fix(sectionplane): persist and clip section modes correctly

Cargo.lock

@@ -79,7 +79,7 @@ checksum = "366ffbaa4442f4684d91e2cd7c5ea7c4ed8add41959a31447066e279e432b618"
 [[package]]
 name = "acadrust"
 version = "0.5.4"
-source = "git+https://github.com/HakanSeven12/cadcodec.git?rev=62628c41670a914d1598a14faafc3c6e3aa4a270#62628c41670a914d1598a14faafc3c6e3aa4a270"
+source = "git+https://github.com/HakanSeven12/cadcodec.git?rev=f23ffc873228e5f41b876485c741e4a8ac20a67d#f23ffc873228e5f41b876485c741e4a8ac20a67d"
 dependencies = [
  "ahash 0.8.12",
  "anyhow",
@@ -885,7 +885,7 @@ checksum = "fc652a48c352aef3ea3aed32080501cf3ef6ed5da78602a020c991775b0aff04"
 [[package]]
 name = "cadkernel"
 version = "0.1.0"
-source = "git+https://github.com/HakanSeven12/cadkernel.git?rev=920ff591028ab4ba13648b920d9d333ec3b7d44b#920ff591028ab4ba13648b920d9d333ec3b7d44b"
+source = "git+https://github.com/HakanSeven12/cadkernel.git?rev=dfd0de176a878c20a1aeb8d23b0b8265197b5f5c#dfd0de176a878c20a1aeb8d23b0b8265197b5f5c"
 dependencies = [
  "acadrust",
  "cavalier_contours",

Cargo.toml

@@ -31,8 +31,8 @@ glam = { version = "0.33", features = ["bytemuck"] }
 rfd = "0.17"
 clap = { version = "4", features = ["derive", "string"] }
 env_logger = "0.11"
-acadrust = { git = "https://github.com/HakanSeven12/cadcodec.git", rev = "62628c41670a914d1598a14faafc3c6e3aa4a270", features = ["serde"] }
-cadkernel = { git = "https://github.com/HakanSeven12/cadkernel.git", rev = "920ff591028ab4ba13648b920d9d333ec3b7d44b", features = ["acis", "offset"] }
+acadrust = { git = "https://github.com/HakanSeven12/cadcodec.git", rev = "f23ffc873228e5f41b876485c741e4a8ac20a67d", features = ["serde"] }
+cadkernel = { git = "https://github.com/HakanSeven12/cadkernel.git", rev = "dfd0de176a878c20a1aeb8d23b0b8265197b5f5c", features = ["acis", "offset"] }
 dwg-thumbnailer = { path = "crates/dwg-thumbnailer" }
 flate2 = "1"
 image = { version = "0.25", default-features = false, features = ["png", "jpeg", "bmp", "tiff"] }

crates/ocs_doc_api/Cargo.toml

@@ -14,8 +14,8 @@ bincode = "1.3"
 thiserror = "1"
 
 # Host adapters convert ObjectId to acadrust handles; kernel handles stay local.
-acadrust = { git = "https://github.com/HakanSeven12/cadcodec.git", rev = "62628c41670a914d1598a14faafc3c6e3aa4a270", features = ["serde"], optional = true }
-cadkernel = { git = "https://github.com/HakanSeven12/cadkernel.git", rev = "920ff591028ab4ba13648b920d9d333ec3b7d44b", features = ["acis", "offset"], optional = true }
+acadrust = { git = "https://github.com/HakanSeven12/cadcodec.git", rev = "f23ffc873228e5f41b876485c741e4a8ac20a67d", features = ["serde"], optional = true }
+cadkernel = { git = "https://github.com/HakanSeven12/cadkernel.git", rev = "dfd0de176a878c20a1aeb8d23b0b8265197b5f5c", features = ["acis", "offset"], optional = true }
 ocs_plugin_api = { path = "../ocs_plugin_api", optional = true, features = ["host"] }
 
 [build-dependencies]

crates/ocs_plugin_api/Cargo.toml

@@ -14,7 +14,7 @@ serde = { version = "1", features = ["derive"] }
 # Pulled in only by the `host` feature, which adds the `acadrust`-typed
 # `HostApi` runtime surface. The default crate stays dependency-free so engine
 # crates and external tooling can depend on the manifest/ribbon contract cheaply.
-acadrust = { git = "https://github.com/HakanSeven12/cadcodec.git", rev = "62628c41670a914d1598a14faafc3c6e3aa4a270", optional = true, features = ["serde"] }
+acadrust = { git = "https://github.com/HakanSeven12/cadcodec.git", rev = "f23ffc873228e5f41b876485c741e4a8ac20a67d", optional = true, features = ["serde"] }
 
 # Runtime IPC and serialization (host feature only).
 interprocess = { version = "2", optional = true }
@@ -38,7 +38,7 @@ serde_json = "1"
 serde = { version = "1", features = ["derive"] }
 cargo-lock = "11"
 # acadrust is scanned at build time to generate the embedded type registry.
-acadrust = { git = "https://github.com/HakanSeven12/cadcodec.git", rev = "62628c41670a914d1598a14faafc3c6e3aa4a270", features = ["serde"] }
+acadrust = { git = "https://github.com/HakanSeven12/cadcodec.git", rev = "f23ffc873228e5f41b876485c741e4a8ac20a67d", features = ["serde"] }
 
 [dev-dependencies]
 serde_json = "1"

crates/ocs_web_worker/Cargo.toml

@@ -8,7 +8,7 @@ publish = false
 crate-type = ["cdylib"]
 
 [dependencies]
-acadrust = { git = "https://github.com/HakanSeven12/cadcodec.git", rev = "62628c41670a914d1598a14faafc3c6e3aa4a270", features = ["serde"] }
+acadrust = { git = "https://github.com/HakanSeven12/cadcodec.git", rev = "f23ffc873228e5f41b876485c741e4a8ac20a67d", features = ["serde"] }
 bincode = "1.3"
 serde = { version = "1", features = ["derive"] }
 console_error_panic_hook = "0.1"

crates/plugin-template-api2/Cargo.toml

@@ -10,4 +10,4 @@ crate-type = ["cdylib"]
 
