Complete Region: create from a profile, plus tuple and int friendliness

RegionFromProfile reuses the REGION command's kernel calls; doc.solids.region
exposes it with layer and delete_source options. The lifecycle test builds
regions from real circle and polyline entities and covers refusals, a move,
both formats and undo. create_entity now accepts coordinate tuples for point
properties and every generated float setter accepts Python ints.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

crates/ocs_plugin_api/src/host.rs

@@ -85,6 +85,11 @@ pub enum SolidOperation {
     /// Apply a rigid transform, given as a column-major 4x4 matrix, to an
     /// existing solid. Scaling and shear are refused.
     Transform { handle: Handle, matrix: [f64; 16] },
+    /// Build a planar region from one closed planar profile entity (a circle,
+    /// ellipse, closed polyline or spline, ...). The new region goes on
+    /// `layer`, or on the source's layer when `None`; `delete_source` erases
+    /// the profile afterwards, as the REGION command does.
+    RegionFromProfile { source: Handle, layer: Option<String>, delete_source: bool },
 }
 
 /// Value of a host-managed drafting or document setting exposed to plugins.

crates/ocs_plugin_api/src/ipc/v4/protocol.rs

@@ -114,6 +114,7 @@ mod tests {
                 layer: Some("SOLIDS".into()),
             },
             SolidOperation::Transform { handle: acadrust::Handle::new(7), matrix: [1.0; 16] },
+            SolidOperation::RegionFromProfile { source: acadrust::Handle::new(3), layer: None, delete_source: true },
         ] {
             let bytes = bincode::serialize(&PluginRequest::SolidOperation { operation: operation.clone() }).unwrap();
             assert!(matches!(bincode::deserialize::<PluginRequest>(&bytes).unwrap(),

docs/cadkernel-body-path.md

@@ -136,4 +136,4 @@ is refused with a clear message instead of being rewritten.
 
 Phase 1 alone would move Solid3D from blocked to complete-in-OCS.
 
-**Status (2026-09-20): phase 1 is done.** `HostApi::solid_operation` (create primitive and rigid transform), the `doc.solids` Python API and `audit_python_solid3d_lifecycle_over_real_ipc` are in; Solid3D is complete, Body moves through the same channel. Design B was implemented as recommended. Booleans, Region creation and Surface remain.
+**Status (2026-09-20): phase 1 is done.** `HostApi::solid_operation` (create primitive and rigid transform), the `doc.solids` Python API and `audit_python_solid3d_lifecycle_over_real_ipc` are in; Solid3D is complete, Body moves through the same channel. Design B was implemented as recommended. Region creation from a closed profile followed (`RegionFromProfile`). Booleans and Surface remain.

