Fix parsing of chunked win32-input-mode sequences (#16466)

Even with the previous fixes we still randomly encounter win32-
input-mode sequences that are broken up in exactly such a way that
e.g. lone escape keys are encounters. Those for instance clear the
current prompt. The remaining parts of the sequence are then visible.

This changeset fixes the issue by skipping the entire force-to-ground
code whenever we saw at least 1 win32-input-mode sequence.

Related to #16343

## Validation Steps Performed
* Host a ConPTY inside ConPTY (= double the trouble) with cmd.exe
* Paste random amounts of text
* In the old code spurious `[..._` strings are seen
* In the new code they're consistently gone ✅

(cherry picked from commit bc18348)
Service-Card-Id: 91337332
Service-Version: 1.19

src/terminal/parser/IStateMachineEngine.hpp

@@ -28,6 +28,8 @@ namespace Microsoft::Console::VirtualTerminal
         IStateMachineEngine& operator=(const IStateMachineEngine&) = default;
         IStateMachineEngine& operator=(IStateMachineEngine&&) = default;
 
+        virtual bool EncounteredWin32InputModeSequence() const noexcept = 0;
+
         virtual bool ActionExecute(const wchar_t wch) = 0;
         virtual bool ActionExecuteFromEscape(const wchar_t wch) = 0;
         virtual bool ActionPrint(const wchar_t wch) = 0;

src/terminal/parser/InputStateMachineEngine.cpp

@@ -102,6 +102,11 @@ InputStateMachineEngine::InputStateMachineEngine(std::unique_ptr<IInteractDispat
     THROW_HR_IF_NULL(E_INVALIDARG, _pDispatch.get());
 }
 
+bool InputStateMachineEngine::EncounteredWin32InputModeSequence() const noexcept
+{
+    return _encounteredWin32InputModeSequence;
+}
+
 void InputStateMachineEngine::SetLookingForDSR(const bool looking) noexcept
 {
     _lookingForDSR = looking;
@@ -448,6 +453,7 @@ bool InputStateMachineEngine::ActionCsiDispatch(const VTID id, const VTParameter
         // Ctrl+C, Ctrl+Break are handled correctly.
         const auto key = _GenerateWin32Key(parameters);
         success = _pDispatch->WriteCtrlKey(key);
+        _encounteredWin32InputModeSequence = true;
         break;
     }
     default:

src/terminal/parser/InputStateMachineEngine.hpp

@@ -132,6 +132,7 @@ namespace Microsoft::Console::VirtualTerminal
         InputStateMachineEngine(std::unique_ptr<IInteractDispatch> pDispatch,
                                 const bool lookingForDSR);
 
+        bool EncounteredWin32InputModeSequence() const noexcept override;
         void SetLookingForDSR(const bool looking) noexcept;
 
         bool ActionExecute(const wchar_t wch) override;
@@ -167,6 +168,7 @@ namespace Microsoft::Console::VirtualTerminal
         const std::unique_ptr<IInteractDispatch> _pDispatch;
         std::function<bool()> _pfnFlushToInputQueue;
         bool _lookingForDSR;
+        bool _encounteredWin32InputModeSequence = false;
         DWORD _mouseButtonState = 0;
         std::chrono::milliseconds _doubleClickTime;
         std::optional<til::point> _lastMouseClickPos{};

src/terminal/parser/OutputStateMachineEngine.cpp

@@ -23,6 +23,11 @@ OutputStateMachineEngine::OutputStateMachineEngine(std::unique_ptr<ITermDispatch
     THROW_HR_IF_NULL(E_INVALIDARG, _dispatch.get());
 }
 
+bool OutputStateMachineEngine::EncounteredWin32InputModeSequence() const noexcept
+{
+    return false;
+}
+
 const ITermDispatch& OutputStateMachineEngine::Dispatch() const noexcept
 {
     return *_dispatch;

src/terminal/parser/OutputStateMachineEngine.hpp

@@ -29,6 +29,8 @@ namespace Microsoft::Console::VirtualTerminal
 
         OutputStateMachineEngine(std::unique_ptr<ITermDispatch> pDispatch);
 
+        bool EncounteredWin32InputModeSequence() const noexcept override;
+
         bool ActionExecute(const wchar_t wch) override;
         bool ActionExecuteFromEscape(const wchar_t wch) override;
 

src/terminal/parser/stateMachine.cpp

@@ -2144,9 +2144,15 @@ void StateMachine::ProcessString(const std::wstring_view string)
         // which breaks up many of our longer sequences, like our Win32InputMode ones.
         //
         // As a heuristic, this code specifically checks for a trailing Esc or Alt+key.
+        // If we encountered a win32-input-mode sequence before, we know that our \x1b[?9001h
+        // request to enable them was successful. While a client may still send \x1b{some char}
+        // intentionally, it's far more likely now that we're looking at a broken up sequence.
+        // The most common win32-input-mode is ConPTY itself after all, and we never emit
+        // \x1b{some char} once it's enabled.
         if (_isEngineForInput)
         {
-            if (run.size() <= 2 && run.front() == L'\x1b')
+            const auto win32 = _engine->EncounteredWin32InputModeSequence();
+            if (!win32 && run.size() <= 2 && run.front() == L'\x1b')
             {
                 _EnterGround();
                 if (run.size() == 1)

src/terminal/parser/ut_parser/StateMachineTest.cpp

@@ -40,6 +40,11 @@ class Microsoft::Console::VirtualTerminal::TestStateMachineEngine : public IStat
         dcsDataString.clear();
     }
 
+    bool EncounteredWin32InputModeSequence() const noexcept override
+    {
+        return false;
+    }
+
     bool ActionExecute(const wchar_t wch) override
     {
         executed += wch;