Implement the FTCS_PROMPT sequence for marking the start of the prompt

.github/actions/spelling/allow/allow.txt

@@ -26,6 +26,7 @@ EDDC
 Enum'd
 Fitt
 formattings
+FTCS
 ftp
 fvar
 gcc

src/terminal/adapter/ITermDispatch.hpp

@@ -137,6 +137,8 @@ class Microsoft::Console::VirtualTerminal::ITermDispatch
 
     virtual bool DoITerm2Action(const std::wstring_view string) = 0;
 
+    virtual bool DoFinalTermAction(const std::wstring_view string) = 0;
+
     virtual StringHandler DownloadDRCS(const VTInt fontNumber,
                                        const VTParameter startChar,
                                        const DispatchTypes::DrcsEraseControl eraseControl,

src/terminal/adapter/adaptDispatch.cpp

@@ -2509,6 +2509,56 @@ bool AdaptDispatch::DoITerm2Action(const std::wstring_view string)
     return false;
 }
 
+// Method Description:
+// - Performs a FinalTerm action
+// - Currently, the actions we support are:
+//   * `OSC133;A`: mark a line as a prompt line
+// - Not actually used in conhost
+// - The remainder of the FTCS prompt sequences are tracked in GH#11000
+// Arguments:
+// - string: contains the parameters that define which action we do
+// Return Value:
+// - false in conhost, true for the SetMark action, otherwise false.
+bool AdaptDispatch::DoFinalTermAction(const std::wstring_view string)
+{
+    // This is not implemented in conhost.
+    if (_api.IsConsolePty())
+    {
+        // Flush the frame manually, to make sure marks end up on the right line, like the alt buffer sequence.
+        _renderer.TriggerFlush(false);
+        return false;
+    }
+
+    if constexpr (!Feature_ScrollbarMarks::IsEnabled())
+    {
+        return false;
+    }
+
+    const auto parts = Utils::SplitString(string, L';');
+
+    if (parts.size() < 1)
+    {
+        return false;
+    }
+
+    const auto action = til::at(parts, 0);
+
+    if (action == L"A") // FTCS_PROMPT
+    {
+        // Simply just mark this line as a prompt line.
+        DispatchTypes::ScrollMark mark;
+        mark.category = DispatchTypes::MarkCategory::Prompt;
+        _api.AddMark(mark);
+        return true;
+    }
+
+    // When we add the rest of the FTCS sequences (GH#11000), we should add a
+    // simple state machine here to track the most recently emitted mark from
+    // this set of sequences, and which sequence was emitted last, so we can
+    // modify the state of that mark as we go.
+    return false;
+}
+
 // Method Description:
 // - DECDLD - Downloads one or more characters of a dynamically redefinable
 //   character set (DRCS) with a specified pixel pattern. The pixel array is

src/terminal/adapter/adaptDispatch.hpp

@@ -132,6 +132,8 @@ namespace Microsoft::Console::VirtualTerminal
 
         bool DoITerm2Action(const std::wstring_view string) override;
 
+        bool DoFinalTermAction(const std::wstring_view string) override;
+
         StringHandler DownloadDRCS(const VTInt fontNumber,
                                    const VTParameter startChar,
                                    const DispatchTypes::DrcsEraseControl eraseControl,

src/terminal/adapter/termDispatch.hpp

@@ -130,6 +130,8 @@ class Microsoft::Console::VirtualTerminal::TermDispatch : public Microsoft::Cons
 
     bool DoITerm2Action(const std::wstring_view /*string*/) override { return false; }
 
+    bool DoFinalTermAction(const std::wstring_view /*string*/) override { return false; }
+
     StringHandler DownloadDRCS(const VTInt /*fontNumber*/,
                                const VTParameter /*startChar*/,
                                const DispatchTypes::DrcsEraseControl /*eraseControl*/,

src/terminal/parser/OutputStateMachineEngine.cpp

@@ -842,6 +842,11 @@ bool OutputStateMachineEngine::ActionOscDispatch(const wchar_t /*wch*/,
         success = _dispatch->DoITerm2Action(string);
         break;
     }
+    case OscActionCodes::FinalTermAction:
+    {
+        success = _dispatch->DoFinalTermAction(string);
+        break;
+    }
     default:
         // If no functions to call, overall dispatch was a failure.
         success = false;

src/terminal/parser/OutputStateMachineEngine.hpp

@@ -188,6 +188,7 @@ namespace Microsoft::Console::VirtualTerminal
             ResetForegroundColor = 110, // Not implemented
             ResetBackgroundColor = 111, // Not implemented
             ResetCursorColor = 112,
+            FinalTermAction = 133,
             ITerm2Action = 1337,
         };