refactor: cut engine-to-UI include violations ahead of the liboakengine split

- slider DisplayType enums sink to node/sliderdisplaytype.h (canonical
  engine home); FloatSlider/RationalSlider alias them for compatibility
- DropWithoutSequenceBehavior enum sinks to common/dropworkflowbehavior.h
- Config errors now go through a registered ErrorHandler hook instead of
  QMessageBox with a MainWindow parent; the style default no longer
  depends on the UI style manager
- MainWindowLayoutInfo moves to node/project/serializer/ and its panel
  dependency is reduced to a plain std::map alias (PanelLayoutInfo),
  breaking the engine -> PanelWidget -> KDDockWidgets chain
- ProjectImportErrorDialog moves from task/ to dialog/projectimport/
- remove confirmed-redundant UI includes and give project.h/import.h/
  project.cpp the direct includes they were borrowing transitively
- project.h includes folder/sequence headers directly (it used both
  types in its own API all along)

app/node/audio/pan/pan.cpp

@@ -21,7 +21,7 @@
 
 #include "pan.h"
 
-#include "widget/slider/floatslider.h"
+#include "node/sliderdisplaytype.h"
 
 namespace olive
 {
@@ -40,7 +40,7 @@ PanNode::PanNode()
 	set_input_property(k_panning_input, QStringLiteral("min"), -1.0);
 	set_input_property(k_panning_input, QStringLiteral("max"), 1.0);
 	set_input_property(k_panning_input, QStringLiteral("view"),
-					 FloatSlider::k_percentage);
+					 slider::k_percentage);
 
 	set_flag(k_audio_effect);
 	set_effect_input(k_samples_input);

app/node/audio/volume/volume.cpp

@@ -21,7 +21,7 @@
 
 #include "volume.h"
 
-#include "widget/slider/floatslider.h"
+#include "node/sliderdisplaytype.h"
 
 namespace olive
 {
@@ -39,7 +39,7 @@ VolumeNode::VolumeNode()
 	add_input(k_volume_input, NodeValue::k_float, 1.0);
 	set_input_property(k_volume_input, QStringLiteral("min"), 0.0);
 	set_input_property(k_volume_input, QStringLiteral("view"),
-					 FloatSlider::k_decibel);
+					 slider::k_decibel);
 
 	set_flag(k_audio_effect);
 	set_effect_input(k_samples_input);

app/node/block/block.cpp

@@ -24,7 +24,7 @@
 #include <QDebug>
 
 #include "node/inputdragger.h"
-#include "widget/slider/rationalslider.h"
+#include "node/sliderdisplaytype.h"
 
 namespace olive
 {
@@ -44,7 +44,7 @@ Block::Block()
 	set_input_property(k_length_input, QStringLiteral("min"),
 					 QVariant::fromValue(Rational(0, 1)));
 	set_input_property(k_length_input, QStringLiteral("view"),
-					 RationalSlider::k_time);
+					 slider::k_time);
 	set_input_property(k_length_input, QStringLiteral("viewlock"), true);
 
 	set_input_flag(k_enabled_input, k_input_flag_not_connectable);

app/node/block/clip/clip.cpp

@@ -26,8 +26,8 @@
 #include "node/output/track/track.h"
 #include "node/output/viewer/viewer.h"
 #include "node/project/sequence/sequence.h"
-#include "widget/slider/floatslider.h"
-#include "widget/slider/rationalslider.h"
+#include "node/sliderdisplaytype.h"
+#include "node/sliderdisplaytype.h"
 
 namespace olive
 {
@@ -51,13 +51,13 @@ ClipBlock::ClipBlock()
 	add_input(k_media_in_input, NodeValue::k_rational,
 			 InputFlags(k_input_flag_not_connectable | k_input_flag_not_keyframable));
 	set_input_property(k_media_in_input, QStringLiteral("view"),
-					 RationalSlider::k_time);
+					 slider::k_time);
 	set_input_property(k_media_in_input, QStringLiteral("viewlock"), true);
 
