Release pending host handles before V8 teardown

experiments/WebScene.NativeEngine.Probe/native/webscene_v8_runtime_lifecycle.inc

@@ -146,6 +146,12 @@
         pending_programmatic_scroll_events.clear();
         pending_interop_promises.clear();
         pending_callback_promises.clear();
+        // Native host and file completions can still be pending when a window
+        // closes. Their persistent context/resolver handles must be released
+        // while the isolate is alive; member destruction happens after this
+        // body and therefore after isolate disposal below.
+        host_promise_targets.clear();
+        file_targets.clear();
         pending_fetches.clear();
         interop_handles.clear();
         pending_promise_rejections.clear();

experiments/WebScene.NativeEngine.Probe/tests/native_v8_runtime_browser_dom_tests.inc

@@ -2956,6 +2956,49 @@ void test_native_legacy_clipboard_completion_stress(webscene_engine*)
     webscene_engine_destroy(engine);
 }
 
+void test_native_pending_legacy_clipboard_shutdown(webscene_engine*)
+{
+    auto* engine = webscene_engine_create(0);
+    require(engine != nullptr,
+        "pending legacy clipboard shutdown engine creation failed");
+    execute_and_wait(engine, R"JS(
+        document.body.innerHTML = '<textarea id="pending-copy"></textarea>';
+        const editor = document.getElementById('pending-copy');
+        editor.addEventListener('keydown', event => {
+          if (event.metaKey && event.key.toLowerCase() === 'c') {
+            event.preventDefault();
+            document.execCommand('copy');
+          }
+        });
+        editor.addEventListener('copy', event => {
+          event.clipboardData.setData('text/plain', 'pending close');
+          event.preventDefault();
+        });
+        editor.focus();
+    )JS", "native-pending-legacy-clipboard-shutdown-setup.js");
+
+    keyboard_input(
+        engine, WEBSCENE_INPUT_KEY_DOWN, 'C', 31001U,
+        WEBSCENE_INPUT_MODIFIER_META);
+    webscene_engine_metrics metrics{};
+    webscene_engine_get_metrics(engine, &metrics);
+    wait_for_consumed_inputs(
+        engine, metrics.enqueued_inputs,
+        "pending legacy clipboard shutdown input was not consumed");
+    const auto request = take_typed_host_request(engine);
+    require(
+        request.kind == WEBSCENE_HOST_REQUEST_CLIPBOARD_WRITE_V1
+            && request.content_type == "text/plain"
+            && std::string(request.bytes.begin(), request.bytes.end())
+                == "pending close",
+        "pending legacy clipboard shutdown did not retain its host promise");
+
+    // A native window may close before the operating-system host completes a
+    // request. Destruction must release the pending persistent resolver while
+    // its V8 isolate is still alive.
+    webscene_engine_destroy(engine);
+}
+
 void test_clipboard_maximum_payload_gate(webscene_engine* engine)
 {
     constexpr size_t maximum_bytes = 16U * 1024U * 1024U;

experiments/WebScene.NativeEngine.Probe/tests/native_v8_runtime_tests.cpp

@@ -833,6 +833,7 @@ int main()
     test_clipboard_read_host_completion(engine);
     test_native_clipboard_shortcut_events(engine);
     test_native_legacy_clipboard_completion_stress(engine);
+    test_native_pending_legacy_clipboard_shutdown(engine);
     test_clipboard_maximum_payload_gate(engine);
     test_clipboard_small_round_trip_performance(engine);
     test_fullscreen_host_completion(engine);