docs/plugin-host-model-completion-plan.md

@@ -7,9 +7,9 @@ Build a general Python document model over the OCS host API for all **43 canvas
 As of 20 September 2026, the working branch is `plugin/host-model-api` at
 `a8dd3640` plus the Leader increment, published as draft PR
 [#1391](https://github.com/HakanSeven12/OpenCADStudio/pull/1391). Host API is
-v7. The Python feature has explicit writes for **41 of 43** canvas kinds: 37
+v7. The Python feature has explicit writes for **41 of 43** canvas kinds: 38
-are creatable (the legacy `Polyline`, `Ole2Frame`, `Body` and `Region` are update-only). This is **not** 41 completed
+are creatable (the legacy `Polyline`, `Ole2Frame` and `Body` are update-only). This is **not** 41 completed
-kinds: Tolerance, Shape, AttributeEntity, Hatch, MLine, Dimension, MultiLeader, Table, PolygonMesh, PolyfaceMesh, Mesh, Wipeout, Point, Line, Circle, Arc, Ellipse, LwPolyline, Spline, Text, MText, Ray, XLine, Solid, Face3D and Solid3D pass every completion gate; Insert now passes every gate too; the audited Polyline (update-only by decision), Polyline2D and Polyline3D pass every gate that their format allows.
+kinds: Tolerance, Shape, AttributeEntity, Hatch, MLine, Dimension, MultiLeader, Table, PolygonMesh, PolyfaceMesh, Mesh, Wipeout, Point, Line, Circle, Arc, Ellipse, LwPolyline, Spline, Text, MText, Ray, XLine, Solid, Face3D, Solid3D and Region pass every completion gate; Insert now passes every gate too; the audited Polyline (update-only by decision), Polyline2D and Polyline3D pass every gate that their format allows.
 AttributeDefinition passes its host and real IPC lifecycle but remains short of
 `Complete` because the previously pinned CAD codec dropped optional ATTDEF
 fields during DXF reads; revalidate that blocker against the current
@@ -178,3 +178,4 @@ exact queue above and update statuses with evidence after each increment.
 - Mapped `Ole2Frame` as update-only (queue item 21, previously blocked). OCS already builds real embedded frames (`build_embedded_ole`), which supplied the fixture the blocker was waiting for. Frame corners and the aspect lock are scriptable; the opaque storage and envelope are excluded and refused on edit. The audit proves the embedded picture survives DWG and DXF unchanged. Creation from Python remains a follow-up. The remaining blocked kinds are SectionSymbol, Region, Body, Solid3D and Surface.
 - Investigated the cadkernel path for the ACIS kinds ([cadkernel-body-path.md](cadkernel-body-path.md)). The earlier "blocked" reasoning was overstated: OCS already builds primitives, transforms bodies and runs booleans through cadkernel, and `solid_to_sat` plus `kernel_acis_body` verify each result lifts back with no loss. Two `#[ignore]` spike tests measured exact volumes and DWG and DXF round trips for a box, moved, rotated and mirrored copies, three booleans, four other primitives and a `Body` entity. The real gap is an operation channel from a script to that pipeline; the note recommends an additive `solid_operation` host method and a phased plan (Solid3D create and transform, then booleans and Body, then Region, then Surface). Booleans took about 23 s each in a debug build and need release timing first. Region, Body, Solid3D and Surface move from blocked to unblocked-by-design; SectionSymbol stays blocked.
 - Built the cadkernel operation channel and completed `Solid3D` (create and rigid move). `HostApi::solid_operation` is additive (default "unsupported"), so older hosts and plugins are unaffected; it travels as `PluginRequest::SolidOperation` and `PluginResponse::SolidResult`, and the host records its own undo step only after validation so a refused operation leaves nothing behind. The Python surface is `doc.solids.*`. Every result is verified lossless by the kernel path before it is accepted and a payload that will not lift is refused untouched. `Body` moves through the same channel and `Region` is accepted but untested. Booleans, Region creation from curves and Surface remain, in that order; booleans wait on release-build timing. Solid3D, Body and Region are now mapped read-only with the opaque payload excluded and preserved.
+- Completed `Region`. `SolidOperation::RegionFromProfile` reuses the REGION command's kernel calls and `doc.solids.region` exposes it; the lifecycle test creates regions from real circle and polyline entities and covers deletion of the source, refusals, a move, both formats and undo. Along the way `create_entity` now accepts `(x, y, z)` tuples for point properties (decided from the schema's property types) and every generated float setter accepts Python ints, so `create_entity('Circle', center=(0, 0, 0), radius=5)` works. Left: booleans (release timing first), holes and open-curve merging for regions, and `Surface`.

docs/plugin-host-model-coverage-ledger.md

@@ -1,6 +1,6 @@
 # OCS canvas kind coverage ledger
 
-Use with [the completion plan](plugin-host-model-completion-plan.md). This ledger is current as of 20 September 2026: **41 of 43 canvas kinds have explicit geometry writes** (37 creatable, plus update-only legacy `Polyline`, `Ole2Frame`, `Body` and `Region`), **27 kinds are complete**, and 2 remain layer-only (SectionSymbol blocked, Surface unblocked by design). `Mapped` means at least one non-layer field is exposed for Python writes; it does **not** mean the kind passes the completion gate. `Update-only` means Python creation is unavailable. `Layer-only` means raw inspection and canvas layer edits exist, but geometry is not mapped. Record actual evidence or a blocking issue before changing any status to `Complete`.
+Use with [the completion plan](plugin-host-model-completion-plan.md). This ledger is current as of 20 September 2026: **41 of 43 canvas kinds have explicit geometry writes** (38 creatable, plus update-only legacy `Polyline`, `Ole2Frame` and `Body`), **28 kinds are complete**, and 2 remain layer-only (SectionSymbol blocked, Surface unblocked by design). `Mapped` means at least one non-layer field is exposed for Python writes; it does **not** mean the kind passes the completion gate. `Update-only` means Python creation is unavailable. `Layer-only` means raw inspection and canvas layer edits exist, but geometry is not mapped. Record actual evidence or a blocking issue before changing any status to `Complete`.
 
