diff --git a/Kernel/src/renderive/render_graph/External_Operation.cpp b/Kernel/src/renderive/render_graph/External_Operation.cpp
index 5c3dd97..3b0a9a6 100644
--- a/Kernel/src/renderive/render_graph/External_Operation.cpp
+++ b/Kernel/src/renderive/render_graph/External_Operation.cpp
@@ -42,8 +42,12 @@ void External_Operation::on_complete(Completion completion) const {
         error = state_->error;
         invoke = true;
     }
-    if (invoke)
-        completion(std::move(error));
+    if (invoke) {
+        try {
+            completion(std::move(error));
+        } catch (...) {
+        }
+    }
 }
 
 External_Operation::operator bool() const noexcept {
diff --git a/Kernel/src/renderive/render_graph/External_Operation.hpp b/Kernel/src/renderive/render_graph/External_Operation.hpp
index cdf5189..8028db8 100644
--- a/Kernel/src/renderive/render_graph/External_Operation.hpp
+++ b/Kernel/src/renderive/render_graph/External_Operation.hpp
@@ -13,6 +13,9 @@ public:
 
     External_Operation() = default;
 
+    // Completion callbacks are notification boundaries. Exceptions thrown by
+    // them are contained regardless of whether completion happened before or
+    // after subscription.
     void on_complete(Completion completion) const;
     [[nodiscard]] explicit operator bool() const noexcept;
 
diff --git a/Kernel/src/renderive/render_graph/Frame_Analysis.cpp b/Kernel/src/renderive/render_graph/Frame_Analysis.cpp
index d29ca88..e62b99b 100644
--- a/Kernel/src/renderive/render_graph/Frame_Analysis.cpp
+++ b/Kernel/src/renderive/render_graph/Frame_Analysis.cpp
@@ -26,6 +26,8 @@ double percentile(std::vector<std::uint64_t> values, double probability) {
 
 struct Node_Samples {
     std::vector<std::uint64_t> durations;
+    std::vector<std::uint64_t> cpu_durations;
+    std::vector<std::uint64_t> external_durations;
     std::vector<std::uint64_t> waits;
     std::size_t critical_count{};
 };
@@ -50,6 +52,18 @@ Node_Statistics statistics_for(Render_Node_Id id, const Node_Samples& samples) {
     result.p99_ns = percentile(samples.durations, 0.99);
     result.minimum_ns = *std::min_element(samples.durations.begin(), samples.durations.end());
     result.maximum_ns = *std::max_element(samples.durations.begin(), samples.durations.end());
+    const auto cpu_sum = std::accumulate(
+        samples.cpu_durations.begin(), samples.cpu_durations.end(),
+        std::uint64_t{});
+    const auto external_sum = std::accumulate(
+        samples.external_durations.begin(), samples.external_durations.end(),
+        std::uint64_t{});
+    result.average_cpu_ns = static_cast<double>(cpu_sum) /
+                            samples.cpu_durations.size();
+    result.average_external_ns = static_cast<double>(external_sum) /
+                                 samples.external_durations.size();
+    result.p95_cpu_ns = percentile(samples.cpu_durations, 0.95);
+    result.p95_external_ns = percentile(samples.external_durations, 0.95);
     result.critical_path_frequency = samples.critical_count;
     result.average_scheduler_wait_ns = samples.waits.empty()
         ? 0.0
@@ -227,6 +241,8 @@ std::vector<Node_Statistics> analyze_node_statistics(
         for (const auto& node : frame.nodes) {
             auto& values = samples[node.node_id];
             values.durations.push_back(node.duration_ns);
+            values.cpu_durations.push_back(node.cpu_duration_ns);
+            values.external_durations.push_back(node.external_duration_ns);
             values.waits.push_back(node.scheduler_wait_ns);
             values.critical_count += node.on_critical_path ? 1 : 0;
         }
diff --git a/Kernel/src/renderive/render_graph/Frame_Analysis.hpp b/Kernel/src/renderive/render_graph/Frame_Analysis.hpp
index 794d0af..4577298 100644
--- a/Kernel/src/renderive/render_graph/Frame_Analysis.hpp
+++ b/Kernel/src/renderive/render_graph/Frame_Analysis.hpp
@@ -52,6 +52,10 @@ struct Node_Statistics {
     double p99_ns{};
     std::uint64_t minimum_ns{};
     std::uint64_t maximum_ns{};
+    double average_cpu_ns{};
+    double average_external_ns{};
+    double p95_cpu_ns{};
+    double p95_external_ns{};
     std::size_t critical_path_frequency{};
     double average_scheduler_wait_ns{};
 };
diff --git a/Kernel/src/renderive/render_graph/Node_Diagnostics.hpp b/Kernel/src/renderive/render_graph/Node_Diagnostics.hpp
new file mode 100644
index 0000000..ade669d
--- /dev/null
+++ b/Kernel/src/renderive/render_graph/Node_Diagnostics.hpp
@@ -0,0 +1,37 @@
+#pragma once
+
+#include <string>
+#include <utility>
+#include <vector>
+
+struct Node_Diagnostic_Attachment {
+    std::string type;
+    std::string content;
+};
+
+class Scene_Base;
+
+class Node_Diagnostic_Sink {
+public:
+    Node_Diagnostic_Sink() = default;
+
+    [[nodiscard]] bool enabled() const noexcept {
+        return attachments_ != nullptr;
+    }
+
+    void attach(std::string type, std::string content) const {
+        if (!attachments_)
+            return;
+        attachments_->push_back(
+            {std::move(type), std::move(content)});
+    }
+
+private:
+    explicit Node_Diagnostic_Sink(
+        std::vector<Node_Diagnostic_Attachment>& attachments) noexcept
+        : attachments_(&attachments) {}
+
+    std::vector<Node_Diagnostic_Attachment>* attachments_{};
+
+    friend class Scene_Base;
+};
diff --git a/Kernel/src/renderive/scene/base/Abstract_Frame.hpp b/Kernel/src/renderive/scene/base/Abstract_Frame.hpp
index 14fe141..bc5d71e 100644
--- a/Kernel/src/renderive/scene/base/Abstract_Frame.hpp
+++ b/Kernel/src/renderive/scene/base/Abstract_Frame.hpp
@@ -4,6 +4,7 @@
 #include <cstdint>
 #include <memory>
 #include <vector>
+#include "renderive/render_graph/Node_Diagnostics.hpp"
 #include "renderive/render_graph/Render_Plan.hpp"
 
 enum class Node_Execution_Status : std::uint8_t {
@@ -28,7 +29,9 @@ enum class Node_Metric_Kind : std::uint8_t {
     submit_duration_ns,
     gpu_fence_wait_ns,
     gpu_render_duration_ns,
+    gpu_transition_duration_ns,
     gpu_copy_duration_ns,
+    gpu_total_duration_ns,
     readback_duration_ns,
     backend_resource_version,
     backend_frame_index,
@@ -60,6 +63,7 @@ struct Node_Execution {
     std::uint32_t worker_id{};
     Node_Execution_Status status{Node_Execution_Status::pending};
     Node_Execution_Metrics metrics;
+    std::vector<Node_Diagnostic_Attachment> attachments;
     [[nodiscard]] std::uint64_t duration_ns() const noexcept;
     [[nodiscard]] std::uint64_t cpu_duration_ns() const noexcept;
     [[nodiscard]] std::uint64_t external_duration_ns() const noexcept;
diff --git a/Kernel/src/renderive/scene/base/Render_Contexts.hpp b/Kernel/src/renderive/scene/base/Render_Contexts.hpp
index 65c7830..aa18f7e 100644
--- a/Kernel/src/renderive/scene/base/Render_Contexts.hpp
+++ b/Kernel/src/renderive/scene/base/Render_Contexts.hpp
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <cstdint>
+#include "renderive/render_graph/Node_Diagnostics.hpp"
 #include "Frame_Render_Snapshot.hpp"
 
 class Color_Cache;
@@ -10,6 +11,7 @@ struct Prepare_Render_Context {
     const Frame_Render_Snapshot& frame;
     const Renderable_Frame_State& renderable;
     Node_Execution_Metrics* metrics{};
+    Node_Diagnostic_Sink diagnostics;
 
     template <class Data>
     void publish(std::shared_ptr<const Data> data) const {
@@ -27,6 +29,7 @@ struct Paint_Render_Context {
     const Renderable_Frame_State& renderable;
     Color_Cache& color_cache;
     Node_Execution_Metrics* metrics{};
+    Node_Diagnostic_Sink diagnostics;
 };
 
 struct Composite_Render_Context {
@@ -34,11 +37,13 @@ struct Composite_Render_Context {
     const Renderable_Frame_State* renderable{};
     const Color_Cache* color_cache{};
     Node_Execution_Metrics* metrics{};
+    Node_Diagnostic_Sink diagnostics;
 };
 
