diff --git a/CMakeLists.txt b/CMakeLists.txt
index 86aeaf743..b7edc1629 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -28,6 +28,7 @@ option(USE_VENDORED_FLATBUFFERS "Use the bundled version of flatbuffers" ON)
 option(USE_VENDORED_LEXY "Use the bundled version of lexy" ON)
 option(USE_VENDORED_MINICORO "Use the bundled version of minicoro" ON)
 option(USE_VENDORED_MINITRACE "Use the bundled version of minitrace" ON)
+option(USE_VENDORED_JSON "Use the bundled version of nlohmann/json" ON)
 
 set(BTCPP_LIB_DESTINATION     lib)
 set(BTCPP_INCLUDE_DESTINATION include)
@@ -150,6 +151,10 @@ else()
     find_package(minitrace REQUIRED)
 endif()
 
+if(NOT USE_VENDORED_JSON)
+    find_package(nlohmann_json 3.10 REQUIRED)
+endif()
+
 list(APPEND BT_SOURCE
     src/action_node.cpp
     src/basic_types.cpp
@@ -263,6 +268,12 @@ target_include_directories(${BTCPP_LIBRARY}
 target_compile_definitions(${BTCPP_LIBRARY} PRIVATE $<$<CONFIG:Debug>:TINYXML2_DEBUG>)
 target_compile_definitions(${BTCPP_LIBRARY} PUBLIC BTCPP_LIBRARY_VERSION="${CMAKE_PROJECT_VERSION}")
 
+if(USE_VENDORED_JSON)
+    target_compile_definitions(${BTCPP_LIBRARY} PUBLIC BTCPP_VENDORED_JSON)
+else()
+    target_link_libraries(${BTCPP_LIBRARY} PUBLIC nlohmann_json::nlohmann_json)
+endif()
+
 target_compile_features(${BTCPP_LIBRARY} PUBLIC cxx_std_17)
 
 if(MSVC)
@@ -332,8 +343,15 @@ INSTALL(TARGETS ${BTCPP_LIBRARY}
     INCLUDES DESTINATION ${BTCPP_INCLUDE_DESTINATION}
     )
 
-INSTALL( DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/include/
-    DESTINATION ${BTCPP_INCLUDE_DESTINATION}
-    FILES_MATCHING PATTERN "*.h*")
+if(USE_VENDORED_JSON)
+    INSTALL( DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/include/
+        DESTINATION ${BTCPP_INCLUDE_DESTINATION}
+        FILES_MATCHING PATTERN "*.h*")
+else()
+    INSTALL( DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/include/
+        DESTINATION ${BTCPP_INCLUDE_DESTINATION}
+        FILES_MATCHING PATTERN "*.h*"
+        REGEX "contrib/json\\.hpp$" EXCLUDE)
+endif()
 