 Completion gate codes: **C** = create through Python document model; **R** = read; **E** = edit defining geometry and another property; **D** = delete; **U** = undo/redo and atomic failure; **I** = real IPC plus GUI/canvas pick or observable behavior; **W** = DWG and DXF save/reopen; **V** = invalid-input checks and untouched-field/reference preservation; **P** = build and load the in-tree bundled plugin with a manifest matching the host toolchain and acadrust source. A kind is `Complete` only when **C/R/E/D/U/I/W/V/P** all pass and its property catalog matches implementation. `Blocked` requires a specific dependency or failing fixture.
 
@@ -44,7 +44,7 @@ Completion gate codes: **C** = create through Python document model; **R** = rea
 | ViewBorder | **Integration-tested / blocked at W by acadrust (DXF kind)** | Writable: `min`, `max`, `center` (2-D pairs), `scale`, `rotation_angle`, `active_viewport` and `scale_handle` (both required at creation). `version` is read-only. Reference rules: `active_viewport` must be an existing Viewport entity and `scale_handle` an existing `Scale` object. Host validation requires finite bounds with `min` below `max` on both axes, a positive scale and a finite rotation. `staged_python_view_border_lifecycle_over_real_ipc` (shared `run_mesh_lifecycle`, driver-made viewport and scale fixtures) passes C/R/E/D/U/I/V/P and DWG W: creation, a resize/recenter/scale/rotation transaction, canvas wires, seven rejection cases plus an atomic rollback, DWG reopen and re-edit, and three-step undo/redo. **W blocker (engine, pinned by a canary):** a DXF `DRAWINGVIEW` reopens as a different, opaque entity kind rather than as a ViewBorder, so only DWG restores the typed record. Not `Complete` until DXF loading restores the typed entity. Not covered: the linked view representation and drawing-view definition records. |
 | SectionSymbol | **Blocked** | Not mapped. A valid section mark needs a `SectionViewStyle` and a `ViewRep` view-representation object that a script cannot create through the host API, and the entity stores raw point counts and flag words (`raw_point_count_90`, `raw_flags_90`, `raw_point_record_count`, `raw_view_symbol_70`) whose relationship to `points` is undocumented in acadrust and is written back verbatim by both writers, so the host cannot keep them consistent after a scripted edit without guessing. Adding the kind needs (1) host-side creation or lookup of a section style and view representation, and (2) a confirmed derivation of the raw counts from a real DWG produced by another CAD application. The kind keeps raw snapshot access and layer edits. |
 | Light | **Integration-tested / blocked at W by acadrust (DXF `cast_shadows`)** | Writable: `name`, `light_type` (1 distant, 2 point, 3 spot), `position`, `target`, `status`, `light_color`, `plot_glyph`, `intensity`, the attenuation type and limits, `hotspot_angle`, `falloff_angle`, `cast_shadows`, `shadow_type`, `shadow_map_size`, `shadow_map_softness`, `photometric_mode`, `photometric_data`; `class_version` is read-only. Host validation requires a non-empty name, a known light type, finite placement, a spot or distant target that differs from the position, non-negative intensity, angles and limits, an attenuation start not above its end, a spot hotspot not above its falloff, and a non-negative shadow map size. `staged_python_light_lifecycle_over_real_ipc` (shared `run_mesh_lifecycle`) passes C/R/E/D/U/I/V/P and DWG W: a spot light with an RGB colour, an intensity/target/position/shadow transaction that preserves the colour and untouched fields, the canvas glyph, eight rejection cases plus an atomic rollback, DWG reopen and re-edit, and three-step undo/redo. **W blocker (engine, pinned by a canary):** the DXF reader does not restore `cast_shadows`, which reopens false; colour, placement and intensity persist. Not covered: photometric web data edits and sun/skylight objects. |
-| Region | **Mapped read-only; transform untested** | Mapped like Solid3D and accepted by `doc.solids.transform`, which lifts the payload with `kernel_acis_body`, but no Region fixture exercises it yet. Creation from curve handles (the REGION command's `add_region_model`) is the next operation to add. |
