diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4ab8fc7..8d83deb 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -79,20 +79,24 @@ target_link_libraries(demo_vgoswec
   PRIVATE vgoswec_chrono
           SEAStack::ChronoAdapter
           SEAStack::HydroIO
-          ${_demo_extra_libs}
 )
 target_compile_features(demo_vgoswec PRIVATE cxx_std_17)
 target_compile_options(demo_vgoswec PRIVATE -Wall -Wextra -Wpedantic)
 
 # Prefer imported VSG targets when available (avoid manual low-level find_library).
+set(_demo_gui_libs "")
 if(TARGET vsg::vsg)
-  target_link_libraries(demo_vgoswec PRIVATE vsg::vsg)
+  list(APPEND _demo_gui_libs vsg::vsg)
 endif()
 if(TARGET vsgXchange::vsgXchange)
-  target_link_libraries(demo_vgoswec PRIVATE vsgXchange::vsgXchange)
+  list(APPEND _demo_gui_libs vsgXchange::vsgXchange)
+elseif(TARGET vsgXchange)
+  list(APPEND _demo_gui_libs vsgXchange)
 endif()
 if(TARGET vsgImGui::vsgImGui)
-  target_link_libraries(demo_vgoswec PRIVATE vsgImGui::vsgImGui)
+  list(APPEND _demo_gui_libs vsgImGui::vsgImGui)
+elseif(TARGET vsgImGui)
+  list(APPEND _demo_gui_libs vsgImGui)
 endif()
 
 # SEA-Stack app library import (parity with working SEA-Stack/HIL integration path).
@@ -134,6 +138,12 @@ else()
   message(WARNING "demo_vgoswec: seastack_app_lib not found; continuing with headless-safe build path")
 endif()
 
+# Link GUI/VSG dependencies after SEAStack::app_lib so static-library consumers
+# resolve Chrono VSG and ImGui symbols in left-to-right link order.
+if(_demo_extra_libs OR _demo_gui_libs)
+  target_link_libraries(demo_vgoswec PRIVATE ${_demo_extra_libs} ${_demo_gui_libs})
+endif()
+
 if(EXISTS "${SEASTACK_SOURCE_DIR_HINT}/apps/seastack/gui/guihelper.h")
   target_include_directories(demo_vgoswec PRIVATE
     "${SEASTACK_SOURCE_DIR_HINT}/apps/seastack"
diff --git a/src/rsda_pto_functor.cpp b/src/rsda_pto_functor.cpp
index f29022e..f4f6160 100644
--- a/src/rsda_pto_functor.cpp
+++ b/src/rsda_pto_functor.cpp
@@ -6,8 +6,11 @@ namespace vgoswec {
 RsdaPtoFunctor::RsdaPtoFunctor(std::shared_ptr<seastack::pto::IPTOModel> model)
     : model_(std::move(model)) {}
 
-double RsdaPtoFunctor::evaluate(double time, double angle, double vel,
+double RsdaPtoFunctor::evaluate(double time, double /*rest_angle*/, double angle, double vel,
                                 const ::chrono::ChLinkRSDA& /*link*/) {
+    // angle -> flap deviation theta [rad] (displacement); vel -> theta_dot [rad/s].
+    // rest_angle is unused: the controllers reference theta from the initialized-at-rest
+    // configuration (rest_angle = 0), matching theta_ref = 0 in the exc_ff_pid controller.
     return model_->ComputeForce(angle, vel, time);
 }
 
diff --git a/src/rsda_pto_functor.h b/src/rsda_pto_functor.h
index 87662f5..73b0da4 100644
--- a/src/rsda_pto_functor.h
+++ b/src/rsda_pto_functor.h
@@ -6,8 +6,9 @@
 // ChLinkRSDA (Rotational Spring-Damper-Actuator) is Chrono 10's rotational
 // counterpart to ChLinkTSDA.  Its TorqueFunctor callback receives:
 //   time  — current simulation time [s]
-//   angle — relative rotation angle [rad]   (maps to IPTOModel::displacement)
-//   vel   — relative angular velocity [rad/s] (maps to IPTOModel::velocity)
+//   rest_angle — undeformed angle [rad] (Chrono 10 signature; unused here)
+//   angle      — relative rotation angle [rad]   (maps to IPTOModel::displacement)
+//   vel        — relative angular velocity [rad/s] (maps to IPTOModel::velocity)
 //
 // Typical wiring (Y-axis hinge):
 //   auto rsda = chrono_types::make_shared<ChLinkRSDA>();
@@ -39,7 +40,10 @@ class RsdaPtoFunctor : public ::chrono::ChLinkRSDA::TorqueFunctor {
     explicit RsdaPtoFunctor(std::shared_ptr<seastack::pto::IPTOModel> model);
 
     /// Called by Chrono at each force-assembly sub-step.
+    /// Signature matches chrono::ChLinkRSDA::TorqueFunctor::evaluate in Chrono 10
+    /// (note the `rest_angle` parameter between `time` and `angle`).
     double evaluate(double time,
+                    double rest_angle,
                     double angle,
                     double vel,
                     const ::chrono::ChLinkRSDA& link) override;