diff --git a/README.md b/README.md
index ef46c90..8b5cf2a 100644
--- a/README.md
+++ b/README.md
@@ -14,8 +14,9 @@ and a **Python application** for supervision, visualization and control.
 
 The pipeline runs as three independent processes connected by lock-free POSIX
 shared-memory ring buffers. Each stage advances on its own, and a slow consumer
-never blocks a producer — the rings are latest-wins, so a reader that falls behind
-skips overwritten frames and continues from the retained tail:
+never blocks a producer — the rings are latest-wins: a full ring overwrites its oldest
+unread frame, a reader that falls behind continues with the frames still retained, and
+one overtaken during a read resumes at the newest frame:
 
 1. **Acquisition** — Python producers configure the radar, acquire frequency sweeps,
    and publish raw S21 traces. Both single and multi-device LibreVNA use
@@ -65,7 +66,8 @@ controls, processing settings and a copy of the live plot through an embedded we
 ## Processing modes
 
 - **pass_through** — magnitude and phase of S21 for each combo.
-- **bscan** — depth-versus-sweep B-scan heatmap.
+- **bscan** — depth-versus-sweep B-scan heatmap. A band selecting fewer than two
+  sweep points gives no range profile, and such sweeps are left out of the image.
 - **gpr** — coherent back-projection on the ground plane, as in `Horns_motion_4x4_ground.py`,
   with object detection. Radar height and look angle define the slice in radar X/Z axes;
   the wave speed is 3×10⁸ m/s (air).
@@ -100,7 +102,7 @@ peak; its size follows the contiguous half-maximum width along the volume axes
 (FWHM, at least one voxel). This measures the imaged response rather than the
 reflector's physical dimensions.
 
-The desktop uses a light theme with dark plot canvases. **Mode** stays below the
+The desktop uses a light theme with white plot canvases. **Mode** stays below the
 **Actions** buttons while the settings sections scroll; the settings panel and
 runtime log can be collapsed with their arrow buttons. SAR3D status, peak
 coordinates and level appear above the projections.
@@ -522,10 +524,14 @@ Profile loading blocks editor signals until all settings are populated.
 `HistoryController` owns retained acquisitions; `PlotController` selects the view
 and supplies independent B-scan, GPR, trace and SAR renderers with typed settings.
 Renderers own their plots and display caches, without access to the acquisition
-processes. Stopped B-scan replay uses the last run's ring, matches exact acquisition
-keys and the requested settings revision, and cancels when that run changes. With
-no retained preprocessed sweeps (including disabled taps), the processor recomputes
-its own retained history. Capture previews preserve the selected processing view.
+processes. Every plot change passes through `PlotController`, which counts changes
+of the shown image for the browser stream. The display shows the newest acquisition,
+including results read while stopping. Stopped B-scan replay uses the last run's
+ring, matches exact acquisition keys and the requested settings revision, and
+cancels when that run changes; sweeps the processor does not return are left out
+rather than mixing settings in one image. With no retained preprocessed sweeps
+(including disabled taps), the processor recomputes its own retained history.
+Capture previews preserve the selected processing view.
 `PipelineController` owns processes, ring readers, polling/recovery, Single Capture
 and replay. Its pause prevents recovery from starting a producer over a hardware
 capture; Stop or Close cancels any pending resumption, including during a drain.
diff --git a/data_acq_and_processing/common_cpp/ipc/include/shm_ring.hpp b/data_acq_and_processing/common_cpp/ipc/include/shm_ring.hpp
index 282c57c..0eee4de 100644
--- a/data_acq_and_processing/common_cpp/ipc/include/shm_ring.hpp
+++ b/data_acq_and_processing/common_cpp/ipc/include/shm_ring.hpp
@@ -29,7 +29,7 @@ class ShmRing {
 
     // Pushes payload with overwrite-oldest policy on overflow.
     [[nodiscard]] auto push(std::span<const std::uint8_t> payload) -> bool;
-    // Pops the next payload if available.
+    // Pops the next unread payload; false only when none remains.
     [[nodiscard]] auto pop(std::vector<std::uint8_t>& payload) -> bool;
 
   private:
diff --git a/data_acq_and_processing/common_cpp/ipc/src/shm_ring.cpp b/data_acq_and_processing/common_cpp/ipc/src/shm_ring.cpp
index cae935c..62a7725 100644
--- a/data_acq_and_processing/common_cpp/ipc/src/shm_ring.cpp
+++ b/data_acq_and_processing/common_cpp/ipc/src/shm_ring.cpp
@@ -1,5 +1,6 @@
 #include "shm_ring.hpp"
 
+#include <algorithm>
 #include <atomic>
 #include <chrono>
 #include <cerrno>
@@ -220,41 +221,43 @@ auto ShmRing::pop(std::vector<std::uint8_t>& payload) -> bool {
         throw std::runtime_error("Ring is not open");
     }
 
-    const auto read_seq = header_->read_seq.load(std::memory_order_relaxed);
-    const auto write_seq = header_->write_seq.load(std::memory_order_acquire);
-    if (read_seq >= write_seq) {
-        return false;
+    while (true) {
+        const auto read_seq = header_->read_seq.load(std::memory_order_relaxed);
+        const auto write_seq = header_->write_seq.load(std::memory_order_acquire);
+        if (read_seq >= write_seq) {
+            return false;
+        }
+        // A lapped, torn or corrupt slot is skipped with the backlog behind the newest
+        // payload, which is read next (latest-wins); a bad slot never stops the consumer.
+        const auto resync = std::max(read_seq + 1U, write_seq - 1U);
+
+        auto* slot = slot_header(read_seq);
+        if (std::atomic_ref(slot->sequence).load(std::memory_order_acquire) != read_seq + 1U) {
+            advance_read_seq(resync);  // Overwritten before this read (lapped).
+            continue;
+        }
+
+        const auto payload_size = slot->payload_size;
+        if (payload_size > header_->slot_size_bytes) {
+            advance_read_seq(resync);
+            continue;
+        }
+
+        std::atomic_thread_fence(std::memory_order_acquire);
+        payload.resize(payload_size);
+        std::memcpy(payload.data(), slot_payload(slot), payload_size);
+
+        // Seqlock verify: if the slot sequence changed during the copy, the producer
+        // lapped us mid-read and the payload is torn.
+        std::atomic_thread_fence(std::memory_order_acquire);
+        if (std::atomic_ref(slot->sequence).load(std::memory_order_acquire) != read_seq + 1U) {
+            advance_read_seq(resync);
+            continue;
+        }
+
+        advance_read_seq(read_seq + 1U);
+        return true;
     }
-
-    auto* slot = slot_header(read_seq);
-    if (std::atomic_ref(slot->sequence).load(std::memory_order_acquire) != read_seq + 1U) {
-        // Slot not published for this seq, or already overwritten (lapped). Resync.
-        advance_read_seq(write_seq);
-        return false;
-    }
-
-    const auto payload_size = slot->payload_size;
-    if (payload_size > header_->slot_size_bytes) {
-        // Corrupt/torn slot: skip it (resync) rather than throw — a single bad slot
-        // must never abort the long-running consumer.
-        advance_read_seq(write_seq);
-        return false;
-    }
-
-    std::atomic_thread_fence(std::memory_order_acquire);
-    payload.resize(payload_size);
-    std::memcpy(payload.data(), slot_payload(slot), payload_size);
-
-    // Seqlock verify: if the slot sequence changed during the copy, the producer
-    // lapped us mid-read and the payload is torn — discard and resync.
-    std::atomic_thread_fence(std::memory_order_acquire);
-    if (std::atomic_ref(slot->sequence).load(std::memory_order_acquire) != read_seq + 1U) {
-        advance_read_seq(write_seq);
-        return false;
-    }
-
-    advance_read_seq(read_seq + 1U);
-    return true;
 }
 
 void ShmRing::advance_read_seq(std::uint64_t target) {
diff --git a/data_acq_and_processing/processing/data_processor/include/data_processor.hpp b/data_acq_and_processing/processing/data_processor/include/data_processor.hpp
index 381dcff..50c41d4 100644
--- a/data_acq_and_processing/processing/data_processor/include/data_processor.hpp
+++ b/data_acq_and_processing/processing/data_processor/include/data_processor.hpp
@@ -38,8 +38,11 @@ class DataProcessor {
         const ProcessingLiveConfig& live_config
     ) -> ipc::ResultCollection;
 
+    [[nodiscard]] auto requested_mode(const ProcessingLiveConfig& live_config) const -> const std::string&;
     [[nodiscard]] auto resolve_processor(const ProcessingLiveConfig& live_config) -> ProcessorInterface&;
     [[nodiscard]] auto should_replay_entire_history(const ProcessingLiveConfig& live_config) const -> bool;
+    // Only gpr and sar3d use the speed, so only they recompute when a locator client changes it.
+    [[nodiscard]] auto uses_socket_speed(const ProcessingLiveConfig& live_config) const -> bool;
 
     // Speed streamed by a locator client (`vlc`), which then replaces
     // `gpr_speed_m_s`; nullopt when `ignore_socket_speed` is set or no fresh
diff --git a/data_acq_and_processing/processing/data_processor/src/data_processor.cpp b/data_acq_and_processing/processing/data_processor/src/data_processor.cpp
index f612cb9..7ad1137 100644
--- a/data_acq_and_processing/processing/data_processor/src/data_processor.cpp
+++ b/data_acq_and_processing/processing/data_processor/src/data_processor.cpp
@@ -76,9 +76,8 @@ void DataProcessor::run(const std::atomic<bool>& stop_requested) {
     std::uint64_t last_replayed_revision = live_config_loader_.revision();
     runtime::CollectionErrors errors;
     std::uint64_t oversized_results = 0;
-    // track the socket-fed speed used for the last reprocess so a change
-    // arriving without a live-config revision bump still triggers a reprocess of
-    // the current result (gated below by reprocess_current_result).
+    // The socket-fed speed used by the last reprocess: in the modes that use the speed, a
+    // change without a live-config revision still recomputes the current result.
     std::optional<double> last_reprocessed_socket_speed = std::nullopt;
 
     while (!stop_requested.load(std::memory_order_relaxed)) {
@@ -97,7 +96,8 @@ void DataProcessor::run(const std::atomic<bool>& stop_requested) {
             }
             auto& processor = resolve_processor(live_config);
             const auto history_limit = processing_history_limit(config_, live_config);
-            const bool socket_speed_dirty = current_socket_speed != last_reprocessed_socket_speed;
+            const bool socket_speed_dirty =
+                uses_socket_speed(live_config) && current_socket_speed != last_reprocessed_socket_speed;
 
             const auto was_removed = [&](const ipc::PreprocessedCollection& collection) {
                 if (live_config.history_clear_before_ns &&
@@ -111,39 +111,36 @@ void DataProcessor::run(const std::atomic<bool>& stop_requested) {
                     });
             };
             if (live_revision != last_replayed_revision || socket_speed_dirty) {
+                // Settled before recomputing: a sweep that fails is reported once rather than
+                // retried every tick, which would stop all new input.
+                last_replayed_revision = live_revision;
+                last_reprocessed_socket_speed = current_socket_speed;
                 std::erase_if(preprocessed_history, was_removed);
                 if (preprocessed_history.size() > history_limit) {
                     preprocessed_history.erase(preprocessed_history.begin(), preprocessed_history.end() - history_limit);
                 }
 
-                if (!live_config.reprocess_current_result) {
-                    // Socket-fed speed updates should affect only future preprocessed collections,
-                    // not replay the current history entry.
-                } else if (should_replay_entire_history(live_config)) {
-                    for (std::size_t index = 0; index < preprocessed_history.size(); ++index) {
-                        const auto replay_result = process_collection(
-                            preprocessed_history[index],
-                            std::span<const ipc::PreprocessedCollection>(preprocessed_history.data(), index),
-                            processor,
-                            live_config
-                        );
-                        publish_result_collection(replay_result, results_ring_, oversized_results);
-                        publish_locator(replay_result);
+                // The GUI turns this off while it re-feeds the sweeps of a stopped B-scan itself.
+                if (live_config.reprocess_current_result && !preprocessed_history.empty()) {
+                    const auto newest = preprocessed_history.size() - 1U;
+                    const auto first = should_replay_entire_history(live_config) ? std::size_t{0} : newest;
+                    for (auto index = first; index <= newest; ++index) {
+                        try {
+                            const auto replay_result = process_collection(
+                                preprocessed_history[index],
+                                std::span<const ipc::PreprocessedCollection>(preprocessed_history.data(), index),
+                                processor,
+                                live_config
+                            );
+                            publish_result_collection(replay_result, results_ring_, oversized_results);
+                            if (index == newest) {
+                                publish_locator(replay_result);  // The locator reports the current scene.
+                            }
+                        } catch (const std::exception& exc) {
+                            errors.report("data_processor", exc);
+                        }
                     }
-                } else if (!preprocessed_history.empty()) {
-                    const auto replay_result = process_collection(
-                        preprocessed_history.back(),
-                        std::span<const ipc::PreprocessedCollection>(preprocessed_history.data(), preprocessed_history.size() - 1U),
-                        processor,
-                        live_config
-                    );
-                    publish_result_collection(replay_result, results_ring_, oversized_results);
-                    publish_locator(replay_result);
                 }
-                last_replayed_revision = live_revision;
-                //record the speed we just reprocessed with so an
-                // unchanged socket value does not retrigger every iteration.
-                last_reprocessed_socket_speed = current_socket_speed;
             }
 
             if (preprocessed_ring_.pop(bytes)) {
@@ -219,11 +216,12 @@ auto DataProcessor::process_collection(
     return result;
 }
 
-auto DataProcessor::resolve_processor(const ProcessingLiveConfig& live_config) -> ProcessorInterface& {
-    const std::string requested_mode =
-        live_config.processor_mode.empty() ? default_processor_mode_ : live_config.processor_mode;
+auto DataProcessor::requested_mode(const ProcessingLiveConfig& live_config) const -> const std::string& {
+    return live_config.processor_mode.empty() ? default_processor_mode_ : live_config.processor_mode;
+}
 