 export_btcpp_package()
diff --git a/FIXME.md b/FIXME.md
new file mode 100644
index 000000000..f99bf414e
--- /dev/null
+++ b/FIXME.md
@@ -0,0 +1,169 @@
+# FIXME - Bug Tracker
+
+This file tracks reported bugs from GitHub issues. For each bug, the workflow is:
+1. Write a unit test that reproduces the issue
+2. Evaluate whether the behavior diverges from intended library semantics
+3. Fix the issue (if confirmed as a bug)
+
+**IMPORTANT:** NEVER modify existing tests that were not created in this branch. Only add new tests.
+
+---
+
+## Control Nodes (Parallel)
+
+### [ ] #1045 - Test PauseWithRetry is flaky
+- **URL:** https://github.com/BehaviorTree/BehaviorTree.CPP/issues/1045
+- **Summary:** The `Parallel.PauseWithRetry` test fails intermittently due to tight timing assertions. Measured time drifts beyond the allowed margin.
+- **Component:** `tests/gtest_parallel.cpp`
+- **Test file:** `tests/gtest_parallel.cpp`
+
+### [ ] #1041 - Performance degradation after prolonged operation in parallel nodes
+- **URL:** https://github.com/BehaviorTree/BehaviorTree.CPP/issues/1041
+- **Summary:** After prolonged operation, when a parallel node's child detects an exception and exits, the interval before other nodes wait for execution becomes increasingly longer. Likely related to resource accumulation or thread management.
+- **Component:** `src/controls/parallel_node.cpp`
+- **Test file:** `tests/gtest_parallel.cpp` (or new)
+
+### [ ] #966 - ParallelAll max_failures off-by-one semantics
+- **URL:** https://github.com/BehaviorTree/BehaviorTree.CPP/issues/966
+- **Summary:** `ParallelAll` documents `max_failures` as "if the number of children returning FAILURE *exceeds* this value" but implements `>=` (greater-than-or-equal). Documentation and implementation disagree.
+- **Component:** `src/controls/parallel_all_node.cpp`
+- **Test file:** `tests/gtest_parallel.cpp`
+
+---
+
+## Control Nodes (Reactive)
+
+### [ ] #1031 - Race condition in ReactiveSequence/ReactiveFallback with async children
+- **URL:** https://github.com/BehaviorTree/BehaviorTree.CPP/issues/1031
+- **Summary:** With backchaining patterns, a previously `RUNNING` child is halted only *after* another child's `onStart` is executed. Two children are in `RUNNING` state simultaneously briefly, causing race conditions.
+- **Component:** `src/controls/reactive_sequence.cpp`, `src/controls/reactive_fallback.cpp`
+- **Test file:** `tests/gtest_reactive.cpp` (or new)
+
+### [ ] #917 - Precondition not re-checked in ReactiveSequence
+- **URL:** https://github.com/BehaviorTree/BehaviorTree.CPP/issues/917
+- **Summary:** When a node has a `_successIf` precondition inside a `ReactiveSequence`, the precondition is never re-evaluated after the node enters `RUNNING` state. The node continues returning `RUNNING` instead of `SUCCESS`.
+- **Component:** `src/controls/reactive_sequence.cpp`, `src/tree_node.cpp`
+- **Test file:** `tests/gtest_reactive.cpp`
+
+---
+
+## XML Parsing
+
+### [ ] #979 - Recursive behavior trees cause stack overflow
+- **URL:** https://github.com/BehaviorTree/BehaviorTree.CPP/issues/979
+- **Summary:** A behavior tree can reference its own ID as a SubTree, causing infinite recursion and stack overflow during XML parsing. The parser does not detect or prevent cyclic subtree references.
+- **Component:** `src/xml_parsing.cpp`
+- **Test file:** `tests/gtest_factory.cpp` (or new)
+
+### [ ] #883 - JSON string in port value interpreted as blackboard reference
+- **URL:** https://github.com/BehaviorTree/BehaviorTree.CPP/issues/883
+- **Summary:** Setting a port value to a JSON string in XML (e.g., `settings='{{"a": 0.8}}'`) causes `{}` content to be interpreted as blackboard variable references instead of literal JSON.
+- **Component:** `src/xml_parsing.cpp`, `src/tree_node.cpp`
+- **Test file:** `tests/gtest_factory.cpp` (or new)
+
+### [ ] #880 - External subtree from file not found when loaded via inline XML
+- **URL:** https://github.com/BehaviorTree/BehaviorTree.CPP/issues/880
+- **Summary:** When a subtree is registered via `registerBehaviorTreeFromFile()` and then referenced from inline XML via `createTreeFromText()`, the factory throws `"Can't find a tree with name: MyTree"`.
+- **Component:** `src/xml_parsing.cpp`, `src/bt_factory.cpp`
+- **Test file:** `tests/gtest_factory.cpp`
+
+### [ ] #672 - Stack buffer overflow in xml_parsing.cpp
+- **URL:** https://github.com/BehaviorTree/BehaviorTree.CPP/issues/672
+- **Summary:** AddressSanitizer detects a stack-buffer-overflow in `xml_parsing.cpp` when parsing certain XML tree definitions. Memory safety issue in the XML parser.
+- **Component:** `src/xml_parsing.cpp`
+- **Test file:** `tests/gtest_factory.cpp` (or new)
+
+---
+
+## BehaviorTreeFactory
+
