Fix copyOnSelect right-click overwriting clipboard with stale selection

[sagarbhure-msft]

Summary of the Pull Request

Fix copyOnSelect right-click paste overwriting the clipboard with a stale selection instead of pasting the current clipboard contents.

References and Relevant Issues

Closes #19942

Detailed Description of the Pull Request / Additional comments

When copyOnSelect is enabled, the selected text is already copied to the clipboard on left mouse button release in PointerReleased. The selection is intentionally left visible as a visual reference (the _selectionNeedsToBeCopied flag is set to false to track that the copy already happened).

However, the right-click handler in PointerPressed unconditionally called CopySelectionToClipboard() before pasting, ignoring both the copyOnSelect setting and the _selectionNeedsToBeCopied flag. This caused any still-visible selection to be re-copied to the clipboard, overwriting whatever the user may have copied from another application (or another terminal tab) in the meantime.

This change splits the right-click behavior based on the copyOnSelect setting:

• copyOnSelect: true — Skip the redundant copy, clear the selection, and paste directly. The text was already copied on mouse-up.
• copyOnSelect: false — Preserve existing behavior: copy the selection (if any), clear it, and paste only if there was no selection to copy.

Validation Steps Performed

1. Set "copyOnSelect": true in settings.json.
2. Selected text in a terminal pane - verified it was copied to clipboard on mouse-up.
3. Switched to Notepad, copied different text ("NEW TEXT").
4. Switched back to Terminal (selection still visible), right-clicked — verified "NEW TEXT" was pasted, not the old selection.
5. Verified right-click with no active selection still pastes clipboard contents.
6. Verified right-click immediately after selecting (no app switch) pastes the just-selected text.
7. Set "copyOnSelect": false — verified right-click still copies selection first, then pastes only when no selection exists (original behavior unchanged).
8. Verified tab-switching with an active selection does not cause stale clipboard overwrites on right-click.

PR Checklist

• Closes Right click paste also does a copy with copyOnSelect #19942
• Tests added/passed
• Documentation updated
  • If checked, please file a pull request on our docs repo and link it here: #xxx
• Schema updated (if necessary)

[sagarbhure-msft]

@microsoft-github-policy-service agree

[lhecker]

This can be shortened IMO:

// GH#19942: With copyOnSelect the selection was already copied when the
// user released the left mouse button. Don't re-copy it on right-click.
// Otherwise, we copy the selection if any.
const auto paste = _core->CopyOnSelect() || !CopySelectionToClipboard(shiftEnabled, false, _core->Settings().CopyFormatting());

_core->ClearSelection();

// With copyOnSelect any right click turns into a paste.
// Otherwise, only if there was no selection to copy, it's a paste.
if (paste)
{
    RequestPasteTextFromClipboard();
}

[zadjii-msft]

Reviewers may want to x-ref this much much older PR of mine:
#14635

[carlos-zamora]

Thanks for the x-ref Mike!

Yeah, the same problem from #14635 happens. Blocking over that.

Bug:

1. ensure copy on select is enabled
2. enter mark mode
3. make a selection with mark mode
4. right-click to copy/paste

expected: selection is copied and pasted immediately

NOTE: similar thing happens when you make a mouse selection, then modify it using quick-edit keys (i.e. shift+right). The selected text is not copied and pasted immediately.

from #14635 (review)

[carlos-zamora]

Root cause from a chat with GH Copilot:

The root cause: _selectionNeedsToBeCopied is only set to true in SetEndSelectionPoint() (mouse drag path, line 699). Mark mode selections go through TryMarkModeKeybinding →
UpdateSelection() → _updateSelectionUI(), which never sets that flag. So for mark mode, the right-click copy was the only opportunity to copy the selection.

[sagarbhure-msft]

Thanks for the x-ref Mike!

Yeah, the same problem from #14635 happens. Blocking over that.

Bug:

1. ensure copy on select is enabled
2. enter mark mode
3. make a selection with mark mode
4. right-click to copy/paste

expected: selection is copied and pasted immediately
NOTE: similar thing happens when you make a mouse selection, then modify it using quick-edit keys (i.e. shift+right). The selected text is not copied and pasted immediately.

from #14635 (review)

ack, looking into this...