 	add_input(k_speed_input, NodeValue::k_float, 1.0,
 			 InputFlags(k_input_flag_not_connectable | k_input_flag_not_keyframable));
 	set_input_property(k_speed_input, QStringLiteral("view"),
-					 FloatSlider::k_percentage);
+					 slider::k_percentage);
 	set_input_property(k_speed_input, QStringLiteral("min"), 0.0);
 
 	add_input(k_reverse_input, NodeValue::k_boolean, false,

app/node/block/transition/transition.cpp

@@ -23,7 +23,7 @@
 
 #include "node/block/clip/clip.h"
 #include "node/output/track/track.h"
-#include "widget/slider/rationalslider.h"
+#include "node/sliderdisplaytype.h"
 
 namespace olive
 {
@@ -51,7 +51,7 @@ TransitionBlock::TransitionBlock()
 	add_input(k_center_input, NodeValue::k_rational,
 			 InputFlags(k_input_flag_not_keyframable | k_input_flag_not_connectable));
 	set_input_property(k_center_input, QStringLiteral("view"),
-					 RationalSlider::k_time);
+					 slider::k_time);
 	set_input_property(k_center_input, QStringLiteral("viewlock"), true);
 
 	set_flag(k_dont_show_in_param_view, false);

app/node/color/ociogradingtransformlinear/ociogradingtransformlinear.cpp

@@ -26,7 +26,7 @@
 #include "common/ocioutils.h"
 #include "node/project.h"
 #include "render/colorprocessor.h"
-#include "widget/slider/floatslider.h"
+#include "node/sliderdisplaytype.h"
 
 namespace olive
 {
@@ -71,7 +71,7 @@ OCIOGradingTransformLinearNode::OCIOGradingTransformLinearNode()
 
 	add_input(k_saturation_input, NodeValue::k_float, 1.0);
 	set_input_property(k_saturation_input, QStringLiteral("view"),
-					 FloatSlider::k_percentage);
+					 slider::k_percentage);
 	set_input_property(k_saturation_input, QStringLiteral("min"), 0.0);
 
 	add_input(k_pivot_input, NodeValue::k_float,

app/node/color/ociogradingtransformlog/ociogradingtransformlog.cpp

@@ -26,7 +26,7 @@
 #include "common/ocioutils.h"
 #include "node/project.h"
 #include "render/colorprocessor.h"
-#include "widget/slider/floatslider.h"
+#include "node/sliderdisplaytype.h"
 
 namespace olive
 {
@@ -71,7 +71,7 @@ OCIOGradingTransformLogNode::OCIOGradingTransformLogNode()
 
 	add_input(k_saturation_input, NodeValue::k_float, 1.0);
 	set_input_property(k_saturation_input, QStringLiteral("view"),
-					 FloatSlider::k_percentage);
+					 slider::k_percentage);
 	set_input_property(k_saturation_input, QStringLiteral("min"), 0.0);
 
 	add_input(k_pivot_input, NodeValue::k_float,

app/node/color/ociolut/ociolut.cpp

@@ -20,10 +20,10 @@
 
 #include "ociolut.h"
 
+#include <QApplication>
 #include <QFileInfo>
 #include <QMetaObject>
 
-#include <QApplication>
 
 #include "core.h"
 #include "node/color/colormanager/colormanager.h"

app/node/color/threewaycolor/threewaycolor.cpp

@@ -24,7 +24,7 @@
 #include <QVector3D>
 
 #include "node/project.h"
-#include "widget/slider/floatslider.h"
+#include "node/sliderdisplaytype.h"
 
 namespace olive
 {
@@ -66,9 +66,9 @@ ThreeWayColorNode::ThreeWayColorNode()
 	set_input_property(k_shadows_amount_input, min, 0.0);
 	set_input_property(k_midtones_amount_input, min, 0.0);
 	set_input_property(k_highlights_amount_input, min, 0.0);
-	set_input_property(k_shadows_amount_input, view, FloatSlider::k_percentage);
-	set_input_property(k_midtones_amount_input, view, FloatSlider::k_percentage);
-	set_input_property(k_highlights_amount_input, view, FloatSlider::k_percentage);
+	set_input_property(k_shadows_amount_input, view, slider::k_percentage);
+	set_input_property(k_midtones_amount_input, view, slider::k_percentage);
+	set_input_property(k_highlights_amount_input, view, slider::k_percentage);
 