 struct Scene_Render_Context {
     const Frame_Render_Snapshot& frame;
     Node_Execution_Metrics* metrics{};
+    Node_Diagnostic_Sink diagnostics;
 
     template <class Data>
     [[nodiscard]] std::shared_ptr<const Data> prepared(
diff --git a/Kernel/src/renderive/scene/base/Scene_Base.cpp b/Kernel/src/renderive/scene/base/Scene_Base.cpp
index 08c5749..05a374a 100644
--- a/Kernel/src/renderive/scene/base/Scene_Base.cpp
+++ b/Kernel/src/renderive/scene/base/Scene_Base.cpp
@@ -1162,19 +1162,23 @@ void Scene_Base::execute_render_graph(Render_Task& task) {
         auto& executor = Execution_Context::executor();
         renderive::render_graph::detail::Render_Graph_Runtime runtime(
             *task.plan, execution_slots,
-            [this, &task, &snapshot](
+            [this, &task, &snapshot, &execution_slots](
                 std::size_t execution_index,
                 Node_Execution_Metrics* metrics) -> Node_Execution_Result {
                 const auto& node = task.plan->graph.nodes.at(execution_index);
                 const auto& binding =
                     task.execution_bindings.at(execution_index);
+                Node_Diagnostic_Sink diagnostics;
+                if (auto* execution = execution_slots.at(execution_index))
+                    diagnostics = Node_Diagnostic_Sink(execution->attachments);
                 Render_Execution_Scope scope(*this);
                 switch (node.kind) {
                 case Render_Node_Kind::prepare: {
                     const auto& state = snapshot.renderables.at(
                         binding.renderable_index.value());
                     std::get<Prepare_Render_Node_Function>(binding.function)(
-                        Prepare_Render_Context{snapshot, state, metrics});
+                        Prepare_Render_Context{snapshot, state, metrics,
+                                               diagnostics});
                     return Node_Execution_Result::completed();
                 }
                 case Render_Node_Kind::paint: {
@@ -1185,7 +1189,8 @@ void Scene_Base::execute_render_graph(Render_Task& task) {
                             "paint node has no frame color cache");
                     std::get<Paint_Render_Node_Function>(binding.function)(
                         Paint_Render_Context{snapshot, state,
-                                             *state.paint_buffer_, metrics});
+                                             *state.paint_buffer_, metrics,
+                                             diagnostics});
                     return Node_Execution_Result::completed();
                 }
                 case Render_Node_Kind::composite: {
@@ -1199,12 +1204,12 @@ void Scene_Base::execute_render_graph(Render_Task& task) {
                         : nullptr;
                     std::get<Composite_Render_Node_Function>(binding.function)(
                         Composite_Render_Context{snapshot, state, cache,
-                                                 metrics});
+                                                 metrics, diagnostics});
                     return Node_Execution_Result::completed();
                 }
                 case Render_Node_Kind::render:
                     return std::get<Scene_Render_Node_Function>(binding.function)(
-                        Scene_Render_Context{snapshot, metrics});
+                        Scene_Render_Context{snapshot, metrics, diagnostics});
                 }
                 throw std::logic_error("unknown render node kind");
             },
diff --git a/Kernel/tests/renderive/render_graph/Render_DAG_Test.cpp b/Kernel/tests/renderive/render_graph/Render_DAG_Test.cpp
index 53af8cc..f4b4217 100644
--- a/Kernel/tests/renderive/render_graph/Render_DAG_Test.cpp
+++ b/Kernel/tests/renderive/render_graph/Render_DAG_Test.cpp
@@ -181,6 +181,13 @@ TEST(render_dag_test,
     ASSERT_EQ(analysis.workers.size(), 1U);
     EXPECT_EQ(analysis.workers.front().work_duration_ns, 20U);
     EXPECT_DOUBLE_EQ(analysis.workers.front().utilization, 0.1);
+    const auto statistics = analyze_node_statistics(
+        std::span<const Frame_Analysis>(&analysis, 1));
+    ASSERT_EQ(statistics.size(), 1U);
+    EXPECT_DOUBLE_EQ(statistics.front().average_cpu_ns, 20.0);
+    EXPECT_DOUBLE_EQ(statistics.front().average_external_ns, 180.0);
+    EXPECT_DOUBLE_EQ(statistics.front().p95_cpu_ns, 20.0);
+    EXPECT_DOUBLE_EQ(statistics.front().p95_external_ns, 180.0);
 }
 
 TEST(render_dag_test, failed_capture_ticket_is_retried_until_the_requested_frame_completes) {
diff --git a/Kernel/tests/renderive/render_graph/Render_Graph_Runtime_Test.cpp b/Kernel/tests/renderive/render_graph/Render_Graph_Runtime_Test.cpp
index 158dfe8..88b4fe6 100644
--- a/Kernel/tests/renderive/render_graph/Render_Graph_Runtime_Test.cpp
+++ b/Kernel/tests/renderive/render_graph/Render_Graph_Runtime_Test.cpp
@@ -106,6 +106,21 @@ TEST(external_operation_test, completion_before_subscription_is_delivered_once)
     EXPECT_EQ(completion_count, 1);
 }
 
+TEST(external_operation_test,
+     callback_exceptions_are_contained_for_both_completion_orders) {
+    External_Operation_Source completed_first;
+    const auto completed_operation = completed_first.operation();
+    ASSERT_TRUE(completed_first.complete());
+    EXPECT_NO_THROW(completed_operation.on_complete(
+        [](std::exception_ptr) { throw std::runtime_error("late callback"); }));
+
+    External_Operation_Source subscribed_first;
+    const auto subscribed_operation = subscribed_first.operation();
+    subscribed_operation.on_complete(
+        [](std::exception_ptr) { throw std::runtime_error("early callback"); });
+    EXPECT_TRUE(subscribed_first.complete());
+}
+
 TEST(render_graph_runtime_test,
      external_successor_stays_blocked_until_operation_completes) {
     const auto plan = two_node_plan();
diff --git a/render_3D/CMakeLists.txt b/render_3D/CMakeLists.txt
index 7b8db82..2885ef7 100644
--- a/render_3D/CMakeLists.txt
+++ b/render_3D/CMakeLists.txt
@@ -121,6 +121,9 @@ if (RENDERIVE_BUILD_TESTS)
         set(Renderive_render_3D_test_target "Renderive_render_3D_${Renderive_render_3D_test_name}_${Renderive_render_3D_test_hash}")
         add_executable("${Renderive_render_3D_test_target}" "${Renderive_render_3D_test_source}")
         target_link_libraries("${Renderive_render_3D_test_target}" PRIVATE Renderive_render_3D GTest::gtest_main)
+        if (Renderive_render_3D_test_name STREQUAL "Gpu_Completion_Service_Tests")
+            target_link_libraries("${Renderive_render_3D_test_target}" PRIVATE volk::volk_headers)
+        endif ()
         renderive_stage_render_3D_runtime("${Renderive_render_3D_test_target}")
         add_test(NAME "${Renderive_render_3D_test_target}" COMMAND "${Renderive_render_3D_test_target}")
     endforeach ()
diff --git a/render_3D/render_3D/Point_Scene.cpp b/render_3D/render_3D/Point_Scene.cpp
index bb55ca5..3566545 100644
--- a/render_3D/render_3D/Point_Scene.cpp
+++ b/render_3D/render_3D/Point_Scene.cpp
@@ -15,7 +15,9 @@
 #include <exception>
 #include <memory>
 #include <mutex>
+#include <optional>
 #include <stdexcept>
+#include <type_traits>
 #include <utility>
 
 namespace renderive::render_3d {
@@ -41,38 +43,46 @@ float datoviz_wheel_step(float pixel_delta, float angle_delta) noexcept {
 }
 