-    if (auto found = processors_.find(requested_mode); found != processors_.end()) {
+auto DataProcessor::resolve_processor(const ProcessingLiveConfig& live_config) -> ProcessorInterface& {
+    if (auto found = processors_.find(requested_mode(live_config)); found != processors_.end()) {
         return *(found->second);
     }
     if (auto fallback = processors_.find(default_processor_mode_); fallback != processors_.end()) {
@@ -233,9 +231,12 @@ auto DataProcessor::resolve_processor(const ProcessingLiveConfig& live_config) -
 }
 
 auto DataProcessor::should_replay_entire_history(const ProcessingLiveConfig& live_config) const -> bool {
-    const std::string requested_mode =
-        live_config.processor_mode.empty() ? default_processor_mode_ : live_config.processor_mode;
-    return requested_mode == "bscan";
+    return requested_mode(live_config) == "bscan";
+}
+
+auto DataProcessor::uses_socket_speed(const ProcessingLiveConfig& live_config) const -> bool {
+    const auto& mode = requested_mode(live_config);
+    return mode == "gpr" || mode == "sar3d";
 }
 
 auto DataProcessor::socket_speed(const ProcessingLiveConfig& live_config) const -> std::optional<double> {
diff --git a/data_acq_and_processing/processing/processors/src/bscan_processor.cpp b/data_acq_and_processing/processing/processors/src/bscan_processor.cpp
index 6206572..bb47bd1 100644
--- a/data_acq_and_processing/processing/processors/src/bscan_processor.cpp
+++ b/data_acq_and_processing/processing/processors/src/bscan_processor.cpp
@@ -93,24 +93,9 @@ void fft_inplace(std::vector<std::complex<double>>& values, bool inverse) {
     return std::abs(sample);
 }
 
-[[nodiscard]] auto fallback_profile(
-    const ipc::SweepTraceBlock& trace,
-    std::span<const ipc::Complex32> selected_samples
-) -> BScanProfile {
-    const std::size_t point_count = std::min(trace.frequency_hz.size(), selected_samples.size());
-    BScanProfile fallback{};
-    fallback.depth_m.reserve(point_count);
-    fallback.response.reserve(point_count);
-
-    const float denominator = point_count > 1U ? static_cast<float>(point_count - 1U) : 1.0F;
-    for (std::size_t index = 0U; index < point_count; ++index) {
-        const auto& sample = selected_samples[index];
-        fallback.depth_m.push_back(static_cast<float>(static_cast<float>(index) / denominator));
-        fallback.response.push_back(std::sqrt(sample.re * sample.re + sample.im * sample.im));
-    }
-    return fallback;
-}
-
+// A range profile needs at least two in-band points on an increasing frequency grid.
+// Otherwise the profile is empty and the display leaves the column out: drawing |S21|
+// against a made-up depth axis would look like a valid B-scan.
 [[nodiscard]] auto compute_bscan_profile(
     const ipc::SweepTraceBlock& trace,
     const ProcessingLiveConfig& live_config
@@ -118,7 +103,7 @@ void fft_inplace(std::vector<std::complex<double>>& values, bool inverse) {
     const auto selected_samples = std::span<const ipc::Complex32>(trace.s21);
     const std::size_t point_count = std::min(trace.frequency_hz.size(), selected_samples.size());
     if (point_count < 2U) {
-        return fallback_profile(trace, selected_samples);
+        return {};
     }
 
     const double configured_start_hz = static_cast<double>(live_config.bscan_start_freq_mhz) * 1'000'000.0;
@@ -142,35 +127,35 @@ void fft_inplace(std::vector<std::complex<double>>& values, bool inverse) {
     }
 
     if (filtered_freq_hz.size() < 2U) {
-        return fallback_profile(trace, selected_samples);
+        return {};
     }
 
     const std::size_t filtered_count = filtered_freq_hz.size();
     const double df = (filtered_freq_hz.back() - filtered_freq_hz.front()) / static_cast<double>(filtered_count - 1U);
     if (df <= 0.0) {
-        return fallback_profile(trace, selected_samples);
+        return {};
     }
 
     const auto start_bin = static_cast<std::int64_t>(std::llround(filtered_freq_hz.front() / df));
     if (start_bin < 0) {
-        return fallback_profile(trace, selected_samples);
+        return {};
     }
 
     const auto start_index = static_cast<std::size_t>(start_bin);
     if (start_index > (std::numeric_limits<std::size_t>::max() / 2U)) {
-        return fallback_profile(trace, selected_samples);
+        return {};
     }
     if (start_index > (std::numeric_limits<std::size_t>::max() - filtered_count + 1U)) {
-        return fallback_profile(trace, selected_samples);
+        return {};
     }
 
     const std::size_t min_fft_len = 2U * (start_index + filtered_count - 1U);
     const std::size_t fft_len = next_power_of_two(min_fft_len);
     if (fft_len < min_fft_len || (fft_len & (fft_len - 1U)) != 0U) {
-        return fallback_profile(trace, selected_samples);
+        return {};
     }
     if (start_index > fft_len || filtered_count > (fft_len - start_index)) {
-        return fallback_profile(trace, selected_samples);
+        return {};
     }
 
     std::vector<std::complex<double>> spectrum(fft_len, std::complex<double>(0.0, 0.0));
diff --git a/device_firmware/librevna_protocol.md b/device_firmware/librevna_protocol.md
index dceac3d..25c4da8 100644
--- a/device_firmware/librevna_protocol.md
+++ b/device_firmware/librevna_protocol.md
@@ -237,6 +237,11 @@ ref» — сигнал на первом приёмнике.
 слейвов на барьере синхронизации. Слив очередей, ожидание начала цикла и
 повторные попытки сбора в окно не входят.
 
+Внутри свипа индекс точки только растёт, поэтому цикл прибора закрывается на
+первой точке с неувеличившимся индексом — начале следующего свипа, даже если его
+точка 0 потеряна. Точки следующего свипа в цикл не попадают. Потерянные точки
+цикла становятся нулём; если таких больше 5 % трассы, цикл собирается заново.
+
 ### Формат коллекций между процессами хоста
 
 Это отдельный формат от USB-пакетов прибора. `RAW3` и `PRP3` — четыре ASCII-байта
diff --git a/python_app/gui/controllers/bscan_replay.py b/python_app/gui/controllers/bscan_replay.py
index 397ea03..cfa3b4a 100644
--- a/python_app/gui/controllers/bscan_replay.py
+++ b/python_app/gui/controllers/bscan_replay.py
@@ -116,14 +116,14 @@ class BscanReplay:
         finally:
             self.active = False
 
-        # Tap and results rings drop independently: only these replayed keys belong
-        # in the refreshed image; unrelated runtime results may still use old settings.
+        # Tap and results rings drop independently: only these replayed keys belong in the
+        # refreshed image. One image never mixes settings, so unreturned sweeps are left out.
         self.history.replay_results[:] = [replayed[key] for key in keys if key in replayed]
         received = sum(key in replayed for key in keys[:sent])
         if received < sent:
             self._warning(
                 f"B-scan replay recovered {received} of {sent} re-sent sweeps; "
-                "some columns may still show their captured settings.",
+                "the image leaves the others out.",
                 once_key=f"bscan_replay_incomplete_{sent}_{received}",
             )
         self._debug(f"B-scan replay finished: sent={sent}, recovered={received}.")
diff --git a/python_app/gui/controllers/live_settings_controller.py b/python_app/gui/controllers/live_settings_controller.py
index 64bd391..feb012a 100644
--- a/python_app/gui/controllers/live_settings_controller.py
+++ b/python_app/gui/controllers/live_settings_controller.py
@@ -120,27 +120,15 @@ class LiveSettingsController:
 
     def _redraw(self) -> None:
         try:
-            mode = self._mode.currentText()
-            pipeline, plots, history = self._pipeline, self._pipeline.plots, self._pipeline.history
-            if mode == "bscan":
-                if pipeline.can_reprocess_history():
-                    pipeline.schedule_replay()
-                else:
-                    pipeline.drain_results(timeout_s=0.25, poll_s=0.01)
-                plots.draw_bscan()
+            mode, pipeline = self._mode.currentText(), self._pipeline
+            if mode == "bscan" and pipeline.can_reprocess_history():
+                pipeline.schedule_replay()
+            elif mode == "bscan":
+                pipeline.drain_results(timeout_s=0.25, poll_s=0.01)
             elif mode in _GEOMETRY_MODES:
-                latest = pipeline.drain_results(timeout_s=0.8, poll_s=0.02)
-                collection = latest if latest is not None else history.results[-1] if history.results else None
-                if mode == "sar3d":
-                    plots.sar3d.clear()
-                    if collection is not None:
-                        plots.draw(collection)
-                elif collection is None or not plots.draw(collection):
-                    plots.clear_gpr()
-            elif history.results:
-                plots.draw(history.results[-1])
-            else:
-                plots.trace.clear()
+                # Only the published revision is drawn: wait for the newest sweep recomputed with it.
+                pipeline.drain_results(timeout_s=0.8, poll_s=0.02, revision=pipeline.plots.required_revision)
+            pipeline.plots.redraw()
         except Exception as exc:
             self._log.show_exception("Failed to render processing settings", exc)
 
@@ -171,7 +159,7 @@ class LiveSettingsController:
 
     def locator_changed(self, *_args: object) -> None:
         if self._mode.currentText() == "gpr" and self._publish_changes():
-            self.visual_changed()
+            self._redraw()
 
     def set_mode_page(self, mode: str) -> None:
         pages = self._processing.pages
diff --git a/python_app/gui/controllers/pipeline_controller.py b/python_app/gui/controllers/pipeline_controller.py
index e2567cf..c1ee6a2 100644
--- a/python_app/gui/controllers/pipeline_controller.py
+++ b/python_app/gui/controllers/pipeline_controller.py
@@ -80,6 +80,9 @@ class PipelineController:
         self._raw_reader: ShmRingReader | None = None
         self._pre_reader: ShmRingReader | None = None
         self._result_reader: ShmRingReader | None = None
+        # Results read anywhere (polling, Stop/pause drains, snapshots) await display;
+        # the next poll shows the newest acquisition, not merely the last one read.
+        self._display_pending = False
         self.active_config: RunConfigModel | None = None
         self.active_config_path: Path | None = None
         self.stop_generation = 0
@@ -203,6 +206,7 @@ class PipelineController:
                 raise error
             if not operation.valid:
                 raise InterruptedError("Pipeline operation cancelled")
+            self._display_pending = False  # the pausing operation owns the display
             return operation
         except BaseException:
             operation.finish(resume=False)
@@ -478,11 +482,14 @@ class PipelineController:
                 finally:
                     if self.single_capture_active:
                         self._check_single_capture_deadline()
-            elif latest[2] is not None:
-                self._restart_count = 0
-                started = time.monotonic_ns()
-                self.plots.draw(latest[2])
-                self.metrics.record("rendering", time.monotonic_ns() - started)
+            elif self._display_pending:
+                if latest[2] is not None:
+                    self._restart_count = 0  # results flow again
+                self._display_pending = False
+                if self.history.results:
+                    started = time.monotonic_ns()
+                    self.plots.draw(self.history.results[-1])
+                    self.metrics.record("rendering", time.monotonic_ns() - started)
         except Exception as exc:
             self._report_ui_error("Result display", exc)
 
@@ -634,6 +641,7 @@ class PipelineController:
                 self.metrics.record("processing", collection.processing_duration_ns)
                 if self.history.record_result(collection):
                     self.recording.record("results", collection)
+                self._display_pending = True
                 latest = collection
         return latest
 
@@ -662,17 +670,20 @@ class PipelineController:
             stable = 0 if self.drain_once() else stable + 1
             self.pump_events(poll_s)
 
-    def drain_results(self, *, timeout_s: float, poll_s: float) -> ResultCollection | None:
-        deadline, stable = time.monotonic() + timeout_s, 0
-        latest_seen = None
-        while self._result_reader is not None and time.monotonic() < deadline and (latest_seen is None or stable < 2):
-            latest = self.read_results()
-            if latest is not None:
-                latest_seen, stable = latest, 0
-            elif latest_seen is not None:
+    def drain_results(self, *, timeout_s: float, poll_s: float, revision: int | None = None) -> None:
+        """Read results until the timeout; stop two quiet polls after results arrive or,
+        given a revision, as soon as the newest result carries it."""
+        deadline, seen, stable = time.monotonic() + timeout_s, False, 0
+        while self._result_reader is not None and time.monotonic() < deadline:
+            if self.read_results() is not None:
+                seen, stable = True, 0
+            elif seen:
                 stable += 1
+            if revision is None and stable >= 2:
+                return
+            if revision is not None and self.history.results and self.history.results[-1].settings_revision == revision:
+                return
             self.pump_events(poll_s)
-        return latest_seen
 
     def drain_snapshot(self) -> None:
         initial_readers = self.readers
diff --git a/python_app/gui/controllers/plot_controller.py b/python_app/gui/controllers/plot_controller.py
index 22ba0ed..09f1152 100644
--- a/python_app/gui/controllers/plot_controller.py
+++ b/python_app/gui/controllers/plot_controller.py
@@ -2,6 +2,7 @@
 
 from collections.abc import Callable
 
+import pyqtgraph as pg
 from PyQt6.QtCore import QSignalBlocker
 from PyQt6.QtWidgets import QComboBox, QPushButton, QStackedWidget, QWidget
 
@@ -14,8 +15,12 @@ from python_app.models.dataset_model import ResultCollection, TraceData
 from python_app.models.gui_profile_schema import GuiProcessingStateModel
 from python_app.models.run_config_schema import GprModel
 
+Renderer = BscanRenderer | GprRenderer | Sar3dRenderer | TraceRenderer
+
 
 class PlotController:
+    """Own the plot views: renderers draw and clear only through it, and it counts image changes."""
+
     def __init__(
         self, history: HistoryController, settings: Callable[[], GuiProcessingStateModel],
         geometry: Callable[[], GprModel], running: Callable[[], bool],
@@ -36,9 +41,28 @@ class PlotController:
         for renderer in (self.bscan, self.gpr, self.sar3d, self.trace):
             self.stack.addWidget(renderer.widget)
         self.stack.setCurrentWidget(self.trace.widget)
+        # Counts changes of the shown image (drawing, page, size, view range, a legend click
+        # hiding a curve) for observers such as the web stream. QGraphicsScene.changed must stay
+        # unconnected: it switches Qt to a legacy update path that leaves stale pixels behind.
+        self.revision = 0
+        self.stack.currentChanged.connect(self._changed)
+        for plot in self.stack.findChildren(pg.PlotWidget):
+            item = plot.getPlotItem()
+            assert item is not None
+            view = item.getViewBox()
+            view.sigResized.connect(self._changed)
+            view.sigRangeChanged.connect(self._changed)
+        for panel in (self.trace.magnitude, self.trace.phase):
+            panel.legend.sigSampleClicked.connect(self._changed)
         self._combo: QComboBox | None = None
         self._next: QPushButton | None = None
 