 	set_effect_input(k_texture_input);
 	set_flag(k_video_effect);

app/node/color/whitebalance/whitebalance.cpp

@@ -25,7 +25,7 @@
 #include "common/filefunctions.h"
 #include "render/job/shaderjob.h"
 #include "render/texture.h"
-#include "widget/slider/floatslider.h"
+#include "node/sliderdisplaytype.h"
 
 namespace olive
 {
@@ -47,7 +47,7 @@ WhiteBalanceNode::WhiteBalanceNode()
 	set_input_property(k_temperature_input, QStringLiteral("min"), 1000.0);
 	set_input_property(k_temperature_input, QStringLiteral("max"), 40000.0);
 	set_input_property(k_temperature_input, QStringLiteral("view"),
-					 FloatSlider::k_normal);
+					 slider::k_normal);
 
 	add_input(k_tint_input, NodeValue::k_float, 0.0);
 	set_input_property(k_tint_input, QStringLiteral("min"), -1.0);

app/node/distort/cornerpin/cornerpindistortnode.cpp

@@ -23,7 +23,6 @@
 
 #include "common/lerp.h"
 #include "core.h"
-#include "widget/slider/floatslider.h"
 
 namespace olive
 {

app/node/distort/crop/cropdistortnode.cpp

@@ -23,7 +23,7 @@
 
 #include "common/util.h"
 #include "core.h"
-#include "widget/slider/floatslider.h"
+#include "node/sliderdisplaytype.h"
 
 namespace olive
 {
@@ -183,7 +183,7 @@ void CropDistortNode::create_crop_side_input(const QString &id)
 	add_input(id, NodeValue::k_float, 0.0);
 	set_input_property(id, QStringLiteral("min"), 0.0);
 	set_input_property(id, QStringLiteral("max"), 1.0);
-	set_input_property(id, QStringLiteral("view"), FloatSlider::k_percentage);
+	set_input_property(id, QStringLiteral("view"), slider::k_percentage);
 }
 
 }

app/node/distort/tile/tiledistortnode.cpp

@@ -21,7 +21,7 @@
 
 #include "tiledistortnode.h"
 
-#include "widget/slider/floatslider.h"
+#include "node/sliderdisplaytype.h"
 
 namespace olive
 {
@@ -43,7 +43,7 @@ TileDistortNode::TileDistortNode()
 	add_input(k_scale_input, NodeValue::k_float, 0.5);
 	set_input_property(k_scale_input, QStringLiteral("min"), 0);
 	set_input_property(k_scale_input, QStringLiteral("view"),
-					 FloatSlider::k_percentage);
+					 slider::k_percentage);
 
 	add_input(k_position_input, NodeValue::k_vec2, QVector2D(0, 0));
 

app/node/effect/opacity/opacityeffect.cpp

@@ -19,7 +19,7 @@
 #include "opacityeffect.h"
 
 #include "node/math/math/math.h"
-#include "widget/slider/floatslider.h"
+#include "node/sliderdisplaytype.h"
 
 namespace olive
 {
@@ -43,7 +43,7 @@ OpacityEffect::OpacityEffect()
 
 	add_input(k_value_input, NodeValue::k_float, 1.0);
 	set_input_property(k_value_input, QStringLiteral("view"),
-					 FloatSlider::k_percentage);
+					 slider::k_percentage);
 	set_input_property(k_value_input, QStringLiteral("min"), 0.0);
 	set_input_property(k_value_input, QStringLiteral("max"), 1.0);
 

app/node/filter/dropshadow/dropshadowfilter.cpp

@@ -21,7 +21,7 @@
 
 #include "dropshadowfilter.h"
 
-#include "widget/slider/floatslider.h"
+#include "node/sliderdisplaytype.h"
 
 namespace olive
 {
@@ -54,7 +54,7 @@ DropShadowFilter::DropShadowFilter()
 	add_input(k_opacity_input, NodeValue::k_float, 1.0);
 	set_input_property(k_opacity_input, QStringLiteral("min"), 0.0);
 	set_input_property(k_opacity_input, QStringLiteral("view"),
-					 FloatSlider::k_percentage);
+					 slider::k_percentage);
 
 	add_input(k_fast_input, NodeValue::k_boolean, false);
 

app/node/filter/stroke/stroke.cpp

@@ -21,7 +21,7 @@
 
 #include "stroke.h"
 