 [dependencies]
 ocs_plugin_api = { path = "../ocs_plugin_api", features = ["host"] }
-acadrust = { git = "https://github.com/HakanSeven12/cadcodec.git", rev = "62628c41670a914d1598a14faafc3c6e3aa4a270", features = ["serde"] }
+acadrust = { git = "https://github.com/HakanSeven12/cadcodec.git", rev = "f23ffc873228e5f41b876485c741e4a8ac20a67d", features = ["serde"] }

src/app/history.rs

@@ -675,6 +675,10 @@ impl OpenCADStudio {
             entity,
             EntityType::Block(_)
                 | EntityType::BlockEnd(_)
+                | EntityType::Extended(acadrust::entities::ExtendedEntity {
+                    data: acadrust::entities::ExtendedEntityData::SectionObject(_),
+                    ..
+                })
         ) {
             return false;
         }

src/entities/extended.rs

@@ -3,6 +3,7 @@ use acadrust::entities::{
     PointCloudData, PointCloudExData, RemoteTextData, SectionObjectData,
 };
 use acadrust::types::{Handle, Transform, Vector3};
+use acadrust::xdata::{ExtendedDataRecord, XDataValue};
 use crate::t;
 
 use crate::command::EntityTransform;
@@ -17,6 +18,69 @@ use crate::scene::model::object::{
 use crate::scene::model::wire_model::SnapHint;
 
 const NAN: [f64; 3] = [f64::NAN; 3];
+const SECTION_SLICE_APP: &str = "IsSlice";
+const SECTION_THICKNESS_APP: &str = "ThicknessDepth";
+
+pub(crate) fn section_is_slice(entity: &ExtendedEntity) -> bool {
+    entity
+        .common
+        .extended_data
+        .get_record(SECTION_SLICE_APP)
+        .is_some_and(|record| {
+            record
+                .values
+                .iter()
+                .rev()
+                .find_map(|value| match value {
+                    XDataValue::Integer16(value) => Some(*value != 0),
+                    XDataValue::Integer32(value) => Some(*value != 0),
+                    _ => None,
+                })
+                .unwrap_or(false)
+        })
+}
+
+pub(crate) fn section_slice_depth(entity: &ExtendedEntity) -> Option<f64> {
+    entity
+        .common
+        .extended_data
+        .get_record(SECTION_THICKNESS_APP)?
+        .values
+        .iter()
+        .find_map(|value| match value {
+            XDataValue::Real(value) | XDataValue::Distance(value) => Some(*value),
+            _ => None,
+        })
+        .filter(|value| value.is_finite())
+        .map(f64::abs)
+}
+
+pub(crate) fn set_section_slice_metadata(
+    entity: &mut ExtendedEntity,
+    enabled: bool,
+    depth: f64,
+) {
+    if !enabled {
+        entity.common.extended_data.remove_record(SECTION_SLICE_APP);
+        entity
+            .common
+            .extended_data
+            .remove_record(SECTION_THICKNESS_APP);
+        return;
+    }
+
+    let mut slice = ExtendedDataRecord::new(SECTION_SLICE_APP);
+    slice.values = vec![XDataValue::Integer16(0), XDataValue::Integer16(1)];
+    entity.common.extended_data.upsert_record(slice);
+
+    let mut thickness = ExtendedDataRecord::new(SECTION_THICKNESS_APP);
+    thickness.values = vec![XDataValue::Real(if depth.is_finite() {
+        depth.abs()
+    } else {
+        0.0
+    })];
+    entity.common.extended_data.upsert_record(thickness);
+}
 
 fn vector_text(value: Vector3) -> String {
     format!("{:.6}, {:.6}, {:.6}", value.x, value.y, value.z)
@@ -558,17 +622,17 @@ fn to_render(entity: &ExtendedEntity, document: &acadrust::CadDocument) -> Optio
     })
 }
 
-fn section_properties(data: &SectionObjectData) -> Vec<PropSection> {
+fn section_properties(entity: &ExtendedEntity, data: &SectionObjectData) -> Vec<PropSection> {
     let vertices = data
         .vertices
         .iter()
         .map(|point| vector_text(*point))
         .collect::<Vec<_>>()
         .join("; ");
-    let kind = section_kind(data);
+    let kind = section_kind(entity, data);
     let viewing = section_viewing_direction(data);
     let offset = section_plane_offset(data);
-    let depth = section_depth(data);
+    let depth = section_slice_depth(entity).unwrap_or_else(|| section_depth(data));
     vec![PropSection {
         title: t!("Section Plane").into_owned(),
         props: vec![
@@ -656,18 +720,14 @@ fn section_depth(data: &SectionObjectData) -> f64 {
         .map_or(0.0, |(front, back)| (*back - *front).length())
 }
 
-fn section_kind(data: &SectionObjectData) -> &'static str {
+fn section_kind(entity: &ExtendedEntity, data: &SectionObjectData) -> &'static str {
+    if section_is_slice(entity) {
+        return "Slice";
+    }
     match data.state {
         1 => "Plane",
         4 => "Volume",
-        2 => {
-            let span = data
-                .vertices
-                .first()
-                .zip(data.vertices.last())
-                .map_or(1.0, |(first, last)| (*last - *first).length().max(1e-9));
-            if section_depth(data) < span * 0.25 { "Slice" } else { "Boundary" }
-        }
+        2 => "Boundary",
         _ => "Plane",
     }
 }
@@ -734,8 +794,8 @@ fn set_section_kind(data: &mut SectionObjectData, value: &str) {
         .map_or(1.0, |(first, last)| (*last - *first).length().max(1e-4));
     match value.trim().to_ascii_uppercase().as_str() {
         "SLICE" => {
-            data.state = 2;
-            set_section_depth(data, span / 60.0);
+            data.state = 1;
+            data.back_line_vertices.clear();
         }
         "BOUNDARY" => {
             data.state = 2;
@@ -1135,7 +1195,7 @@ fn properties(entity: &ExtendedEntity) -> Vec<PropSection> {
             title: t!("Camera").into_owned(),
             props: vec![ro_prop(t!("View").as_ref(), "ext_camera_view", handle_text(*view_handle))],
         }],
-        ExtendedEntityData::SectionObject(data) => section_properties(data),
+        ExtendedEntityData::SectionObject(data) => section_properties(entity, data),
         ExtendedEntityData::ArcAlignedText(data) => arc_text_properties(data),
         ExtendedEntityData::RemoteText(data) => remote_text_properties(data),
         ExtendedEntityData::GeoPositionMarker(data) => geo_marker_properties(data),
@@ -1282,65 +1342,97 @@ fn set_f64(value: &str, target: &mut f64) {
     }
 }
 