+    def _changed(self, *_args: object) -> None:
+        self.revision += 1
+
+    def _renderer(self, mode: str) -> Renderer:
+        return {"bscan": self.bscan, "gpr": self.gpr, "sar3d": self.sar3d}.get(mode, self.trace)
+
     def bind_display_controls(self, combo: QComboBox, next_button: QPushButton) -> None:
         self._combo, self._next = combo, next_button
         combo.currentIndexChanged.connect(self.on_display_combo_changed)
@@ -55,8 +79,7 @@ class PlotController:
         return self.sar3d.grid if current is self.sar3d.widget else current
 
     def set_mode(self, mode: str) -> None:
-        renderer = {"bscan": self.bscan, "gpr": self.gpr, "sar3d": self.sar3d}.get(mode, self.trace)
-        self.stack.setCurrentWidget(renderer.widget)
+        self.stack.setCurrentWidget(self._renderer(mode).widget)
         self.sync_display_combos()
 
     def select_combo(self, input_pos: int, output_pos: int) -> None:
@@ -96,6 +119,7 @@ class PlotController:
         self.sync_display_combos()
 
     def draw_bscan(self) -> bool:
+        self._changed()
         self.sync_bscan()
         window, retained = self.window_scans(), len(self.history.preprocessed)
         if retained < window and self.bscan.history_by_combo:
@@ -119,6 +143,7 @@ class PlotController:
                 return False
         if mode == "bscan":
             return self.draw_bscan()
+        self._changed()
         if mode == "gpr":
             return self.gpr.draw(collection, settings.gpr, self._geometry())
         if mode == "sar3d":
@@ -126,42 +151,36 @@ class PlotController:
         return self.trace.draw(collection, settings.pass_through)
 
     def redraw(self, *_args: object) -> None:
+        """Show the newest result with the current settings."""
         mode = self._settings().selected_mode
         if mode == "bscan":
             self.draw_bscan()
-        elif mode == "sar3d":
-            self.sar3d.clear()
-            if self.history.results:
-                self.draw(self.history.results[-1])
-        elif not self.history.results or not self.draw(self.history.results[-1]):
-            self.clear_current()
+            return
+        # Cleared first: a result of another settings revision is not drawn and must not
+        # leave the previous image, while a renderer's own failure message is kept.
+        self._changed()
+        self._renderer(mode).clear()
+        if self.history.results:
+            self.draw(self.history.results[-1])
 
     def draw_trace(self, trace: TraceData, title: str) -> None:
+        self._changed()
         self.trace.draw_trace(trace, title, self._settings().pass_through)
 
+    def clear_trace(self) -> None:
+        self._changed()
+        self.trace.clear()
+
     def clear_bscan(self) -> None:
+        self._changed()
         self.bscan.clear()
         self.sync_display_combos()
 
-    def clear_gpr(self) -> None:
-        self.gpr.clear()
-
-    def clear_current(self) -> None:
-        mode = self._settings().selected_mode
-        if mode == "bscan":
-            self.clear_bscan()
-        elif mode == "gpr":
-            self.clear_gpr()
-        elif mode == "sar3d":
-            self.sar3d.clear()
-        else:
-            self.trace.clear()
-
     def clear(self) -> None:
-        self.clear_bscan()
-        self.clear_gpr()
-        self.sar3d.clear()
-        self.trace.clear()
+        self._changed()
+        for renderer in (self.bscan, self.gpr, self.sar3d, self.trace):
+            renderer.clear()
+        self.sync_display_combos()
 
     @staticmethod
     def has_output(collection: ResultCollection) -> bool:
diff --git a/python_app/gui/controllers/preprocess_controller.py b/python_app/gui/controllers/preprocess_controller.py
index 726b946..6bd2366 100644
--- a/python_app/gui/controllers/preprocess_controller.py
+++ b/python_app/gui/controllers/preprocess_controller.py
@@ -324,7 +324,7 @@ class PreprocessController:
             dialog.clear_capture_log()
             dialog.reset_preview()
             dialog.set_status(f"{preprocess_asset_display_name(kind)} sequence started")
-            self._plots.trace.clear()
+            self._plots.clear_trace()
             self._update_capture_state()
             logger.info("%s sequence started: set=%s, combos=%d, radar_variants=%d, median_sweeps=%d",
                         kind, name, session.state().total_count, len(keys), settings.median_sweep_count)
@@ -417,7 +417,7 @@ class PreprocessController:
             trace = session.last_captured_trace()
             if trace is None:
                 dialog.reset_preview()
-                self._plots.trace.clear()
+                self._plots.clear_trace()
             else:
                 dialog.draw_last_trace(trace, title=f"{display} last trace")
                 self._plots.draw_trace(trace, f"{display} last trace")
diff --git a/python_app/gui/controllers/renderers/bscan.py b/python_app/gui/controllers/renderers/bscan.py
index f255109..e63b3c4 100644
--- a/python_app/gui/controllers/renderers/bscan.py
+++ b/python_app/gui/controllers/renderers/bscan.py
@@ -4,14 +4,13 @@ from __future__ import annotations
 
 from collections import deque
 
-from PyQt6.QtCore import QRectF
 import numpy as np
 import pyqtgraph as pg
 
 from python_app.models.collection_identity import collection_key
 from python_app.models.dataset_model import ResultCollection
 from python_app.models.gui_profile_schema import GuiBscanStateModel
-from python_app.gui.controllers.renderers.common import build_lut, create_plot
+from python_app.gui.controllers.renderers.common import build_lut, create_plot, image_rect
 
 
 def _result_tail(
@@ -109,16 +108,18 @@ def bscan_levels(sweeps: np.ndarray, axis_mode: str) -> tuple[float, float]:
     return -max_abs, max_abs
 
 
+_TITLE = "B-scan S21"
+
+
 class BscanRenderer:
     """Own the heatmap and its per-combination arrays; input history stays external."""
 
     def __init__(self) -> None:
-        self.widget = create_plot()
+        self.widget = create_plot(_TITLE)
         self.widget.setLabel("bottom", "Sweep #")
         self.widget.setLabel("left", "Range", units="m")
         item = self.widget.getPlotItem()
         assert item is not None
-        item.getViewBox().invertY(False)
         item.getViewBox().enableAutoRange(x=False, y=False)
         self.image = pg.ImageItem(axisOrder="row-major")
         item.addItem(self.image)
@@ -139,24 +140,28 @@ class BscanRenderer:
         history = self.history_by_combo.get(key) if key is not None else None
         depth = self.depth_axis_by_combo.get(key) if key is not None else None
         if not history or depth is None:
-            self.image.clear()
+            self._show_empty()
             return False
         sweeps = apply_mean_ascan_subtraction(history, enabled=settings.subtract_mean_ascan)
-        depth_min, depth_max = float(np.min(depth)), float(np.max(depth))
         count = sweeps.shape[0]
+        rect = image_rect(np.arange(1, count + 1), depth)
         self.image.setImage(sweeps.T, autoLevels=False)
-        self.image.setRect(QRectF(.5, depth_min, float(count), max(depth_max - depth_min, 1e-6)))
+        self.image.setRect(rect)
         self.image.setLookupTable(bscan_lookup_table(settings.axis))
         self.image.setLevels(bscan_levels(sweeps, settings.axis))
         item = self.widget.getPlotItem()
         assert item is not None
-        item.getViewBox().setRange(xRange=(.5, .5 + count), yRange=(depth_min, depth_max), padding=.02)
+        item.getViewBox().setRange(rect, padding=.02)
         assert key is not None
-        self.widget.setTitle(f"B-scan S21 in{key[0]}/out{key[1]} | sweeps={count}")
+        self.widget.setTitle(f"{_TITLE} in{key[0]}/out{key[1]} | sweeps={count}")
         return True
 
     def clear(self) -> None:
         self.history_by_combo.clear()
         self.depth_axis_by_combo.clear()
         self.signature = None
+        self._show_empty()
+
+    def _show_empty(self) -> None:
         self.image.clear()
+        self.widget.setTitle(_TITLE)
diff --git a/python_app/gui/controllers/renderers/common.py b/python_app/gui/controllers/renderers/common.py
index bab5a46..84a4fe8 100644
--- a/python_app/gui/controllers/renderers/common.py
+++ b/python_app/gui/controllers/renderers/common.py
@@ -1,15 +1,25 @@
-"""Plot construction and color tables shared by radar views."""
+"""Plot construction, colors and color tables shared by radar views."""
 
 import numpy as np
 import pyqtgraph as pg
+from PyQt6.QtCore import QRectF
 
+from python_app.gui.theme import PLOT_FOREGROUND
 from python_app.models.run_config_schema import GprModel
 from python_app.models.run_config_validation import parse_position_csv
-from python_app.gui.theme import PLOT_BACKGROUND
+
+# Series identity colors in fixed order, checked for the white plot surface: lightness band,
+# chroma floor and neighbour separation under normal and colorblind vision. Aqua, yellow and
+# pink stay under 3:1 contrast with white, so lines are 2 px wide and the legend names pairs.
+SERIES_COLORS = ("#2a78d6", "#eb6834", "#1baf7a", "#eda100", "#e87ba4", "#008300", "#6250d6", "#e34948")
+# A captured trace shown on its own (main view, capture preview, PNG export).
+CAPTURED_TRACE_PEN = pg.mkPen(SERIES_COLORS[0], width=2)
+# Behind legends and labels, so their text stays legible over curves and heatmaps.
+OVERLAY_FILL = (255, 255, 255, 200)
 
 
 def create_plot(title: str = "") -> pg.PlotWidget:
-    plot = pg.PlotWidget(background=PLOT_BACKGROUND, enableMenu=False, title=title)
+    plot = pg.PlotWidget(enableMenu=False, title=title)
     plot.showGrid(x=True, y=True, alpha=0.2)
     return plot
 
@@ -26,8 +36,20 @@ def build_lut(stops: list[str], *, size: int = 256) -> np.ndarray:
     return lut
 
 
-# Same Tx/Rx markers on ground BP and the three planar SAR views.
-ANTENNA_STYLES = (("t", "#ff595e", "#ffca3a"), ("t1", "#4cc9f0", "#e0fbfc"))
+def image_rect(x_axis: np.ndarray, y_axis: np.ndarray) -> QRectF:
+    """Rectangle covering image pixels centred on the axis samples; a lone sample spans one unit."""
+    (x, width), (y, height) = (_pixel_span(axis) for axis in (x_axis, y_axis))
+    return QRectF(x, y, width, height)
+
+
+def _pixel_span(axis: np.ndarray) -> tuple[float, float]:
+    first, last = float(axis[0]), float(axis[-1])
+    pitch = (last - first) / (len(axis) - 1) if len(axis) > 1 else 1.0
+    return first - pitch / 2, last - first + pitch
+
+
+# Same Tx/Rx markers (symbol, fill, outline) on ground BP and the three planar SAR views.
+ANTENNA_STYLES = (("t", SERIES_COLORS[7], PLOT_FOREGROUND), ("t1", SERIES_COLORS[0], PLOT_FOREGROUND))
 
 
 def selected_antenna_coordinates(geometry: GprModel, inputs: str, outputs: str) -> tuple[np.ndarray, np.ndarray]:
diff --git a/python_app/gui/controllers/renderers/gpr.py b/python_app/gui/controllers/renderers/gpr.py
index 8e94f8e..554241e 100644
--- a/python_app/gui/controllers/renderers/gpr.py
+++ b/python_app/gui/controllers/renderers/gpr.py
@@ -6,10 +6,13 @@ from PyQt6.QtCore import QRectF
 import numpy as np
 import pyqtgraph as pg
 
-from python_app.gui.controllers.renderers.common import ANTENNA_STYLES, build_lut, create_plot, selected_antenna_coordinates
+from python_app.gui.controllers.renderers.common import (
+    ANTENNA_STYLES, OVERLAY_FILL, build_lut, create_plot, image_rect, selected_antenna_coordinates,
+)
 from python_app.gui.result_payloads import (
     collection_payload_by_name, gpr_object_rows,
 )
+from python_app.gui.theme import PLOT_FOREGROUND
 from python_app.models.dataset_model import ResultCollection, ResultPayload
 from python_app.models.gui_profile_schema import GuiGprStateModel
 from python_app.models.run_config_schema import GprModel
@@ -59,13 +62,16 @@ class GprRenderer:
     """Draw one collection from explicit display settings and antenna geometry."""
 
     def __init__(self) -> None:
-        self.widget = create_plot("GPR coherent BP — ground plane")
+        self.widget = create_plot(_title())
         plot = self.widget.getPlotItem()
         assert plot is not None
         self._plot = plot
         self._view = plot.getViewBox()
-        self._plot.showGrid(x=True, y=True, alpha=0.2)
-        self._configure_axes()
+        plot.setLabel("bottom", "X", units="m")
+        plot.setLabel("left", "Range", units="m")
+        plot.hideButtons()
+        self._view.enableAutoRange(x=False, y=False)
+        self._view.setMouseEnabled(x=False, y=False)
         self._lookup_table = build_lut(["#081c15", "#1b4332", "#ffd166", "#f94144"])
         self._image = pg.ImageItem(axisOrder="row-major")
         self._tx = pg.ScatterPlotItem()
@@ -80,21 +86,6 @@ class GprRenderer:
         self._geometry_signature: tuple[object, ...] | None = None
         self._selected_geometry = (np.empty((0, 3)), np.empty((0, 3)))
 
