This fixes #9109

  This is kind of annoying that the auto-scrolling is handled by the
  TermControl, but it uses a timer that's still a WinUI construct.

  We only want to start the auto-scrolling behavior when the drag started
  _inside_ the control. Otherwise, in the tab drag scenario, dragging into the
  bounds of the TermControl will trick it into thinking it should start a
  scroll.

src/cascadia/TerminalControl/TermControl.cpp

@@ -1049,6 +1049,8 @@ namespace winrt::Microsoft::Terminal::Control::implementation
             Focus(FocusState::Pointer);
         }
 
+        _pointerPressedInBounds = true;
+
         if (type == Windows::Devices::Input::PointerDeviceType::Touch)
         {
             const auto contactRect = point.Properties().ContactRect();
@@ -1103,8 +1105,12 @@ namespace winrt::Microsoft::Terminal::Control::implementation
                                         _focused,
                                         pixelPosition);
 
-            if (_focused && point.Properties().IsLeftButtonPressed())
+            if (_focused && _pointerPressedInBounds && point.Properties().IsLeftButtonPressed())
             {
+                // We want to find the distance relative to the bounds of the
+                // SwapChainPanel, not the entire control. If they drag out of
+                // the bounds of the text, into the padding, we still what that
+                // to auto-scroll
                 const double cursorBelowBottomDist = cursorPosition.Y - SwapChainPanel().Margin().Top - SwapChainPanel().ActualHeight();
                 const double cursorAboveTopDist = -1 * cursorPosition.Y + SwapChainPanel().Margin().Top;
 
@@ -1154,6 +1160,8 @@ namespace winrt::Microsoft::Terminal::Control::implementation
             return;
         }
 
+        _pointerPressedInBounds = false;
+
         const auto ptr = args.Pointer();
         const auto point = args.GetCurrentPoint(*this);
         const auto cursorPosition = point.Position();

src/cascadia/TerminalControl/TermControl.h

@@ -167,11 +167,13 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         std::shared_ptr<ThrottledFuncTrailing<ScrollBarUpdate>> _updateScrollBar;
         bool _isInternalScrollBarUpdate;
 
-        // Auto scroll occurs when user, while selecting, drags cursor outside viewport. View is then scrolled to 'follow' the cursor.
+        // Auto scroll occurs when user, while selecting, drags cursor outside
+        // viewport. View is then scrolled to 'follow' the cursor.
         double _autoScrollVelocity;
         std::optional<Windows::UI::Input::PointerPoint> _autoScrollingPointerPoint;
         Windows::UI::Xaml::DispatcherTimer _autoScrollTimer;
         std::optional<std::chrono::high_resolution_clock::time_point> _lastAutoScrollUpdateTime;
+        bool _pointerPressedInBounds{ false };
 
         winrt::Windows::UI::Composition::ScalarKeyFrameAnimation _bellLightAnimation{ nullptr };
         Windows::UI::Xaml::DispatcherTimer _bellLightTimer{ nullptr };