Preserve numeric types for literal subtree port values

When literal values are passed to SubTree ports (not blackboard remapping),
detect numeric types (int64_t, double) before storing them in the child
blackboard. Previously all literals were stored as std::string, which caused
type-mismatch errors in Script expressions that tried to do arithmetic.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: L4co77

src/xml_parsing.cpp

@@ -12,10 +12,12 @@
 
 #include "behaviortree_cpp/basic_types.h"
 
+#include <charconv>
 #include <cstdio>
 #include <cstring>
 #include <functional>
 #include <iostream>
+#include <limits>
 #include <list>
 #include <sstream>
 #include <string>
@@ -1147,10 +1149,59 @@ void BT::XMLParser::PImpl::recursivelyCreateSubtree(
         }
         else
         {
-          // constant string: just set that constant value into the BB
+          // constant value: set it into the BB with appropriate type
           // IMPORTANT: this must not be autoremapped!!!
           new_bb->enableAutoRemapping(false);
-          new_bb->set(attr_name, static_cast<std::string>(attr_value));
+          const std::string str_value(attr_value);
+
+          // Try to preserve numeric types so that Script expressions
+          // can perform arithmetic without type-mismatch errors.
+          // Use std::from_chars with strict full-string validation to avoid
+          // false positives on compound strings like "1;2;3" or "2.2;2.4".
+          bool stored = false;
+          if(!str_value.empty())
+          {
+            const char* begin = str_value.data();
+            const char* end = begin + str_value.size();
+            // Try integer first (no decimal point, no exponent notation).
+            // Use int when the value fits, to match the most common port
+            // declarations. Fall back to int64_t for larger values.
+            if(str_value.find('.') == std::string::npos &&
+               str_value.find('e') == std::string::npos &&
+               str_value.find('E') == std::string::npos)
+            {
+              int64_t int_val = 0;
+              auto [ptr, ec] = std::from_chars(begin, end, int_val);
+              if(ec == std::errc() && ptr == end)
+              {
+                if(int_val >= std::numeric_limits<int>::min() &&
+                   int_val <= std::numeric_limits<int>::max())
+                {
+                  new_bb->set(attr_name, static_cast<int>(int_val));
+                }
+                else
+                {
+                  new_bb->set(attr_name, int_val);
+                }
+                stored = true;
+              }
+            }
+            // Try double
+            if(!stored)
+            {
+              double dbl_val = 0;
+              auto [ptr, ec] = std::from_chars(begin, end, dbl_val);
+              if(ec == std::errc() && ptr == end)
+              {
+                new_bb->set(attr_name, dbl_val);
+                stored = true;
+              }
+            }
+          }
+          if(!stored)
+          {
+            new_bb->set(attr_name, str_value);
+          }
           new_bb->enableAutoRemapping(do_autoremap);
         }
       }

tests/gtest_subtree.cpp

@@ -974,3 +974,41 @@ TEST(SubTree, NestedDuplicateNames_ShouldFail)
   // Should throw RuntimeError because of duplicate SubTree names
   ASSERT_THROW((void)factory.createTreeFromText(xml_text), RuntimeError);
 }
+
+// Regression test: literal numeric values passed to subtrees should preserve
+// their numeric type so that Script expressions can do arithmetic.
+TEST(SubTree, LiteralNumericPortsPreserveType)
+{
+  // clang-format off
+  static const char* xml_text = R"(
+<root BTCPP_format="4" main_tree_to_execute="MainTree">
+
+    <BehaviorTree ID="MainTree">
+        <Sequence>
+            <SubTree ID="DoMath" int_val="42" dbl_val="3.14" str_val="hello"
+                     remapped_val="{from_parent}" />
+        </Sequence>
+    </BehaviorTree>
+
+    <BehaviorTree ID="DoMath">
+        <Sequence>
+            <ScriptCondition code=" int_val + 1 == 43 " />
+            <ScriptCondition code=" dbl_val > 3.0 " />
+            <ScriptCondition code=" remapped_val + 1 == 101 " />
+        </Sequence>
+    </BehaviorTree>
+
+</root>
+)";
+  // clang-format on
+
+  BehaviorTreeFactory factory;
+
+  auto tree = factory.createTreeFromText(xml_text);
+
+  // Set the remapped parent value as an integer
+  tree.rootBlackboard()->set("from_parent", 100);
+
+  const auto status = tree.tickWhileRunning();
+  ASSERT_EQ(status, NodeStatus::SUCCESS);
+}