-fn apply_geom_prop(entity: &mut ExtendedEntity, field: &str, value: &str) {
-    match &mut entity.data {
-        ExtendedEntityData::SectionObject(data) => match field {
-            "ext_section_name" => data.name = value.to_string(),
-            "ext_section_state" | "ext_section_state2" => set_section_kind(data, value),
-            "ext_section_viewing" => {
-                if let Some(direction) = parse_vector(value) {
-                    set_viewing_direction(data, direction);
-                }
+fn apply_section_prop(entity: &mut ExtendedEntity, field: &str, value: &str) {
+    let was_slice = section_is_slice(entity);
+    let stored_slice_depth = section_slice_depth(entity).unwrap_or(0.0);
+    let ExtendedEntityData::SectionObject(data) = &mut entity.data else {
+        return;
+    };
+    let mut slice_update = None;
+    match field {
+        "ext_section_name" => data.name = value.to_string(),
+        "ext_section_state" | "ext_section_state2" => {
+            let kind = value.trim().to_ascii_uppercase();
+            let span = data
+                .vertices
+                .first()
+                .zip(data.vertices.last())
+                .map_or(1.0, |(first, last)| (*last - *first).length().max(1e-4));
+            set_section_kind(data, &kind);
+            slice_update = Some((kind == "SLICE", (span / 60.0).max(1e-4)));
+        }
+        "ext_section_viewing" => {
+            if let Some(direction) = parse_vector(value) {
+                set_viewing_direction(data, direction);
             }
-            "ext_section_vertical" => {
-                if let Some(direction) = parse_vector(value) {
-                    let depth = section_depth(data);
-                    let direction = normalized(direction, data.vertical_direction);
-                    if direction.dot(&section_tangent(data)).abs() < 1.0 - 1e-9 {
-                        data.vertical_direction = direction;
-                        if depth > 0.0 {
-                            set_section_depth(data, depth);
-                        }
-                    }
-                }
-            }
-            "ext_section_live" => data.flags ^= 1,
-            "ext_section_alpha" => {
-                if let Ok(alpha) = value.trim().parse::<i16>() {
-                    data.indicator_alpha = alpha.clamp(0, 100);
-                }
-            }
-            "ext_section_elevation" | "ext_section_offset" => {
-                if let Some(offset) = parse_f64(value) {
-                    move_section_to_offset(data, offset);
-                }
-            }
-            "ext_section_top" => {
-                if let Some(height) = parse_f64(value).filter(|height| *height >= 0.0) {
-                    data.top_height = height;
-                }
-            }
-            "ext_section_bottom" => {
-                if let Some(height) = parse_f64(value).filter(|height| *height >= 0.0) {
-                    data.bottom_height = height;
-                }
-            }
-            "ext_section_vertices" => {
-                if let Some(vertices) = parse_vertices(value) {
-                    let depth = section_depth(data);
-                    data.vertices = vertices;
+        }
+        "ext_section_vertical" => {
+            if let Some(direction) = parse_vector(value) {
+                let depth = section_depth(data);
+                let direction = normalized(direction, data.vertical_direction);
+                if direction.dot(&section_tangent(data)).abs() < 1.0 - 1e-9 {
+                    data.vertical_direction = direction;
                     if depth > 0.0 {
                         set_section_depth(data, depth);
                     }
                 }
             }
-            "ext_section_depth" => {
-                if let Some(depth) = parse_f64(value) {
+        }
+        "ext_section_live" => data.flags ^= 1,
+        "ext_section_alpha" => {
+            if let Ok(alpha) = value.trim().parse::<i16>() {
+                data.indicator_alpha = alpha.clamp(0, 100);
+            }
+        }
+        "ext_section_elevation" | "ext_section_offset" => {
+            if let Some(offset) = parse_f64(value) {
+                move_section_to_offset(data, offset);
+            }
+        }
+        "ext_section_top" => {
+            if let Some(height) = parse_f64(value).filter(|height| *height >= 0.0) {
+                data.top_height = height;
+            }
+        }
+        "ext_section_bottom" => {
+            if let Some(height) = parse_f64(value).filter(|height| *height >= 0.0) {
+                data.bottom_height = height;
+            }
+        }
+        "ext_section_vertices" => {
+            if let Some(vertices) = parse_vertices(value) {
+                let depth = section_depth(data);
+                data.vertices = vertices;
+                if depth > 0.0 {
                     set_section_depth(data, depth);
                 }
             }
-            _ => {}
-        },
+        }
+        "ext_section_depth" => {
+            if let Some(depth) = parse_f64(value) {
+                if was_slice {
+                    slice_update = Some((true, depth));
+                } else {
+                    set_section_depth(data, depth);
+                }
+            }
+        }
+        _ => {}
+    }
+
+    if let Some((enabled, depth)) = slice_update {
+        set_section_slice_metadata(entity, enabled, depth);
+    } else if was_slice && field != "ext_section_depth" {
+        set_section_slice_metadata(entity, true, stored_slice_depth);
+    }
+}
+
+fn apply_geom_prop(entity: &mut ExtendedEntity, field: &str, value: &str) {
+    if matches!(entity.data, ExtendedEntityData::SectionObject(_)) {
+        apply_section_prop(entity, field, value);
+        return;
+    }
+    match &mut entity.data {
         ExtendedEntityData::ArcAlignedText(data) => match field {
             "ext_arc_text" => data.text = value.to_string(),
             "ext_arc_font" => data.font_name = value.to_string(),
@@ -1692,6 +1784,8 @@ fn transformed_planar_angle(
 fn apply_transform(entity: &mut ExtendedEntity, requested: &EntityTransform) {
     let transform = entity_transform(requested);
     let scale = scalar_scale(requested);
+    let slice_depth = section_is_slice(entity)
+        .then(|| section_slice_depth(entity).unwrap_or(0.0) * scale);
     match &mut entity.data {
         ExtendedEntityData::SectionObject(data) => {
             for point in data
@@ -1830,6 +1924,9 @@ fn apply_transform(entity: &mut ExtendedEntity, requested: &EntityTransform) {
         }
         _ => {}
     }
+    if let Some(depth) = slice_depth {
+        set_section_slice_metadata(entity, true, depth);
+    }
 }
 
