Fix Reactive Sequence async control node validation (#1183)

The XML check that rejects more than one asynchronous control node under a
ReactiveSequence (they livelock: the reactive parent restarts the first one
every tick and halts the second) recognized AsyncSequence but not
AsyncFallback. Add it, and drop ThreadedAction / StatefulActionNode /
CoroActionNode from the list: they are base classes, never registered as
CONTROL nodes, so those names could not match. Async *actions* are still not
detected by this check (#1184).

Behavior change: a ReactiveSequence with two or more direct children among
AsyncSequence / AsyncFallback, at least one of them an AsyncFallback, now
fails to load, like two AsyncSequence already did.

Author: vivoeiva

src/xml_parsing.cpp

@@ -679,10 +679,11 @@ void VerifyXML(const std::string& xml_text,
                          std::string("Unknown node type: ") + child_name);
             }
             const auto child_type = child_search->second;
+            // Only the asynchronous CONTROL nodes can be detected here: the
+            // manifest does not record whether an ACTION is asynchronous, so
+            // async leaf actions are not caught.
             if(child_type == NodeType::CONTROL &&
-               ((child_name == "ThreadedAction") ||
-                (child_name == "StatefulActionNode") ||
-                (child_name == "CoroActionNode") || (child_name == "AsyncSequence")))
+               ((child_name == "AsyncSequence") || (child_name == "AsyncFallback")))
             {
               ++async_count;
               if(async_count > 1)

tests/gtest_reactive.cpp

@@ -187,6 +187,83 @@ TEST(Reactive, TwoAsyncNodesInReactiveSequence)
   EXPECT_ANY_THROW(auto tree = factory.createTreeFromText(reactive_xml_text));
 }
 
+TEST(Reactive, TwoAsyncFallbacksInReactiveSequence)
+{
+  static const char* reactive_xml_text = R"(
+<root BTCPP_format="4" >
+  <BehaviorTree ID="MainTree">
+    <ReactiveSequence>
+      <AsyncFallback name="first">
+        <TestA/>
+        <TestB/>
+        <TestC/>
+      </AsyncFallback>
+      <AsyncFallback name="second">
+        <TestD/>
+        <TestE/>
+        <TestF/>
+      </AsyncFallback>
+    </ReactiveSequence>
+  </BehaviorTree>
+</root>
+)";
+
+  BT::BehaviorTreeFactory factory;
+  std::array<int, 6> counters{};
+  RegisterTestTick(factory, "Test", counters);
+
+  EXPECT_ANY_THROW(auto tree = factory.createTreeFromText(reactive_xml_text));
+}
+
+TEST(Reactive, AsyncSequenceAndAsyncFallbackInReactiveSequence)
+{
+  static const char* reactive_xml_text = R"(
+<root BTCPP_format="4" >
+  <BehaviorTree ID="MainTree">
+    <ReactiveSequence>
+      <AsyncSequence name="first">
+        <TestA/>
+        <TestB/>
+      </AsyncSequence>
+      <AsyncFallback name="second">
+        <TestC/>
+        <TestD/>
+      </AsyncFallback>
+    </ReactiveSequence>
+  </BehaviorTree>
+</root>
+)";
+
+  BT::BehaviorTreeFactory factory;
+  std::array<int, 6> counters{};
+  RegisterTestTick(factory, "Test", counters);
+
+  EXPECT_ANY_THROW(auto tree = factory.createTreeFromText(reactive_xml_text));
+}
+
+TEST(Reactive, SingleAsyncChildInReactiveSequenceIsAllowed)
+{
+  static const char* reactive_xml_text = R"(
+<root BTCPP_format="4" >
+  <BehaviorTree ID="MainTree">
+    <ReactiveSequence>
+      <TestA/>
+      <AsyncFallback name="only_async">
+        <TestB/>
+        <TestC/>
+      </AsyncFallback>
+    </ReactiveSequence>
+  </BehaviorTree>
+</root>
+)";
+
+  BT::BehaviorTreeFactory factory;
+  std::array<int, 6> counters{};
+  RegisterTestTick(factory, "Test", counters);
+
+  EXPECT_NO_THROW(auto tree = factory.createTreeFromText(reactive_xml_text));
+}
+
 // ============ Phase 4: Additional Reactive Tests ============
 
 TEST(Reactive, ReactiveSequence_FirstChildFails)