 void publish_trace(Node_Execution_Metrics* metrics,
-                   const detail::Datoviz_Frame_Trace& trace) {
-    if (!metrics)
-        return;
-    metrics->set(Node_Metric_Kind::queue_wait_ns,
-                 trace.render_domain_queue_wait_ns);
-    metrics->set(Node_Metric_Kind::apply_duration_ns, trace.apply_ns);
-    metrics->set(Node_Metric_Kind::plan_emit_duration_ns, trace.emit_ns);
-    metrics->set(Node_Metric_Kind::backend_execute_duration_ns,
-                 trace.execute_ns);
-    metrics->set(Node_Metric_Kind::submit_duration_ns, trace.submit_ns);
-    metrics->set(Node_Metric_Kind::gpu_fence_wait_ns,
-                 trace.gpu_fence_wait_ns);
-    metrics->set(Node_Metric_Kind::readback_duration_ns,
-                 trace.readback_ns);
-    if (trace.gpu) {
-        metrics->set(Node_Metric_Kind::gpu_render_duration_ns,
-                     trace.gpu->render_ns);
-        metrics->set(Node_Metric_Kind::gpu_copy_duration_ns,
-                     trace.gpu->copy_ns);
+                   Node_Diagnostic_Sink diagnostics,
+                   detail::Datoviz_Frame_Trace trace) {
+    if (metrics) {
+        metrics->set(Node_Metric_Kind::queue_wait_ns,
+                     trace.render_domain_queue_wait_ns);
+        metrics->set(Node_Metric_Kind::apply_duration_ns, trace.apply_ns);
+        metrics->set(Node_Metric_Kind::plan_emit_duration_ns, trace.emit_ns);
+        metrics->set(Node_Metric_Kind::backend_execute_duration_ns,
+                     trace.execute_ns);
+        metrics->set(Node_Metric_Kind::submit_duration_ns, trace.submit_ns);
+        metrics->set(Node_Metric_Kind::gpu_fence_wait_ns,
+                     trace.gpu_fence_wait_ns);
+        metrics->set(Node_Metric_Kind::readback_duration_ns,
+                     trace.readback_ns);
+        if (trace.gpu) {
+            metrics->set(Node_Metric_Kind::gpu_render_duration_ns,
+                         trace.gpu->render_ns);
+            metrics->set(Node_Metric_Kind::gpu_transition_duration_ns,
+                         trace.gpu->transition_ns);
+            metrics->set(Node_Metric_Kind::gpu_copy_duration_ns,
+                         trace.gpu->copy_ns);
+            metrics->set(Node_Metric_Kind::gpu_total_duration_ns,
+                         trace.gpu->total_ns);
+        }
+        metrics->set(Node_Metric_Kind::backend_resource_version,
+                     trace.artifact_resource_version);
+        metrics->set(Node_Metric_Kind::backend_frame_index,
+                     trace.artifact_frame_index);
+        metrics->set(Node_Metric_Kind::backend_artifact_status,
+                     trace.artifact_status);
+        metrics->set(Node_Metric_Kind::backend_validation_code,
+                     trace.validation_code);
+        metrics->set(Node_Metric_Kind::backend_validation_command,
+                     trace.validation_command_index);
+        metrics->set(Node_Metric_Kind::backend_artifact_json_bytes,
+                     trace.artifact_json.size());
     }
-    metrics->set(Node_Metric_Kind::backend_resource_version,
-                 trace.artifact_resource_version);
-    metrics->set(Node_Metric_Kind::backend_frame_index,
-                 trace.artifact_frame_index);
-    metrics->set(Node_Metric_Kind::backend_artifact_status,
-                 trace.artifact_status);
-    metrics->set(Node_Metric_Kind::backend_validation_code,
-                 trace.validation_code);
-    metrics->set(Node_Metric_Kind::backend_validation_command,
-                 trace.validation_command_index);
-    metrics->set(Node_Metric_Kind::backend_artifact_json_bytes,
-                 trace.artifact_json.size());
+    if (!trace.artifact_json.empty())
+        diagnostics.attach("datoviz.drp2.artifact.json",
+                           std::move(trace.artifact_json));
 }
 
 struct Scene_Model {
@@ -301,22 +311,100 @@ struct Basic_Point_Scene final
         const std::uint64_t frame_sequence =
             context.frame.render_sequence;
         Node_Execution_Metrics* const metrics = context.metrics;
+        const Node_Diagnostic_Sink diagnostics = context.diagnostics;
+        const bool observe = metrics != nullptr;
         auto source = std::make_shared<External_Operation_Source>();
         const auto operation = source->operation();
-        const auto queued_at = std::chrono::steady_clock::now();
+        using Pending_Frame = detail::Datoviz_Visual_Backend::Pending_Frame;
+        static_assert(std::is_nothrow_move_constructible_v<Pending_Frame>);
+        using Completion_Result = detail::Gpu_Completion_Service::Result;
+        static_assert(std::is_nothrow_move_assignable_v<Completion_Result>);
+        struct Async_Frame_State {
+            std::optional<Pending_Frame> pending;
+            Completion_Result completion;
+        };
+        auto async_frame = std::make_shared<Async_Frame_State>();
+        auto render_completion = std::make_shared<
+            detail::Render_Domain::Prepared_Task>(
+                render_domain.prepare(
+                    [this, async_frame, metrics, diagnostics, source]() mutable {
+                        if (!async_frame->pending) {
+                            static_cast<void>(source->fail(
+                                std::make_exception_ptr(std::logic_error(
+                                    "GPU completion has no pending frame"))));
+                            return;
+                        }
+                        auto pending = std::move(*async_frame->pending);
+                        async_frame->pending.reset();
+                        pending.trace.gpu_fence_wait_ns =
+                            async_frame->completion.wait_duration_ns;
+                        if (async_frame->completion.error) {
+                            try {
+                                backend->discard(std::move(pending));
+                                static_cast<void>(source->fail(
+                                    std::move(async_frame->completion.error)));
+                            } catch (...) {
+                                static_cast<void>(source->fail(
+                                    std::current_exception()));
+                            }
+                            return;
+                        }
+                        try {
+                            auto completed = backend->collect(
+                                std::move(pending));
+                            auto frame = std::move(completed.frame);
+                            if (metrics && frame) {
+                                metrics->set(
+                                    Node_Metric_Kind::pixel_count,
+                                    static_cast<std::uint64_t>(
+                                        frame->extent.width) *
+                                        frame->extent.height);
+                            }
+                            publish_trace(metrics, diagnostics,
+                                          std::move(completed.trace));
+                            {
+                                std::lock_guard lock(frame_mutex);
+                                latest = std::move(frame);
+                            }
+                            static_cast<void>(source->complete());
+                        } catch (...) {
+                            static_cast<void>(source->fail(
+                                std::current_exception()));
+                        }
+                    }));
+        auto completion = std::make_shared<
+            detail::Gpu_Completion_Service::Reservation>(
+                gpu_completion.prepare(
+                    [this, async_frame, render_completion](
+                        Completion_Result result) noexcept {
+                        async_frame->completion = std::move(result);
+                        render_domain.post(std::move(*render_completion));
+                    },
+                    observe));
+        const auto queued_at = observe
+            ? std::chrono::steady_clock::now()
+            : std::chrono::steady_clock::time_point{};
 
         try {
             render_domain.post(
                 [this, scene_state, scene_revision, frame_sequence, prepared,
-                 metrics, source, queued_at] {
+                 source, async_frame, completion, observe,
+                 queued_at] {
                     try {
-                        const auto queue_wait =
-                            std::chrono::duration_cast<std::chrono::nanoseconds>(
-                                std::chrono::steady_clock::now() - queued_at)
-                                .count();
+                        std::uint64_t queue_wait_ns{};
+                        if (observe) {
+                            const auto queue_wait =
+                                std::chrono::duration_cast<
+                                    std::chrono::nanoseconds>(
+                                    std::chrono::steady_clock::now() -
+                                    queued_at).count();
+                            queue_wait_ns = queue_wait > 0
+                                ? static_cast<std::uint64_t>(queue_wait)
+                                : 0;
+                        }
                         auto pending = backend->submit(
                             scene_state, scene_revision, *prepared,
-                            frame_sequence, metrics != nullptr);
+                            frame_sequence, observe);
                         if (!pending) {
                             {
                                 std::lock_guard lock(frame_mutex);
@@ -326,70 +414,10 @@ struct Basic_Point_Scene final
                             return;
                         }
                         pending->trace.render_domain_queue_wait_ns =
-                            queue_wait > 0
-                                ? static_cast<std::uint64_t>(queue_wait)
-                                : 0;
-                        gpu_completion.watch(
-                            pending->device, pending->fence,
-                            [this, pending = *pending, metrics, source](
-                                detail::Gpu_Completion_Service::Result result)
-                                mutable {
-                                pending.trace.gpu_fence_wait_ns =
-                                    result.wait_duration_ns;
-                                try {
-                                    render_domain.post(
-                                        [this, pending = std::move(pending),
-                                         metrics, source,
-                                         wait_error = std::move(result.error)]()
-                                            mutable {
-                                            if (wait_error) {
-                                                try {
-                                                    backend->discard(
-                                                        std::move(pending));
-                                                    static_cast<void>(
-                                                        source->fail(std::move(
-                                                            wait_error)));
-                                                } catch (...) {
-                                                    static_cast<void>(
-                                                        source->fail(
-                                                            std::current_exception()));
-                                                }
-                                                return;
-                                            }
-                                            try {
-                                                auto completed =
-                                                    backend->collect(
-                                                        std::move(pending));
-                                                auto frame =
-                                                    std::move(completed.frame);
-                                                if (metrics && frame) {
-                                                    metrics->set(
-                                                        Node_Metric_Kind::
-                                                            pixel_count,
-                                                        static_cast<
-                                                            std::uint64_t>(
-                                                            frame->extent.width) *
-                                                            frame->extent.height);
-                                                }
-                                                publish_trace(
-                                                    metrics, completed.trace);
-                                                {
-                                                    std::lock_guard lock(
-                                                        frame_mutex);
-                                                    latest = std::move(frame);
-                                                }
-                                                static_cast<void>(
-                                                    source->complete());
-                                            } catch (...) {
-                                                static_cast<void>(source->fail(
-                                                    std::current_exception()));
-                                            }
-                                        });
-                                } catch (...) {
-                                    static_cast<void>(source->fail(
-                                        std::current_exception()));
-                                }
-                            });
+                            queue_wait_ns;
+                        auto& owned = async_frame->pending.emplace(
+                            std::move(*pending));
+                        completion->watch(owned.device, owned.fence);
                     } catch (...) {
                         static_cast<void>(
                             source->fail(std::current_exception()));
diff --git a/render_3D/render_3D/detail/Datoviz_Frame_Trace.h b/render_3D/render_3D/detail/Datoviz_Frame_Trace.h
index b0d4100..c89361a 100644
--- a/render_3D/render_3D/detail/Datoviz_Frame_Trace.h
+++ b/render_3D/render_3D/detail/Datoviz_Frame_Trace.h
@@ -8,11 +8,14 @@ namespace renderive::render_3d::detail {
 