 impl RenderConvertible for ExtendedEntity {

src/modules/model/sectionplane_cmd.rs

@@ -26,8 +26,8 @@ impl SectionKind {
 
     fn state(self) -> i32 {
         match self {
-            Self::Plane => 1,
-            Self::Slice | Self::Boundary => 2,
+            Self::Plane | Self::Slice => 1,
+            Self::Boundary => 2,
             Self::Volume => 4,
         }
     }
@@ -140,12 +140,12 @@ impl SectionPlaneCommand {
             SectionKind::Slice => (span / 60.0).max(1e-4),
             SectionKind::Boundary | SectionKind::Volume => span,
         };
-        let back_line_vertices = if depth > 0.0 {
+        let back_line_vertices = if matches!(self.kind, SectionKind::Boundary | SectionKind::Volume) {
             vertices.iter().map(|point| *point + viewing * depth).collect()
         } else {
             Vec::new()
         };
-        EntityType::Extended(ExtendedEntity {
+        let mut entity = ExtendedEntity {
             common: EntityCommon::new(),
             data: ExtendedEntityData::SectionObject(SectionObjectData {
                 state: self.kind.state(),
@@ -166,7 +166,13 @@ impl SectionPlaneCommand {
                     .collect(),
                 settings_handle: Handle::NULL,
             }),
-        })
+        };
+        crate::entities::extended::set_section_slice_metadata(
+            &mut entity,
+            self.kind == SectionKind::Slice,
+            depth,
+        );
+        EntityType::Extended(entity)
     }
 
     fn line_at(&self, point: DVec3, viewing: DVec3, vertical_hint: DVec3) -> (Vec<DVec3>, DVec3) {
@@ -482,3 +488,50 @@ impl CadCommand for SectionPlaneCommand {
 inventory::submit!(crate::command::CommandRegistration {
     names: &["SECTIONPLANE"]
 });
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn data(entity: &EntityType) -> (&ExtendedEntity, &SectionObjectData) {
+        let EntityType::Extended(entity) = entity else {
+            panic!("expected extended entity");
+        };
+        let ExtendedEntityData::SectionObject(data) = &entity.data else {
+            panic!("expected section object");
+        };
+        (entity, data)
+    }
+
+    #[test]
+    fn slice_uses_persistent_thickness_without_boundary_geometry() {
+        let mut command = SectionPlaneCommand::new(
+            Some((DVec3::ZERO, DVec3::splat(10.0))),
+            3,
+        );
+        command.kind = SectionKind::Slice;
+        let entity = command.entity(vec![DVec3::ZERO, DVec3::Y * 6.0], DVec3::Z, true);
+        let (entity, section) = data(&entity);
+
+        assert_eq!(section.state, 1);
+        assert!(section.back_line_vertices.is_empty());
+        assert!(crate::entities::extended::section_is_slice(entity));
+        assert!((crate::entities::extended::section_slice_depth(entity).unwrap() - 0.1).abs()
+            < 1e-12);
+    }
+
+    #[test]
+    fn boundary_keeps_a_real_back_line_and_no_slice_marker() {
+        let mut command = SectionPlaneCommand::new(
+            Some((DVec3::ZERO, DVec3::splat(10.0))),
+            1,
+        );
+        command.kind = SectionKind::Boundary;
+        let entity = command.entity(vec![DVec3::ZERO, DVec3::Y * 6.0], DVec3::Z, true);
+        let (entity, section) = data(&entity);
+
+        assert_eq!(section.state, 2);
+        assert_eq!(section.back_line_vertices.len(), section.vertices.len());
+        assert!(!crate::entities::extended::section_is_slice(entity));
+    }
+}

src/scene/convert/solid3d_tess.rs

@@ -167,7 +167,7 @@ pub fn kernel_surface_body(surface: &Surface) -> Option<KernelBody> {
     kernel_acis_body(&surface.acis_data)
 }
 
-fn kernel_acis_body(acis: &acadrust::entities::AcisData) -> Option<KernelBody> {
+pub(crate) fn kernel_acis_body(acis: &acadrust::entities::AcisData) -> Option<KernelBody> {
     let sat = parse_acis(
         || acis.parse(),
         acis.is_binary,

src/scene/entity.rs

@@ -143,6 +143,106 @@ impl Scene {
         let _ = self.document.app_ids.add(app_id);
     }
 
+    fn prepare_section_objects(&mut self, entity: &mut EntityType) -> bool {
+        use acadrust::entities::ExtendedEntityData;
+        use acadrust::objects::{
+            ClassObject, ClassObjectData, SectionManager, SectionSettings,
+            SectionTypeSettings,
+        };
+
+        let EntityType::Extended(extended) = entity else {
+            return false;
+        };
+        let ExtendedEntityData::SectionObject(data) = &mut extended.data else {
+            return false;
+        };
+
+        if extended.common.handle.is_null() {
+            extended.common.handle = self.document.allocate_handle();
+        }
+        let entity_handle = extended.common.handle;
+
+        let valid_settings = matches!(
+            self.document.objects.get(&data.settings_handle),
+            Some(ObjectType::ClassObject(object))
+                if matches!(&object.data, ClassObjectData::SectionSettings(_))
+        );
+        if !valid_settings {
+            let settings_handle = self.document.allocate_handle();
+            let mut settings = ClassObject::new(ClassObjectData::SectionSettings(
+                SectionSettings {
+                    current_type: 4,
+                    types: vec![SectionTypeSettings {
+                        section_type: 4,
+                        generation: 17,
+                        ..SectionTypeSettings::default()
+                    }],
+                },
+            ));
+            settings.handle = settings_handle;
+            settings.owner = entity_handle;
+            self.document
+                .objects
+                .insert(settings_handle, ObjectType::ClassObject(settings));
+            data.settings_handle = settings_handle;
+        } else if let Some(ObjectType::ClassObject(settings)) =
+            self.document.objects.get_mut(&data.settings_handle)
+        {
+            settings.owner = entity_handle;
+        }
+
+        let root = crate::scene::annotative::root_named_dict_handle(&mut self.document);
+        let manager_handle = self
+            .document
+            .objects
+            .get(&root)
+            .and_then(|object| match object {
+                ObjectType::Dictionary(dictionary) => dictionary
+                    .entries
+                    .iter()
+                    .find(|(name, _)| name.eq_ignore_ascii_case("ACAD_SECTION_MANAGER"))
+                    .map(|(_, handle)| *handle),
+                _ => None,
+            })
+            .filter(|handle| {
+                matches!(
+                    self.document.objects.get(handle),
+                    Some(ObjectType::ClassObject(object))
+                        if matches!(&object.data, ClassObjectData::SectionManager(_))
+                )
+            })
+            .unwrap_or_else(|| {
+                let handle = self.document.allocate_handle();
+                let mut manager =
+                    ClassObject::new(ClassObjectData::SectionManager(SectionManager::default()));
+                manager.handle = handle;
+                manager.owner = root;
+                self.document
+                    .objects
+                    .insert(handle, ObjectType::ClassObject(manager));
+                if let Some(ObjectType::Dictionary(dictionary)) =
+                    self.document.objects.get_mut(&root)
+                {
+                    dictionary.entries.retain(|(name, _)| {
+                        !name.eq_ignore_ascii_case("ACAD_SECTION_MANAGER")
+                    });
+                    dictionary.add_entry("ACAD_SECTION_MANAGER", handle);
+                }
+                handle
+            });
+        if let Some(ObjectType::ClassObject(manager)) =
+            self.document.objects.get_mut(&manager_handle)
+        {
+            manager.owner = root;
+            if let ClassObjectData::SectionManager(manager) = &mut manager.data {
+                if !manager.sections.contains(&entity_handle) {
+                    manager.sections.push(entity_handle);
+                }
+            }
+        }
+        true
+    }
+
     pub fn add_entity(&mut self, entity: EntityType) -> Handle {
         self.add_entity_internal(entity, true)
     }
@@ -195,6 +295,7 @@ impl Scene {
         // bookkeeping and remains in place while an entity delta is undone.
         let mutates_block_structure =
             matches!(&entity, EntityType::Block(_) | EntityType::BlockEnd(_));
+        let creates_section_structure = self.prepare_section_objects(&mut entity);
         let hatch_seed = if let EntityType::Hatch(dxf) = &entity {
             let color = self.render_style(&entity).0;
             Self::hatch_model_from_dxf(dxf, color)
@@ -337,7 +438,11 @@ impl Scene {
             // state (a new layer, application ID, or block).
             if self.is_recording_undo() {
                 self.record_undo_before(handle, None);
-                if creates_layer || creates_app_id || mutates_block_structure {
+                if creates_layer
+                    || creates_app_id
+                    || mutates_block_structure
+                    || creates_section_structure
+                {
                     self.poison_undo_recording();
                 }
             }

