diff --git a/CMakeLists.txt b/CMakeLists.txt
index 840077f..0094216 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -118,6 +118,7 @@ if (BUILD_TESTING)
         tests/WorldQueryTests.cpp
         tests/CommandBufferTests.cpp
         tests/SystemSchedulerTests.cpp
+        tests/EngineIntegrationTests.cpp
     )
 
     target_include_directories(safecrowd_tests
diff --git a/tests/EngineIntegrationTests.cpp b/tests/EngineIntegrationTests.cpp
new file mode 100644
index 0000000..adb2c63
--- /dev/null
+++ b/tests/EngineIntegrationTests.cpp
@@ -0,0 +1,101 @@
+#include "TestSupport.h"
+
+#include <cstddef>
+#include <memory>
+
+#include "engine/EngineRuntime.h"
+
+namespace {
+
+struct Position {
+    float x{0.0f};
+    float y{0.0f};
+};
+
+struct Activated {
+    int fixedStepSeen{0};
+};
+
+class StartupSpawnPositionSystem : public safecrowd::engine::EngineSystem {
+public:
+    void update(safecrowd::engine::EngineWorld& world,
+                const safecrowd::engine::EngineStepContext&) override {
+        world.commands().spawnEntity(Position{3.0f, 4.0f});
+    }
+};
+
+class QueryAndActivateSystem : public safecrowd::engine::EngineSystem {
+public:
+    std::size_t& queriedCount;
+    std::size_t& visibleActivatedCountDuringUpdate;
+    std::size_t& scheduledActivationCount;
+
+    QueryAndActivateSystem(std::size_t& queriedCountRef,
+                           std::size_t& visibleActivatedCountDuringUpdateRef,
+                           std::size_t& scheduledActivationCountRef)
+        : queriedCount(queriedCountRef),
+          visibleActivatedCountDuringUpdate(visibleActivatedCountDuringUpdateRef),
+          scheduledActivationCount(scheduledActivationCountRef) {}
+
+    void update(safecrowd::engine::EngineWorld& world,
+                const safecrowd::engine::EngineStepContext& step) override {
+        const auto positionedEntities = world.query().view<Position>();
+        queriedCount = positionedEntities.size();
+        scheduledActivationCount = 0;
+
+        for (const auto entity : positionedEntities) {
+            if (!world.query().contains<Activated>(entity)) {
+                world.commands().addComponent(entity, Activated{
+                                                         .fixedStepSeen = static_cast<int>(step.fixedStepIndex),
+                                                     });
+                ++scheduledActivationCount;
+            }
+        }
+
+        visibleActivatedCountDuringUpdate = world.query().view<Activated>().size();
+    }
+};
+
+}  // namespace
+
+SC_TEST(EngineIntegration_QueryReadAndDeferredMutationFlow_AppliesAfterStepFrame) {
+    std::size_t queriedCount = 0;
+    std::size_t visibleActivatedCountDuringUpdate = 0;
+    std::size_t scheduledActivationCount = 0;
+
+    safecrowd::engine::EngineRuntime runtime({
+        .fixedDeltaTime = 0.25,
+        .maxCatchUpSteps = 4,
+        .baseSeed = 7,
+    });
+
+    runtime.addSystem(
+        std::make_unique<StartupSpawnPositionSystem>(),
+        {.phase = safecrowd::engine::UpdatePhase::Startup,
+         .triggerPolicy = safecrowd::engine::TriggerPolicy::EveryFrame});
+    runtime.addSystem(std::make_unique<QueryAndActivateSystem>(
+        queriedCount,
+        visibleActivatedCountDuringUpdate,
+        scheduledActivationCount));
+
+    runtime.play();
+
+    const auto beforeStepPositioned = runtime.world().query().view<Position>();
+    const auto beforeStepActivated = runtime.world().query().view<Activated>();
+    SC_EXPECT_EQ(beforeStepPositioned.size(), std::size_t{1});
+    SC_EXPECT_TRUE(beforeStepActivated.empty());
+
+    runtime.stepFrame(0.25);
+
+    const auto activatedEntities = runtime.world().query().view<Activated>();
+    const auto fullyMatchedEntities = runtime.world().query().view<Position, Activated>();
+
+    SC_EXPECT_EQ(queriedCount, std::size_t{1});
+    SC_EXPECT_EQ(scheduledActivationCount, std::size_t{1});
+    SC_EXPECT_EQ(visibleActivatedCountDuringUpdate, std::size_t{0});
+    SC_EXPECT_EQ(activatedEntities.size(), std::size_t{1});
+    SC_EXPECT_EQ(fullyMatchedEntities.size(), std::size_t{1});
+
+    const auto& activated = runtime.world().query().get<Activated>(activatedEntities.front());
+    SC_EXPECT_EQ(activated.fixedStepSeen, 1);
+}