 struct Datoviz_Gpu_Timing {
     std::uint64_t render_ns{};
+    std::uint64_t transition_ns{};
     std::uint64_t copy_ns{};
+    std::uint64_t total_ns{};
 };
 
 struct Datoviz_Frame_Trace {
     std::uint64_t render_sequence{};
+    bool observed{};
     std::uint64_t render_domain_queue_wait_ns{};
     std::uint64_t apply_ns{};
     std::uint64_t emit_ns{};
diff --git a/render_3D/render_3D/detail/Datoviz_Visual_Backend.cpp b/render_3D/render_3D/detail/Datoviz_Visual_Backend.cpp
index a7ab670..758ebc0 100644
--- a/render_3D/render_3D/detail/Datoviz_Visual_Backend.cpp
+++ b/render_3D/render_3D/detail/Datoviz_Visual_Backend.cpp
@@ -238,7 +238,6 @@ public:
             dvz_buffer_usage(readback_, VK_BUFFER_USAGE_TRANSFER_DST_BIT);
             if (dvz_buffer_create(readback_) != 0)
                 throw std::runtime_error("failed to create Datoviz readback buffer");
-            initialize_timestamps(device, queue);
         } catch (...) {
             destroy();
             throw;
@@ -247,9 +246,15 @@ public:
 
     ~Frame_Target() { destroy(); }
 
-    void begin() {
+    void begin(bool observe) {
         if (in_flight_)
             throw std::logic_error("Datoviz frame target is still in flight");
+        observing_ = observe;
+        if (observing_ && !timestamps_initialized_) {
+            initialize_timestamps(
+                dvz_gpu_ctx_device(gpu_context_),
+                dvz_gpu_ctx_queue(gpu_context_, DVZ_QUEUE_MAIN));
+        }
         dvz_cmd_reset(commands_);
         if (dvz_cmd_begin_result(commands_) != 0)
             throw std::runtime_error("failed to begin Datoviz command buffer");
@@ -278,7 +283,7 @@ public:
         dvz_barrier_image_mip(image_barrier, 0, 1);
         dvz_barrier_image_layers(image_barrier, 0, 1);
         dvz_cmd_barriers(commands_, &barriers);
-        if (timestamps_supported_) {
+        if (observing_ && timestamps_supported_) {
             const VkCommandBuffer command_buffer =
                 dvz_commands_handle(commands_);
             vkCmdResetQueryPool(command_buffer, query_pool_, 0, 4);
@@ -315,7 +320,7 @@ public:
         if (!recording_)
             throw std::logic_error("Datoviz frame target is not recording");
         const VkCommandBuffer command_buffer = dvz_commands_handle(commands_);
-        if (timestamps_supported_) {
+        if (observing_ && timestamps_supported_) {
             vkCmdWriteTimestamp(
                 command_buffer,
                 VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT,
@@ -338,7 +343,7 @@ public:
         dvz_barrier_image_mip(image_barrier, 0, 1);
         dvz_barrier_image_layers(image_barrier, 0, 1);
         dvz_cmd_barriers(commands_, &image_barriers);
-        if (timestamps_supported_) {
+        if (observing_ && timestamps_supported_) {
             vkCmdWriteTimestamp(command_buffer, VK_PIPELINE_STAGE_TRANSFER_BIT,
                                 query_pool_, 2);
         }
@@ -360,7 +365,7 @@ public:
         dvz_barrier_buffer_access(buffer_barrier, VK_ACCESS_2_TRANSFER_WRITE_BIT,
                                   VK_ACCESS_2_HOST_READ_BIT);
         dvz_cmd_barriers(commands_, &buffer_barriers);
-        if (timestamps_supported_) {
+        if (observing_ && timestamps_supported_) {
             vkCmdWriteTimestamp(command_buffer,
                                 VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT,
                                 query_pool_, 3);
@@ -390,9 +395,11 @@ public:
             result.gpu_timing = collect_gpu_timing();
         } catch (...) {
             in_flight_ = false;
+            observing_ = false;
             throw;
         }
         in_flight_ = false;
+        observing_ = false;
         return result;
     }
 
@@ -400,6 +407,7 @@ public:
         if (!in_flight_)
             throw std::logic_error("Datoviz frame target has no pending frame");
         in_flight_ = false;
+        observing_ = false;
     }
 
     [[nodiscard]] VkDevice device() const {
@@ -418,10 +426,12 @@ public:
         if (recording_ && commands_ != nullptr)
             dvz_cmd_reset(commands_);
         recording_ = false;
+        observing_ = false;
     }
 
 private:
     void initialize_timestamps(DvzDevice* device, DvzQueue* queue) noexcept {
+        timestamps_initialized_ = true;
         if (device == nullptr || queue == nullptr ||
             vkGetPhysicalDeviceQueueFamilyProperties == nullptr ||
             vkGetPhysicalDeviceProperties == nullptr ||
@@ -467,7 +477,8 @@ private:
 
     [[nodiscard]] std::optional<Datoviz_Gpu_Timing>
     collect_gpu_timing() const noexcept {
-        if (!timestamps_supported_ || query_pool_ == VK_NULL_HANDLE)
+        if (!observing_ || !timestamps_supported_ ||
+            query_pool_ == VK_NULL_HANDLE)
             return std::nullopt;
         const VkDevice device =
             dvz_device_handle(dvz_gpu_ctx_device(gpu_context_));
@@ -497,7 +508,9 @@ private:
         };
         return Datoviz_Gpu_Timing{
             elapsed(timestamps[0], timestamps[1]),
-            elapsed(timestamps[2], timestamps[3])};
+            elapsed(timestamps[1], timestamps[2]),
+            elapsed(timestamps[2], timestamps[3]),
+            elapsed(timestamps[0], timestamps[3])};
     }
 
     void destroy() noexcept {
@@ -556,6 +569,8 @@ private:
     std::uint32_t timestamp_valid_bits_{};
     bool recording_{};
     bool in_flight_{};
+    bool observing_{};
+    bool timestamps_initialized_{};
     bool timestamps_supported_{};
 };
 
@@ -1023,15 +1038,17 @@ std::optional<Datoviz_Visual_Backend::Pending_Frame>
 Datoviz_Visual_Backend::submit(
     const Scene_State& scene, std::uint64_t scene_revision,
     const Prepared_Point& point, std::uint64_t frame_sequence,
-    bool capture_trace) {
+    bool observe) {
     require_domain();
     if (scene.viewport.empty())
         return std::nullopt;
     Datoviz_Frame_Trace trace;
     trace.render_sequence = frame_sequence;
-    auto phase_started = trace_now_ns();
+    trace.observed = observe;
+    std::uint64_t phase_started = observe ? trace_now_ns() : 0;
     apply(scene, scene_revision, point);
-    trace.apply_ns = trace_now_ns() - phase_started;
+    if (observe)
+        trace.apply_ns = trace_now_ns() - phase_started;
 
     if (target_ == nullptr || target_extent_ != scene.viewport) {
         target_.reset();
@@ -1040,36 +1057,42 @@ Datoviz_Visual_Backend::submit(
                                                  ++target_generation_);
     }
 
