Update 'restart connection' action to reset internal state (#19971)

## Summary of the Pull Request
I was becoming frustrated with getting in a state where a CLI app (i.e.
Copilot CLI) enters some VT state (like mouse mode) then doesn't unset
it when it accidentally exits. I normally use "Restart connection" to
keep the buffer and connect again. Problem is, "restart connection"
didn't actually reset the internal state! So I would type and get a
bunch of lingering VT escape sequences. This bug is tracked over in
#18425 in a more generic way.

This fixes that bug by doing the following:
- update `ITermDispatch::HardReset()` -->`HardReset(bool erase)`
   - `erase=true` does what `HardReset()` already did
- `erase=false` skips over clearing the screen and resetting the cursor
position
- expose `HardReset(false)` as `HardResetWithoutErase()` by piping it up
through `Terminal` --> `ControlCore` --> `TermControl`
-  update the restart connection handler
- `TerminalPage::_restartPaneConnection()` now calls
`HardResetWithoutErase()` before setting the new connection
- this is also the same route for the "Enter to restart connection"
scenario (text displayed when connection ends)

Relevant notes from PR discussion:
- `PSEUDOCONSOLE_INHERIT_CURSOR` is passed into the new connection via
`_restartPaneConnection()` --> `_duplicateConnectionForRestart()` -->
`_CreateConnectionFromSettings(profile,
*controlSettings.DefaultSettings(), true)`

## Validation Steps Performed
- Used this to enter mouse tracking mode: `Write-Host -NoNewline
"`e[?1003h`e[?1006h"`
- mouse selection doesn't work as usual (expected)
- invoke "restart connection" action
- mouse selection works as usual

Closes #18425

(cherry picked from commit ec939aa)
Service-Card-Id: PVTI_lADOAF3p4s4BBcTlzgpBL5w
Service-Version: 1.24

Author: carlos-zamora

src/cascadia/TerminalApp/TerminalPage.cpp

@@ -3707,7 +3707,13 @@ 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.HardResetWithoutErase();
+            termControl.Connection(connection);
             connection.Start();
         }
     }

src/cascadia/TerminalControl/ControlCore.cpp

@@ -349,6 +349,12 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         }
     }
 
+    void ControlCore::HardResetWithoutErase()
+    {
+        const auto lock = _terminal->LockForWriting();
+        _terminal->HardResetWithoutErase();
+    }
+
     bool ControlCore::Initialize(const float actualWidth,
                                  const float actualHeight,
                                  const float compositionScale)

src/cascadia/TerminalControl/ControlCore.h

@@ -260,6 +260,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
 
         TerminalConnection::ITerminalConnection Connection();
         void Connection(const TerminalConnection::ITerminalConnection& connection);
+        void HardResetWithoutErase();
 
         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 HardResetWithoutErase();
 
         IControlSettings Settings { get; };
         IControlAppearance FocusedAppearance { get; };

src/cascadia/TerminalControl/TermControl.cpp

@@ -536,6 +536,11 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         _core.Connection(newConnection);
     }
 
+    void TermControl::HardResetWithoutErase()
+    {
+        _core.HardResetWithoutErase();
+    }
+
     void TermControl::_throttledUpdateScrollbar(const ScrollBarUpdate& update)
     {
         if (!_initializedTerminal)

src/cascadia/TerminalControl/TermControl.h

@@ -194,6 +194,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
 
         TerminalConnection::ITerminalConnection Connection();
         void Connection(const TerminalConnection::ITerminalConnection& connection);
+        void HardResetWithoutErase();
 
         Control::CursorDisplayState CursorVisibility() const noexcept;
         void CursorVisibility(Control::CursorDisplayState cursorVisibility);

src/cascadia/TerminalControl/TermControl.idl

@@ -47,6 +47,7 @@ namespace Microsoft.Terminal.Control
         void UpdateControlSettings(IControlSettings settings, IControlAppearance unfocusedAppearance);
 
         Microsoft.Terminal.TerminalConnection.ITerminalConnection Connection;
+        void HardResetWithoutErase();
 
         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::HardResetWithoutErase()
+{
+    _assertLocked();
+    _stateMachine->ResetState();
+    auto& engine = reinterpret_cast<OutputStateMachineEngine&>(_stateMachine->Engine());
+    engine.Dispatch().HardReset(false);
+}
+
 // Method Description:
 // - Initializes the Terminal from the given set of settings.
 // Arguments:

src/cascadia/TerminalCore/Terminal.hpp

@@ -86,6 +86,7 @@ class Microsoft::Terminal::Core::Terminal final :
     void Create(til::size viewportSize,
                 til::CoordType scrollbackLines,
                 Microsoft::Console::Render::Renderer& renderer);
+    void HardResetWithoutErase();
 
     void CreateFromSettings(winrt::Microsoft::Terminal::Core::ICoreSettings settings,
                             Microsoft::Console::Render::Renderer& renderer);

src/terminal/adapter/ITermDispatch.hpp

@@ -135,7 +135,7 @@ class Microsoft::Console::VirtualTerminal::ITermDispatch
     virtual void AnnounceCodeStructure(const VTInt ansiLevel) = 0; // ACS
 
     virtual void SoftReset() = 0; // DECSTR
-    virtual void HardReset() = 0; // RIS
+    virtual void HardReset(bool erase) = 0; // RIS
     virtual void ScreenAlignmentPattern() = 0; // DECALN
 
     virtual void SetCursorStyle(const DispatchTypes::CursorStyle cursorStyle) = 0; // DECSCUSR