fix(macos): preserve Flutter quit approval after AppKit cancellation

Distinguish native NSTerminateLater replies from AppKit acknowledgements of synchronous cancellation while Flutter is still deciding asynchronously. Keep the pending Flutter ticket alive until its channel response and cover the acknowledgement in the real-engine regression. Refs #65.

Author: lijy91

src/platform/macos/application_quit_macos.mm

@@ -45,6 +45,7 @@ void Reset(id object) {
   WeakObject host;
   std::shared_ptr<nativeapi::EventRequest> request;
   bool asking = true, decided = false, approved = false, waiting_host = false;
+  bool waiting_appkit_reply = false;
   explicit Session(id target) : host(target) {}
 };
 struct FlutterBridge;
@@ -92,6 +93,7 @@ NSApplicationTerminateReply Continue(
       const std::function<NSApplicationTerminateReply()>& original) {
     owner->ObserveHost(target->host.Get());
     target->waiting_host = false;
+    target->waiting_appkit_reply = false;
     ++entering;
     NSApplicationTerminateReply reply;
     @try {
@@ -104,6 +106,7 @@ NSApplicationTerminateReply Continue(
       End(target);
     } else if (reply == NSTerminateLater) {
       target->waiting_host = true;
+      target->waiting_appkit_reply = true;
     } else if (!target->waiting_host) {
       End(target);  // An ordinary host cancellation, without an async bridge.
     }
@@ -281,7 +284,11 @@ void InstallFlutterBridge(const std::shared_ptr<FlutterBridge>& bridge) {
   if (!impl_->app)
     return;
   auto target = impl_->session;
-  if (impl_->Current(target) && target->waiting_host) {
+  // AppKit also calls this with NO after a synchronous NSTerminateCancel.
+  // Flutter returns Cancel while its own channel reply is pending; that
+  // notification must not invalidate the ticket for its eventual approval.
+  // Only NSTerminateLater delegates finish through this AppKit reply API.
+  if (impl_->Current(target) && target->waiting_appkit_reply) {
     if (allowed)
       impl_->announced_termination = true;
     impl_->End(target);

tests/application_flutter_engine_macos_test.mm

@@ -15,7 +15,11 @@ @interface HeadlessQuitApplication : NSApplication
 @end
 @implementation HeadlessQuitApplication
 - (void)terminate:(id)sender {
-  [self.delegate applicationShouldTerminate:self];
+  const auto reply = [self.delegate applicationShouldTerminate:self];
+  // Real AppKit acknowledges NSTerminateCancel this way even when Flutter
+  // still has its own asynchronous Dart decision outstanding (#65).
+  if (reply == NSTerminateCancel)
+    [self replyToApplicationShouldTerminate:NO];
 }
 @end
 
@@ -149,7 +153,7 @@ int main(int argc, char** argv) {
     std::thread worker([&] { b->Accept(); });
     worker.join();
     check(WaitFor([&] { return state->requests == 3; }) && pending(),
-          "worker approval resumes the real Flutter request on UI");
+          "AppKit cancel acknowledgement preserves the pending Dart request after worker approval");
     check([[coordinator valueForKey:@"shouldTerminate"] boolValue] && ask() == NSTerminateCancel,
           "Flutter's early shouldTerminate flag cannot authorize a repeated user quit");
     app.Quit(23);