-    target_->begin();
+    target_->begin(observe);
     DvzSceneFrameArtifact* artifact{};
     try {
-        phase_started = trace_now_ns();
+        if (observe)
+            phase_started = trace_now_ns();
         artifact = emit(scene);
-        trace.emit_ns = trace_now_ns() - phase_started;
+        if (observe)
+            trace.emit_ns = trace_now_ns() - phase_started;
     } catch (...) {
         target_->abort();
         throw;
     }
-    trace.artifact_status = static_cast<std::uint32_t>(
-        dvz_scene_frame_artifact_status(artifact));
-    trace.artifact_resource_version =
-        dvz_scene_frame_artifact_resource_version(artifact);
-    trace.artifact_frame_index =
-        dvz_scene_frame_artifact_frame_index(artifact);
+    if (observe) {
+        trace.artifact_status = static_cast<std::uint32_t>(
+            dvz_scene_frame_artifact_status(artifact));
+        trace.artifact_resource_version =
+            dvz_scene_frame_artifact_resource_version(artifact);
+        trace.artifact_frame_index =
+            dvz_scene_frame_artifact_frame_index(artifact);
+    }
     const DvzDrp2CommandStream* stream = dvz_scene_frame_artifact_stream(artifact);
     const DvzStreamFrame target_frame = target_->stream_frame();
-    phase_started = trace_now_ns();
+    if (observe)
+        phase_started = trace_now_ns();
     const bool attached = stream != nullptr &&
                           dvz_drp2_runtime_attach_frame_target(
                               runtime_, color_target_id, &target_frame);
     const DvzDrp2ValidationResult result =
         attached ? dvz_drp2_runtime_execute(runtime_, stream)
                  : DvzDrp2ValidationResult{};
-    trace.execute_ns = trace_now_ns() - phase_started;
+    if (observe)
+        trace.execute_ns = trace_now_ns() - phase_started;
     trace.validation_ok = attached && result.ok;
     trace.validation_code = static_cast<std::uint32_t>(result.code);
     trace.validation_command_index = result.command_index;
-    if (capture_trace || !trace.validation_ok) {
+    if (observe || !trace.validation_ok) {
         if (char* json = dvz_scene_frame_artifact_json(
                 artifact, "renderive_frame")) {
             trace.artifact_json = json;
@@ -1095,9 +1118,11 @@ Datoviz_Visual_Backend::submit(
         throw std::runtime_error(std::move(message));
     }
 
-    phase_started = trace_now_ns();
+    if (observe)
+        phase_started = trace_now_ns();
     target_->submit();
-    trace.submit_ns = trace_now_ns() - phase_started;
+    if (observe)
+        trace.submit_ns = trace_now_ns() - phase_started;
     return Pending_Frame{target_->device(), target_->fence(), scene.viewport,
                          frame_sequence, target_->generation(),
                          std::move(trace)};
@@ -1109,9 +1134,12 @@ Datoviz_Visual_Backend::Completed_Frame Datoviz_Visual_Backend::collect(
     if (target_ == nullptr ||
         target_->generation() != pending.target_generation)
         throw std::logic_error("Datoviz pending frame target no longer exists");
-    const std::uint64_t readback_started = trace_now_ns();
+    const std::uint64_t readback_started = pending.trace.observed
+        ? trace_now_ns()
+        : 0;
     auto collection = target_->collect();
-    pending.trace.readback_ns = trace_now_ns() - readback_started;
+    if (pending.trace.observed)
+        pending.trace.readback_ns = trace_now_ns() - readback_started;
     pending.trace.gpu = std::move(collection.gpu_timing);
     auto output = std::make_shared<Pixel_Frame>();
     output->extent = pending.extent;
diff --git a/render_3D/render_3D/detail/Datoviz_Visual_Backend.h b/render_3D/render_3D/detail/Datoviz_Visual_Backend.h
index ffed201..d87c090 100644
--- a/render_3D/render_3D/detail/Datoviz_Visual_Backend.h
+++ b/render_3D/render_3D/detail/Datoviz_Visual_Backend.h
@@ -45,7 +45,7 @@ public:
     [[nodiscard]] std::optional<Pending_Frame> submit(
         const Scene_State& scene, std::uint64_t scene_revision,
         const Prepared_Point& point, std::uint64_t frame_sequence,
-        bool capture_trace);
+        bool observe);
     [[nodiscard]] Completed_Frame collect(Pending_Frame pending);
     void discard(Pending_Frame pending);
 
diff --git a/render_3D/render_3D/detail/Gpu_Completion_Service.cpp b/render_3D/render_3D/detail/Gpu_Completion_Service.cpp
index ddb5249..37f73eb 100644
--- a/render_3D/render_3D/detail/Gpu_Completion_Service.cpp
+++ b/render_3D/render_3D/detail/Gpu_Completion_Service.cpp
@@ -14,19 +14,61 @@ Gpu_Completion_Service::~Gpu_Completion_Service() {
     shutdown();
 }
 
-void Gpu_Completion_Service::watch(
-    VkDevice device, VkFence fence, Completion completion) {
-    if (device == VK_NULL_HANDLE || fence == VK_NULL_HANDLE)
-        throw std::invalid_argument("GPU completion fence is invalid");
+Gpu_Completion_Service::Reservation::Reservation(
+    std::shared_ptr<Pending_Fence> pending) noexcept
+    : pending_(std::move(pending)) {}
+
+Gpu_Completion_Service::Reservation::~Reservation() {
+    cancel();
+}
+
+Gpu_Completion_Service::Reservation::Reservation(
+    Reservation&& other) noexcept
+    : pending_(std::exchange(other.pending_, {})) {}
+
+void Gpu_Completion_Service::Reservation::watch(
+    VkDevice device, VkFence fence) noexcept {
+    if (!pending_ || device == VK_NULL_HANDLE || fence == VK_NULL_HANDLE)
+        std::terminate();
+    auto pending = std::exchange(pending_, {});
+    {
+        std::lock_guard lock(pending->mutex);
+        if (pending->status != Pending_Fence::Status::reserved)
+            std::terminate();
+        pending->device = device;
+        pending->fence = fence;
+        pending->status = Pending_Fence::Status::watched;
+    }
+    pending->ready.notify_one();
+}
+
+void Gpu_Completion_Service::Reservation::cancel() noexcept {
+    if (!pending_)
+        return;
+    auto pending = std::exchange(pending_, {});
+    {
+        std::lock_guard lock(pending->mutex);
+        if (pending->status == Pending_Fence::Status::reserved)
+            pending->status = Pending_Fence::Status::canceled;
+    }
+    pending->ready.notify_one();
+}
+
+Gpu_Completion_Service::Reservation Gpu_Completion_Service::prepare(
+    Completion completion, bool observe) {
     if (!completion)
         throw std::invalid_argument("GPU completion callback is empty");
+    auto pending = std::make_shared<Pending_Fence>();
+    pending->completion = std::move(completion);
+    pending->observe = observe;
     {
         std::lock_guard lock(mutex_);
         if (stopping_)
             throw std::runtime_error("GPU completion service is stopping");
-        pending_.push({device, fence, std::move(completion)});
+        pending_.push_back(pending);
     }
     ready_.notify_one();
+    return Reservation(std::move(pending));
 }
 
 void Gpu_Completion_Service::shutdown() noexcept {
@@ -35,6 +77,19 @@ void Gpu_Completion_Service::shutdown() noexcept {
         if (stopping_ && !thread_.joinable())
             return;
         stopping_ = true;
+        const auto cancel_reserved = [](const auto& pending) {
+            if (!pending)
+                return;
+            {
+                std::lock_guard pending_lock(pending->mutex);
+                if (pending->status == Pending_Fence::Status::reserved)
+                    pending->status = Pending_Fence::Status::canceled;
+            }
+            pending->ready.notify_one();
+        };
+        cancel_reserved(active_);
+        for (const auto& pending : pending_)
+            cancel_reserved(pending);
     }
     ready_.notify_one();
     if (thread_.joinable())
@@ -43,7 +98,7 @@ void Gpu_Completion_Service::shutdown() noexcept {
 
 void Gpu_Completion_Service::run() noexcept {
     for (;;) {
-        Pending_Fence pending;
+        std::shared_ptr<Pending_Fence> pending;
         {
             std::unique_lock lock(mutex_);
             ready_.wait(lock, [this] {
@@ -52,19 +107,45 @@ void Gpu_Completion_Service::run() noexcept {
             if (stopping_ && pending_.empty())
                 return;
             pending = std::move(pending_.front());
-            pending_.pop();
+            pending_.pop_front();
+            active_ = pending;
         }
 
