Update 'restart connection' action to reset internal state

src/cascadia/TerminalApp/TerminalPage.cpp

@@ -3742,7 +3742,13 @@ namespace winrt::TerminalApp::implementation
         // for nulls
         if (const auto& connection{ _duplicateConnectionForRestart(paneContent) })
         {
-            paneContent.GetTermControl().Connection(connection);
+            // Reset the terminal's VT state before attaching the new connection.
+            // The previous client may have left dirty modes (e.g., bracketed
+            // paste, mouse tracking, alternate buffer, kitty keyboard) that
+            // would corrupt input/output for the new shell process.
+            const auto& termControl = paneContent.GetTermControl();
+            termControl.ResetConnection();
+            termControl.Connection(connection);
             connection.Start();
         }
     }

src/cascadia/TerminalControl/ControlCore.cpp

@@ -355,6 +355,12 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         }
     }
 
+    void ControlCore::ResetConnection()
+    {
+        const auto lock = _terminal->LockForWriting();
+        _terminal->ResetConnection();
+    }
+
     bool ControlCore::Initialize(const float actualWidth,
                                  const float actualHeight,
                                  const float compositionScale)

src/cascadia/TerminalControl/ControlCore.h

@@ -257,6 +257,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
 
         TerminalConnection::ITerminalConnection Connection();
         void Connection(const TerminalConnection::ITerminalConnection& connection);
+        void ResetConnection();
 
         void AnchorContextMenu(til::point viewportRelativeCharacterPosition);
 

src/cascadia/TerminalControl/ControlCore.idl

@@ -98,6 +98,7 @@ namespace Microsoft.Terminal.Control
         void ApplyAppearance(Boolean focused);
 
         Microsoft.Terminal.TerminalConnection.ITerminalConnection Connection;
+        void ResetConnection();
 
         IControlSettings Settings { get; };
         IControlAppearance FocusedAppearance { get; };

src/cascadia/TerminalControl/TermControl.cpp

@@ -532,6 +532,11 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         _core.Connection(newConnection);
     }
 
+    void TermControl::ResetConnection()
+    {
+        _core.ResetConnection();
+    }
+
     void TermControl::_throttledUpdateScrollbar(const ScrollBarUpdate& update)
     {
         if (!_initializedTerminal)

src/cascadia/TerminalControl/TermControl.h

@@ -192,6 +192,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
 
         TerminalConnection::ITerminalConnection Connection();
         void Connection(const TerminalConnection::ITerminalConnection& connection);
+        void ResetConnection();
 
         Control::CursorDisplayState CursorVisibility() const noexcept;
         void CursorVisibility(Control::CursorDisplayState cursorVisibility);

src/cascadia/TerminalControl/TermControl.idl

@@ -53,6 +53,7 @@ namespace Microsoft.Terminal.Control
         void SetOverrideColorScheme(Microsoft.Terminal.Core.ICoreScheme scheme);
 
         Microsoft.Terminal.TerminalConnection.ITerminalConnection Connection;
+        void ResetConnection();
 
         UInt64 ContentId{ get; };
 

src/cascadia/TerminalCore/Terminal.cpp

@@ -55,6 +55,18 @@ void Terminal::Create(til::size viewportSize, til::CoordType scrollbackLines, Re
     _stateMachine = std::make_unique<StateMachine>(std::move(engine));
 }
 
+// Method Description:
+// - Resets all VT state to defaults without clearing the buffer content.
+// Called when a connection is restarted so that any dirty modes left
+// behind by a crashed application don't affect the new connection.
+void Terminal::ResetConnection()
+{
+    _assertLocked();
+    _stateMachine->ResetState();
+    auto& engine = reinterpret_cast<OutputStateMachineEngine&>(_stateMachine->Engine());
+    engine.Dispatch().HardResetWithoutBufferClear();
+}
+
 // Method Description:
 // - Initializes the Terminal from the given set of settings.
 // Arguments:

src/cascadia/TerminalCore/Terminal.hpp

@@ -85,6 +85,7 @@ class Microsoft::Terminal::Core::Terminal final :
     void Create(til::size viewportSize,
                 til::CoordType scrollbackLines,
                 Microsoft::Console::Render::Renderer& renderer);
+    void ResetConnection();
 
     void CreateFromSettings(winrt::Microsoft::Terminal::Core::ICoreSettings settings,
                             Microsoft::Console::Render::Renderer& renderer);