+| Region | **Complete (create from a profile + rigid move)** | New `SolidOperation::RegionFromProfile` and `doc.solids.region(profile, layer=None, delete_source=False)`. The host builds the region exactly as the REGION command does (`presspull_model::profile_geometry` then `cadkernel::brep::planar_region`), verifies it with `solid_to_sat`, puts it on `layer` or on the profile's layer, and erases the profile only when `delete_source` is set. One closed planar profile per call (a circle, ellipse, closed polyline, spline and so on); an open profile, a ray, a region, a missing entity or an empty layer is refused with a message before anything changes. Rigid moves go through the same `doc.solids.transform` channel as Solid3D. `audit_python_region_lifecycle_over_real_ipc` passes C/R/E/D/U/I/W/V/P through the real runner: regions from a circle (source kept), a closed rectangle (source deleted) and a second circle on its own layer with exact extents, canvas geometry, six refusals that change nothing and record no undo step, a move with the exact shifted extent, DWG and DXF reopen with the payload lifting and the same extent, a reopened region moving again, and undo restoring the region exactly. Not covered: regions with holes and merging open curves into a boundary (the REGION command's second path), and AutoCAD acceptance of the payload. |
 | Body | **Integration-tested (rigid move only)** | Mapped read-only like Solid3D (same payload container). `audit_python_body_transform_over_real_ipc` moves a Body carrying a kernel box through `doc.solids.translate`, checks the exact extent, DWG reopen with a losslessly lifting payload and the exact volume, and the explanatory refusal of `create_entity('Body')`. Scripts cannot create a Body, and a non-solid (sheet or wire) body that does not lift is refused untouched. |
 | Solid3D | **Complete (create + rigid move)** | New in this session: an additive `HostApi::solid_operation` (`SolidOperation::Create` and `Transform`, plus a `SolidPrimitive` enum) carried by `PluginRequest::SolidOperation` / `PluginResponse::SolidResult` through both IPC clients, the server and `HostSession`, and a Python `doc.solids` API: `box`, `wedge`, `cylinder`, `sphere`, `torus`, `pyramid`, `transform`, `translate`, `rotate`, `mirror`. The host builds bodies with cadkernel, and every result goes through `solid_to_sat`, which lifts its own output back and refuses anything lossy. A transform first lifts the existing payload with `kernel_acis_body` and is refused, leaving the payload untouched, when that is lossy. Only rigid moves and mirrors are accepted (scaling and shear are refused). Regenerated `wires` follow the body, `silhouettes` are cleared and `history_handle` is dropped. Python sees `uid`, `point_of_reference` and `history_handle` read-only; `acis_data`, `wires` and `silhouettes` are excluded and preserved; creation through `create_entity` is refused with a message pointing at `doc.solids`. `audit_python_solid3d_lifecycle_over_real_ipc` passes C/R/E/D/U/I/W/V/P through the real runner with the kernel as oracle: all six primitives match their analytic volumes (box, wedge and cube exactly, curved solids within 2 percent of the tessellated volume), a translate, a rotate and a mirror keep the volume and move the extent exactly and keep 12 edge wires, 13 refusals (zero and non-finite sizes, a torus with minor above major, too few pyramid sides, an empty layer, an unknown primitive, a wrong number count, a scaling matrix, a non-finite offset, a payload the kernel cannot lift, a missing entity) change nothing and leave no undo step, DWG and DXF reopen with the payload lifting losslessly and the same volume and extent, a reopened payload moves again, and undo restores the original solid exactly. Not covered: booleans (about 23 s each in a debug build; release timing needed first), solids that carry parametric history, and AutoCAD acceptance of the written payload, which cannot be tested here. |
 | Surface | **Blocked, unblocked by design** | Not mapped yet, and the most involved: a surface carries `surface_data` beside `acis_data`, and only a plane keeps its kind when regenerated. Plan: planes first, then extruded and revolved from a profile. See [cadkernel-body-path.md](cadkernel-body-path.md). |

plugins/opencad-python/build/generate.rs

@@ -406,6 +406,10 @@ fn leaf_to_py(registry: &TypeRegistry, type_id: &str, item_expr: &str) -> String
 