-        const auto wait_started = std::chrono::steady_clock::now();
+        VkDevice device{VK_NULL_HANDLE};
+        VkFence fence{VK_NULL_HANDLE};
+        Completion completion;
+        bool observe{};
+        {
+            std::unique_lock lock(pending->mutex);
+            pending->ready.wait(lock, [&pending] {
+                return pending->status != Pending_Fence::Status::reserved;
+            });
+            if (pending->status == Pending_Fence::Status::canceled) {
+                lock.unlock();
+                std::lock_guard service_lock(mutex_);
+                active_.reset();
+                continue;
+            }
+            device = pending->device;
+            fence = pending->fence;
+            completion = std::move(pending->completion);
+            observe = pending->observe;
+        }
+
+        const auto wait_started = observe
+            ? std::chrono::steady_clock::now()
+            : std::chrono::steady_clock::time_point{};
         const VkResult result = vkWaitForFences(
-            pending.device, 1, &pending.fence, VK_TRUE, UINT64_MAX);
-        const auto wait_duration =
-            std::chrono::duration_cast<std::chrono::nanoseconds>(
-                std::chrono::steady_clock::now() - wait_started).count();
+            device, 1, &fence, VK_TRUE, UINT64_MAX);
         Result completion_result;
-        completion_result.wait_duration_ns = wait_duration > 0
-            ? static_cast<std::uint64_t>(wait_duration)
-            : 0;
+        if (observe) {
+            const auto wait_duration =
+                std::chrono::duration_cast<std::chrono::nanoseconds>(
+                    std::chrono::steady_clock::now() - wait_started).count();
+            completion_result.wait_duration_ns = wait_duration > 0
+                ? static_cast<std::uint64_t>(wait_duration)
+                : 0;
+        }
         if (result != VK_SUCCESS) {
             try {
                 throw std::runtime_error(
@@ -75,9 +156,13 @@ void Gpu_Completion_Service::run() noexcept {
             }
         }
         try {
-            pending.completion(std::move(completion_result));
+            completion(std::move(completion_result));
         } catch (...) {
         }
+        {
+            std::lock_guard lock(mutex_);
+            active_.reset();
+        }
     }
 }
 
diff --git a/render_3D/render_3D/detail/Gpu_Completion_Service.h b/render_3D/render_3D/detail/Gpu_Completion_Service.h
index 457ab94..c38dc8e 100644
--- a/render_3D/render_3D/detail/Gpu_Completion_Service.h
+++ b/render_3D/render_3D/detail/Gpu_Completion_Service.h
@@ -4,15 +4,18 @@
 
 #include <condition_variable>
 #include <cstdint>
+#include <deque>
 #include <exception>
 #include <functional>
 #include <mutex>
-#include <queue>
+#include <memory>
 #include <thread>
 
 namespace renderive::render_3d::detail {
 
 class Gpu_Completion_Service final {
+    struct Pending_Fence;
+
 public:
     struct Result {
         std::exception_ptr error;
@@ -21,27 +24,59 @@ public:
 
     using Completion = std::function<void(Result)>;
 
+    class Reservation final {
+    public:
+        Reservation() = default;
+        ~Reservation();
+
+        Reservation(const Reservation&) = delete;
+        Reservation& operator=(const Reservation&) = delete;
+        Reservation(Reservation&& other) noexcept;
+        Reservation& operator=(Reservation&&) = delete;
+
+        void watch(VkDevice device, VkFence fence) noexcept;
+
+    private:
+        explicit Reservation(std::shared_ptr<Pending_Fence> pending) noexcept;
+        void cancel() noexcept;
+
+        std::shared_ptr<Pending_Fence> pending_;
+
+        friend class Gpu_Completion_Service;
+    };
+
     Gpu_Completion_Service();
     ~Gpu_Completion_Service();
 
     Gpu_Completion_Service(const Gpu_Completion_Service&) = delete;
     Gpu_Completion_Service& operator=(const Gpu_Completion_Service&) = delete;
 
-    void watch(VkDevice device, VkFence fence, Completion completion);
+    [[nodiscard]] Reservation prepare(Completion completion, bool observe);
     void shutdown() noexcept;
 
 private:
     struct Pending_Fence {
+        enum class Status {
+            reserved,
+            watched,
+            canceled
+        };
+
+        std::mutex mutex;
+        std::condition_variable ready;
         VkDevice device{VK_NULL_HANDLE};
         VkFence fence{VK_NULL_HANDLE};
         Completion completion;
+        Status status{Status::reserved};
+        bool observe{};
     };
 
     void run() noexcept;
 
     std::mutex mutex_;
     std::condition_variable ready_;
-    std::queue<Pending_Fence> pending_;
+    std::deque<std::shared_ptr<Pending_Fence>> pending_;
+    std::shared_ptr<Pending_Fence> active_;
     std::thread thread_;
     bool stopping_{};
 };
diff --git a/render_3D/render_3D/detail/Render_Domain.h b/render_3D/render_3D/detail/Render_Domain.h
index e7560f1..dcdee51 100644
--- a/render_3D/render_3D/detail/Render_Domain.h
+++ b/render_3D/render_3D/detail/Render_Domain.h
@@ -5,7 +5,6 @@
 #include <future>
 #include <memory>
 #include <mutex>
-#include <queue>
 #include <stdexcept>
 #include <thread>
 #include <type_traits>
@@ -14,7 +13,34 @@
 namespace renderive::render_3d::detail {
 
 class Render_Domain final {
+    struct Task {
+        explicit Task(std::function<void()> value)
+            : function(std::move(value)) {}
+
+        std::function<void()> function;
+        std::unique_ptr<Task> next;
+    };
+
 public:
+    class Prepared_Task final {
+    public:
+        Prepared_Task() = default;
+        ~Prepared_Task() = default;
+
+        Prepared_Task(const Prepared_Task&) = delete;
+        Prepared_Task& operator=(const Prepared_Task&) = delete;
+        Prepared_Task(Prepared_Task&&) noexcept = default;
+        Prepared_Task& operator=(Prepared_Task&&) noexcept = default;
+
+    private:
+        explicit Prepared_Task(std::unique_ptr<Task> task) noexcept
+            : task_(std::move(task)) {}
+
+        std::unique_ptr<Task> task_;
+
+        friend class Render_Domain;
+    };
+
     Render_Domain() : thread_([this] { run(); }) {}
     ~Render_Domain() {
         {
@@ -29,14 +55,32 @@ public:
     Render_Domain(const Render_Domain&) = delete;
     Render_Domain& operator=(const Render_Domain&) = delete;
 
-    void post(std::function<void()> function) {
+    [[nodiscard]] Prepared_Task prepare(std::function<void()> function) {
         if (!function)
             throw std::invalid_argument("render domain task is empty");
+        return Prepared_Task(
+            std::make_unique<Task>(std::move(function)));
+    }
+
+    void post(std::function<void()> function) {
+        auto task = prepare(std::move(function));
         {
             std::lock_guard lock(mutex_);
             if (stopping_)
                 throw std::runtime_error("Point_Scene render domain is stopping");
-            tasks_.push(std::move(function));
+            enqueue_locked(std::move(task.task_));
+        }
+        condition_.notify_one();
+    }
+
+    void post(Prepared_Task task) noexcept {
+        if (!task.task_)
+            std::terminate();
+        {
+            std::lock_guard lock(mutex_);
+            if (stopping_)
+                std::terminate();
+            enqueue_locked(std::move(task.task_));
         }
         condition_.notify_one();
     }
@@ -57,22 +101,34 @@ public:
 private:
     void run() {
         for (;;) {
-            std::function<void()> task;
+            std::unique_ptr<Task> task;
             {
                 std::unique_lock lock(mutex_);
-                condition_.wait(lock, [&] { return stopping_ || !tasks_.empty(); });
-                if (stopping_ && tasks_.empty())
+                condition_.wait(lock, [&] { return stopping_ || first_; });
+                if (stopping_ && !first_)
                     return;
-                task = std::move(tasks_.front());
-                tasks_.pop();
+                task = std::move(first_);
+                first_ = std::move(task->next);
+                if (!first_)
+                    last_ = nullptr;
             }
-            task();
+            task->function();
         }
     }
 