src/scene/mod.rs

@@ -2040,6 +2040,53 @@ fn section_frame(
     Some((origin, tangent, vertical, viewing))
 }
 
+#[derive(Clone)]
+struct LiveSection {
+    data: acadrust::entities::SectionObjectData,
+    slice_depth: Option<f64>,
+}
+
+fn section_plane(
+    origin: glam::DVec3,
+    tangent: glam::DVec3,
+    normal: glam::DVec3,
+    body_to_world: Option<&acadrust::types::Transform>,
+) -> Option<cadkernel::space::Plane> {
+    let Some(transform) = body_to_world else {
+        return cadkernel::space::Plane::orthonormal(
+            origin.to_array(),
+            tangent.to_array(),
+            normal.to_array(),
+        );
+    };
+    let matrix = transform.matrix.m;
+    let linear = acadrust::types::Matrix3::from_rows(
+        [matrix[0][0], matrix[0][1], matrix[0][2]],
+        [matrix[1][0], matrix[1][1], matrix[1][2]],
+        [matrix[2][0], matrix[2][1], matrix[2][2]],
+    );
+    let inverse = linear.inverse()?;
+    let translation = acadrust::types::Vector3::new(
+        matrix[0][3],
+        matrix[1][3],
+        matrix[2][3],
+    );
+    let origin = inverse.transform_point(
+        acadrust::types::Vector3::new(origin.x, origin.y, origin.z) - translation,
+    );
+    let tangent = inverse.transform_point(acadrust::types::Vector3::new(
+        tangent.x, tangent.y, tangent.z,
+    ));
+    let normal = linear
+        .transpose()
+        .transform_point(acadrust::types::Vector3::new(normal.x, normal.y, normal.z));
+    cadkernel::space::Plane::orthonormal(
+        [origin.x, origin.y, origin.z],
+        [tangent.x, tangent.y, tangent.z],
+        [normal.x, normal.y, normal.z],
+    )
+}
+
 fn keep_section_positive(
     body: &cadkernel::brep::Body,
     plane: cadkernel::space::Plane,
@@ -6906,6 +6953,7 @@ impl Scene {
             annotation_scale_handle,
             all_visible,
             viewport,
+            live_section.as_ref(),
         ));
         all
     }
@@ -6913,7 +6961,7 @@ impl Scene {
     fn active_live_section(
         &self,
         target_block: Handle,
-    ) -> Option<acadrust::entities::SectionObjectData> {
+    ) -> Option<LiveSection> {
         self.document
             .entities()
             .filter_map(|entity| {
@@ -6927,7 +6975,14 @@ impl Scene {
                 (data.flags & 1 != 0
                     && !extended.common.invisible
                     && (owner.is_null() || owner == target_block))
-                    .then(|| data.clone())
+                    .then(|| LiveSection {
+                        data: data.clone(),
+                        slice_depth: crate::entities::extended::section_is_slice(extended)
+                            .then(|| {
+                                crate::entities::extended::section_slice_depth(extended)
+                                    .unwrap_or(0.0)
+                            }),
+                    })
             })
             .last()
     }
@@ -6935,43 +6990,74 @@ impl Scene {
     fn sectioned_body(
         &self,
         handle: Handle,
+        section: &LiveSection,
+    ) -> Result<Option<cadkernel::brep::Body>, ()> {
+        let body = self.section_source_body(handle).ok_or(())?;
+        Self::section_body(&body, &section.data, section.slice_depth, None)
+    }
+
+    fn section_source_body(
+        &self,
+        handle: Handle,
+    ) -> Option<std::borrow::Cow<'_, cadkernel::brep::Body>> {
+        if let Some(body) = self.solid_models.get(&handle) {
+            return Some(std::borrow::Cow::Borrowed(body));
+        }
+        let body = match self.document.get_entity(handle) {
+            Some(EntityType::Solid3D(solid)) => {
+                crate::scene::convert::solid3d_tess::kernel_body(solid)
+            }
+            Some(EntityType::Region(region)) => {
+                crate::scene::convert::solid3d_tess::kernel_region_body(region)
+            }
+            Some(EntityType::Body(body)) => {
+                crate::scene::convert::solid3d_tess::kernel_acis_body(&body.acis_data)
+            }
+            Some(EntityType::Surface(surface)) => {
+                crate::scene::convert::solid3d_tess::kernel_surface_body(surface)
+            }
+            _ => None,
+        }?;
+        Some(std::borrow::Cow::Owned(body))
+    }
+
+    fn section_body(
+        body: &cadkernel::brep::Body,
         data: &acadrust::entities::SectionObjectData,
+        slice_depth: Option<f64>,
+        body_to_world: Option<&acadrust::types::Transform>,
     ) -> Result<Option<cadkernel::brep::Body>, ()> {
-        let body = self.solid_models.get(&handle).ok_or(())?;
         let Some((origin, tangent, vertical, viewing)) = section_frame(data) else {
             return Err(());
         };
-        let front = cadkernel::space::Plane::orthonormal(
-            origin.to_array(),
-            tangent.to_array(),
-            viewing.to_array(),
-        )
-        .ok_or(())?;
+        let front = section_plane(origin, tangent, viewing, body_to_world).ok_or(())?;
         let mut clipped = keep_section_positive(body, front)?;
         let Some(mut current) = clipped.take() else {
             return Ok(None);
         };
-        if data.state == 1 {
+        if data.state == 1 && slice_depth.is_none() {
             return Ok(Some(current));
         }
 