-    def _configure_axes(self) -> None:
-        plot = self._plot
-        plot.showAxis("left", show=True)
-        plot.showAxis("bottom", show=True)
-        plot.setClipToView(True)
-        plot.setLabel("bottom", "X", units="m")
-        plot.setLabel("left", "Range", units="m")
-        plot.setMenuEnabled(False)
-        plot.hideButtons()
-        view = self._view
-        view.invertY(False)
-        view.enableAutoRange(x=False, y=False)
-        view.setMouseEnabled(x=False, y=False)
-        view.setMenuEnabled(False)
-
     def _clear_annotations(self) -> None:
         for item in self._labels:
             self._plot.removeItem(item)
@@ -102,11 +93,9 @@ class GprRenderer:
 
     def clear(self) -> None:
         """Clear displayed data while retaining reusable graphics items."""
-        self._configure_axes()
         self._clear_annotations()
         self._image.hide()
         for marker in self._markers:
-            marker.setData(x=[], y=[])
             marker.hide()
         self._plot.setTitle(_title())
 
@@ -128,8 +117,16 @@ class GprRenderer:
                            brush=pg.mkBrush(brush), pen=pg.mkPen(pen, width=1.0))
             marker.setVisible(len(coordinates) > 0)
 
-    def _label(self, text: str, x: float, y: float, color: str) -> pg.TextItem:
-        label = pg.TextItem(text=text, color=color, anchor=(0.0, 1.0))
+    def _draw_image(self, accumulator: ResultPayload) -> None:
+        image = np.asarray(accumulator.image, dtype=np.float32)
+        self._image.setImage(image, autoLevels=False)
+        self._image.setRect(image_rect(accumulator.image_x_axis, accumulator.image_y_axis))
+        self._image.setLookupTable(self._lookup_table)
+        self._image.setLevels((float(np.min(image)), float(np.max(image) + 1e-6)))
+        self._image.show()
+
+    def _label(self, text: str, x: float, y: float) -> pg.TextItem:
+        label = pg.TextItem(text=text, color=PLOT_FOREGROUND, fill=pg.mkBrush(*OVERLAY_FILL), anchor=(0.0, 1.0))
         label.setZValue(40)
         label.setPos(x, y)
         self._plot.addItem(label)
@@ -153,6 +150,7 @@ class GprRenderer:
         self, rows: np.ndarray, objects_only: bool, x_span: float, z_span: float,
     ) -> None:
         if rows.size == 0:
+            self._points.hide()
             return
         self._points.setData(
             x=rows[:, 0], y=rows[:, 1], symbol="o" if objects_only else "d",
@@ -167,7 +165,7 @@ class GprRenderer:
             text = f"{float(score):.2f}"
             if objects_only:
                 text += f" | x={x:.1f} | z={z:.1f}"
-            label = self._label(text, x, z, "#ffd6d9" if objects_only else "#ffffff")
+            label = self._label(text, x, z)
             if objects_only:
                 self._place_object_label(label, x, z, x_span, z_span, occupied)
 
@@ -175,8 +173,6 @@ class GprRenderer:
         """Render a heatmap or object-only view, returning whether data is present."""
         objects_only = settings.render_mode == "objects_only"
         accumulator = collection_payload_by_name(collection, "gpr_accumulator", kind=3)
-        x_min, x_max = normalized_display_range(settings.visible_x_min_m, settings.visible_x_max_m)
-        z_min, z_max = normalized_display_range(settings.visible_z_min_m, settings.visible_z_max_m)
         rows = gpr_object_rows(collection)
         if objects_only:
             if accumulator is None and rows.size == 0:
@@ -186,42 +182,18 @@ class GprRenderer:
             self.clear()
             return False
 
-        self.widget.setUpdatesEnabled(False)
-        try:
-            self._clear_annotations()
+        x_min, x_max = normalized_display_range(settings.visible_x_min_m, settings.visible_x_max_m)
+        z_min, z_max = normalized_display_range(settings.visible_z_min_m, settings.visible_z_max_m)
+        self._view.setXRange(x_min, x_max, padding=0.0)
+        self._view.setYRange(display_y_min(z_min, z_max), z_max, padding=0.0)
+        self._clear_annotations()
+        self._draw_geometry(settings, geometry)
+        if objects_only or accumulator is None:
             self._image.hide()
-            for marker in (self._points,):
-                marker.setData(x=[], y=[])
-                marker.hide()
-            self._view.invertY(False)
-            self._draw_geometry(settings, geometry)
-            rect: QRectF | None = None
-            if not objects_only and accumulator is not None:
-                image = np.asarray(accumulator.image, dtype=np.float32)
-                xs = np.asarray(accumulator.image_x_axis, dtype=np.float32)
-                ys = np.asarray(accumulator.image_y_axis, dtype=np.float32)
-                rect = QRectF(
-                    float(xs[0]), float(ys[0]),
-                    max(float(xs[-1]) - float(xs[0]), 1e-6),
-                    max(float(ys[-1]) - float(ys[0]), 1e-6),
-                )
-                self._image.setImage(image, autoLevels=False)
-                self._image.setRect(rect)
-                self._image.setLookupTable(self._lookup_table)
-                self._image.setLevels((float(np.min(image)), float(np.max(image) + 1e-6)))
-                self._image.show()
-                self._view.setXRange(x_min, x_max, padding=0.0)
-                self._view.setYRange(display_y_min(z_min, z_max), z_max, padding=0.0)
-                points = collection_payload_by_name(collection, "gpr_points", kind=4)
-                if points is None or np.asarray(points.table).size == 0:
-                    rows = np.zeros((0, 3), dtype=np.float32)
-            self._draw_points(rows, objects_only, x_max - x_min, z_max - z_min)
-            if objects_only:
-                self._view.setXRange(x_min, x_max, padding=0.0)
-                self._view.setYRange(display_y_min(z_min, z_max), z_max, padding=0.0)
-            self._plot.setTitle(_title(objects_only=objects_only))
-        finally:
-            self.widget.setUpdatesEnabled(True)
+        else:
+            self._draw_image(accumulator)
+        self._draw_points(rows, objects_only, x_max - x_min, z_max - z_min)
+        self._plot.setTitle(_title(objects_only=objects_only))
         return True
 
     @staticmethod
diff --git a/python_app/gui/controllers/renderers/sar3d.py b/python_app/gui/controllers/renderers/sar3d.py
index a4425c8..2d93508 100644
--- a/python_app/gui/controllers/renderers/sar3d.py
+++ b/python_app/gui/controllers/renderers/sar3d.py
@@ -24,8 +24,11 @@ import pyqtgraph as pg
 from PyQt6.QtCore import QRectF, Qt
 from PyQt6.QtWidgets import QGridLayout, QLabel, QVBoxLayout, QWidget
 
-from python_app.gui.controllers.renderers.common import ANTENNA_STYLES, build_lut, create_plot, selected_antenna_coordinates
+from python_app.gui.controllers.renderers.common import (
+    ANTENNA_STYLES, build_lut, create_plot, image_rect, selected_antenna_coordinates,
+)
 from python_app.gui.result_payloads import collection_payload_by_name
+from python_app.gui.theme import PLOT_FOREGROUND
 from python_app.models.dataset_model import ResultCollection, ResultPayload
 from python_app.models.gui_profile_schema import GuiSar3dStateModel
 from python_app.models.run_config_schema import GprModel
@@ -33,6 +36,9 @@ from python_app.models.run_config_schema import GprModel
 # Status codes published by the sar3d processor in its "sar3d_status" table.
 SAR3D_STATES = {0: "ready", 1: "no signal", 2: "error", 3: "warning"}
 
+_GROUND_COLOR = (115, 105, 88)
+_SCENE_BOX_COLOR = "#898781"
+
 # payload -> (title, x label, y label, scene axes (0 = X, 1 = Y, 2 = Z) along the plot axes)
 SAR3D_VIEWS: dict[str, tuple[str, str, str, tuple[int, int] | None]] = {
     "sar3d_front": ("Front (X-Y)", "X", "Y", (0, 1)),
@@ -61,13 +67,6 @@ def sar3d_status(collection: ResultCollection) -> tuple[int, str] | None:
     return code, bytes(row[1:].astype(np.uint8)).decode("utf-8", errors="replace")
 
 
-def _image_rect(x_axis: np.ndarray, y_axis: np.ndarray) -> QRectF:
-    """Rectangle covering the pixels centred on the axis samples."""
-    dx = (x_axis[-1] - x_axis[0]) / max(len(x_axis) - 1, 1)
-    dy = (y_axis[-1] - y_axis[0]) / max(len(y_axis) - 1, 1)
-    return QRectF(x_axis[0] - dx / 2, y_axis[0] - dy / 2, x_axis[-1] - x_axis[0] + dx, y_axis[-1] - y_axis[0] + dy)
-
-
 class Sar3dRenderer:
     """Draws the 3D SAR views."""
 
@@ -85,21 +84,19 @@ class Sar3dRenderer:
         grid_layout.setContentsMargins(0, 0, 0, 0)
         grid_layout.setSpacing(6)
         layout.addWidget(self.grid, stretch=1)
-        self.plots: dict[str, pg.PlotWidget] = {}
-        for index, (name, (title, *_rest)) in enumerate(SAR3D_VIEWS.items()):
-            plot = create_plot(title)
-            grid_layout.addWidget(plot, index // 2, index % 2)
-            self.plots[name] = plot
         lut = build_lut(["#081c15", "#1b4332", "#ffd166", "#f94144"])   # the GPR palette
         lut = np.column_stack([lut, np.full(len(lut), 255, dtype=np.uint8)])
         lut[0, 3] = 0   # below SAR_CLOUD_THRESHOLD
+        self.plots: dict[str, pg.PlotWidget] = {}
         self.antennas: dict[str, tuple[pg.ScatterPlotItem, pg.ScatterPlotItem]] = {}
         self.images: dict[str, pg.ImageItem] = {}
         self.targets: dict[str, pg.PlotCurveItem] = {}
-        for name, (_title, x_label, y_label, _axes) in SAR3D_VIEWS.items():
-            plot = self.plots[name]
+        for index, (name, (title, x_label, y_label, axes)) in enumerate(SAR3D_VIEWS.items()):
+            plot = create_plot(title)
+            grid_layout.addWidget(plot, index // 2, index % 2)
+            self.plots[name] = plot
             plot.setAspectLocked(True)
-            if _axes is not None:
+            if axes is not None:
                 markers = (pg.ScatterPlotItem(), pg.ScatterPlotItem())
                 for marker in markers:
                     marker.setZValue(4)
@@ -109,42 +106,40 @@ class Sar3dRenderer:
             assert item is not None
             view = item.getViewBox()
             view.setMouseEnabled(x=False, y=False)
-            view.setMenuEnabled(False)
             view.enableAutoRange(x=False, y=False)
             item.hideButtons()
             image = pg.ImageItem(axisOrder="row-major", lut=lut)
             plot.addItem(image)
             # Hollow, so the response at the maximum stays visible.
-            peak = pg.PlotCurveItem(pen=pg.mkPen("w", width=1.5))
+            peak = pg.PlotCurveItem(pen=pg.mkPen(PLOT_FOREGROUND, width=1.5))
             peak.setZValue(3)
             plot.addItem(peak)
             self.images[name] = image
             self.targets[name] = peak
             if x_label:
-                plot.showGrid(x=True, y=True, alpha=0.2)
                 plot.setLabel("bottom", x_label, units="m")
                 plot.setLabel("left", y_label, units="m")
             if y_label == "Y":
-                ground = pg.InfiniteLine(pos=0.0, angle=0, pen=pg.mkPen("w", width=1, style=Qt.PenStyle.DashLine))
+                ground = pg.InfiniteLine(pos=0.0, angle=0,
+                                         pen=pg.mkPen(_GROUND_COLOR, width=1, style=Qt.PenStyle.DashLine))
                 ground.setZValue(2)
                 plot.addItem(ground)
 
         oblique = self.plots["sar3d_oblique"]
         oblique.hideAxis("bottom")
         oblique.hideAxis("left")
-        oblique.setAspectLocked(True)
         # The notebook scene's ground, under the image so it shows through weak voxels.
         self.ground = pg.PlotCurveItem(
-            pen=pg.mkPen(115, 105, 88), brush=pg.mkBrush(115, 105, 88, 110), fillLevel="enclosed"
+            pen=pg.mkPen(_GROUND_COLOR), brush=pg.mkBrush(*_GROUND_COLOR, 110), fillLevel="enclosed"
         )
         self.ground.setZValue(-1)
         oblique.addItem(self.ground)
-        self.box = pg.PlotCurveItem(pen=pg.mkPen(190, 190, 190, 170), connect="pairs")
+        self.box = pg.PlotCurveItem(pen=pg.mkPen(_SCENE_BOX_COLOR), connect="pairs")
         self.box.setZValue(2)
         oblique.addItem(self.box)
         self.axis_labels: dict[str, pg.TextItem] = {}
         for axis_name in _AXIS_EDGES:
-            label = pg.TextItem(axis_name, color=(190, 190, 190), anchor=(0.5, 0.5))
+            label = pg.TextItem(axis_name, color=PLOT_FOREGROUND, anchor=(0.5, 0.5))
             oblique.addItem(label)
             self.axis_labels[axis_name] = label
         self.clear()
@@ -195,7 +190,7 @@ class Sar3dRenderer:
         zoom = settings.zoom_percent / 100.0
         for name, payload in payloads.items():
             title, _x_label, _y_label, axes = SAR3D_VIEWS[name]
-            rect = _image_rect(payload.image_x_axis, payload.image_y_axis)
+            rect = image_rect(payload.image_x_axis, payload.image_y_axis)
             image = self.images[name]
             image.setImage(np.where(payload.image >= settings.cloud_threshold, payload.image, 0),
                            autoLevels=False, levels=(0, 1))
diff --git a/python_app/gui/controllers/renderers/trace.py b/python_app/gui/controllers/renderers/trace.py
index 0911aa5..13ac98f 100644
--- a/python_app/gui/controllers/renderers/trace.py
+++ b/python_app/gui/controllers/renderers/trace.py
@@ -6,10 +6,10 @@ from typing import Protocol
 
 import numpy as np
 import pyqtgraph as pg
-from PyQt6.QtCore import Qt
+from PyQt6.QtGui import QPen
 from PyQt6.QtWidgets import QVBoxLayout, QWidget
 
