diff --git a/docker/smoke_test.sh b/docker/smoke_test.sh
index c6f09a0..06ad0db 100755
--- a/docker/smoke_test.sh
+++ b/docker/smoke_test.sh
@@ -2,22 +2,29 @@
 # Integration smoke test for the sas_core thin wrapper.
 #
 # Runs inside the docker environment provided by docker/compose.yml:
-#   [1/3] colcon build of the wrapper package
-#   [2/3] Python shim smoke test (sas_core -> marinholab.sas.core)
-#   [3/3] C++ compatibility-header consumer compiled against the installed
+#   [1/4] colcon build of the wrapper package
+#   [2/4] Python shim smoke test (sas_core -> marinholab.sas.core)
+#   [3/4] C++ compatibility-header consumer compiled against the installed
 #         libmarinholab_sas_core (legacy include path + namespace sas)
+#   [4/4] C++ namespace-ambiguity regression test (downstream-style consumer
+#         with `using namespace rclcpp;` + bare `Clock` in `namespace sas`)
+#
+# Note on CI gating: the `run` step uses `docker compose up`, which does not
+# propagate the container's exit code. The checks here are therefore
+# informational in CI today; run this script manually (or via
+# `docker compose run --rm sas_core`) to get a real pass/fail signal.
 set -e
 
 cd /root/sas_core_devel/src/
 
-echo '=== [1/3] colcon build (thin wrapper) ==='
+echo '=== [1/4] colcon build (thin wrapper) ==='
 colcon build
 
-echo '=== [2/3] Python shim smoke test ==='
+echo '=== [2/4] Python shim smoke test ==='
 source install/setup.bash
 python3 sas_core/scripts/sas_core_smoke_test.py
 
-echo '=== [3/3] C++ compatibility header + installed library test ==='
+echo '=== [3/4] C++ compatibility header + installed library test ==='
 # Wrapper-installed compat headers and the .deb-installed shared library.
 SAS_INC=/root/sas_core_devel/src/install/sas_core/include
 LIBDIR="$(dirname "$(ldconfig -p | awk '/libmarinholab_sas_core\.so/ {print $NF; exit}')")"
@@ -43,4 +50,61 @@ g++ /tmp/sas_core_compat_test.cpp -o /tmp/sas_core_compat_test \
     -Wl,-rpath,"${LIBDIR}"
 /tmp/sas_core_compat_test
 
+echo '=== [4/4] C++ namespace-ambiguity regression test (downstream-style) ==='
+# Reproduces SmartArmStack/smart_arm_stack_ROS2 PPA build failure:
+# a downstream package does `using namespace rclcpp;` and declares a bare
+# `Clock` inside `namespace sas`. With the thin wrapper's using-directive
+# shim, `Clock` was ambiguous between rclcpp::Clock and
+# marinholab::sas::core::Clock. The `using Clock = ...` declaration in the
+# shim makes it a real member of `namespace sas`, shadowing rclcpp::Clock.
+#
+# A minimal `rclcpp` stub (Clock + Node) is used instead of the full rclcpp
+# runtime: the bug is purely about *name lookup*, and a stub rclcpp::Clock /
+# rclcpp::Node is name-lookup-identical to the real ones. This keeps the test
+# hermetic and independent of the ROS include layout.
+STUB=/tmp/sas_ambig_stub/rclcpp
+mkdir -p "${STUB}"
+cat > "${STUB}/rclcpp.hpp" <<'CPP'
+#pragma once
+#include <memory>
+namespace rclcpp
+{
+    class Clock {};
+    class Node  { public: std::shared_ptr<Clock> get_clock() { return nullptr; } };
+}
+CPP
+
+cat > /tmp/sas_core_ambig_test.cpp <<'CPP'
+#include <memory>
+#include <rclcpp/rclcpp.hpp>
+#include <sas_core/sas_clock.hpp>
+
+using namespace rclcpp;
+
+namespace sas
+{
+class Consumer
+{
+private:
+    std::shared_ptr<Node> node_;  // must resolve to rclcpp::Node
+    Clock clock_;                 // must resolve to marinholab::sas::core::Clock
+public:
+    void use()
+    {
+        clock_.init();            // core Clock::init()
+        (void)node_;
+    }
+};
+}
+
+int main()
+{
+    return 0;
+}
+CPP
+
+g++ /tmp/sas_core_ambig_test.cpp -c -o /tmp/sas_core_ambig_test.o \
+    -I"${STUB%/*}" -I"${SAS_INC}"
+echo 'Ambiguity regression test compiled (no ambiguous Clock).'
+
 echo '=== ALL CHECKS PASSED ==='
diff --git a/include/sas_core/sas_clock.hpp b/include/sas_core/sas_clock.hpp
index af12b98..fe00023 100644
--- a/include/sas_core/sas_clock.hpp
+++ b/include/sas_core/sas_clock.hpp
@@ -7,4 +7,12 @@
 namespace sas
 {
     using namespace marinholab::sas::core;
+    // `Clock` must be a *real member* of namespace sas (a using-declaration),
+    // not merely findable via the using-directive above. Otherwise a downstream
+    // package that also does `using namespace rclcpp;` sees a bare `Clock`
+    // reference as ambiguous between marinholab::sas::core::Clock and
+    // rclcpp::Clock (name lookup through the directive finds both). Declaring
+    // it here shadows rclcpp::Clock, matching the old monolithic sas_core where
+    // `namespace sas` had its own `class Clock`.
+    using Clock = marinholab::sas::core::Clock;
 }