-        let depth = data
-            .vertices
-            .first()
-            .zip(data.back_line_vertices.first())
-            .map_or(0.0, |(front, back)| {
-                (glam::DVec3::new(back.x, back.y, back.z)
-                    - glam::DVec3::new(front.x, front.y, front.z))
-                .dot(viewing)
-                .abs()
-            });
+        let depth = slice_depth.unwrap_or_else(|| {
+            data.vertices
+                .first()
+                .zip(data.back_line_vertices.first())
+                .map_or(0.0, |(front, back)| {
+                    (glam::DVec3::new(back.x, back.y, back.z)
+                        - glam::DVec3::new(front.x, front.y, front.z))
+                    .dot(viewing)
+                    .abs()
+                })
+        });
         if depth <= 1e-12 {
             return Ok(Some(current));
         }
-        let back = cadkernel::space::Plane::orthonormal(
-            (origin + viewing * depth).to_array(),
-            tangent.to_array(),
-            (-viewing).to_array(),
+        let back = section_plane(
+            origin + viewing * depth,
+            tangent,
+            -viewing,
+            body_to_world,
         )
         .ok_or(())?;
         let Some(next) = keep_section_positive(&current, back)? else {
@@ -6979,6 +7065,10 @@ impl Scene {
         };
         current = next;
 
+        if data.state == 1 {
+            return Ok(Some(current));
+        }
+
         let span = data
             .vertices
             .first()
@@ -6988,25 +7078,41 @@ impl Scene {
                     - glam::DVec3::new(first.x, first.y, first.z))
                 .length()
             });
-        let bounded = data.state == 4 || (data.state == 2 && depth >= span * 0.25);
-        if !bounded || span <= 1e-12 {
+        if span <= 1e-12 {
             return Ok(Some(current));
         }
 
         let first = data.vertices.first().map(|point| glam::DVec3::new(point.x, point.y, point.z)).ok_or(())?;
         let last = data.vertices.last().map(|point| glam::DVec3::new(point.x, point.y, point.z)).ok_or(())?;
         for plane in [
-            cadkernel::space::Plane::orthonormal(first.to_array(), vertical.to_array(), tangent.to_array()),
-            cadkernel::space::Plane::orthonormal(last.to_array(), vertical.to_array(), (-tangent).to_array()),
-            cadkernel::space::Plane::orthonormal(
-                (origin - vertical * data.bottom_height).to_array(),
-                tangent.to_array(),
-                vertical.to_array(),
+            section_plane(first, vertical, tangent, body_to_world),
+            section_plane(last, vertical, -tangent, body_to_world),
+        ] {
+            let Some(plane) = plane else {
+                return Err(());
+            };
+            let Some(next) = keep_section_positive(&current, plane)? else {
+                return Ok(None);
+            };
+            current = next;
+        }
+
+        if data.state != 4 {
+            return Ok(Some(current));
+        }
+
+        for plane in [
+            section_plane(
+                origin - vertical * data.bottom_height,
+                tangent,
+                vertical,
+                body_to_world,
             ),
-            cadkernel::space::Plane::orthonormal(
-                (origin + vertical * data.top_height).to_array(),
-                tangent.to_array(),
-                (-vertical).to_array(),
+            section_plane(
+                origin + vertical * data.top_height,
+                tangent,
+                -vertical,
+                body_to_world,
             ),
         ] {
             let Some(plane) = plane else {
@@ -7299,6 +7405,7 @@ impl Scene {
         annotation_scale_handle: Option<Handle>,
         all_visible: bool,
         viewport: Option<Handle>,
+        live_section: Option<&LiveSection>,
     ) -> Vec<MeshLodSet> {
         if self.block_meshes.is_empty() {
             return Vec::new();
@@ -7325,9 +7432,37 @@ impl Scene {
                     return;
                 }
                 let handle = entity.common().handle;
-                let Some(set) = self.block_meshes.get(&handle) else {
+                let Some(original) = self.block_meshes.get(&handle) else {
                     return;
                 };
+                let sectioned;
+                let set = if let Some((section, body)) = live_section.and_then(|section| {
+                    self.section_source_body(handle)
+                        .map(|body| (section, body))
+                }) {
+                    match Self::section_body(
+                        &body,
+                        &section.data,
+                        section.slice_depth,
+                        Some(&context.transform),
+                    ) {
+                        Ok(Some(body)) => {
+                            if let Some((mut mesh, _, _)) =
+                                self.prepare_solid_model_display(handle, &body)
+                            {
+                                mesh.prepare_instance_source(handle);
+                                sectioned = mesh;
+                                &sectioned
+                            } else {
+                                original
+                            }
+                        }
+                        Ok(None) => return,
+                        Err(()) => original,
+                    }
+                } else {
+                    original
+                };
                 let inherit = self.mesh_inherit_for_path(&context.insert_path);
                 let own_alpha = set.display_color().map_or(1.0, |color| color[3]);
                 let mut transformed =
@@ -10698,6 +10833,169 @@ impl Default for Scene {
     }
 }
 