-#include "widget/slider/floatslider.h"
+#include "node/sliderdisplaytype.h"
 
 namespace olive
 {
@@ -47,7 +47,7 @@ StrokeFilterNode::StrokeFilterNode()
 
 	add_input(k_opacity_input, NodeValue::k_float, 1.0f);
 	set_input_property(k_opacity_input, QStringLiteral("view"),
-					 FloatSlider::k_percentage);
+					 slider::k_percentage);
 	set_input_property(k_opacity_input, QStringLiteral("min"), 0.0f);
 	set_input_property(k_opacity_input, QStringLiteral("max"), 1.0f);
 

app/node/generator/matrix/matrix.cpp

@@ -24,7 +24,7 @@
 #include <QMatrix4x4>
 #include <QVector2D>
 
-#include "widget/slider/floatslider.h"
+#include "node/sliderdisplaytype.h"
 
 namespace olive
 {
@@ -47,7 +47,7 @@ MatrixGenerator::MatrixGenerator()
 	add_input(k_scale_input, NodeValue::k_vec2, QVector2D(1.0f, 1.0f));
 	set_input_property(k_scale_input, QStringLiteral("min"), QVector2D(0, 0));
 	set_input_property(k_scale_input, QStringLiteral("view"),
-					 FloatSlider::k_percentage);
+					 slider::k_percentage);
 	set_input_property(k_scale_input, QStringLiteral("disable1"), true);
 
 	add_input(k_uniform_scale_input, NodeValue::k_boolean, true,

app/node/generator/noise/noise.cpp

@@ -21,7 +21,7 @@
 
 #include "noise.h"
 
-#include "widget/slider/floatslider.h"
+#include "node/sliderdisplaytype.h"
 
 namespace olive
 {
@@ -40,7 +40,7 @@ NoiseGeneratorNode::NoiseGeneratorNode()
 
 	add_input(k_strength_input, NodeValue::k_float, 0.2);
 	set_input_property(k_strength_input, QStringLiteral("view"),
-					 FloatSlider::k_percentage);
+					 slider::k_percentage);
 	set_input_property(k_strength_input, QStringLiteral("min"), 0);
 
 	add_input(k_color_input, NodeValue::k_boolean, false);

app/node/output/track/track.cpp

@@ -21,7 +21,6 @@
 
 #include "track.h"
 
-#include <QApplication>
 #include <QDebug>
 #include <QFontMetrics>
 

app/node/project.cpp

@@ -28,14 +28,14 @@
 #include "common/qtutils.h"
 #include "common/xmlutils.h"
 #include "core.h"
-#include "dialog/progress/progress.h"
 #include "node/color/ociobase/ociobase.h"
 #include "node/factory.h"
+#include "node/group/group.h"
+#include "node/project/folder/folder.h"
 #include "node/serializeddata.h"
 #include "pluginSupport/olivehost.h"
 #include "ofxhPluginCache.h"
 #include "render/diskmanager.h"
-#include "window/mainwindow/mainwindow.h"
 
 namespace olive
 {

app/node/project.h

@@ -27,9 +27,10 @@
 #include <QUuid>
 
 #include "node/output/viewer/viewer.h"
+#include "node/project/folder/folder.h"
 #include "node/project/footage/footage.h"
+#include "node/project/sequence/sequence.h"
 #include "node/color/colormanager/colormanager.h"
-#include "window/mainwindow/mainwindowlayoutinfo.h"
 
 namespace olive
 {

app/node/project/sequence/sequence.cpp

@@ -23,7 +23,6 @@
 
 #include <QThread>
 
-#include "panel/timeline/timeline.h"
 #include "ui/icons/icons.h"
 #include "timeline/timelineundogeneral.h"
 

app/node/project/serializer/CMakeLists.txt

@@ -33,6 +33,9 @@ set(OLIVE_SOURCES
         node/project/serializer/serializer230220.h
 
