The field ‘totalFrames’ which is total number of frames available, is mandatory in StackTraces response for VSCode extension that implements DAP and declares capability 'supportsDelayedStackTraceLoading':

"The debug adapter supports the delayed loading of parts of the stack,
which requires that both the 'startFrame' and 'levels' arguments and the
'totalFrames' result of the 'StackTrace' request are supported."

Lack of this field makes VSCode incorrectly display stack traces information

D71034

lldb/tools/lldb-vscode/lldb-vscode.cpp

@@ -2166,6 +2166,8 @@ void request_stackTrace(const llvm::json::Object &request) {
         break;
       stackFrames.emplace_back(CreateStackFrame(frame));
     }
+    const auto totalFrames = thread.GetNumFrames();
+    body.try_emplace("totalFrames", totalFrames);
   }
   body.try_emplace("stackFrames", std::move(stackFrames));
   response.try_emplace("body", std::move(body));