mac: subclass NSApplication for CEF and fix close handling

Add NebulaApplication (NSApplication<CefAppProtocol>) to implement isHandlingSendEvent/setHandlingSendEvent and override sendEvent to use CefScopedSendingEvent, preventing "unrecognized selector" crashes during CEF event/window teardown. Instantiate NebulaApplication in PrepareApp. Also relax the Windows-only guard in NebulaController::OnWindowCloseRequested and update the comment so per-tab closes on macOS don't trigger full app shutdown. Files changed: src/platform/mac/startup_mac.mm, src/app/nebula_controller.cpp.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/app/nebula_controller.cpp

@@ -241,13 +241,12 @@ void NebulaController::OnWindowResized(const nebula::window::BrowserLayout& layo
 }
 
 void NebulaController::OnWindowCloseRequested() {
-#if defined(_WIN32)
     if (!closing_ && !closing_tab_browsers_.empty()) {
         // CEF Alloy can bubble a child browser close as WM_CLOSE on the host
-        // window. Per-tab closes should not turn into full app shutdown.
+        // window (Windows) or performClose: on the host window (OS X). Per-tab
+        // closes should not turn into full app shutdown.
         return;
     }
-#endif
 
     if (launch_options_.mode == AppMode::BigPicture && !closing_) {
         if (!SwitchToSiblingMode(AppMode::Desktop)) {

src/platform/mac/startup_mac.mm

@@ -8,9 +8,40 @@
 #include <sys/file.h>
 #include <unistd.h>
 
+#include "include/cef_application_mac.h"
 #include "include/cef_command_line.h"
 #include "ui/paths.h"
 
+// All CEF client applications must subclass NSApplication and implement the
+// CefAppProtocol. CEF's message pump and window teardown code calls
+// -[NSApplication isHandlingSendEvent:]/setHandlingSendEvent: (through
+// CefScopedSendingEvent) while dispatching events. Against the plain
+// NSApplication those selectors do not exist, so any code path that reaches
+// them (for example closing a tab while a browser view is being torn down)
+// raises "unrecognized selector sent to NSApplication" and crashes.
+@interface NebulaApplication : NSApplication <CefAppProtocol> {
+ @private
+    BOOL handling_send_event_;
+}
+@end
+
+@implementation NebulaApplication
+
+- (BOOL)isHandlingSendEvent {
+    return handling_send_event_;
+}
+
+- (void)setHandlingSendEvent:(BOOL)handlingSendEvent {
+    handling_send_event_ = handlingSendEvent;
+}
+
+- (void)sendEvent:(NSEvent*)event {
+    CefScopedSendingEvent sending_event_scoper;
+    [super sendEvent:event];
+}
+
+@end
+
 namespace nebula::platform {
 namespace {
 
@@ -20,7 +51,10 @@ int g_single_instance_lock = -1;
 
 void PrepareApp() {
     @autoreleasepool {
-        [NSApplication sharedApplication];
+        // Create the shared application as NebulaApplication (CefAppProtocol)
+        // before anything else touches NSApp so the CEF pipeline always sees
+        // the protocol methods it requires.
+        [NebulaApplication sharedApplication];
         [NSApp setActivationPolicy:NSApplicationActivationPolicyRegular];
         [NSApp finishLaunching];
     }