 /// `value_expr` must already be an owned `PyObjectRef` expression. Result: a `PyResult<T>` expression.
 fn leaf_from_py(registry: &TypeRegistry, type_id: &str, value_expr: &str) -> String {
+    if type_id == "f64" {
+        // RustPython's f64 conversion rejects ints; scripts write `radius=5`.
+        return format!("py_number_to_f64({value_expr}, vm)");
+    }
     if type_id == "u64" {
         // serde reports Rust `usize` as `u64`; the inferred cast serves both.
         return format!("{value_expr}.try_into_value::<u64>(vm).map(|n| n as _)");

plugins/opencad-python/src/document_model.py

@@ -1,5 +1,27 @@
 """Thin Python view over OCS host API v7 entity transactions and coverage."""
 
+def _coordinates(value, width):
+    return dict(zip("xyz"[:width], (float(axis) for axis in value)))
+
+
+def _coerce_points(kind, properties):
+    """Let create_entity take (x, y, z) tuples for point properties, as
+    transaction edits already do, by using the property types in the schema."""
+    schema = ocs.entity_coverage(kind)
+    types = {row["name"]: row for row in schema["properties"]} if schema else {}
+    result = {}
+    for name, value in properties.items():
+        row = types.get(name)
+        if row is not None and row["type"] in ("Vector2", "Vector3"):
+            width = 2 if row["type"] == "Vector2" else 3
+            if row["sequence"]:
+                value = [_coordinates(item, width) if isinstance(item, (tuple, list)) else item for item in value]
+            elif isinstance(value, (tuple, list)):
+                value = _coordinates(value, width)
+        result[name] = value
+    return result
+
+
 class _Entity:
     def __init__(self, document, handle):
         object.__setattr__(self, "_document", document)
@@ -117,6 +139,13 @@ class _Solids:
     def pyramid(self, center=(0, 0, 0), radius=1, height=1, sides=4, layer=None):
         return self._create("pyramid", tuple(center) + (radius, height, sides), layer)
 
+    def region(self, profile, layer=None, delete_source=False):
+        """Make a planar region from one closed planar profile (a circle,
+        ellipse, closed polyline or spline). Keeps the profile unless
+        `delete_source` is true, and uses the profile's layer by default."""
+        handle = profile.handle if isinstance(profile, _Entity) else int(profile)
+        return self._document.entities[ocs.solid_region(handle, layer, bool(delete_source))]
+
     def transform(self, entity, matrix):
         """Apply a column-major 4x4 rigid transform (16 numbers) in place."""
         handle = entity.handle if isinstance(entity, _Entity) else int(entity)
@@ -151,7 +180,7 @@ class _Document:
         """Create one mapped entity and return its live document descriptor."""
         if "kind" in properties or "handle" in properties:
             raise ValueError("kind and handle are managed by create_entity")
-        handle = ocs.add(dict(kind=kind, **properties))
+        handle = ocs.add(dict(kind=kind, **_coerce_points(kind, properties)))
         return self.entities[handle]
 
     def delete_entity(self, entity):

plugins/opencad-python/src/ocs_module.rs

@@ -458,6 +458,23 @@ mod ocs {
             .map_err(|error| vm.new_runtime_error(format!("ocs.solid_create: {error}")))
     }
 