 
+        node/project/serializer/mainwindowlayoutinfo.cpp
+        node/project/serializer/mainwindowlayoutinfo.h
+
         node/project/serializer/typeserializer.cpp
         node/project/serializer/typeserializer.h
 

app/node/project/serializer/mainwindowlayoutinfo.cpp

@@ -0,0 +1,232 @@
+/*
+ * Oak Video Editor - Non-Linear Video Editor
+ * Copyright (C) 2025 Olive CE Team
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "mainwindowlayoutinfo.h"
+
+namespace olive
+{
+
+void MainWindowLayoutInfo::to_xml(QXmlStreamWriter *writer) const
+{
+	writer->writeAttribute(QStringLiteral("version"),
+						   QString::number(k_version));
+
+	writer->writeStartElement(QStringLiteral("folders"));
+
+	foreach (Folder *folder, open_folders_) {
+		writer->writeTextElement(
+			QStringLiteral("folder"),
+			QString::number(reinterpret_cast<quintptr>(folder)));
+	}
+
+	writer->writeEndElement(); // folders
+
+	writer->writeStartElement(QStringLiteral("timeline"));
+
+	foreach (Sequence *sequence, open_sequences_) {
+		writer->writeTextElement(
+			QStringLiteral("sequence"),
+			QString::number(reinterpret_cast<quintptr>(sequence)));
+	}
+
+	writer->writeEndElement(); // timeline
+
+	writer->writeStartElement(QStringLiteral("viewers"));
+
+	foreach (ViewerOutput *viewer, open_viewers_) {
+		writer->writeTextElement(
+			QStringLiteral("viewer"),
+			QString::number(reinterpret_cast<quintptr>(viewer)));
+	}
+
+	writer->writeEndElement(); // viewers
+
+	writer->writeStartElement(QStringLiteral("data"));
+
+	for (auto it = panel_data_.cbegin(); it != panel_data_.cend(); it++) {
+		writer->writeStartElement(QStringLiteral("panel"));
+
+		writer->writeAttribute(QStringLiteral("id"), it->first);
+
+		const PanelLayoutInfo &info = it->second;
+		for (auto jt = info.cbegin(); jt != info.cend(); jt++) {
+			writer->writeStartElement(QStringLiteral("option"));
+
+			writer->writeAttribute(QStringLiteral("name"), jt->first);
+
+			writer->writeCharacters(jt->second);
+
+			writer->writeEndElement(); // option
+		}
+
+		writer->writeEndElement(); // panel
+	}
+
+	writer->writeEndElement(); // data
+
+	writer->writeTextElement(QStringLiteral("state"),
+							 QString(state_.toBase64()));
+}
+
+MainWindowLayoutInfo
+MainWindowLayoutInfo::from_xml(QXmlStreamReader *reader,
+							  const QHash<quintptr, Node *> &node_ptrs)
+{
+	MainWindowLayoutInfo info;
+
+	unsigned int file_version = 0;
+
+	XMLAttributeLoop(reader, attr)
+	{
+		if (attr.name() == QStringLiteral("version")) {
+			file_version = attr.value().toUInt();
+		}
+	}
+
+	// Really basic version checking, in the future we may use this to parse multiple versions
+	if (file_version != k_version) {
+	}
+
+	while (xml_read_next_start_element(reader)) {
+		if (reader->name() == QStringLiteral("folders")) {
+			while (xml_read_next_start_element(reader)) {
+				if (reader->name() == QStringLiteral("folder")) {
+					quintptr item_id = reader->readElementText().toULongLong();
+
+					Folder *open_item =
+						static_cast<Folder *>(node_ptrs.value(item_id));
+					info.open_folders_.push_back(open_item);
+				} else {
+					reader->skipCurrentElement();
+				}
+			}
+
+		} else if (reader->name() == QStringLiteral("timeline")) {
+			while (xml_read_next_start_element(reader)) {
+				if (reader->name() == QStringLiteral("sequence")) {
+					quintptr item_id = reader->readElementText().toULongLong();
+
+					Sequence *open_seq =
+						static_cast<Sequence *>(node_ptrs.value(item_id));
+					info.open_sequences_.push_back(open_seq);
+				} else {
+					reader->skipCurrentElement();
+				}
+			}
+
+		} else if (reader->name() == QStringLiteral("viewers")) {
+			while (xml_read_next_start_element(reader)) {
+				if (reader->name() == QStringLiteral("viewer")) {
+					quintptr item_id = reader->readElementText().toULongLong();
+
+					ViewerOutput *open_viewer =
+						static_cast<ViewerOutput *>(node_ptrs.value(item_id));
+					info.open_viewers_.push_back(open_viewer);
+				} else {
+					reader->skipCurrentElement();
+				}
+			}
+
+		} else if (reader->name() == QStringLiteral("state")) {
+			info.state_ =
+				QByteArray::fromBase64(reader->readElementText().toLatin1());
+
+		} else if (reader->name() == QStringLiteral("data")) {
+			while (xml_read_next_start_element(reader)) {
+				if (reader->name() == QStringLiteral("panel")) {
+					QString id;
+					XMLAttributeLoop(reader, attr)
+					{
+						if (attr.name() == QStringLiteral("id")) {
+							id = attr.value().toString();
+						}
+					}
+
+					if (!id.isEmpty()) {
+						PanelLayoutInfo i;
+
+						while (xml_read_next_start_element(reader)) {
+							if (reader->name() == QStringLiteral("option")) {
+								QString name;
+
+								XMLAttributeLoop(reader, attr)
+								{
+									if (attr.name() == QStringLiteral("name")) {
+										name = attr.value().toString();
+									}
+								}
+
+								if (!name.isEmpty()) {
+									i[name] = reader->readElementText();
+								}
+							} else {
+								reader->skipCurrentElement();
+							}
+						}
+
+						info.panel_data_[id] = i;
+					}
+
+				} else {
+					reader->skipCurrentElement();
+				}
+			}
+
+		} else {
+			reader->skipCurrentElement();
+		}
+	}
+
+	return info;
+}
+
+void MainWindowLayoutInfo::add_folder(olive::Folder *f)
+{
+	open_folders_.push_back(f);
+}
+
+void MainWindowLayoutInfo::add_sequence(Sequence *seq)
+{
+	open_sequences_.push_back(seq);
+}
+
+void MainWindowLayoutInfo::add_viewer(ViewerOutput *viewer)
+{
+	open_viewers_.push_back(viewer);
+}
+
+void MainWindowLayoutInfo::set_panel_data(const QString &id,
+										  const PanelLayoutInfo &data)
+{
+	panel_data_[id] = data;
+}
+
+void MainWindowLayoutInfo::move_panel_data(const QString &old,
+										   const QString &now)
+{
+	PanelLayoutInfo tmp = panel_data_.at(old);
+	panel_data_.erase(old);
+	panel_data_[now] = tmp;
+}
+
+void MainWindowLayoutInfo::set_state(const QByteArray &layout)
+{
+	state_ = layout;
+}
+
+}