-from python_app.gui.controllers.renderers.common import create_plot
+from python_app.gui.controllers.renderers.common import CAPTURED_TRACE_PEN, OVERLAY_FILL, SERIES_COLORS, create_plot
 from python_app.models.dataset_model import ComboKey, ResultCollection, TraceData
 from python_app.models.gui_profile_schema import GuiPassThroughStateModel
 from python_app.models.run_config_validation import parse_combos_from_text
@@ -21,9 +21,7 @@ class WarningLogger(Protocol):
 
 
 CurveKey = tuple[ComboKey, int, str]
-Series = tuple[CurveKey, np.ndarray, np.ndarray, str]
-_PALETTE = ("#4cc9f0", "#f72585", "#b8f2e6", "#ffd166",
-            "#90be6d", "#ff595e", "#6a4c93", "#1982c4")
+Series = tuple[CurveKey, np.ndarray, np.ndarray, QPen]
 
 
 class _TracePanel:
@@ -35,57 +33,49 @@ class _TracePanel:
         assert item is not None
         self.item = item
         self.view = item.getViewBox()
-        self.item.showGrid(x=True, y=True, alpha=0.2)
         self.item.setLabel("left", label, units=units)
         self.item.setLabel("bottom", "Frequency", units="Hz")
-        self.item.setDownsampling(mode="peak")
-        self.item.setClipToView(True)
-        self.curves: dict[CurveKey, pg.PlotCurveItem] = {}
-        self.legend: pg.LegendItem | None = None
-        self._legend_sources: dict[ComboKey, pg.PlotCurveItem] = {}
+        # Sweeps denser than the screen are drawn as per-bin min/max, so narrow peaks
+        # and notches stay visible; ordinary sweeps keep every point.
+        self.item.setDownsampling(auto=True, mode="peak")
+        self.curves: dict[CurveKey, pg.PlotDataItem] = {}
+        self.legend = self.item.addLegend(offset=(8, 8), brush=pg.mkBrush(*OVERLAY_FILL), colCount=2)
+        self.legend.hide()
+        self._legend_sources: dict[ComboKey, pg.PlotDataItem] = {}
 
     def clear(self) -> None:
         self.item.clear()
         self.curves.clear()
         self.sync_legend({})
 
-    def update_curve(self, key: CurveKey, x: np.ndarray, y: np.ndarray,
-                     color: str, *, width: float, dashed: bool = False) -> pg.PlotCurveItem:
-        pen = pg.mkPen(color, width=width,
-                      style=Qt.PenStyle.DashLine if dashed else Qt.PenStyle.SolidLine)
+    def update_curve(self, key: CurveKey, x: np.ndarray, y: np.ndarray, pen: QPen) -> pg.PlotDataItem:
         curve = self.curves.get(key)
         if curve is None:
-            curve = pg.PlotCurveItem(pen=pen, antialias=False)
+            curve = pg.PlotDataItem(antialias=False)
             self.curves[key] = curve
             self.item.addItem(curve)
-        else:
-            curve.setPen(pen)
-        curve.setData(x, y)
+        curve.setData(x, y, pen=pen)  # one update; a separate setPen would redraw the old data first
         return curve
 
     def retain_curves(self, active_keys: set[CurveKey]) -> None:
         for key in self.curves.keys() - active_keys:
             self.item.removeItem(self.curves.pop(key))
 
-    def sync_legend(self, sources: dict[ComboKey, pg.PlotCurveItem]) -> None:
+    def sync_legend(self, sources: dict[ComboKey, pg.PlotDataItem]) -> None:
         if self._legend_sources == sources:
             return
-        if self.legend is None and sources:
-            self.legend = self.item.addLegend(offset=(8, 8))
-        if self.legend is not None:
-            self.legend.clear()
-            for combo in sorted(sources, key=lambda key: (key.input, key.output)):
-                self.legend.addItem(sources[combo], f"in{combo.input}/out{combo.output}")
-            self.legend.setVisible(bool(sources))
+        self.legend.clear()
+        for combo in sorted(sources, key=lambda key: (key.input, key.output)):
+            self.legend.addItem(sources[combo], f"in{combo.input}/out{combo.output}")
+        self.legend.setVisible(bool(sources))
         self._legend_sources = sources
 
 
 class TraceRenderer:
     """Render result traces or a captured trace using explicit display settings."""
 
-    def __init__(self, log_warning: WarningLogger, max_points: int = 800) -> None:
+    def __init__(self, log_warning: WarningLogger) -> None:
         self._log_warning = log_warning
-        self.max_points = max_points
         self.widget = QWidget()
         layout = QVBoxLayout(self.widget)
         layout.setContentsMargins(0, 0, 0, 0)
@@ -102,23 +92,24 @@ class TraceRenderer:
 
     def draw(self, collection: ResultCollection, settings: GuiPassThroughStateModel) -> bool:
         combo_filter = self._combo_filter(settings.combo_filter)
-        colors: dict[ComboKey, str] = {}
         series: list[Series] = []
-        for block in collection.blocks:
+        # The color follows the pair's place in the run, so filtering never repaints shown pairs.
+        for position, block in enumerate(collection.blocks):
             if combo_filter is not None and block.combo not in combo_filter:
                 continue
-            color = colors.setdefault(block.combo, _PALETTE[len(colors) % len(_PALETTE)])
+            pen = pg.mkPen(SERIES_COLORS[position % len(SERIES_COLORS)], width=2)
             for index, payload in enumerate(block.payloads):
-                if payload.kind != 1 or not payload.trace.size or payload.frequency_hz.size != payload.trace.size:
+                # Another mode's result (a B-scan range profile) is not S21 over frequency.
+                if payload.processing_name != "pass_through" or payload.kind != 1:
                     continue
                 series.append(((block.combo, index, payload.processing_name),
-                               payload.frequency_hz, payload.trace, color))
+                               payload.frequency_hz, payload.trace, pen))
         return self._render(series, settings, "Pass-Through S21")
 
     def draw_trace(self, trace: TraceData, title: str, settings: GuiPassThroughStateModel) -> None:
         self.clear()
         self._render([((trace.combo, 0, "__single_trace__"), trace.frequency_hz,
-                       trace.s21, "#ffd166")], settings, title, single=True)
+                       trace.s21, CAPTURED_TRACE_PEN)], settings, title, single=True)
 
     def _combo_filter(self, text: str) -> set[ComboKey] | None:
         text = text.strip()
@@ -142,27 +133,23 @@ class TraceRenderer:
             return False
         mag.item.showAxis("bottom", show=not settings.show_phase)
         active: set[CurveKey] = set()
-        mag_sources: dict[ComboKey, pg.PlotCurveItem] = {}
-        phase_sources: dict[ComboKey, pg.PlotCurveItem] = {}
+        mag_sources: dict[ComboKey, pg.PlotDataItem] = {}
+        phase_sources: dict[ComboKey, pg.PlotDataItem] = {}
         x_min, x_max = np.inf, -np.inf
-        for key, frequency, samples, color in series:
+        for key, frequency, samples, pen in series:
             if not samples.size or frequency.size != samples.size:
                 continue
             active.add(key)
             x_min, x_max = min(x_min, float(np.min(frequency))), max(x_max, float(np.max(frequency)))
-            step = max(1, int(np.ceil(samples.size / self.max_points))) if self.max_points > 0 else 1
             if settings.show_magnitude:
-                magnitude = 20.0 * np.log10(np.maximum(np.abs(samples[::step]), 1e-12))
-                curve = mag.update_curve(key, frequency[::step], magnitude, color,
-                                         width=1.8 if single else 1.4)
+                magnitude = 20.0 * np.log10(np.maximum(np.abs(samples), 1e-12))
+                curve = mag.update_curve(key, frequency, magnitude, pen)
                 mag_sources.setdefault(key[0], curve)
             if settings.show_phase:
                 angles = np.angle(samples)
                 if settings.unwrap_phase:
                     angles = np.unwrap(angles)
-                curve = phase.update_curve(key, frequency[::step], np.degrees(angles[::step]),
-                                           "#80ed99" if single else color,
-                                           width=1.4 if single else 1.2, dashed=single)
+                curve = phase.update_curve(key, frequency, np.degrees(angles), pen)
                 phase_sources.setdefault(key[0], curve)
 
         for panel, visible, sources in ((mag, settings.show_magnitude, mag_sources),
@@ -171,7 +158,6 @@ class TraceRenderer:
             panel.sync_legend(sources if not single else {})
             if visible:
                 panel.item.setTitle(title)
-                panel.view.invertY(False)
                 if active and np.isfinite(x_min) and np.isfinite(x_max):
                     panel.view.setXRange(x_min, x_max, padding=0.02)
         if settings.show_magnitude:
diff --git a/python_app/gui/controllers/snapshot_controller.py b/python_app/gui/controllers/snapshot_controller.py
index f9ca1c8..7e2306a 100644
--- a/python_app/gui/controllers/snapshot_controller.py
+++ b/python_app/gui/controllers/snapshot_controller.py
@@ -109,6 +109,8 @@ class SnapshotController:
                     return
                 self.pipeline.history_changed()
                 self.pipeline.plots.redraw()
+                # Removing the newest sweep brings an older one, maybe never replayed, into a stopped B-scan.
+                self.pipeline.schedule_replay()
                 self._log(
                     f"{action}: dropped raw={dropped_raw}, "
                     f"preprocessed={dropped_pre}, results={dropped_results}"
diff --git a/python_app/gui/controllers/web_controller.py b/python_app/gui/controllers/web_controller.py
index ef4e512..5d7648a 100644
--- a/python_app/gui/controllers/web_controller.py
+++ b/python_app/gui/controllers/web_controller.py
@@ -12,7 +12,6 @@ import threading
 import time
 from typing import TYPE_CHECKING
 
-import pyqtgraph as pg
 from PyQt6.QtCore import QBuffer, QIODevice, QObject, pyqtSignal
 from PyQt6.QtWidgets import QLineEdit, QSpinBox, QWidget
 
@@ -100,20 +99,13 @@ class WebBridge(QObject):
         self._frame: dict | None = None
         self._pending_lock = threading.Lock()
         self._pending_calls: set[_WebActionCall] = set()
-        self._closed = self._streaming = self._grabbing = False
-        self._dirty = True
+        self._closed = self._streaming = False
+        self._grabbed_revision: int | None = None  # plot revision shown by the last grab; None forces one
         self._last_png: str | None = None
         self._last_grab_s = 0.0
         self._frame_seq = self._snapshot_errors = 0
         self._action_requested.connect(self._run_action)
         self._streaming_changed.connect(self._set_streaming)
-        plots = pipeline.plots
-        plots.stack.currentChanged.connect(self._mark_dirty)
-        for plot in plots.stack.findChildren(pg.PlotWidget):
-            scene = plot.scene()
-            assert scene is not None
-            scene.changed.connect(self._mark_dirty)
-            plot.sigDeviceRangeChanged.connect(self._mark_dirty)
 
     def start_server(self) -> None:
         if self._closed or self._server is not None:
@@ -295,26 +287,19 @@ class WebBridge(QObject):
         if not self._closed:
             self._streaming = enabled
             if enabled:
-                self._dirty = True
-
-    def _mark_dirty(self, *_args: object) -> None:
-        if not self._closed and not self._grabbing:
-            self._dirty = True
+                self._grabbed_revision = None
 
     def _grab_frame_if_due(self) -> dict | None:
-        if self._closed or not self._streaming or not self._dirty:
+        plots = self._pipeline.plots
+        if self._closed or not self._streaming or plots.revision == self._grabbed_revision:
             return None
         now = time.monotonic()
         if now - self._last_grab_s < _GRAB_INTERVAL_S:
             return None
-        self._last_grab_s, self._dirty, self._grabbing = now, False, True
-        try:
-            png = self._grab_png()
-        except Exception:
-            self._dirty = True
-            raise
-        finally:
-            self._grabbing = False
+        self._last_grab_s = now
+        png = self._grab_png()
+        # Rendering applies pending resizes and lazy auto-ranges; this image already shows them.
+        self._grabbed_revision = plots.revision
         if png is None or png == self._last_png:
             return None
         self._last_png = png
diff --git a/python_app/gui/main.py b/python_app/gui/main.py
index fffbc12..3e87393 100644
--- a/python_app/gui/main.py
+++ b/python_app/gui/main.py
@@ -7,7 +7,6 @@ from pathlib import Path
 import signal
 import sys
 
-import pyqtgraph as pg
 from PyQt6.QtCore import QTimer
 from PyQt6.QtWidgets import QApplication
 
@@ -54,8 +53,6 @@ def main() -> int:
     """Run Qt event loop and show main radar control window."""
     app = QApplication(sys.argv)
     apply_light_theme(app)
-    # PyQtGraph foreground controls axis lines, tick text, labels, and titles.
-    pg.setConfigOptions(antialias=True, background="#ffffff", foreground="#ffffff")
     window = AppWindow(PROJECT_ROOT)
     if env_enabled("RADAR_SYSTEM_HEADLESS"):
         _install_unix_signal_handlers(app, window)
diff --git a/python_app/gui/object_calibration_dialog.py b/python_app/gui/object_calibration_dialog.py
index 60445d1..4e5d402 100644
--- a/python_app/gui/object_calibration_dialog.py
+++ b/python_app/gui/object_calibration_dialog.py
@@ -15,7 +15,6 @@ from PyQt6.QtWidgets import (
 )
 
 from python_app.models.dataset_model import SweepCollection
-from python_app.gui.theme import PLOT_BACKGROUND
 
 
 class ObjectCalibrationDialog(QDialog):
@@ -132,7 +131,6 @@ class ObjectCalibrationDialog(QDialog):
         self._target_combo = QComboBox(self)
         layout.addWidget(self._target_combo)
         self._phase_view = pg.GraphicsLayoutWidget(parent=self)
-        self._phase_view.setBackground(PLOT_BACKGROUND)
         self._phase_view.setMinimumHeight(270)
         self._phase_plots = []
         self._phase_images = []
diff --git a/python_app/gui/preprocess_dialog.py b/python_app/gui/preprocess_dialog.py
index 9a5538a..b9728a6 100644
--- a/python_app/gui/preprocess_dialog.py
+++ b/python_app/gui/preprocess_dialog.py
@@ -26,7 +26,7 @@ from PyQt6.QtWidgets import (
 import numpy as np
 import pyqtgraph as pg
 
