docs: [SDK-5083] correct why the demo extender is conditional

The comment claimed an extender makes the SDK display a data-only push, so
installing a no-op one would not be inert. That is not how 5.x behaves.
processHandlerResponse gates on canDisplay, a non-empty notification body,
before it reaches shouldDisplayNotification, so hasExtender() is never read
for a bodyless push and an extender cannot rescue one.

The code stays as it is. Setting an extender only when a switch needs one is
still right, just for the duller reason that nothing asked for it otherwise.
Left uncorrected, a customer reading the demo could design around SDK
behavior that does not exist.

Author: nan-li

examples/build.md

@@ -232,7 +232,7 @@ The five behavior switches sit behind a Show options / Hide options row so the s
 
 The channel readout comes from `NotificationCompat.getChannelId(builder.build())` inside the extender, the only place an extension can see the SDK's choice. A restored notification lands on `restored_OS_notifications` no matter what the payload asked for, which the payload alone never shows. `event.restoring` is not on `INotificationReceivedEvent` yet; see the TODO in the class and SDK-5011.
 
-An extender also makes the SDK display a data-only push that carries no `alert` (`NotificationGenerationProcessor.shouldDisplayNotification`), so the class sets one only when a switch needs it.
+The class sets an extender only when a switch needs one rather than installing a no-op whenever the extension is on, which is about not doing work nothing asked for. An extender cannot change what displays. `NotificationGenerationProcessor.shouldDisplayNotification` does read `hasExtender()`, but `processHandlerResponse` has already dropped a push with an empty body on `canDisplay` by the time it runs.
 
 ---
 

examples/demo/app/src/main/java/com/onesignal/example/notification/DemoNotificationServiceExtension.kt

@@ -53,9 +53,11 @@ class DemoNotificationServiceExtension : INotificationServiceExtension {
             return
         }
 
-        // Set an extender only when a switch needs one. An extender makes the SDK display a
-        // data-only push that carries no `alert` (NotificationGenerationProcessor
-        // .shouldDisplayNotification), so an always-installed no-op extender is not free.
+        // Set an extender only when a switch needs one, rather than installing a no-op
+        // whenever the extension is on. This is about not doing work nothing asked for.
+        // An extender cannot change what displays: NotificationGenerationProcessor
+        // .shouldDisplayNotification does read hasExtender(), but processHandlerResponse
+        // has already dropped a push with an empty body on canDisplay by the time it runs.
         if (options.logDetails || options.applyExtender || options.forceHighImportanceChannel) {
             notification.setExtender(buildExtender(event.context, notification, options))
         }