fix(connectivity_plus): defer Windows COM cleanup to final manager owner

packages/connectivity_plus/connectivity_plus/windows/connectivity_plus_plugin.cpp

@@ -82,7 +82,9 @@ ConnectivityPlusWindowsPlugin::ConnectivityPlusWindowsPlugin() {
 }
 
 ConnectivityPlusWindowsPlugin::~ConnectivityPlusWindowsPlugin() {
-  manager->Cleanup();
+  // The event stream can still own the manager. Stop callbacks now, and let
+  // the last shared owner release COM through NetworkManager's destructor.
+  manager->StopListen();
 }
 
 std::shared_ptr<NetworkManager>

packages/connectivity_plus/connectivity_plus/windows/tests/CMakeLists.txt

@@ -0,0 +1,37 @@
+cmake_minimum_required(VERSION 3.15)
+project(connectivity_cleanup_test LANGUAGES CXX)
+enable_testing()
+
+if(NOT WIN32)
+  message(FATAL_ERROR "This regression exercises real Windows COM.")
+endif()
+foreach(required FLUTTER_WRAPPER_DIR FLUTTER_ENGINE_DIR)
+  if(NOT IS_DIRECTORY "${${required}}")
+    message(FATAL_ERROR "Set ${required} to the existing Flutter SDK directory.")
+  endif()
+endforeach()
+
+add_library(flutter_wrapper_plugin STATIC
+  "${FLUTTER_WRAPPER_DIR}/core_implementations.cc"
+  "${FLUTTER_WRAPPER_DIR}/plugin_registrar.cc"
+  "${FLUTTER_WRAPPER_DIR}/standard_codec.cc")
+target_compile_features(flutter_wrapper_plugin PUBLIC cxx_std_17)
+target_compile_options(flutter_wrapper_plugin PRIVATE /utf-8)
+target_include_directories(flutter_wrapper_plugin PUBLIC
+  "${FLUTTER_WRAPPER_DIR}/include" "${FLUTTER_ENGINE_DIR}")
+target_link_libraries(flutter_wrapper_plugin PUBLIC
+  "${FLUTTER_ENGINE_DIR}/flutter_windows.dll.lib")
+
+add_executable(connectivity_cleanup_test
+  connectivity_cleanup_test.cpp "../network_manager.cpp")
+target_compile_features(connectivity_cleanup_test PRIVATE cxx_std_17)
+target_compile_options(connectivity_cleanup_test PRIVATE /utf-8)
+target_compile_definitions(connectivity_cleanup_test PRIVATE FLUTTER_PLUGIN_IMPL)
+target_link_libraries(connectivity_cleanup_test PRIVATE
+  flutter_wrapper_plugin ole32 oleaut32 uuid iphlpapi)
+add_custom_command(TARGET connectivity_cleanup_test POST_BUILD
+  COMMAND ${CMAKE_COMMAND} -E copy_if_different
+    "${FLUTTER_ENGINE_DIR}/flutter_windows.dll"
+    "$<TARGET_FILE_DIR:connectivity_cleanup_test>")
+
+add_test(NAME preserves_callers_com_apartment COMMAND connectivity_cleanup_test)

packages/connectivity_plus/connectivity_plus/windows/tests/README.md

@@ -0,0 +1,31 @@
+# Windows COM cleanup regression
+
+This standalone CTest compiles the actual plugin and `NetworkManager` with the
+Flutter Windows wrapper. It exercises the real COM apartment and network
+listener without launching a Flutter app. It does not change production builds
+or require an additional test framework.
+
+Use an existing Flutter Windows project's `windows/flutter/ephemeral` directory,
+generated by a Windows build, for the headers, wrapper sources, and engine DLL.
+From the `connectivity_plus` package directory on Windows:
+
+```powershell
+$engine = "<flutter-project>/windows/flutter/ephemeral"
+cmake -S windows/tests -B build/windows-cleanup-test -A x64 `
+  "-DFLUTTER_ENGINE_DIR=$engine" `
+  "-DFLUTTER_WRAPPER_DIR=$engine/cpp_client_wrapper"
+cmake --build build/windows-cleanup-test --config Release
+ctest --test-dir build/windows-cleanup-test -C Release --output-on-failure
+```
+
+The caller first initializes its own COM apartment. The plugin and the event
+stream then share a manager. After the plugin is destroyed, the listener must
+already be stopped but the manager must still be usable. Releasing the stream's
+owner must preserve the caller's apartment (`S_OK`).
+
+With the original plugin destructor calling `Cleanup()`, this test fails with
+`listener_stopped=false caller_apartment_hresult=0x800401f0`
+(`CO_E_NOTINITIALIZED`): the plugin and the manager each call `CoUninitialize()`
+for a single manager initialization. With `StopListen()` in the plugin
+destructor, it passes with `listener_stopped=true caller_apartment_hresult=0x0`.
+A COM initialization or listener setup failure is a test failure, not a pass.

packages/connectivity_plus/connectivity_plus/windows/tests/connectivity_cleanup_test.cpp

@@ -0,0 +1,41 @@
+// Include the actual plugin class, which is private to this translation unit.
+#include "../connectivity_plus_plugin.cpp"
+
+#include <iostream>
+
+int main() {
+  if (FAILED(CoInitializeEx(nullptr, COINIT_APARTMENTTHREADED))) {
+    std::cerr << "Could not initialize the caller's COM apartment."
+              << std::endl;
+    return 10;
+  }
+
+  auto plugin = std::make_unique<ConnectivityPlusWindowsPlugin>();
+  // The event-channel handler retains this owner until channel teardown.
+  auto stream_owner = plugin->GetManager();
+  if (!stream_owner->StartListen([] {})) {
+    std::cerr << "Could not start the initial listener." << std::endl;
+    return 11;
+  }
+
+  plugin.reset();
+  // Teardown must unregister the old listener without invalidating the shared
+  // manager. Starting another listener checks both conditions.
+  const bool listener_stopped = stream_owner->StartListen([] {});
+  if (listener_stopped) {
+    stream_owner->StopListen();
+  }
+  stream_owner.reset();
+
+  APTTYPE type;
+  APTTYPEQUALIFIER qualifier;
+  const HRESULT apartment = CoGetApartmentType(&type, &qualifier);
+  std::cout << "listener_stopped=" << std::boolalpha << listener_stopped
+            << " caller_apartment_hresult=0x" << std::hex
+            << static_cast<unsigned long>(apartment) << std::endl;
+  if (SUCCEEDED(apartment)) {
+    CoUninitialize();
+  }
+
+  return listener_stopped && apartment == S_OK ? 0 : 1;
+}