-from python_app.gui.controllers.renderers.common import create_plot
+from python_app.gui.controllers.renderers.common import CAPTURED_TRACE_PEN, create_plot
 from python_app.models.gui_profile_schema import GuiPreprocessDialogStateModel
 from python_app.models.dataset_model import TraceData
 from python_app.orchestration.preprocess_assets import (
@@ -470,17 +470,9 @@ class PreprocessDialog(QDialog):
             assert self._amplitude_plot is not None
             assert self._phase_plot is not None
             self._amplitude_plot.clear()
-            self._amplitude_plot.plot(
-                trace.frequency_hz,
-                magnitude_db,
-                pen=pg.mkPen("#4cc9f0", width=1.8),
-            )
+            self._amplitude_plot.plot(trace.frequency_hz, magnitude_db, pen=CAPTURED_TRACE_PEN)
             self._phase_plot.clear()
-            self._phase_plot.plot(
-                trace.frequency_hz,
-                phase_deg,
-                pen=pg.mkPen("#f48c06", width=1.8),
-            )
+            self._phase_plot.plot(trace.frequency_hz, phase_deg, pen=CAPTURED_TRACE_PEN)
         elif self._preview_placeholder is not None:
             self._preview_placeholder.setText(
                 f"{title}\n"
diff --git a/python_app/gui/theme.py b/python_app/gui/theme.py
index 733eace..f37620c 100644
--- a/python_app/gui/theme.py
+++ b/python_app/gui/theme.py
@@ -1,11 +1,14 @@
-"""Application-wide Qt palette and stylesheet configuration."""
+"""Application-wide Qt palette, stylesheet and plot colors."""
 
 from __future__ import annotations
 
+import pyqtgraph as pg
 from PyQt6.QtGui import QColor, QPalette
 from PyQt6.QtWidgets import QApplication, QStyleFactory
 
-PLOT_BACKGROUND = "#0f141c"
+TEXT_COLOR = "#1f2937"
+PLOT_BACKGROUND = "#ffffff"
+PLOT_FOREGROUND = TEXT_COLOR  # axes, ticks, titles, legends and annotations
 
 _LIGHT_STYLESHEET = """
 QGroupBox {
@@ -82,7 +85,8 @@ QLabel#hintLabel {
 
 
 def apply_light_theme(app: QApplication) -> None:
-    """Apply a minimal light theme shared by all windows."""
+    """Apply a minimal light theme shared by all windows and plots; call before creating them."""
+    pg.setConfigOptions(antialias=True, background=PLOT_BACKGROUND, foreground=PLOT_FOREGROUND)
     app.setStyle(QStyleFactory.create("Fusion"))
     font = app.font()
     font.setPointSize(10)
@@ -90,14 +94,14 @@ def apply_light_theme(app: QApplication) -> None:
 
     palette = QPalette()
     palette.setColor(QPalette.ColorRole.Window, QColor("#f3f6fb"))
-    palette.setColor(QPalette.ColorRole.WindowText, QColor("#1f2937"))
+    palette.setColor(QPalette.ColorRole.WindowText, QColor(TEXT_COLOR))
     palette.setColor(QPalette.ColorRole.Base, QColor("#ffffff"))
     palette.setColor(QPalette.ColorRole.AlternateBase, QColor("#eef3f8"))
     palette.setColor(QPalette.ColorRole.ToolTipBase, QColor("#ffffff"))
-    palette.setColor(QPalette.ColorRole.ToolTipText, QColor("#1f2937"))
-    palette.setColor(QPalette.ColorRole.Text, QColor("#1f2937"))
+    palette.setColor(QPalette.ColorRole.ToolTipText, QColor(TEXT_COLOR))
+    palette.setColor(QPalette.ColorRole.Text, QColor(TEXT_COLOR))
     palette.setColor(QPalette.ColorRole.Button, QColor("#f8fafc"))
-    palette.setColor(QPalette.ColorRole.ButtonText, QColor("#1f2937"))
+    palette.setColor(QPalette.ColorRole.ButtonText, QColor(TEXT_COLOR))
     palette.setColor(QPalette.ColorRole.BrightText, QColor("#ffffff"))
     palette.setColor(QPalette.ColorRole.Link, QColor("#2f7ee6"))
     palette.setColor(QPalette.ColorRole.Highlight, QColor("#2f7ee6"))
diff --git a/python_app/gui/trace_png_export.py b/python_app/gui/trace_png_export.py
index b4bf1f7..8a112b3 100644
--- a/python_app/gui/trace_png_export.py
+++ b/python_app/gui/trace_png_export.py
@@ -8,7 +8,6 @@ preview into off-screen PNG files, letting us persist a graph for every config.
 
 from __future__ import annotations
 
-import logging
 from pathlib import Path
 
 import numpy as np
@@ -16,13 +15,9 @@ import pyqtgraph as pg
 from PyQt6.QtCore import QRectF
 from pyqtgraph.exporters import ImageExporter
 
+from python_app.gui.controllers.renderers.common import CAPTURED_TRACE_PEN
 from python_app.models.dataset_model import TraceData
-from python_app.gui.theme import PLOT_BACKGROUND
 
-logger = logging.getLogger(__name__)
-
-_MAGNITUDE_PEN = pg.mkPen("#4cc9f0", width=1.8)
-_PHASE_PEN = pg.mkPen("#f48c06", width=1.8)
 _EXPORT_SIZE = (1400, 520)
 
 
@@ -43,7 +38,6 @@ def export_trace_png(
     phase_deg = np.degrees(np.angle(samples))
 
     layout = pg.GraphicsLayoutWidget(show=False, size=_EXPORT_SIZE)
-    layout.setBackground(PLOT_BACKGROUND)
     try:
         layout.ci.addLabel(title, row=0, col=0, colspan=2)
 
@@ -51,13 +45,13 @@ def export_trace_png(
         magnitude_plot.showGrid(x=True, y=True, alpha=0.2)
         magnitude_plot.setLabel("bottom", "Frequency", units="Hz")
         magnitude_plot.setLabel("left", "Magnitude", units="dB")
-        magnitude_plot.plot(trace.frequency_hz, magnitude_db, pen=_MAGNITUDE_PEN)
+        magnitude_plot.plot(trace.frequency_hz, magnitude_db, pen=CAPTURED_TRACE_PEN)
 
         phase_plot = layout.ci.addPlot(row=1, col=1)
         phase_plot.showGrid(x=True, y=True, alpha=0.2)
         phase_plot.setLabel("bottom", "Frequency", units="Hz")
         phase_plot.setLabel("left", "Phase", units="deg")
-        phase_plot.plot(trace.frequency_hz, phase_deg, pen=_PHASE_PEN)
+        phase_plot.plot(trace.frequency_hz, phase_deg, pen=CAPTURED_TRACE_PEN)
 
         # An off-screen widget never receives a resizeEvent, so its central
         # GraphicsLayout keeps its small preferred size and both plots would be
diff --git a/python_app/hardware_full/librevna_multi_device_driver/cycle_collection.py b/python_app/hardware_full/librevna_multi_device_driver/cycle_collection.py
index 545b0e1..5b50dae 100644
--- a/python_app/hardware_full/librevna_multi_device_driver/cycle_collection.py
+++ b/python_app/hardware_full/librevna_multi_device_driver/cycle_collection.py
@@ -68,11 +68,11 @@ class _DeviceCollectionState:
     """Mutable per-device flag marking that this device's capture has finished.
 
     A device finishes when its final requested sweep cycle closes — either every
-    point of that cycle was delivered, or the free-running hardware sweep wrapped
-    back to point 0, proving the still-missing points are dropped frames that will
-    never arrive. The collector thread polls this flag so a gap ends the cycle at
-    the wrap instead of stalling until the no-progress timeout fires; the missing
-    points are zero-filled when the S-parameters are computed.
+    point of that cycle was delivered, or the point index stopped rising because the
+    free-running hardware sweep started over, proving the still-missing points are
+    dropped frames that will never arrive. The collector thread polls this flag so a
+    gap ends the cycle there instead of stalling until the no-progress timeout fires;
+    the missing points are zero-filled when the S-parameters are computed.
     """
 
     __slots__ = ("last_cycle_closed", "capture_start_ns", "capture_end_ns")
@@ -449,8 +449,8 @@ def collect_complete_running_sweep_cycle(
         """Wrap a cycle-aware handler with cross-device cycle tracking.
 
         Returns a per-datapoint handler that anchors cycle 0 on the first
-        ``point_index == 0`` seen, closes on the next point-index wrap, and reports whether each
-        datapoint was consumed.
+        ``point_index == 0`` seen, closes once the point index stops rising (the next
+        sweep began), and reports whether each datapoint was consumed.
         """
         # In steady state the controller leaves the hardware sweep FREE-RUNNING
         # between collections (the unchanged-config fast path only drains the host
@@ -468,6 +468,8 @@ def collect_complete_running_sweep_cycle(
             # stale point 0 could still have been in flight; a large count means the
             # remainder of the in-progress sweep was safely skipped.
             "pre_anchor_skipped": 0,
+            # Newest point index of the anchored cycle; indices only rise within a sweep.
+            "last_point_index": 0,
         }
 
         def handle_datapoint(parsed_datapoint: ParsedVnaDatapoint) -> bool:
@@ -504,10 +506,12 @@ def collect_complete_running_sweep_cycle(
                 cycle_aware_handler(parsed_datapoint)
                 return True
 
-            if current_point_index == 0:
-                # A second point 0 closes this cycle; absent points are now losses.
+            if current_point_index <= cycle_tracking_state["last_point_index"]:
+                # The next sweep began: this closes the cycle even when its point 0 was
+                # lost, so its points never overwrite this one. Absent points are losses.
                 device_state.last_cycle_closed = True
                 return False
+            cycle_tracking_state["last_point_index"] = current_point_index
             cycle_aware_handler(parsed_datapoint)
             device_state.capture_end_ns = received_ns
             return True
diff --git a/python_app/orchestration/shm/ring_reader.py b/python_app/orchestration/shm/ring_reader.py
index d91a059..53ec716 100644
--- a/python_app/orchestration/shm/ring_reader.py
+++ b/python_app/orchestration/shm/ring_reader.py
@@ -49,52 +49,50 @@ class ShmRingReader:
         logger.debug("Closed SHM ring reader %s", self.name)
 
     def pop_payload(self) -> bytes | None:
-        """Read next payload from ring, or `None` if no unread payload exists."""
-        write_seq = self._read_u64(24)
-        read_seq = self._read_u64(32)
-        if read_seq >= write_seq:
-            return None
+        """Read the next unread payload, or `None` once none remains."""
+        while True:
+            write_seq = self._read_u64(24)
+            read_seq = self._read_u64(32)
+            if read_seq >= write_seq:
+                return None
+            # As in the C++ pop, a lapped, torn or corrupt slot is skipped with the backlog
+            # behind the newest payload, which is read next (latest-wins).
+            resync = max(read_seq + 1, write_seq - 1)
 
-        index = read_seq % self.capacity
-        slot_offset = HEADER.size + index * (SLOT_HEADER_SIZE + self.slot_size_bytes)
+            index = read_seq % self.capacity
+            slot_offset = HEADER.size + index * (SLOT_HEADER_SIZE + self.slot_size_bytes)
 
-        # Seqlock read mirroring the C++ pop: a slot is valid for read_seq R only if
-        # its sequence equals R+1 and is unchanged across the payload copy (i.e. the
-        # producer did not overwrite this slot mid-copy). Sequence and payload_size
-        # are read first; the slot is only accepted after the re-read confirms both.
-        sequence = self._read_u64(slot_offset + 8)
-        if sequence != read_seq + 1:
-            # Producer overwrote this slot before we read it. Resync to latest.
-            logger.debug("Ring %s: slot lapped before read, resyncing to write_seq=%d", self.name, write_seq)
-            atomics.advance(self._mmap, 32, write_seq)
-            return None
+            # Seqlock read mirroring the C++ pop: a slot is valid for read_seq R only if
+            # its sequence equals R+1 and is unchanged across the payload copy (i.e. the
+            # producer did not overwrite this slot mid-copy). Sequence and payload_size
+            # are read first; the slot is only accepted after the re-read confirms both.
+            if self._read_u64(slot_offset + 8) != read_seq + 1:
+                logger.debug("Ring %s: slot lapped before read, resyncing to %d", self.name, resync)
+                atomics.advance(self._mmap, 32, resync)
+                continue
 
-        payload_size = self._read_u32(slot_offset)
-        # Bound payload_size against the slot before slicing so a torn/garbage size
-        # can never read out of the slot region; resync and skip on violation.
-        if payload_size > self.slot_size_bytes:
-            logger.debug(
-                "Ring %s: payload_size %d exceeds slot %d, resyncing",
-                self.name,
-                payload_size,
-                self.slot_size_bytes,
-            )
-            atomics.advance(self._mmap, 32, write_seq)
-            return None
+            payload_size = self._read_u32(slot_offset)
+            # Bound payload_size against the slot before slicing so a torn/garbage size
+            # can never read out of the slot region.
+            if payload_size > self.slot_size_bytes:
+                logger.debug("Ring %s: payload_size %d exceeds slot %d, resyncing to %d",
+                             self.name, payload_size, self.slot_size_bytes, resync)
+                atomics.advance(self._mmap, 32, resync)
+                continue
 
-        payload_offset = slot_offset + SLOT_HEADER_SIZE
-        payload = bytes(self._mmap[payload_offset : payload_offset + payload_size])
-        atomics.fence()
+            payload_offset = slot_offset + SLOT_HEADER_SIZE
+            payload = bytes(self._mmap[payload_offset : payload_offset + payload_size])
+            atomics.fence()
 
-        # Re-read the slot sequence after the copy; if it changed, the producer
-        # overwrote this slot mid-copy and the payload is torn — discard and resync.
-        if self._read_u64(slot_offset + 8) != read_seq + 1:
-            logger.debug("Ring %s: slot overwritten mid-copy, discarding torn payload", self.name)
-            atomics.advance(self._mmap, 32, write_seq)
-            return None
+            # Re-read the slot sequence after the copy; if it changed, the producer
+            # overwrote this slot mid-copy and the payload is torn.
+            if self._read_u64(slot_offset + 8) != read_seq + 1:
+                logger.debug("Ring %s: slot overwritten mid-copy, resyncing to %d", self.name, resync)
+                atomics.advance(self._mmap, 32, resync)
+                continue
 