app/node/project/serializer/mainwindowlayoutinfo.h

@@ -0,0 +1,102 @@
+/*
+ * Oak Video Editor - Non-Linear Video Editor
+ * Copyright (C) 2025 Olive CE Team
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef OAK_MAINWINDOWLAYOUTINFO_H
+#define OAK_MAINWINDOWLAYOUTINFO_H
+
+#include <map>
+
+#include "node/project/folder/folder.h"
+#include "node/project/sequence/sequence.h"
+
+namespace olive
+{
+
+/**
+ * @brief Per-panel layout data (key/value pairs)
+ *
+ * Identical to PanelWidget::Info in the UI layer; defined here so the
+ * engine-side layout data structure does not depend on widget headers.
+ */
+using PanelLayoutInfo = std::map<QString, QString>;
+
+class MainWindowLayoutInfo {
+public:
+	MainWindowLayoutInfo() = default;
+
+	void to_xml(QXmlStreamWriter *writer) const;
+
+	static MainWindowLayoutInfo
+	from_xml(QXmlStreamReader *reader, const QHash<quintptr, Node *> &node_map);
+
+	void add_folder(Folder *f);
+
+	void add_sequence(Sequence *seq);
+
+	void add_viewer(ViewerOutput *viewer);
+
+	void set_panel_data(const QString &id, const PanelLayoutInfo &data);
+
+	void move_panel_data(const QString &old, const QString &now);
+
+	void set_state(const QByteArray &layout);
+
+	const std::vector<Folder *> &open_folders() const
+	{
+		return open_folders_;
+	}
+
+	const std::vector<Sequence *> &open_sequences() const
+	{
+		return open_sequences_;
+	}
+
+	const std::vector<ViewerOutput *> &open_viewers() const
+	{
+		return open_viewers_;
+	}
+
+	const std::map<QString, PanelLayoutInfo> &panel_data() const
+	{
+		return panel_data_;
+	}
+
+	const QByteArray &state() const
+	{
+		return state_;
+	}
+
+private:
+	QByteArray state_;
+
+	std::vector<Folder *> open_folders_;
+
+	std::vector<Sequence *> open_sequences_;
+
+	std::vector<ViewerOutput *> open_viewers_;
+
+	std::map<QString, PanelLayoutInfo> panel_data_;
+
+	static const unsigned int k_version = 1;
+};
+
+}
+
+Q_DECLARE_METATYPE(olive::MainWindowLayoutInfo)
+
+#endif // OAK_MAINWINDOWLAYOUTINFO_H