+### [ ] #1046 - Heap use-after-free when factory is destroyed before ticking
+- **URL:** https://github.com/BehaviorTree/BehaviorTree.CPP/issues/1046
+- **Summary:** If `BehaviorTreeFactory` is destroyed before its created tree is ticked, `NodeConfig` holds a dangling pointer to `TreeNodeManifest` owned by the factory. Accessing it causes heap-use-after-free.
+- **Component:** `src/bt_factory.cpp`, `include/behaviortree_cpp/tree_node.h`
+- **Test file:** `tests/gtest_factory.cpp`
+
+### [ ] #937 - BehaviorTreeFactory cannot be returned by value
+- **URL:** https://github.com/BehaviorTree/BehaviorTree.CPP/issues/937
+- **Summary:** Making `BehaviorTreeFactory` non-copyable also inadvertently prevents returning it by value from functions. Some compilers do not apply guaranteed copy elision in all contexts.
+- **Component:** `include/behaviortree_cpp/bt_factory.h`
+- **Test file:** `tests/gtest_factory.cpp` (or new)
+
+### [ ] #934 - Segfault when substituting subtree
+- **URL:** https://github.com/BehaviorTree/BehaviorTree.CPP/issues/934
+- **Summary:** `factory.loadSubstitutionRuleFromJSON()` followed by `factory.createTree()` causes a segmentation fault when the substitution target is a subtree node.
+- **Component:** `src/bt_factory.cpp`
+- **Test file:** `tests/gtest_factory.cpp`
+
+### [ ] #930 - Mock substitution with registerSimpleAction causes tree to hang
+- **URL:** https://github.com/BehaviorTree/BehaviorTree.CPP/issues/930
+- **Summary:** When using mock node substitution rules with `registerSimpleAction()`, the behavior tree gets stuck after an async delay finishes. The substituted node does not behave like the original.
+- **Component:** `src/bt_factory.cpp`
+- **Test file:** `tests/gtest_factory.cpp` (or new)
+
+---
+
+## Loggers
+
+### [ ] #1057 - Groot2Publisher enters infinite loop on exception
+- **URL:** https://github.com/BehaviorTree/BehaviorTree.CPP/issues/1057
+- **Summary:** `Groot2Publisher` can enter an infinite loop during destruction. When `active_server` is set to `false`, it can be reset to `true` depending on timing, causing `server_thread.join()` to hang indefinitely.
+- **Component:** `src/loggers/groot2_publisher.cpp`
+- **Test file:** New test needed
+
+---
+
+## Tree Execution
+
+### [ ] #686 - haltTree doesn't effectively halt tickWhileRunning
+- **URL:** https://github.com/BehaviorTree/BehaviorTree.CPP/issues/686
+- **Summary:** `haltTree()` resets tree status to `IDLE`, which only breaks the inner loop of `tickRoot`. The outer loop then restarts execution because `IDLE` satisfies its condition, so the tree is never truly halted with `tickWhileRunning()`.
+- **Component:** `src/bt_factory.cpp`, `include/behaviortree_cpp/bt_factory.h`
+- **Test file:** `tests/gtest_tree.cpp` (or new)
+
+---
+
+## TreeNode
+
+### [ ] #861 - Tick time monitoring can measure 0 due to instruction reordering
+- **URL:** https://github.com/BehaviorTree/BehaviorTree.CPP/issues/861
+- **Summary:** The `std::chrono` calls around `executeTick()` in `tree_node.cpp` can be reordered by the compiler, resulting in a measured tick duration of 0.
+- **Component:** `src/tree_node.cpp`
+- **Test file:** `tests/gtest_tree.cpp` (or new)
+
+---
+
+## JSON Exporter
+
+### [ ] #989 - JsonExporter throws during vector conversion
+- **URL:** https://github.com/BehaviorTree/BehaviorTree.CPP/issues/989
+- **Summary:** A `bad_function_call` exception is thrown when converting `std::vector` types to JSON via `JsonExporter`. The conversion function is not properly registered for vector types.
+- **Component:** `include/behaviortree_cpp/json_export.h`
+- **Test file:** New test needed
+
+---
+
+## Platform-Specific
+
+### [ ] #869 - Read access violation on Windows debug build
+- **URL:** https://github.com/BehaviorTree/BehaviorTree.CPP/issues/869
+- **Summary:** Running on VS 2022 in Debug mode causes a read access violation in string hashing within the library DLL. Release mode works fine, suggesting a debug-mode-specific memory issue.
+- **Component:** Core library (platform-specific)
+- **Test file:** Requires Windows environment
+
+---
+
+## Summary
+
+| Category | Count | Issue Numbers |
+|----------|-------|---------------|
+| Control Nodes (Parallel) | 3 | #1045, #1041, #966 |
+| Control Nodes (Reactive) | 2 | #1031, #917 |
+| XML Parsing | 4 | #979, #883, #880, #672 |
+| BehaviorTreeFactory | 4 | #1046, #937, #934, #930 |
+| Loggers | 1 | #1057 |
+| Tree Execution | 1 | #686 |
+| TreeNode | 1 | #861 |
+| JSON Exporter | 1 | #989 |
+| Platform-Specific | 1 | #869 |
+| **Total** | **18** | |
diff --git a/cmake/Config.cmake.in b/cmake/Config.cmake.in
index eaed471b8..1f7954588 100644
--- a/cmake/Config.cmake.in
+++ b/cmake/Config.cmake.in
@@ -1,5 +1,10 @@
 @PACKAGE_INIT@
 