-        atomics.advance(self._mmap, 32, read_seq + 1)
-        return payload
+            atomics.advance(self._mmap, 32, read_seq + 1)
+            return payload
 
     def pop_raw_collection(self) -> SweepCollection | None:
         """Read next raw collection from ring."""
diff --git a/python_app/tests/test_bscan_replay.py b/python_app/tests/test_bscan_replay.py
index 9605aaa..2ca3934 100644
--- a/python_app/tests/test_bscan_replay.py
+++ b/python_app/tests/test_bscan_replay.py
@@ -140,6 +140,25 @@ class ReplayTest(unittest.TestCase):
         self.assertIn(unrelated, self.history.results)
         self.writer_factory.assert_called_once_with(self.ring.name, self.ring.capacity, self.ring.slot_size_bytes)
 
+    def test_unreturned_sweeps_are_left_out_instead_of_mixing_settings(self) -> None:
+        sweeps = [_sweep(cid) for cid in range(1, 7)]
+        self.history.preprocessed.extend(sweeps)
+        self.history.results.extend(replace(_result_of(sweep), settings_revision=3) for sweep in sweeps)
+
+        def push_dropping_two(payload: bytes) -> bool:
+            accepted = self.processor.push(payload)
+            if self.processor.received[-1].collection_id in {2, 5}:
+                self.processor.published.pop()
+            return accepted
+
+        self.writer.push = push_dropping_two
+        with patch("python_app.gui.controllers.bscan_replay._REPLAY_CHUNK_TIMEOUT_S", .01):
+            self.assertTrue(self.run_replay())
+        source = self.history.bscan_source()
+        self.assertEqual([item.collection_id for item in source], [1, 3, 4, 6])
+        self.assertTrue(all(item.settings_revision == 7 for item in source))
+        self.assertEqual(self.warnings[-1], "B-scan replay recovered 4 of 6 re-sent sweeps; the image leaves the others out.")
+
     def test_refuses_without_reader_or_active_ring_geometry(self) -> None:
         self.history.preprocessed.append(_sweep(1))
         self.assertFalse(self.replay.run(window=1, revision=7, ring=self.ring, reader=None,
diff --git a/python_app/tests/test_librevna_multidevice.py b/python_app/tests/test_librevna_multidevice.py
index 9b347f3..7a5aa8e 100644
--- a/python_app/tests/test_librevna_multidevice.py
+++ b/python_app/tests/test_librevna_multidevice.py
@@ -160,6 +160,36 @@ class CaptureWindowTest(unittest.TestCase):
                     np.testing.assert_array_equal(trace.s21, np.full(5, 0.5))
 
 
+class CycleClosureTest(unittest.TestCase):
+    def test_next_sweep_without_its_point_zero_still_closes_the_cycle(self) -> None:
+        # A point of this sweep and point 0 of the next are lost: the next sweep's point 1
+        # must close the cycle instead of overwriting this sweep's point 1.
+        points = 40
+        configuration = SweepConfiguration(1_000_000, 2_000_000, points, 1000, -10.0)
+        frames = [*((point, 1 + 0j) for point in range(points) if point != 3),
+                  *((point, 7 + 0j) for point in range(1, points))]
+
+        def connection(serial: str) -> Mock:
+            sequence = iter(frames)
+
+            def receive(*, timeout_seconds):
+                point, measured = next(sequence)
+                values = [(0x13, 2 + 0j), (0x01, measured), (0x02, measured),
+                          (0x33, 2 + 0j), (0x21, measured), (0x22, measured)]
+                return 27, _datapoint_frame(1_000_000 + point * 25_000, point, values)[4:-4]
+
+            return Mock(serial_number=serial, receive_packet=receive)
+
+        result = collect_complete_running_sweep_cycle(
+            master_device_connection=connection("M"), slave_device_connections=[connection("A"), connection("B")],
+            active_sweep_configuration=configuration, master_stimulus_ports=(1, 2),
+        )
+        expected = np.full(points, .5)
+        expected[3] = 0  # the lost point is zero-filled
+        for trace in result.s_parameters.values():
+            np.testing.assert_array_equal(trace, expected)
+
+
 class CrossDeviceCycleSynchronizerTest(unittest.TestCase):
     """N1: cycle-0 anchors are accepted only when all devices saw the same wrap."""
 
diff --git a/python_app/tests/test_processor_history.py b/python_app/tests/test_processor_history.py
index e2a4070..17fe4a0 100644
--- a/python_app/tests/test_processor_history.py
+++ b/python_app/tests/test_processor_history.py
@@ -209,6 +209,44 @@ class FedBackSweepsTest(_ProcessorTestCase):
         self._live_writer.write(self._live)
         self.assertEqual(self._published_ids(_SWEEPS), expected)
 
+    def test_sweep_failing_to_recompute_does_not_stall_new_input(self) -> None:
+        self._live.processor_mode = "gpr"
+        self._live.gpr_input_positions = self._live.gpr_output_positions = [0]
+        self._live.gpr_background_subtract_enabled = False
+        self._live.tx_geometry = [{"output_pos": 0, "x_m": 0.0, "y_m": 0.0, "z_m": 0.0}]
+        self._live.rx_geometry = [{"input_pos": 0, "x_m": 0.0, "y_m": 0.0, "z_m": 0.0}]
+        self._live_writer.write(self._live)
+        start = time.monotonic_ns()
+        self._push([_sweep(1, start)])
+        self._result_for_revision(0, 1)
+        failing = _sweep(2, start + 1_000_000)
+        failing.traces[0].capture_end_ns = failing.traces[0].capture_start_ns  # GPR rejects an empty trace window
+        self._push([failing])
+        deadline = time.monotonic() + _TIMEOUT_S
+        while self._input._read_u64(32) != self._input._read_u64(24):  # now the newest retained sweep
+            self.assertLess(time.monotonic(), deadline, self._stderr_path.read_text())
+            time.sleep(.01)
+        # Both arrive while the processor is stopped past its 100 ms live-file check, so on
+        # resuming it recomputes that failing sweep before it takes the next one.
+        self._processor.send_signal(signal.SIGSTOP)
+        os.waitpid(self._processor.pid, os.WUNTRACED)
+        try:
+            self._live.settings_revision = 1
+            self._live_writer.write(self._live)
+            self._push([_sweep(3, start + 2_000_000)])
+            time.sleep(.2)
+        finally:
+            self._processor.send_signal(signal.SIGCONT)
+        self._result_for_revision(1, 3)
+
+    def test_bscan_band_without_two_sweep_points_gives_an_empty_profile(self) -> None:
+        self._live.bscan_start_freq_mhz, self._live.bscan_stop_freq_mhz = 7000.0, 8000.0  # sweep is 1-6 GHz
+        self._live.settings_revision = 1
+        self._live_writer.write(self._live)
+        self._push([_sweep(1, time.monotonic_ns())])
+        payload = self._result_for_revision(1, 1).blocks[0].payloads[0]
+        self.assertEqual((payload.processing_name, payload.frequency_hz.size, payload.trace.size), ("bscan", 0, 0))
+
     def test_live_geometry_recomputes_retained_gpr_without_restarting(self) -> None:
         self._live.processor_mode = "gpr"
         self._live.gpr_input_positions = [0]
diff --git a/python_app/tests/test_result_display.py b/python_app/tests/test_result_display.py
new file mode 100644
index 0000000..718de15
--- /dev/null
+++ b/python_app/tests/test_result_display.py
@@ -0,0 +1,79 @@
+"""The display shows the newest acquisition: after polls, Stop drains and settings changes."""
+
+from __future__ import annotations
+
+import os
+import unittest
+from unittest import mock
+
+import numpy as np
+
+os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
+from PyQt6.QtWidgets import QApplication  # noqa: E402
+
+from python_app.gui.controllers.renderers.trace import TraceRenderer  # noqa: E402
+from python_app.models.dataset_model import ComboKey, ResultBlock, ResultCollection, ResultPayload  # noqa: E402
+from python_app.models.gui_profile_schema import GuiPassThroughStateModel  # noqa: E402
+from python_app.tests.test_reader_recovery import pipeline_fixture  # noqa: E402
+
+
+def _result(collection_id: int, capture_start_ns: int, revision: int = 0) -> ResultCollection:
+    return ResultCollection(collection_id, capture_start_ns + 1, settings_revision=revision,
+                            capture_start_ns=capture_start_ns, capture_end_ns=capture_start_ns + 1)
+
+
+class NewestResultDisplayTest(unittest.TestCase):
+    def setUp(self) -> None:
+        self.pipeline, _supervisor = pipeline_fixture(self)
+        self.pipeline.pump_events = mock.Mock()
+        draw = mock.patch.object(self.pipeline.plots, "draw")
+        self.draw = draw.start()
+        self.addCleanup(draw.stop)
+
+    def read(self, *results: ResultCollection | None) -> None:
+        reader = mock.Mock()
+        reader.pop_result_collection.side_effect = [*results, *[None] * 10]
+        self.pipeline._result_reader = reader
+
+    def test_poll_shows_the_newest_acquisition_rather_than_the_last_one_read(self) -> None:
+        newest = _result(2, 200)
+        self.read(newest, _result(1, 100))  # a re-fed earlier sweep arrives after the newest
+        self.pipeline.poll()
+        self.draw.assert_called_once_with(newest)
+
+    def test_results_drained_by_stop_are_shown_once_stopped(self) -> None:
+        last = _result(2, 200)
+        self.read(_result(1, 100), last)
+        self.pipeline.stop()
+        self.draw.assert_not_called()
+        self.pipeline.poll()
+        self.pipeline.poll()
+        self.draw.assert_called_once_with(last)
+
+    def test_revision_drain_waits_past_quiet_polls_for_the_published_revision(self) -> None:
+        stale, fresh = _result(1, 100, revision=1), _result(1, 100, revision=2)
+        for revision, expected in ((None, stale), (2, fresh)):
+            with self.subTest(revision=revision):
+                self.pipeline.history.results.clear()
+                self.read(stale, None, None, None, fresh)
+                self.pipeline.drain_results(timeout_s=60, poll_s=0, revision=revision)
+                self.assertIs(self.pipeline.history.results[-1], expected)
+
+
+class TraceViewTest(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls) -> None:
+        cls.app = QApplication.instance() or QApplication([])
+
+    def test_draws_only_pass_through_payloads(self) -> None:
+        renderer = TraceRenderer(mock.Mock())
+        self.addCleanup(renderer.widget.close)
+        payloads = [ResultPayload(name, 1, frequency_hz=np.array([1e9, 2e9]), trace=np.ones(2, np.complex64))
+                    for name in ("bscan", "pass_through")]
+        collection = ResultCollection(1, 1, blocks=[ResultBlock(ComboKey(0, 0), payloads)])
+        self.assertTrue(renderer.draw(collection, GuiPassThroughStateModel()))
+        self.assertEqual([name for _combo, _index, name in renderer.magnitude.curves], ["pass_through"])
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/python_app/tests/test_review_gui_regressions.py b/python_app/tests/test_review_gui_regressions.py
index 0d05f16..42a94ef 100644
--- a/python_app/tests/test_review_gui_regressions.py
+++ b/python_app/tests/test_review_gui_regressions.py
@@ -129,8 +129,9 @@ class ReviewGuiRegressions(unittest.TestCase):
         pipeline, supervisor = pipeline_fixture(self)
         pipeline.should_run = True
         supervisor.pids.return_value = dict.fromkeys(("acquisition", "data_preprocessor", "data_processor"), 1)
-        with mock.patch.object(pipeline, "read_results", return_value=ResultCollection(1, 2)), \
-                mock.patch.object(pipeline.plots, "draw", side_effect=ValueError("bad display")), \
+        results = iter([ResultCollection(1, 2), None, ResultCollection(2, 3)])
+        pipeline._result_reader = mock.Mock(pop_result_collection=lambda: next(results, None))
+        with mock.patch.object(pipeline.plots, "draw", side_effect=ValueError("bad display")), \
                 mock.patch.object(pipeline, "stop_all") as stop, \
                 self.assertLogs("python_app.gui.controllers.pipeline_controller", "ERROR") as logs:
             pipeline.poll()
diff --git a/python_app/tests/test_sar3d_plot.py b/python_app/tests/test_sar3d_plot.py
index 42cf572..cc868eb 100644
--- a/python_app/tests/test_sar3d_plot.py
+++ b/python_app/tests/test_sar3d_plot.py
@@ -234,7 +234,9 @@ class Sar3dIntegrationTest(unittest.TestCase):
                                  (_collection(_status(2, "fewer than two frequency points")), "error"),
                                  (_collection(_status(1, "No signal in selected depth range")), "no signal"),
                                  (_projections(), "ready — CUDA")):
-            self.view._pipeline.drain_results = mock.Mock(return_value=result)
+            # Like the real drain, the recomputed result replaces its sweep in history.
+            self.view._pipeline.drain_results = mock.Mock(
+                side_effect=lambda result=result, **_timing: self.view._history.record_result(result))
             self.view._live.changed()
             self.assertIn(expected, self.renderer.status_label.text())
         self.view._log.show_exception.assert_not_called()
diff --git a/python_app/tests/test_shm_ipc.py b/python_app/tests/test_shm_ipc.py
index d0635d3..dccc830 100644
--- a/python_app/tests/test_shm_ipc.py
+++ b/python_app/tests/test_shm_ipc.py
@@ -34,6 +34,7 @@ from python_app.orchestration.shm.decoder import (
     decode_result_collection,
     decode_trace_collection,
 )
+from python_app.orchestration.shm.ring_layout import HEADER
 from python_app.orchestration.shm.ring_reader import ShmRingReader
 from python_app.orchestration.shm.ring_writer import ShmRingWriter
 from python_app.storage.npz.serialize import serialize_trace_collection
@@ -304,8 +305,18 @@ class RingOverflowTest(_RingTestCase):
                 writer.push(b"new")
 
         with mock.patch.object(atomics, "fence", side_effect=overwrite_after_copy):
-            self.assertIsNone(reader.pop_payload())
-        self.assertEqual(reader.pop_payload(), b"new")
+            self.assertEqual(reader.pop_payload(), b"new")  # the torn copy is never returned
+        self.assertIsNone(reader.pop_payload())
+
+    def test_lapped_reader_continues_with_the_newest_payload(self) -> None:
+        name = self._ring_name()
+        writer = self._writer(name, capacity=4, slot_size=64)
+        reader = self._reader(name)
+        for i in range(3):
+            writer.push(f"f{i}".encode())
+        writer._write_u64(HEADER.size + 8, 0)  # the producer is overwriting the unread f0
+        self.assertEqual(reader.pop_payload(), b"f2")
+        self.assertIsNone(reader.pop_payload())
 
     def test_reader_cannot_rewind_cursor_after_producer_laps_during_commit(self) -> None:
         from python_app.orchestration.shm import atomics
diff --git a/python_app/tests/test_web_frame_streaming.py b/python_app/tests/test_web_frame_streaming.py
index e5cfc0f..6310d65 100644
--- a/python_app/tests/test_web_frame_streaming.py
+++ b/python_app/tests/test_web_frame_streaming.py
@@ -1,16 +1,54 @@
-
-from contextlib import ExitStack
-"""Plot capture follows client demand and actual Qt scene changes."""
+"""Plot capture follows client demand and plot changes; redraws leave no stale pixels."""
 