app/node/project/serializer/serializer.h

@@ -26,6 +26,7 @@
 
 #include "common/define.h"
 #include "node/project.h"
+#include "node/project/serializer/mainwindowlayoutinfo.h"
 #include "typeserializer.h"
 
 namespace olive

app/node/sliderdisplaytype.h

@@ -0,0 +1,47 @@
+/***
+
+  Oak - Non-Linear Video Editor
+  Copyright (C) 2026 Oak Team
+
+  This program is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+***/
+
+#ifndef OAK_SLIDERDISPLAYTYPE_H
+#define OAK_SLIDERDISPLAYTYPE_H
+
+namespace olive
+{
+
+/**
+ * @brief Slider display type enums shared by nodes and widgets
+ *
+ * Nodes reference these enums in their input properties ("view"); the
+ * slider widgets in app/widget/slider use the same values to render. The
+ * definitions live in the engine layer so nodes do not depend on widget
+ * headers. Enumerator order is ABI/feature compatible with the previous
+ * FloatSlider::DisplayType and RationalSlider::DisplayType.
+ */
+namespace slider
+{
+
+enum FloatDisplayType { k_normal, k_decibel, k_percentage };
+
+enum RationalDisplayType { k_time, k_float, k_rational };
+
+} // namespace slider
+
+} // namespace olive
+
+#endif // OAK_SLIDERDISPLAYTYPE_H

app/node/time/timeoffset/timeoffsetnode.cpp

@@ -21,7 +21,7 @@
 
 #include "timeoffsetnode.h"
 
-#include "widget/slider/rationalslider.h"
+#include "node/sliderdisplaytype.h"
 
 namespace olive
 {
@@ -35,7 +35,7 @@ TimeOffsetNode::TimeOffsetNode()
 {
 	add_input(k_time_input, NodeValue::k_rational, QVariant::fromValue(Rational(0)),
 			 InputFlags(k_input_flag_not_connectable));
-	set_input_property(k_time_input, QStringLiteral("view"), RationalSlider::k_time);
+	set_input_property(k_time_input, QStringLiteral("view"), slider::k_time);
 	set_input_property(k_time_input, QStringLiteral("viewlock"), true);
 
 	add_input(k_input_input, NodeValue::k_none,

app/node/time/timeremap/timeremap.cpp

@@ -21,7 +21,7 @@
 
 #include "timeremap.h"
 
-#include "widget/slider/rationalslider.h"
+#include "node/sliderdisplaytype.h"
 
 namespace olive
 {
@@ -35,7 +35,7 @@ TimeRemapNode::TimeRemapNode()
 {
 	add_input(k_time_input, NodeValue::k_rational, QVariant::fromValue(Rational(0)),
 			 InputFlags(k_input_flag_not_connectable));
-	set_input_property(k_time_input, QStringLiteral("view"), RationalSlider::k_time);
+	set_input_property(k_time_input, QStringLiteral("view"), slider::k_time);
 	set_input_property(k_time_input, QStringLiteral("viewlock"), true);
 
 	add_input(k_input_input, NodeValue::k_none,