+if(NOT @USE_VENDORED_JSON@)
+    include(CMakeFindDependencyMacro)
+    find_dependency(nlohmann_json 3.10)
+endif()
+
 include("${CMAKE_CURRENT_LIST_DIR}/@PROJECT_NAME@Targets.cmake")
 
 set(@PROJECT_NAME@_TARGETS "BT::@PROJECT_NAME@")
diff --git a/include/behaviortree_cpp/blackboard.h b/include/behaviortree_cpp/blackboard.h
index f661a96c0..e9b1fb5a2 100644
--- a/include/behaviortree_cpp/blackboard.h
+++ b/include/behaviortree_cpp/blackboard.h
@@ -1,7 +1,11 @@
 #pragma once
 
 #include "behaviortree_cpp/basic_types.h"
+#ifdef BTCPP_VENDORED_JSON
 #include "behaviortree_cpp/contrib/json.hpp"
+#else
+#include <nlohmann/json.hpp>
+#endif
 #include "behaviortree_cpp/exceptions.h"
 #include "behaviortree_cpp/utils/locked_reference.hpp"
 #include "behaviortree_cpp/utils/safe_any.hpp"
diff --git a/include/behaviortree_cpp/bt_factory.h b/include/behaviortree_cpp/bt_factory.h
index 3471f51bf..c472ebd95 100644
--- a/include/behaviortree_cpp/bt_factory.h
+++ b/include/behaviortree_cpp/bt_factory.h
@@ -15,7 +15,11 @@
 #define BT_FACTORY_H
 
 #include "behaviortree_cpp/behavior_tree.h"
+#ifdef BTCPP_VENDORED_JSON
 #include "behaviortree_cpp/contrib/json.hpp"
+#else
+#include <nlohmann/json.hpp>
+#endif
 #include "behaviortree_cpp/contrib/magic_enum.hpp"
 
 #include <filesystem>
diff --git a/include/behaviortree_cpp/json_export.h b/include/behaviortree_cpp/json_export.h
index b33243e17..08c372e14 100644
--- a/include/behaviortree_cpp/json_export.h
+++ b/include/behaviortree_cpp/json_export.h
@@ -3,8 +3,11 @@
 #include "behaviortree_cpp/basic_types.h"
 #include "behaviortree_cpp/utils/safe_any.hpp"
 
-// Use the version nlohmann::json embedded in BT.CPP
+#ifdef BTCPP_VENDORED_JSON
 #include "behaviortree_cpp/contrib/json.hpp"
+#else
+#include <nlohmann/json.hpp>
+#endif
 
 namespace BT
 {
diff --git a/include/behaviortree_cpp/loggers/groot2_protocol.h b/include/behaviortree_cpp/loggers/groot2_protocol.h
index 1e3e51545..f11e91a78 100644
--- a/include/behaviortree_cpp/loggers/groot2_protocol.h
+++ b/include/behaviortree_cpp/loggers/groot2_protocol.h
@@ -1,7 +1,11 @@
 #pragma once
 
 #include "behaviortree_cpp/basic_types.h"
+#ifdef BTCPP_VENDORED_JSON
 #include "behaviortree_cpp/contrib/json.hpp"
+#else
+#include <nlohmann/json.hpp>
+#endif
 
 #include <array>
 #include <condition_variable>