+    /// Build a planar region from a closed planar profile entity.
+    #[pyfunction]
+    fn solid_region(source: u64, layer: Option<String>, delete_source: bool, vm: &VirtualMachine) -> PyResult<u64> {
+        use ocs_plugin_api::host::SolidOperation;
+        let result = host_ctx::with_host(|host| {
+            host.solid_operation(SolidOperation::RegionFromProfile {
+                source: Handle::new(source),
+                layer,
+                delete_source,
+            })
+        })
+        .ok_or_else(|| vm.new_runtime_error("ocs: not running inside a PY_ command".to_owned()))?;
+        result
+            .map(|handle| handle.value())
+            .map_err(|error| vm.new_runtime_error(format!("ocs.solid_region: {error}")))
+    }
+
     /// Apply a column-major 4x4 rigid transform to a solid, body or region.
     #[pyfunction]
     fn solid_transform(handle: u64, matrix: Vec<f64>, vm: &VirtualMachine) -> PyResult<u64> {

src/app/plugin_host.rs

@@ -620,6 +620,47 @@ impl<'a> HostSession<'a> {
                 }
                 Ok(handle)
             }
+            SolidOperation::RegionFromProfile { source, layer, delete_source } => {
+                if layer.as_ref().is_some_and(|name| name.trim().is_empty()) {
+                    return Err("layer name is empty".into());
+                }
+                let entity = self
+                    .document()
+                    .get_entity(source)
+                    .cloned()
+                    .ok_or_else(|| format!("entity {source:?} does not exist"))?;
+                if matches!(entity, EntityType::Region(_)) {
+                    return Err("the source is already a region".into());
+                }
+                if delete_source && self.app.tabs[self.tab].scene.is_layer_locked(source) {
+                    return Err(format!("entity {source:?} is on a locked layer"));
+                }
+                let (plane, loops, closed) = crate::scene::model::presspull_model::profile_geometry(&entity)
+                    .ok_or("the source is not a planar profile a region can be made from")?;
+                if !closed {
+                    return Err("the profile must be closed".into());
+                }
+                let body = cadkernel::brep::planar_region(plane, &loops)
+                    .ok_or("the geometry kernel could not build a region from this profile")?;
+                let sat = crate::scene::convert::acis_export::solid_to_sat(&body)
+                    .ok_or("the region could not be exported losslessly")?;
+                let mut region = acadrust::entities::Region::new();
+                region.point_of_reference =
+                    acadrust::types::Vector3::new(plane.origin[0], plane.origin[1], plane.origin[2]);
+                region.wires = model::edge_wires(&body);
+                region.set_sat_document(&sat);
+                region.common.layer = layer.unwrap_or_else(|| entity.common().layer.clone());
+                self.push_undo("Create region");
+                let handle = self.add_entity(EntityType::Region(region));
+                if handle.is_null() {
+                    return Err("the region could not be added".into());
+                }
+                if delete_source {
+                    self.app.tabs[self.tab].scene.erase_entities(&[source]);
+                    self.publish_document_view();
+                }
+                Ok(handle)
+            }
             SolidOperation::Transform { handle, matrix } => {
                 if matrix.iter().any(|v| !v.is_finite()) {
                     return Err("transform matrix must be finite".into());
@@ -4902,6 +4943,134 @@ mod tests {
         assert!(host.app.command_line.history.last().unwrap().text.contains("use doc.solids"), "{}", host.app.command_line.history.last().unwrap().text);
     }
 