 from collections import deque
+from contextlib import ExitStack
 import unittest
 from unittest import mock
 
 import numpy as np
-from PyQt6.QtCore import QSignalBlocker
-from PyQt6.QtWidgets import QApplication, QComboBox
+import pyqtgraph as pg
+from PyQt6.QtCore import QPoint, QSignalBlocker
+from PyQt6.QtGui import QImage
+from PyQt6.QtWidgets import QApplication, QCheckBox
 
-from python_app.tests.gui_test_support import isolated_window
+from python_app.gui.controllers.renderers.sar3d import SAR3D_VIEWS
+from python_app.models.dataset_model import ComboKey, ResultBlock, ResultCollection, ResultPayload, TraceData
+from python_app.tests.gui_test_support import isolated_window, widget
+
+
+def _phase_result(phase_deg: np.ndarray) -> ResultCollection:
+    trace = (0.5 * np.exp(1j * np.radians(phase_deg))).astype(np.complex64)
+    payload = ResultPayload("pass_through", 1, frequency_hz=np.linspace(1e9, 2e9, phase_deg.size), trace=trace)
+    return ResultCollection(1, 1, blocks=[ResultBlock(ComboKey(0, 0), [payload])])
+
+
+def _gpr_result(revision: int, point: tuple[float, float], size: int) -> ResultCollection:
+    image = np.linspace(0, 1, size * size, dtype=np.float32).reshape(size, size)
+    return ResultCollection(1, 1, settings_revision=revision, collection_payloads=[
+        ResultPayload("gpr_accumulator", 3, image=image,
+                      image_x_axis=np.linspace(-1.5, 1.5, size), image_y_axis=np.linspace(1, 12, size)),
+        ResultPayload("gpr_points", 4, table=np.array([[*point, 0.9]], dtype=np.float32)),
+    ])
+
+
+def _sar3d_result(revision: int, peak: tuple[float, float, float]) -> ResultCollection:
+    x, y, z = np.linspace(-1, 1, 9), np.linspace(-.5, .5, 5), np.linspace(1, 3, 9)
+    payloads = [ResultPayload(name, 3, image_x_axis=xx, image_y_axis=yy,
+                              image=np.full((yy.size, xx.size), .5, dtype=np.float32))
+                for name, (xx, yy) in zip(SAR3D_VIEWS, ((x, y), (z, y), (x, z), (x, y)))]
+    return ResultCollection(1, 1, settings_revision=revision, collection_payloads=[
+        *payloads,
+        ResultPayload("sar3d_status", 4, table=np.zeros((1, 1), dtype=np.float32)),
+        ResultPayload("sar3d_oblique_basis", 4, table=np.array([[1, 0, 0], [0, 1, 0]], dtype=np.float32)),
+        ResultPayload("sar3d_peak", 4, table=np.array([[1, *peak]], dtype=np.float32)),
+    ])
+
+
+def _bscan_result(collection_id: int, depth_m: np.ndarray) -> ResultCollection:
+    trace = np.full(depth_m.size, collection_id, dtype=np.complex64)
+    payload = ResultPayload("bscan", 1, frequency_hz=depth_m.astype(np.float32), trace=trace)
+    return ResultCollection(collection_id, collection_id, capture_start_ns=collection_id,
+                            capture_end_ns=collection_id + 1, blocks=[ResultBlock(ComboKey(0, 0), [payload])])
 
 
 class WebPlotCaptureTest(unittest.TestCase):
@@ -37,49 +75,53 @@ class WebPlotCaptureTest(unittest.TestCase):
             self.web._last_grab_s = 0
             self.web._grab_frame_if_due()
 
-    def test_no_clients_never_grabs_and_first_client_gets_current_plot(self) -> None:
-        self.w._plots.bscan.widget.plot([0, 1], [1, 2])
-        self.settle()
-        self.grab.assert_not_called()
-        controller = self.web
+    def show_mode(self, name: str) -> None:
         mode = self.w._view.processing.mode
         with QSignalBlocker(mode):
-            mode.setCurrentText("bscan")
-        self.w._live.active_mode = "bscan"
+            mode.setCurrentText(name)
+        self.w._live.active_mode = name
+        self.w._plots.set_mode(name)
+
+    def test_no_clients_never_grabs_and_first_client_gets_current_plot(self) -> None:
+        trace = TraceData(ComboKey(0, 0), np.array([1., 2.]), np.array([.1 + 0j, .2 + 0j]))
+        self.w._plots.draw_trace(trace, "Captured")
+        self.settle()
+        self.grab.assert_not_called()
+        self.show_mode("bscan")
         self.w._plots.bscan.history_by_combo = {(2, 3): deque([np.array([1., 2.])])}
         self.w._plots.sync_display_combos()
         self.web.refresh_snapshot()
-        self.assertEqual(controller.status()["display_combo"],
+        self.assertEqual(self.web.status()["display_combo"],
                          {"enabled": True, "input": 2, "output": 3, "options": [(2, 3)]})
         self.grab.assert_not_called()
-        controller.set_frame_streaming(True)
+        self.web.set_frame_streaming(True)
         self.settle()
         self.assertGreater(self.grab.call_count, 0)
         self.assertIsNotNone(self.web._last_png)
         calls = self.grab.call_count
         self.settle()
-        self.assertEqual(self.grab.call_count, calls)  # grab does not keep itself dirty
-        controller.set_frame_streaming(False)
-        self.w._plots.bscan.widget.clear()
+        self.assertEqual(self.grab.call_count, calls)  # a grab does not trigger another one
+        self.web.set_frame_streaming(False)
+        self.w._plots.clear()
         self.settle()
         self.assertEqual(self.grab.call_count, calls)
 
-    def test_data_clear_zoom_resize_and_sar_grid_trigger_capture_after_idle(self) -> None:
+    def test_drawing_clearing_zoom_resize_and_page_switch_trigger_capture_after_idle(self) -> None:
+        plots = self.w._plots
+        self.show_mode("pass_through")
         self.web.set_frame_streaming(True)
-        plot = self.w._plots.bscan.widget
-        item = plot.getPlotItem()
-        assert item is not None
-        view = item.getViewBox()
-        self.w._plots.stack.setCurrentWidget(plot)
         self.settle()
+        view = plots.trace.magnitude.view
         actions = [
-            lambda: plot.plot([0, 1, 2], [1, 4, 2]),
-            lambda: view.setXRange(0.25, 1.5, padding=0),
-            plot.clear,
+            lambda: plots.draw(_phase_result(np.full(50, 30.0))),
+            lambda: view.setXRange(1.2e9, 1.5e9, padding=0),
+            plots.redraw,
+            plots.clear,
             lambda: self.w.resize(self.w.width() + 50, self.w.height() + 50),
-            lambda: self.w._plots.stack.setCurrentWidget(self.w._plots.sar3d.widget),
+            lambda: plots.set_mode("sar3d"),
+            lambda: plots.draw_trace(TraceData(ComboKey(0, 0), np.array([1., 2.]), np.array([.1 + 0j, .2 + 0j])),
+                                     "Captured"),
         ]
-        actions.extend(lambda plot=plot: plot.plot([0, 1], [1, 3]) for plot in self.w._plots.sar3d.plots.values())
         for action in actions:
             with self.subTest(action=action):
                 calls = self.grab.call_count
@@ -90,18 +132,88 @@ class WebPlotCaptureTest(unittest.TestCase):
         self.settle()
         self.assertEqual(self.grab.call_count, calls)
 
-    def test_throttle_keeps_dirty_and_ignores_changes_emitted_during_grab(self) -> None:
+    def test_throttle_defers_a_change_and_a_grab_absorbs_changes_it_renders(self) -> None:
+        plots = self.w._plots
         self.web.set_frame_streaming(True)
         self.settle()
-        self.web._mark_dirty()
+        self.grab.reset_mock()
+        plots.clear()
         self.web._last_grab_s = 100
         with mock.patch("python_app.gui.controllers.web_controller.time.monotonic", return_value=100.1):
             self.assertIsNone(self.web._grab_frame_if_due())
-        self.assertTrue(self.web._dirty)
-        self.grab.side_effect = lambda: (self.web._mark_dirty(), "changed-png")[1]
+        self.grab.assert_not_called()
+        self.grab.side_effect = lambda: (plots.clear(), "changed-png")[1]
         with mock.patch("python_app.gui.controllers.web_controller.time.monotonic", return_value=100.3):
             self.assertIsNotNone(self.web._grab_frame_if_due())
-        self.assertFalse(self.web._dirty)
+        self.assertEqual(self.web._grabbed_revision, plots.revision)
+        with mock.patch("python_app.gui.controllers.web_controller.time.monotonic", return_value=100.6):
+            self.assertIsNone(self.web._grab_frame_if_due())
+        self.assertEqual(self.grab.call_count, 1)
+
+    def test_failed_grab_is_retried(self) -> None:
+        plots = self.w._plots
+        self.web.set_frame_streaming(True)
+        self.settle()
+        plots.clear()
+        self.grab.reset_mock(side_effect=True)
+        self.grab.side_effect = RuntimeError("render failed")
+        self.web._last_grab_s = 0
+        with self.assertRaises(RuntimeError):
+            self.web._grab_frame_if_due()
+        self.assertNotEqual(self.web._grabbed_revision, plots.revision)
+        self.grab.side_effect = None
+        self.settle()
+        self.assertEqual(self.grab.call_count, 2)
+        self.assertEqual(self.web._grabbed_revision, plots.revision)
+
+    def assert_window_shows_fresh_render(self) -> None:
+        screen, page = QApplication.primaryScreen(), self.w._plots.stack.currentWidget()
+        assert screen is not None and page is not None
+        for plot in [page] if isinstance(page, pg.PlotWidget) else page.findChildren(pg.PlotWidget):
+            if plot.isVisible():
+                origin = plot.mapTo(self.w, QPoint())
+                shown = screen.grabWindow(self.w.winId(), origin.x(), origin.y(), plot.width(), plot.height())
+                self.assertEqual(shown.toImage().convertToFormat(QImage.Format.Format_RGB32),
+                                 plot.grab().toImage().convertToFormat(QImage.Format.Format_RGB32))
+
+    def test_redrawn_views_leave_no_stale_pixels_on_screen(self) -> None:
+        # Qt repaints only changed regions, yet the window must equal a fresh render: once
+        # a phase redrawn from 100 to 0 deg left the old curve visible where none was drawn.
+        plots, history = self.w._plots, self.w._history
+        for plot in plots.stack.findChildren(pg.PlotWidget):
+            scene = plot.scene()
+            assert scene is not None
+            self.assertEqual(scene.receivers(scene.changed), 0)  # a receiver selects that update path
+        phase = widget(self.w._view.processing, "_show_phase_checkbox", QCheckBox)
+        self.addCleanup(phase.setChecked, phase.isChecked())
+        phase.setChecked(True)
+        self.web.set_frame_streaming(True)
+        revision = plots.required_revision or 0
+        later_phase = np.zeros(400)
+        later_phase[200:] = np.nan
+
+        def bscan(count: int, depth_m: np.ndarray) -> bool:
+            history.results.clear()
+            history.results.extend(_bscan_result(index, depth_m) for index in range(1, count + 1))
+            return plots.draw_bscan()
+
+        frames = {
+            "pass_through": (lambda: plots.draw(_phase_result(np.full(400, 100.0))),
+                             lambda: plots.draw(_phase_result(later_phase))),
+            "gpr": (lambda: plots.draw(_gpr_result(revision, (-1.0, 4.0), 20)),
+                    lambda: plots.draw(_gpr_result(revision, (1.0, 9.0), 8))),
+            "sar3d": (lambda: plots.draw(_sar3d_result(revision, (.6, .3, 2.6))),
+                      lambda: plots.draw(_sar3d_result(revision, (-.6, -.3, 1.4)))),
+            "bscan": (lambda: bscan(6, np.linspace(.5, 3., 12)), lambda: bscan(3, np.linspace(.5, 2., 4))),
+        }
+        self.addCleanup(history.results.clear)
+        for mode, (first, second) in frames.items():
+            with self.subTest(mode=mode):
+                self.show_mode(mode)
+                for draw in (first, second):
+                    self.assertTrue(draw())
+                    self.settle()
+                self.assert_window_shows_fresh_render()
 
 
 if __name__ == "__main__":
diff --git a/python_app/webui/static/style.css b/python_app/webui/static/style.css
index e481ff7..9a30ea4 100644
--- a/python_app/webui/static/style.css
+++ b/python_app/webui/static/style.css
@@ -122,7 +122,7 @@ body {
   min-height: 0;
   border: 1px solid var(--border);
   border-radius: 8px;
-  background: #0f141c; /* matches the pyqtgraph plot background behind letterboxing */
+  background: #ffffff; /* PLOT_BACKGROUND in python_app/gui/theme.py, shown around the letterboxed plot */
   overflow: hidden;
 }
 #plot { display: block; width: 100%; height: 100%; object-fit: contain; }