+    void enqueue_locked(std::unique_ptr<Task> task) noexcept {
+        Task* const inserted = task.get();
+        if (last_)
+            last_->next = std::move(task);
+        else
+            first_ = std::move(task);
+        last_ = inserted;
+    }
+
     std::mutex mutex_;
     std::condition_variable condition_;
-    std::queue<std::function<void()>> tasks_;
+    std::unique_ptr<Task> first_;
+    Task* last_{};
     bool stopping_{};
     std::thread thread_;
 };
diff --git a/render_3D/tests/Gpu_Completion_Service_Tests.cpp b/render_3D/tests/Gpu_Completion_Service_Tests.cpp
new file mode 100644
index 0000000..8d7dc20
--- /dev/null
+++ b/render_3D/tests/Gpu_Completion_Service_Tests.cpp
@@ -0,0 +1,63 @@
+#include "render_3D/detail/Gpu_Completion_Service.h"
+#include "render_3D/detail/Render_Domain.h"
+
+#include <gtest/gtest.h>
+
+#include <atomic>
+#include <stdexcept>
+#include <utility>
+
+namespace renderive::render_3d::detail {
+namespace {
+
+static_assert(noexcept(
+    std::declval<Gpu_Completion_Service::Reservation&>().watch(
+        VK_NULL_HANDLE, VK_NULL_HANDLE)));
+static_assert(noexcept(
+    std::declval<Render_Domain&>().post(
+        std::declval<Render_Domain::Prepared_Task>())));
+
+TEST(GpuCompletionService, AbandonedReservationCancelsBeforeFenceWait) {
+    Gpu_Completion_Service service;
+    std::atomic<int> completion_count{};
+    {
+        auto reservation = service.prepare(
+            [&](Gpu_Completion_Service::Result) {
+                completion_count.fetch_add(1, std::memory_order_relaxed);
+            },
+            false);
+    }
+    service.shutdown();
+    EXPECT_EQ(completion_count.load(std::memory_order_relaxed), 0);
+}
+
+TEST(GpuCompletionService, PrepareRejectsAStoppedServiceBeforeSubmission) {
+    Gpu_Completion_Service service;
+    service.shutdown();
+    EXPECT_THROW({
+        auto reservation = service.prepare(
+            [](Gpu_Completion_Service::Result) {}, false);
+        static_cast<void>(reservation);
+    }, std::runtime_error);
+}
+
+TEST(GpuCompletionService, ShutdownCancelsAnUnarmedReservation) {
+    Gpu_Completion_Service service;
+    auto reservation = service.prepare(
+        [](Gpu_Completion_Service::Result) {}, false);
+    service.shutdown();
+}
+
+TEST(RenderDomain, PreparedTaskRunsAfterNoThrowHandoff) {
+    Render_Domain domain;
+    std::atomic<bool> executed{};
+    auto task = domain.prepare([&] {
+        executed.store(true, std::memory_order_release);
+    });
+    domain.post(std::move(task));
+    domain.invoke([] {});
+    EXPECT_TRUE(executed.load(std::memory_order_acquire));
+}
+
+} // namespace
+} // namespace renderive::render_3d::detail
diff --git a/render_3D/tests/Point_Render_Integration_Tests.cpp b/render_3D/tests/Point_Render_Integration_Tests.cpp
index a854f03..bc72a68 100644
--- a/render_3D/tests/Point_Render_Integration_Tests.cpp
+++ b/render_3D/tests/Point_Render_Integration_Tests.cpp
@@ -139,8 +139,36 @@ TEST(PointRenderIntegration,
             Node_Metric_Kind::gpu_fence_wait_ns));
         EXPECT_TRUE(execution.metrics.contains(
             Node_Metric_Kind::readback_duration_ns));
-        EXPECT_GT(execution.metrics.get(
-            Node_Metric_Kind::backend_artifact_json_bytes), 0U);
+        const auto artifact_bytes = execution.metrics.get(
+            Node_Metric_Kind::backend_artifact_json_bytes);
+        EXPECT_GT(artifact_bytes, 0U);
+        const auto artifact = std::find_if(
+            execution.attachments.begin(), execution.attachments.end(),
+            [](const Node_Diagnostic_Attachment& attachment) {
+                return attachment.type == "datoviz.drp2.artifact.json";
+            });
+        ASSERT_NE(artifact, execution.attachments.end());
+        EXPECT_EQ(artifact->content.size(), artifact_bytes);
+        EXPECT_FALSE(artifact->content.empty());
+
+        const bool gpu_timing = execution.metrics.contains(
+            Node_Metric_Kind::gpu_render_duration_ns);
+        EXPECT_EQ(gpu_timing, execution.metrics.contains(
+            Node_Metric_Kind::gpu_transition_duration_ns));
+        EXPECT_EQ(gpu_timing, execution.metrics.contains(
+            Node_Metric_Kind::gpu_copy_duration_ns));
+        EXPECT_EQ(gpu_timing, execution.metrics.contains(
+            Node_Metric_Kind::gpu_total_duration_ns));
+        if (gpu_timing) {
+            const auto total = execution.metrics.get(
+                Node_Metric_Kind::gpu_total_duration_ns);
+            EXPECT_GE(total, execution.metrics.get(
+                Node_Metric_Kind::gpu_render_duration_ns));
+            EXPECT_GE(total, execution.metrics.get(
+                Node_Metric_Kind::gpu_transition_duration_ns));
+            EXPECT_GE(total, execution.metrics.get(
+                Node_Metric_Kind::gpu_copy_duration_ns));
+        }
     } catch (const std::exception& error) {
         GTEST_SKIP() << "Vulkan/Datoviz unavailable: " << error.what();
     }
diff --git a/web_server/app/Gallery_Capture_Json.h b/web_server/app/Gallery_Capture_Json.h
index c0e4161..c284e58 100644
--- a/web_server/app/Gallery_Capture_Json.h
+++ b/web_server/app/Gallery_Capture_Json.h
@@ -59,7 +59,8 @@ inline Json metrics_json(const Node_Execution_Metrics& metrics) {
         "primitive_count", "queue_wait_ns", "apply_duration_ns",
         "plan_emit_duration_ns", "backend_execute_duration_ns",
         "submit_duration_ns", "gpu_fence_wait_ns",
-        "gpu_render_duration_ns", "gpu_copy_duration_ns",
+        "gpu_render_duration_ns", "gpu_transition_duration_ns",
+        "gpu_copy_duration_ns", "gpu_total_duration_ns",
         "readback_duration_ns", "backend_resource_version",
         "backend_frame_index", "backend_artifact_status",
         "backend_validation_code", "backend_validation_command",
@@ -147,6 +148,11 @@ inline Json plan_json(const Scene_Base& scene, const Render_Plan& plan) {
 
 inline Json execution_json(const Node_Execution& execution,
                            const Frame_Snapshot& frame) {
+    Json attachments = Json::array();
+    for (const auto& attachment : execution.attachments) {
+        attachments.push_back({{"type", attachment.type},
+                               {"content", attachment.content}});
+    }
     return {
         {"node_id", execution.node_id},
         {"ready_time_ns", execution.ready_time_ns},
@@ -172,7 +178,8 @@ inline Json execution_json(const Node_Execution& execution,
         {"external_duration_ns", execution.external_duration_ns()},
         {"worker_id", execution.worker_id},
         {"status", execution_status(execution.status)},
-        {"metrics", metrics_json(execution.metrics)}
+        {"metrics", metrics_json(execution.metrics)},
+        {"attachments", std::move(attachments)}
     };
 }
 
@@ -240,6 +247,10 @@ inline Json node_statistics_json(const Node_Statistics& statistics) {
         {"p99_ns", statistics.p99_ns},
         {"minimum_ns", statistics.minimum_ns},
         {"maximum_ns", statistics.maximum_ns},
+        {"average_cpu_ns", statistics.average_cpu_ns},
+        {"average_external_ns", statistics.average_external_ns},
+        {"p95_cpu_ns", statistics.p95_cpu_ns},
+        {"p95_external_ns", statistics.p95_external_ns},
         {"critical_path_frequency", statistics.critical_path_frequency},
         {"average_scheduler_wait_ns", statistics.average_scheduler_wait_ns}
     };
diff --git a/web_server/tests/Web_Bridge_Tests.cpp b/web_server/tests/Web_Bridge_Tests.cpp
index 4f3483b..0c84ec6 100644
--- a/web_server/tests/Web_Bridge_Tests.cpp
+++ b/web_server/tests/Web_Bridge_Tests.cpp
@@ -551,6 +551,7 @@ TEST(RenderiveWebGallery, PerformanceCaptureReturnsPlanFrameAnalysisAndStatistic
         EXPECT_TRUE(execution.contains("end_time_ns"));
         EXPECT_TRUE(execution.contains("worker_id"));
         EXPECT_TRUE(execution.contains("status"));
+        EXPECT_TRUE(execution.contains("attachments"));
         const auto& analysis = frame.at("analysis");
         EXPECT_TRUE(analysis.contains("critical_path"));
         EXPECT_TRUE(analysis.contains("parallel_overlap_ns"));
@@ -570,6 +571,10 @@ TEST(RenderiveWebGallery, PerformanceCaptureReturnsPlanFrameAnalysisAndStatistic
     EXPECT_TRUE(statistic.contains("p50_ns"));
     EXPECT_TRUE(statistic.contains("p95_ns"));
     EXPECT_TRUE(statistic.contains("p99_ns"));
+    EXPECT_TRUE(statistic.contains("average_cpu_ns"));
+    EXPECT_TRUE(statistic.contains("average_external_ns"));
+    EXPECT_TRUE(statistic.contains("p95_cpu_ns"));
+    EXPECT_TRUE(statistic.contains("p95_external_ns"));
     EXPECT_TRUE(statistic.contains("critical_path_frequency"));
     EXPECT_TRUE(statistic.contains("average_scheduler_wait_ns"));
 }
diff --git a/webapp_gallery/src/capture/node_detail.tsx b/webapp_gallery/src/capture/node_detail.tsx
index 19ab0a1..4820f44 100644
--- a/webapp_gallery/src/capture/node_detail.tsx
+++ b/webapp_gallery/src/capture/node_detail.tsx
@@ -1,9 +1,14 @@
 import {Stack,Typography} from "@mui/material";
-import type {Gallery_Capture_Session,Gallery_Captured_Frame,Gallery_Render_Plan} from "../protocol/gallery_types";
+import type {Gallery_Capture_Session,Gallery_Captured_Frame,Gallery_Render_Plan,Json_Value} from "../protocol/gallery_types";
 import {Metric_Grid} from "../common/metric_grid";
 import {Json_Viewer} from "../common/json_viewer";
 import {format_nanoseconds} from "../protocol/format";
 