+    #[test]
+    fn audit_python_region_lifecycle_over_real_ipc() {
+        use crate::scene::convert::solid3d_tess::kernel_acis_body;
+        use crate::scene::model::solid_model as sm;
+        let Some(plugin_path) = std::env::var_os("OCS_TEST_PYTHON_PLUGIN") else {
+            return;
+        };
+        let mut app = OpenCADStudio::new_for_test();
+        app.tabs[0].is_start = false;
+        let mut host = HostSession::new(&mut app, 0);
+        let process = ocs_plugin_api::process::PluginProcess::spawn(
+            std::path::Path::new(&plugin_path), &mut host, crate::plugin::v4_support::notification_handler(),
+        ).unwrap();
+        let dispatch = |host: &mut HostSession<'_>, command: &str| {
+            assert!(process.dispatch(host, command, &mut |_| {}).expect("Python dispatch"));
+        };
+        let last = |host: &HostSession<'_>| host.app.command_line.history.last().unwrap().text.clone();
+        let regions = |host: &HostSession<'_>| -> Vec<Handle> {
+            let mut list: Vec<_> = host.document().entities().filter_map(|e| match e {
+                EntityType::Region(r) => Some(r.common.handle), _ => None }).collect();
+            list.sort_by_key(|h| h.value());
+            list
+        };
+        let extent_in = |document: &CadDocument, handle: Handle| {
+            let Some(EntityType::Region(region)) = document.get_entity(handle) else { panic!("no region {handle:?}") };
+            let body = kernel_acis_body(&region.acis_data).expect("region payload lifts losslessly");
+            sm::extent(&body).unwrap()
+        };
+        let close = |a: f64, b: f64| (a - b).abs() < 1e-6;
+
+        // C: regions from a circle (source kept), a closed rectangle (source
+        // deleted) and a second circle on its own layer.
+        let script = std::env::temp_dir().join(format!("ocs_region_create_{}.py", std::process::id()));
+        std::fs::write(&script, concat!(
+            "doc = ocs.active_document\n",
+            "circle = doc.create_entity('Circle', center=(0, 0, 0), radius=5)\n",
+            "rect = doc.create_entity('LwPolyline', is_closed=True, vertices=[{'location': {'x': 20.0, 'y': 0.0}}, {'location': {'x': 30.0, 'y': 0.0}}, {'location': {'x': 30.0, 'y': 6.0}}, {'location': {'x': 20.0, 'y': 6.0}}])\n",
+            "doc.solids.region(circle)\n",
+            "doc.solids.region(rect, delete_source=True)\n",
+            "other = doc.create_entity('Circle', center=(50, 0, 0), radius=2, layer='PROFILES')\n",
+            "doc.solids.region(other, layer='REGIONS')\n",
+        )).unwrap();
+        dispatch(&mut host, &format!("PY_RUN {}", script.display()));
+        let _ = std::fs::remove_file(&script);
+        let list = regions(&host);
+        assert_eq!(list.len(), 3, "{}", last(&host));
+        let (low, high) = extent_in(host.document(), list[0]);
+        assert!(close(low[0], -5.0) && close(high[0], 5.0) && close(low[1], -5.0) && close(high[1], 5.0) && close(low[2], 0.0) && close(high[2], 0.0), "{low:?} {high:?}");
+        let (low, high) = extent_in(host.document(), list[1]);
+        assert!(close(low[0], 20.0) && close(high[0], 30.0) && close(high[1], 6.0), "{low:?} {high:?}");
+        let layer_of = |host: &HostSession<'_>, handle: Handle| host.document().get_entity(handle).unwrap().common().layer.clone();
+        assert_eq!(layer_of(&host, list[0]), "0", "defaults to the profile's layer");
+        assert_eq!(layer_of(&host, list[2]), "REGIONS");
+        let circles = host.document().entities().filter(|e| matches!(e, EntityType::Circle(_))).count();
+        let polylines = host.document().entities().filter(|e| matches!(e, EntityType::LwPolyline(_))).count();
+        assert_eq!((circles, polylines), (2, 0), "delete_source removed only the rectangle");
+        let Some(EntityType::Region(first)) = host.document().get_entity(list[0]) else { unreachable!() };
+        assert_eq!((first.wires.is_empty(), first.point_of_reference.z), (false, 0.0));
+        assert!(!host.app.tabs[0].scene.wire_models_for(&[list[0]]).is_empty(), "no canvas geometry");
+        dispatch(&mut host, &format!("PY_EVAL ocs.active_document.entities[{}].kind", list[0].value()));
+        assert!(last(&host).contains("Region"));
+
+        // V: refusals change nothing and leave no undo step.
+        let open_line = host.add_entity(EntityType::Line(acadrust::entities::Line::from_points(
+            acadrust::types::Vector3::ZERO, acadrust::types::Vector3::new(5.0, 0.0, 0.0))));