+#[cfg(test)]
+mod section_tests {
+    use super::*;
+    use acadrust::entities::{
+        EntityCommon, ExtendedEntity, ExtendedEntityData, SectionObjectData, Solid3D,
+    };
+    use acadrust::objects::ClassObjectData;
+    use acadrust::types::{Color, Vector3};
+
+    fn section(state: i32, depth: f64) -> SectionObjectData {
+        let vertices = vec![Vector3::new(5.0, 2.0, 5.0), Vector3::new(5.0, 8.0, 5.0)];
+        SectionObjectData {
+            state,
+            flags: 5,
+            name: "Section Plane (1)".to_string(),
+            vertical_direction: Vector3::UNIT_Z,
+            top_height: 1.0,
+            bottom_height: 2.0,
+            indicator_alpha: 70,
+            indicator_color: Color::from_index(9),
+            back_line_vertices: (depth > 0.0)
+                .then(|| {
+                    vertices
+                        .iter()
+                        .map(|point| *point + Vector3::new(-depth, 0.0, 0.0))
+                        .collect()
+                })
+                .unwrap_or_default(),
+            vertices,
+            settings_handle: Handle::NULL,
+        }
+    }
+
+    fn bounds(body: Option<cadkernel::brep::Body>) -> ([f64; 3], [f64; 3]) {
+        let body = body.expect("section should retain material");
+        assert!(body.validate().is_empty());
+        let bounds = cadkernel::brep::body_bounds(&body).expect("sectioned body should be bounded");
+        (bounds.min, bounds.max)
+    }
+
+    fn assert_near(actual: [f64; 3], expected: [f64; 3]) {
+        for (actual, expected) in actual.into_iter().zip(expected) {
+            assert!((actual - expected).abs() < 1e-8, "{actual} != {expected}");
+        }
+    }
+
+    #[test]
+    fn kernel_clipping_obeys_plane_slice_boundary_and_volume_limits() {
+        let body = cadkernel::brep::make::cuboid([0.0; 3], [10.0; 3]).unwrap();
+
+        let (min, max) = bounds(Scene::section_body(&body, &section(1, 0.0), None, None).unwrap());
+        assert_near(min, [0.0, 0.0, 0.0]);
+        assert_near(max, [5.0, 10.0, 10.0]);
+
+        let (min, max) = bounds(
+            Scene::section_body(&body, &section(1, 0.0), Some(2.0), None).unwrap(),
+        );
+        assert_near(min, [3.0, 0.0, 0.0]);
+        assert_near(max, [5.0, 10.0, 10.0]);
+
+        let (min, max) = bounds(Scene::section_body(&body, &section(2, 4.0), None, None).unwrap());
+        assert_near(min, [1.0, 2.0, 0.0]);
+        assert_near(max, [5.0, 8.0, 10.0]);
+
+        let (min, max) = bounds(Scene::section_body(&body, &section(4, 4.0), None, None).unwrap());
+        assert_near(min, [1.0, 2.0, 3.0]);
+        assert_near(max, [5.0, 8.0, 6.0]);
+    }
+
+    #[test]
+    fn instance_transform_pulls_the_section_plane_into_body_space() {
+        let body = cadkernel::brep::make::cuboid([0.0; 3], [10.0; 3]).unwrap();
+        let transform = acadrust::types::Transform::from_scaling(
+            acadrust::types::Vector3::new(2.0, 1.0, 1.0),
+        )
+        .then(&acadrust::types::Transform::from_translation(
+            acadrust::types::Vector3::new(10.0, 0.0, 0.0),
+        ));
+        let mut data = section(1, 0.0);
+        for point in &mut data.vertices {
+            point.x = 20.0;
+        }
+
+        let (min, max) = bounds(
+            Scene::section_body(&body, &data, None, Some(&transform)).unwrap(),
+        );
+        assert_near(min, [0.0, 0.0, 0.0]);
+        assert_near(max, [5.0, 10.0, 10.0]);
+    }
+
+    #[test]
+    fn adding_and_erasing_a_section_keeps_its_object_graph_consistent() {
+        let mut scene = Scene::new();
+        let handle = scene.add_entity(EntityType::Extended(ExtendedEntity {
+            common: EntityCommon::new(),
+            data: ExtendedEntityData::SectionObject(section(1, 0.0)),
+        }));
+        let settings_handle = match scene.document.get_entity(handle).unwrap() {
+            EntityType::Extended(ExtendedEntity {
+                data: ExtendedEntityData::SectionObject(data),
+                ..
+            }) => data.settings_handle,
+            _ => unreachable!(),
+        };
+        assert!(matches!(
+            scene.document.objects.get(&settings_handle),
+            Some(ObjectType::ClassObject(object))
+                if object.owner == handle
+                    && matches!(&object.data, ClassObjectData::SectionSettings(_))
+        ));
+
+        let root = scene.document.header.named_objects_dict_handle;
+        let manager_handle = match scene.document.objects.get(&root).unwrap() {
+            ObjectType::Dictionary(dictionary) => dictionary
+                .entries
+                .iter()
+                .find(|(name, _)| name == "ACAD_SECTION_MANAGER")
+                .map(|(_, handle)| *handle)
+                .unwrap(),
+            _ => panic!("root must be a dictionary"),
+        };
+        assert!(matches!(
+            scene.document.objects.get(&manager_handle),
+            Some(ObjectType::ClassObject(object))
+                if matches!(&object.data, ClassObjectData::SectionManager(manager)
+                    if manager.sections == vec![handle])
+        ));
+
+        scene.erase_entities(&[handle]);
+        assert!(!scene.document.objects.contains_key(&settings_handle));
+        assert!(matches!(
+            scene.document.objects.get(&manager_handle),
+            Some(ObjectType::ClassObject(object))
+                if matches!(&object.data, ClassObjectData::SectionManager(manager)
+                    if manager.sections.is_empty())
+        ));
+    }
+
+    #[test]
+    fn live_section_rebuilds_an_uncached_persisted_solid() {
+        let body = cadkernel::brep::make::cuboid([0.0; 3], [10.0; 3]).unwrap();
+        let sat = crate::scene::convert::acis_export::solid_to_sat(&body).unwrap();
+        let mut solid = Solid3D::new();
+        solid.set_sat_document(&sat);
+        let mut scene = Scene::new();
+        let handle = scene.add_entity(EntityType::Solid3D(solid));
+        assert!(!scene.solid_models.contains_key(&handle));
+
+        let clipped = scene
+            .sectioned_body(
+                handle,
+                &LiveSection {
+                    data: section(1, 0.0),
+                    slice_depth: None,
+                },
+            )
+            .unwrap();
+        let (min, max) = bounds(clipped);
+        assert_near(min, [0.0, 0.0, 0.0]);
+        assert_near(max, [5.0, 10.0, 10.0]);
+    }
+}
+
 #[cfg(test)]
 mod journal_tests {
     use super::*;