+function attachment_value(type:string,content:string):Json_Value {
+    if(!type.endsWith(".json"))return content;
+    try{return JSON.parse(content) as Json_Value;}catch{return content;}
+}
+
 export function Node_Detail({frame,plan,session,selected_node_id}:{frame:Gallery_Captured_Frame;plan:Gallery_Render_Plan;session:Gallery_Capture_Session;selected_node_id:number|null}) {
     const node=plan.nodes.find(item=>item.node_id===selected_node_id);
     const execution=frame.node_executions.find(item=>item.node_id===selected_node_id);
@@ -22,6 +27,10 @@ export function Node_Detail({frame,plan,session,selected_node_id}:{frame:Gallery
         ["Critical",`${((analysis?.critical_path_contribution??0)*100).toFixed(2)}%`],
         ["Moving avg",format_nanoseconds(history?.moving_average_ns)],
         ["P95",format_nanoseconds(history?.p95_ns)],
-        ["P99",format_nanoseconds(history?.p99_ns)]
-    ]}/>{execution.metrics&&<Json_Viewer value={execution.metrics}/>}</Stack>;
+        ["P99",format_nanoseconds(history?.p99_ns)],
+        ["CPU avg",format_nanoseconds(history?.average_cpu_ns)],
+        ["CPU P95",format_nanoseconds(history?.p95_cpu_ns)],
+        ["External avg",format_nanoseconds(history?.average_external_ns)],
+        ["External P95",format_nanoseconds(history?.p95_external_ns)]
+    ]}/>{execution.metrics&&<Json_Viewer value={execution.metrics}/>} {execution.attachments.map((attachment,index)=><Stack key={`${attachment.type}:${index}`} spacing={1}><Typography variant="subtitle2">{attachment.type}</Typography><Json_Viewer value={attachment_value(attachment.type,attachment.content)}/></Stack>)}</Stack>;
 }
diff --git a/webapp_gallery/src/protocol/gallery_types.ts b/webapp_gallery/src/protocol/gallery_types.ts
index e3ee0e0..3f272fc 100644
--- a/webapp_gallery/src/protocol/gallery_types.ts
+++ b/webapp_gallery/src/protocol/gallery_types.ts
@@ -31,10 +31,11 @@ export interface Gallery_Render_Node {node_id: number; id?: string | number; nam
 export interface Gallery_Render_Edge {from: number | string; to: number | string;}
 export interface Gallery_Renderable_Cache {owner_id: number; name: string; prepare_cache: string; paint_cache: string;}
 export interface Gallery_Render_Plan {version: number; nodes: Gallery_Render_Node[]; edges: Gallery_Render_Edge[]; renderables: Gallery_Renderable_Cache[];}
-export interface Gallery_Node_Execution {node_id: number; worker_id: number; start_offset_ns: number; cpu_end_offset_ns: number; external_start_offset_ns: number; external_end_offset_ns: number; end_offset_ns: number; duration_ns: number; cpu_duration_ns: number; external_duration_ns: number; status: "pending"|"ready"|"running"|"waiting_external"|"complete"|"failed"; metrics?: Record<string, Json_Primitive>;}
+export interface Gallery_Node_Diagnostic_Attachment {type: string; content: string;}
+export interface Gallery_Node_Execution {node_id: number; worker_id: number; start_offset_ns: number; cpu_end_offset_ns: number; external_start_offset_ns: number; external_end_offset_ns: number; end_offset_ns: number; duration_ns: number; cpu_duration_ns: number; external_duration_ns: number; status: "pending"|"ready"|"running"|"waiting_external"|"complete"|"failed"; metrics?: Record<string, Json_Primitive>; attachments: Gallery_Node_Diagnostic_Attachment[];}
 export interface Gallery_Node_Analysis {node_id: number; duration_ns: number; cpu_duration_ns: number; external_duration_ns: number; scheduler_wait_ns: number; critical_path_contribution: number; on_critical_path: boolean;}
 export interface Gallery_Captured_Frame {frame_id: number; render_plan_version: number; render_duration_ns: number; node_executions: Gallery_Node_Execution[]; analysis?: {total_work_duration_ns?: number; total_external_duration_ns?: number; nodes: Gallery_Node_Analysis[]};}
-export interface Gallery_Node_Statistics {node_id: number; moving_average_ns: number; p95_ns: number; p99_ns: number; critical_path_frequency: number;}
+export interface Gallery_Node_Statistics {node_id: number; moving_average_ns: number; p95_ns: number; p99_ns: number; average_cpu_ns: number; average_external_ns: number; p95_cpu_ns: number; p95_external_ns: number; critical_path_frequency: number;}
 export interface Gallery_Plan_Statistics {render_plan_version: number; frame_count: number; render_average_ns: number; render_p95_ns: number; average_parallelism: number; peak_parallelism: number; scheduler_wait_average_ns: number; nodes: Gallery_Node_Statistics[];}
 export interface Gallery_Capture_Session {session_id: number; active: boolean; requested_count: number; captured_count: number; frames: Gallery_Captured_Frame[]; node_statistics: Gallery_Node_Statistics[]; plan_statistics: Gallery_Plan_Statistics[]; summary?: Record<string, Json_Value>;}
 export interface Gallery_Performance_Capture {controller: {enabled?: boolean; session_id?: number}; sessions: Gallery_Capture_Session[]; plans: Gallery_Render_Plan[];}
diff --git a/webapp_gallery/tests/dag/dag_model.test.ts b/webapp_gallery/tests/dag/dag_model.test.ts
index 7152bd8..2163809 100644
--- a/webapp_gallery/tests/dag/dag_model.test.ts
+++ b/webapp_gallery/tests/dag/dag_model.test.ts
@@ -1,2 +1,2 @@
 import {describe,expect,it} from "vitest";import {build_dag_model} from "../../src/dag/dag_model";
-describe("DAG view model",()=>{it("uses node_id for current plan and capture overlays",()=>{const plan={version:2,nodes:[{node_id:7,name:"paint",owner:"plot",kind:"paint"}],edges:[],renderables:[]};const frame={frame_id:1,render_plan_version:2,render_duration_ns:10,node_executions:[{node_id:7,worker_id:3,start_offset_ns:0,cpu_end_offset_ns:10,external_start_offset_ns:0,external_end_offset_ns:0,end_offset_ns:10,duration_ns:10,cpu_duration_ns:10,external_duration_ns:0,status:"complete" as const}],analysis:{total_work_duration_ns:10,total_external_duration_ns:0,nodes:[{node_id:7,duration_ns:10,cpu_duration_ns:10,external_duration_ns:0,scheduler_wait_ns:1,critical_path_contribution:1,on_critical_path:true}]}};const model=build_dag_model(plan,frame,[],7);expect(model.nodes[0].id).toBe("7");expect(model.nodes[0].data).toMatchObject({duration_ns:10,worker_id:3,critical:true,selected:true});});});
+describe("DAG view model",()=>{it("uses node_id for current plan and capture overlays",()=>{const plan={version:2,nodes:[{node_id:7,name:"paint",owner:"plot",kind:"paint"}],edges:[],renderables:[]};const frame={frame_id:1,render_plan_version:2,render_duration_ns:10,node_executions:[{node_id:7,worker_id:3,start_offset_ns:0,cpu_end_offset_ns:10,external_start_offset_ns:0,external_end_offset_ns:0,end_offset_ns:10,duration_ns:10,cpu_duration_ns:10,external_duration_ns:0,status:"complete" as const,attachments:[]}],analysis:{total_work_duration_ns:10,total_external_duration_ns:0,nodes:[{node_id:7,duration_ns:10,cpu_duration_ns:10,external_duration_ns:0,scheduler_wait_ns:1,critical_path_contribution:1,on_critical_path:true}]}};const model=build_dag_model(plan,frame,[],7);expect(model.nodes[0].id).toBe("7");expect(model.nodes[0].data).toMatchObject({duration_ns:10,worker_id:3,critical:true,selected:true});});});