+        let mut open_poly = acadrust::entities::LwPolyline::new();
+        open_poly.vertices = vec![
+            acadrust::entities::LwVertex::new(acadrust::types::Vector2::new(0.0, 0.0)),
+            acadrust::entities::LwVertex::new(acadrust::types::Vector2::new(4.0, 0.0)),
+            acadrust::entities::LwVertex::new(acadrust::types::Vector2::new(4.0, 4.0)),
+        ];
+        let open_poly = host.add_entity(EntityType::LwPolyline(open_poly));
+        let ray = host.add_entity(EntityType::Ray(acadrust::entities::Ray::default()));
+        let entity_count = host.document().entities().count();
+        let undo_now = host.app.tabs[0].history.undo_stack.len();
+        for (command, message) in [
+            (format!("ocs.active_document.solids.region({})", open_line.value()), "must be closed"),
+            (format!("ocs.active_document.solids.region({})", open_poly.value()), "must be closed"),
+            (format!("ocs.active_document.solids.region({})", ray.value()), "planar profile"),
+            (format!("ocs.active_document.solids.region({})", list[0].value()), "already a region"),
+            ("ocs.active_document.solids.region(999999)".to_string(), "does not exist"),
+            (format!("ocs.active_document.solids.region({}, layer='')", open_line.value()), "layer name is empty"),
+        ] {
+            dispatch(&mut host, &format!("PY_EVAL {command}"));
+            assert!(last(&host).contains(message), "{command}: {}", last(&host));
+        }
+        assert_eq!(host.document().entities().count(), entity_count);
+        assert_eq!(host.app.tabs[0].history.undo_stack.len(), undo_now, "refusals record no undo step");
+
+        // E: a region moves through the same kernel channel.
+        let before = host.document().get_entity(list[0]).unwrap().clone();
+        dispatch(&mut host, &format!("PY_EVAL ocs.active_document.solids.translate({}, (10, 5, 0)).handle", list[0].value()));
+        let (low, high) = extent_in(host.document(), list[0]);
+        assert!(close(low[0], 5.0) && close(high[0], 15.0) && close(low[1], 0.0) && close(high[1], 10.0), "{low:?} {high:?}");
+
+        // W: both formats reopen a region that lifts with the same extent, and
+        // a reopened region moves again.
+        let dwg = crate::io::load_bytes("region.dwg", acadrust::DwgWriter::write_to_vec(host.document()).unwrap()).unwrap();
+        let dxf = crate::io::load_bytes("region.dxf", acadrust::DxfWriter::new(host.document()).write_to_vec().unwrap()).unwrap();
+        let moved = extent_in(host.document(), list[0]);
+        for (format, document) in [("DWG", &dwg), ("DXF", &dxf)] {
+            assert_eq!(regions_in(document).len(), 3, "{format}");
+            let reopened = extent_in(document, list[0]);
+            for axis in 0..3 {
+                assert!(close(reopened.0[axis], moved.0[axis]) && close(reopened.1[axis], moved.1[axis]), "{format} extent {reopened:?} vs {moved:?}");
+            }
+            let Some(EntityType::Region(back)) = document.get_entity(list[0]) else { unreachable!() };
+            let again = host.add_entity(EntityType::Region(back.clone()));
+            dispatch(&mut host, &format!("PY_EVAL ocs.active_document.solids.translate({}, (100, 0, 0)).handle", again.value()));
+            assert!(close(extent_in(host.document(), again).0[0], reopened.0[0] + 100.0), "{format} re-edit");
+        }
+        fn regions_in(document: &CadDocument) -> Vec<Handle> {
+            document.entities().filter_map(|e| match e { EntityType::Region(r) => Some(r.common.handle), _ => None }).collect()
+        }
+
+        // D and U: delete, undo, and undo the creation steps exactly.
+        dispatch(&mut host, &format!("PY_EVAL ocs.active_document.delete_entity({})", list[2].value()));
+        assert!(host.document().get_entity(list[2]).is_none());
+        drop(process);
+        drop(host);
+        app.finish_pending_history(0);
+        app.undo_steps(1);
+        assert!(app.tabs[0].scene.document.get_entity(list[2]).is_some(), "undo restores the deleted region");
+        // Two re-edits of reopened copies, then the move of the first region.
+        app.undo_steps(3);
+        assert_eq!(app.tabs[0].scene.document.get_entity(list[0]), Some(&before), "undoing the move restores the region exactly");
+    }
+
     #[test]
     fn staged_python_point_pick_and_cancel_over_real_ipc() {
         let Some(plugin_path) = std::env::var_os("OCS_TEST_PYTHON_PLUGIN") else {