zamora]

Closing in favor of #20358