src/scene/selection.rs

@@ -938,12 +938,57 @@ impl Scene {
             if respect_layer_locks && self.is_layer_locked(h) {
                 continue;
             }
+            let settings_handle = self.document.get_entity(h).and_then(|entity| match entity {
+                EntityType::Extended(acadrust::entities::ExtendedEntity {
+                    data: acadrust::entities::ExtendedEntityData::SectionObject(data),
+                    ..
+                }) if !data.settings_handle.is_null() => Some(data.settings_handle),
+                _ => None,
+            });
+            let section_managers: Vec<Handle> = self
+                .document
+                .objects
+                .iter()
+                .filter_map(|(handle, object)| match object {
+                    ObjectType::ClassObject(object) => match &object.data {
+                        acadrust::objects::ClassObjectData::SectionManager(manager)
+                            if manager.sections.contains(&h) =>
+                        {
+                            Some(*handle)
+                        }
+                        _ => None,
+                    },
+                    _ => None,
+                })
+                .collect();
             // Delta-undo: capture the removed entity so an undo can re-insert it.
             if self.is_recording_undo() {
                 let before = self.document.get_entity_arc(h);
                 self.record_undo_before(h, before);
+                if let Some(settings_handle) = settings_handle {
+                    let before = self.document.objects.get(&settings_handle).cloned();
+                    self.record_undo_object_before(settings_handle, before);
+                }
+                for &manager_handle in &section_managers {
+                    let before = self.document.objects.get(&manager_handle).cloned();
+                    self.record_undo_object_before(manager_handle, before);
+                }
             }
             self.delete_solid_history(h);
+            if let Some(settings_handle) = settings_handle {
+                self.document.objects.remove(&settings_handle);
+            }
+            for manager_handle in section_managers {
+                if let Some(ObjectType::ClassObject(object)) =
+                    self.document.objects.get_mut(&manager_handle)
+                {
+                    if let acadrust::objects::ClassObjectData::SectionManager(manager) =
+                        &mut object.data
+                    {
+                        manager.sections.retain(|section| *section != h);
+                    }
+                }
+            }
             self.remember_removed_cache_categories(h);
             self.document.remove_entity_arc(h);
             selection_changed |= self.selected.remove(&h);

tests/section_plane_roundtrip.rs

@@ -0,0 +1,110 @@
+use acadrust::entities::{EntityCommon, ExtendedEntity, ExtendedEntityData, SectionObjectData};
+use acadrust::objects::{ClassObjectData, ObjectType};
+use acadrust::types::{Color, Handle, Vector3};
+use acadrust::xdata::{ExtendedDataRecord, XDataValue};
+use acadrust::EntityType;
+use OpenCADStudio::scene::Scene;
+
+fn add_slice(scene: &mut Scene) -> Handle {
+    let mut common = EntityCommon::new();
+    let mut slice = ExtendedDataRecord::new("IsSlice");
+    slice.values = vec![XDataValue::Integer16(0), XDataValue::Integer16(1)];
+    common.extended_data.add_record(slice);
+    let mut thickness = ExtendedDataRecord::new("ThicknessDepth");
+    thickness.values = vec![XDataValue::Real(0.75)];
+    common.extended_data.add_record(thickness);
+
+    scene.add_entity(EntityType::Extended(ExtendedEntity {
+        common,
+        data: ExtendedEntityData::SectionObject(SectionObjectData {
+            state: 1,
+            flags: 5,
+            name: "Section Plane (1)".to_string(),
+            vertical_direction: Vector3::UNIT_Z,
+            top_height: 5.0,
+            bottom_height: 5.0,
+            indicator_alpha: 70,
+            indicator_color: Color::from_index(9),
+            vertices: vec![Vector3::ZERO, Vector3::new(10.0, 0.0, 0.0)],
+            back_line_vertices: Vec::new(),
+            settings_handle: Handle::NULL,
+        }),
+    }))
+}
+
+fn assert_section_graph(document: &acadrust::CadDocument, extension: &str) {
+    let (handle, section) = document
+        .entities()
+        .find_map(|entity| match entity {
+            EntityType::Extended(extended) => match &extended.data {
+                ExtendedEntityData::SectionObject(_) => Some((extended.common.handle, extended)),
+                _ => None,
+            },
+            _ => None,
+        })
+        .unwrap_or_else(|| panic!("section entity should round-trip through {extension}"));
+    let ExtendedEntityData::SectionObject(data) = &section.data else {
+        unreachable!();
+    };
+    assert_eq!(data.state, 1);
+    assert!(data.back_line_vertices.is_empty());
+    assert!(matches!(
+        section
+            .common
+            .extended_data
+            .get_record("IsSlice")
+            .map(|record| record.values.as_slice()),
+        Some([XDataValue::Integer16(0), XDataValue::Integer16(1)])
+    ));
+    assert!(matches!(
+        section
+            .common
+            .extended_data
+            .get_record("ThicknessDepth")
+            .and_then(|record| record.values.first()),
+        Some(XDataValue::Real(value)) if (*value - 0.75).abs() < 1e-12
+    ));
+    assert!(matches!(
+        document.objects.get(&data.settings_handle),
+        Some(ObjectType::ClassObject(object))
+            if object.owner == handle
+                && matches!(&object.data, ClassObjectData::SectionSettings(_))
+    ));
+
+    let root = document
+        .objects
+        .get(&document.header.named_objects_dict_handle)
+        .expect("root dictionary should round-trip");
+    let ObjectType::Dictionary(root) = root else {
+        panic!("root should be a dictionary");
+    };
+    let manager_handle = root
+        .entries
+        .iter()
+        .find(|(name, _)| name == "ACAD_SECTION_MANAGER")
+        .map(|(_, handle)| *handle)
+        .expect("section manager should be registered");
+    let Some(ObjectType::ClassObject(manager)) = document.objects.get(&manager_handle) else {
+        panic!("section manager handle should resolve");
+    };
+    let ClassObjectData::SectionManager(manager) = &manager.data else {
+        panic!("registered object should be a section manager");
+    };
+    assert_eq!(manager.sections, vec![handle]);
+}
+
+#[test]
+fn section_plane_graph_survives_dxf_and_dwg_roundtrips() {
+    let mut scene = Scene::new();
+    add_slice(&mut scene);
+
+    for extension in ["dxf", "dwg"] {
+        let bytes =
+            OpenCADStudio::io::save_to_bytes(&scene.document, extension, scene.document.version)
+                .expect("section document should save");
+        let document =
+            OpenCADStudio::io::load_bytes(&format!("section-roundtrip.{extension}"), bytes)
+                .expect("section document should reload");
+        assert_section_graph(&document, extension);
+    }
+}