src/terminal/adapter/ITermDispatch.hpp

@@ -140,6 +140,7 @@ class Microsoft::Console::VirtualTerminal::ITermDispatch
 
     virtual void SoftReset() = 0; // DECSTR
     virtual void HardReset() = 0; // RIS
+    virtual void HardResetWithoutBufferClear() = 0;
     virtual void ScreenAlignmentPattern() = 0; // DECALN
 
     virtual void SetCursorStyle(const DispatchTypes::CursorStyle cursorStyle) = 0; // DECSCUSR

src/terminal/adapter/adaptDispatch.cpp

@@ -2994,6 +2994,31 @@ void AdaptDispatch::SoftReset()
 //Arguments:
 // <none>
 void AdaptDispatch::HardReset()
+{
+    _hardResetCore(true);
+}
+
+// Routine Description:
+// - Performs a hard reset of all VT state without clearing the buffer content
+//   or scrollback. This is used when a connection is restarted to clean up
+//   any dirty state left behind by a crashed application (e.g., bracketed
+//   paste, mouse tracking, alternate buffer, kitty keyboard, etc.).
+// Arguments:
+// - None
+void AdaptDispatch::HardResetWithoutBufferClear()
+{
+    _hardResetCore(false);
+}
+
+// Routine Description:
+// - Shared implementation for HardReset and HardResetWithoutBufferClear.
+//   Resets all VT state (parser, input modes, display modes, character sets,
+//   color table, tab stops, macros, etc.) to initial defaults. When
+//   clearBuffers is true, the screen and scrollback are also erased (full
+//   RIS behavior). When false, buffer content is preserved.
+// Arguments:
+// - clearBuffers: if true, erase the screen and scrollback
+void AdaptDispatch::_hardResetCore(const bool clearBuffers)
 {
     // If in the alt buffer, switch back to main before doing anything else.
     if (_usingAltBuffer)
@@ -3020,9 +3045,12 @@ void AdaptDispatch::HardReset()
     //      to ensure that it clears with the default background color.
     SoftReset();
 
-    // Clears the screen - Needs to be done in two operations.
-    EraseInDisplay(DispatchTypes::EraseType::All);
-    EraseInDisplay(DispatchTypes::EraseType::Scrollback);
+    if (clearBuffers)
+    {
+        // Clears the screen - Needs to be done in two operations.
+        EraseInDisplay(DispatchTypes::EraseType::All);
+        EraseInDisplay(DispatchTypes::EraseType::Scrollback);
+    }
 
     // Set the color table and render modes back to their initial startup values.
     _renderSettings.RestoreDefaultSettings();
@@ -3033,8 +3061,14 @@ void AdaptDispatch::HardReset()
         _renderer->SynchronizedOutputChanged();
     }
 
-    // Cursor to 1,1 - the Soft Reset guarantees this is absolute
-    CursorPosition(1, 1);
+    if (clearBuffers)
+    {
+        // Cursor to 1,1 - the Soft Reset guarantees this is absolute.
+        // Only done when clearing buffers, because when preserving content
+        // the cursor should stay where the previous shell left it so the
+        // new shell prompt appears in the right place.
+        CursorPosition(1, 1);
+    }
 
     // We only reset the system line feed mode if the input mode is set. If it
     // isn't set, that either means they're both reset, and there's nothing for

src/terminal/adapter/adaptDispatch.hpp

@@ -129,6 +129,7 @@ namespace Microsoft::Console::VirtualTerminal
         void AnnounceCodeStructure(const VTInt ansiLevel) override; // ACS
         void SoftReset() override; // DECSTR
         void HardReset() override; // RIS
+        void HardResetWithoutBufferClear() override;
         void ScreenAlignmentPattern() override; // DECALN
         void SetCursorStyle(const DispatchTypes::CursorStyle cursorStyle) override; // DECSCUSR
 
@@ -195,6 +196,7 @@ namespace Microsoft::Console::VirtualTerminal
         void SetOptionalFeatures(const til::enumset<OptionalFeature> features) noexcept override;
 
     private:
+        void _hardResetCore(const bool clearBuffers);
         enum class Mode
         {
             InsertReplace,

src/terminal/adapter/termDispatch.hpp

@@ -127,6 +127,7 @@ class Microsoft::Console::VirtualTerminal::TermDispatch : public Microsoft::Cons
 
     void SoftReset() override {} // DECSTR
     void HardReset() override {} // RIS
+    void HardResetWithoutBufferClear() override {}
     void ScreenAlignmentPattern() override {} // DECALN
 
     void SetCursorStyle(const DispatchTypes::CursorStyle /*cursorStyle*/) override {} // DECSCUSR