[BugFix][Harmony] Bind NativeFacade actor to UI runner and clarify callback threads

Fix Harmony standalone runtime initialization by binding the NativeFacade
actor to the UI task runner, matching Harmony's single UI thread model
for native callbacks.

Also document callback thread expectations across platforms:
- Android: mark background runtime callbacks as invoked on the JS thread
- iOS: update header comments to state callbacks are on the JS thread
- Harmony: annotate ETS callbacks as invoked on the UI thread

AutoSubmit: True
issue: m-7305562623
AutoLand: release/3.9, release/3.8, release_3.8_weekly_20260522
SkipChecks:macro

Author: lybvinci

core/shell/runtime/bts/bts_runtime_standalone_helper.cc

@@ -8,6 +8,7 @@
 #include <utility>
 #include <vector>
 
+#include "core/base/threading/task_runner_manufactor.h"
 #include "core/base/threading/vsync_monitor.h"
 #include "core/runtime/js/jsi/jsi.h"
 #include "core/services/event_report/event_tracker_platform_impl.h"
@@ -42,7 +43,15 @@ BTSRuntimeStandalone::InitRuntimeStandalone(
       lynx::base::TaskRunnerManufactor::GetJSRunner(group_name);
   auto native_runtime_facade =
       std::make_shared<lynx::shell::LynxActor<lynx::shell::NativeFacade>>(
-          std::move(native_facade_runtime), js_task_runner, instance_id, true);
+          std::move(native_facade_runtime),
+#if OS_HARMONY
+          // Harmony only exposes a single UI thread for native callbacks,
+          // so the NativeFacade actor must be bound to the UI runner.
+          base::UIThread::GetRunner(),
+#else
+          js_task_runner,
+#endif
+          instance_id, true);
   std::shared_ptr<base::VSyncMonitor> vsync_monitor =
       base::VSyncMonitor::Create();
 

platform/android/lynx_android/src/main/java/com/lynx/tasm/LynxBackgroundRuntime.java

@@ -23,6 +23,7 @@
 import com.lynx.tasm.base.LLog;
 import com.lynx.tasm.core.JSProxy;
 import com.lynx.tasm.core.resource.LynxResourceLoader;
+import com.lynx.tasm.utils.UIThreadUtils;
 import java.lang.ref.WeakReference;
 import java.nio.charset.Charset;
 import java.util.HashMap;
@@ -352,27 +353,36 @@ public void unsubscribeSessionStorage(String key, double id) {
     }
   }
 
+  // Invoked on the JS thread, dispatched to the UI thread before notifying clients.
   @RestrictTo(RestrictTo.Scope.LIBRARY)
   @Override
   @CalledByNative
   public void onErrorOccurred(LynxError error) {
-    for (LynxBackgroundRuntimeClient client : mRuntimeClients) {
-      client.onReceivedError(error);
-    }
+    UIThreadUtils.runOnUiThread(() -> {
+      for (LynxBackgroundRuntimeClient client : mRuntimeClients) {
+        client.onReceivedError(error);
+      }
+    });
   }
 
+  // Invoked on the JS thread, dispatched to the UI thread before notifying clients.
   @CalledByNative
   public void onModuleMethodInvoked(String module, String method, int error_code) {
-    for (LynxBackgroundRuntimeClient client : mRuntimeClients) {
-      client.onModuleMethodInvoked(module, method, error_code);
-    }
+    UIThreadUtils.runOnUiThread(() -> {
+      for (LynxBackgroundRuntimeClient client : mRuntimeClients) {
+        client.onModuleMethodInvoked(module, method, error_code);
+      }
+    });
   }
 
+  // Invoked on the JS thread, dispatched to the UI thread before notifying clients.
   @CalledByNative
   public void onEvaluateJavaScriptEnd(String url) {
-    for (LynxBackgroundRuntimeClient client : mRuntimeClients) {
-      client.onEvaluateJavaScriptEnd(url);
-    }
+    UIThreadUtils.runOnUiThread(() -> {
+      for (LynxBackgroundRuntimeClient client : mRuntimeClients) {
+        client.onEvaluateJavaScriptEnd(url);
+      }
+    });
   }
 
   public boolean attachToLynxView() {

platform/android/lynx_android/src/main/java/com/lynx/tasm/LynxBackgroundRuntimeClient.java

@@ -5,7 +5,10 @@
 package com.lynx.tasm;
 
 public abstract class LynxBackgroundRuntimeClient {
+  // Invoked on the UI thread.
   public void onReceivedError(LynxError error) {}
+  // Invoked on the UI thread.
   public void onModuleMethodInvoked(String module, String method, int error_code) {}
+  // Invoked on the UI thread.
   public void onEvaluateJavaScriptEnd(String url) {}
 }

platform/harmony/lynx_harmony/src/main/ets/tasm/LynxBackgroundRuntime.ets

@@ -67,6 +67,7 @@ export class LynxBackgroundRuntime extends lynx.LynxRuntimeWrapper {
   }
 
   // client callback
+  // Invoked on the UI thread.
   onErrorOccurred(level: string, errorCode: number, message: string, suggestion: string,
     customInfo: Record<string, string>, logboxOnly: boolean) {
     let err = new LynxError(LynxErrorLevel[level], errorCode, message, suggestion, LynxError.NATIVE_ERROR, customInfo);
@@ -81,12 +82,14 @@ export class LynxBackgroundRuntime extends lynx.LynxRuntimeWrapper {
     });
   }
 
+  // Invoked on the UI thread.
   onModuleMethodInvoked(module: string, method: string, error_code: number) {
     this.clients.forEach(client => {
       client.onModuleMethodInvoked(module, method, error_code);
     });
   }
 
+  // Invoked on the UI thread.
   onEvaluateJavaScriptEnd(url: string) {
     this.clients.forEach(client => {
       client.onEvaluateJavaScriptEnd(url);