Map Helix in the Python host model; record DXF handedness blocker

The host rebuilds the derived spline from the generating parameters on
scripted create/edit. staged_python_helix_lifecycle_over_real_ipc passes
every gate except DXF handedness, which acadrust's reader never applies;
the gap is pinned by a canary via per-format expectations in the shared
mesh lifecycle driver.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

crates/ocs_plugin_api/build.rs

@@ -790,6 +790,7 @@ fn generate_entity_coverage(out_dir: &Path, registry: &TypeRegistry) {
                     | ("PolygonMesh", _)
                     | ("PolyfaceMesh", _)
                     | ("Mesh", _)
+                    | ("Helix", _)
                     | (
                         "MLine",
                         "flags"

crates/ocs_plugin_api/entity_coverage_policy.json

@@ -377,6 +377,17 @@
       "faces",
       "edges",
       "override_option"
+    ],
+    "Helix": [
+      "layer",
+      "axis_base_point",
+      "start_point",
+      "axis_vector",
+      "radius",
+      "turns",
+      "turn_height",
+      "handedness",
+      "constraint"
     ]
   },
   "readable": {
@@ -432,6 +443,11 @@
     ],
     "Mesh": [
       "version"
+    ],
+    "Helix": [
+      "spline",
+      "major_version",
+      "maintenance_version"
     ]
   },
   "aliases": {

crates/ocs_plugin_api/src/entity_coverage.rs

@@ -743,6 +743,44 @@ fn validate_mesh(
     Ok(())
 }
 
+/// Helix generating parameters. The spline is derived by the host, so only
+/// the parameters are validated.
+#[cfg(feature = "host")]
+fn validate_helix(
+    old: Option<&crate::host::acadrust::entities::Helix>,
+    new: &crate::host::acadrust::entities::Helix,
+) -> Result<(), String> {
+    if old.is_some_and(|old| {
+        old.axis_base_point == new.axis_base_point
+            && old.start_point == new.start_point
+            && old.axis_vector == new.axis_vector
+            && old.radius.to_bits() == new.radius.to_bits()
+            && old.turns.to_bits() == new.turns.to_bits()
+            && old.turn_height.to_bits() == new.turn_height.to_bits()
+            && old.handedness == new.handedness
+            && old.constraint == new.constraint
+    }) {
+        return Ok(());
+    }
+    finite_vector("Helix.axis_base_point", &new.axis_base_point)?;
+    finite_vector("Helix.start_point", &new.start_point)?;
+    solid_normal("Helix.axis_vector", &new.axis_vector)?;
+    for (name, value) in [("radius", new.radius), ("turns", new.turns), ("turn_height", new.turn_height)] {
+        if !value.is_finite() || value <= 0.0 {
+            return Err(format!("Helix.{name} must be finite and greater than zero"));
+        }
+    }
+    let axis = new.axis_vector;
+    let length = axis.x.hypot(axis.y).hypot(axis.z);
+    let delta = new.start_point - new.axis_base_point;
+    let along = (delta.x * axis.x + delta.y * axis.y + delta.z * axis.z) / length;
+    let radial = ((delta.x * delta.x + delta.y * delta.y + delta.z * delta.z) - along * along).max(0.0).sqrt();
+    if radial <= 1.0e-9 {
+        return Err("Helix.start_point must not lie on the axis".into());
+    }
+    Ok(())
+}
+
 /// Validate newly created geometry for the kinds whose mapped fields have
 /// host checks. Called by the Python add path before an entity enters the document.
 #[cfg(feature = "host")]
@@ -842,6 +880,7 @@ pub fn validate_new_canvas_entity(entity: &crate::host::EntityType) -> Result<()
         EntityType::PolygonMesh(value) => validate_polygon_mesh(None, value)?,
         EntityType::PolyfaceMesh(value) => validate_polyface_mesh(None, value)?,
         EntityType::Mesh(value) => validate_mesh(None, value)?,
+        EntityType::Helix(value) => validate_helix(None, value)?,
         EntityType::AttributeDefinition(value) => {
             finite_vector(
                 "AttributeDefinition.insertion_point",
@@ -1202,6 +1241,7 @@ pub fn validate_entity_mutation(
         (EntityType::PolygonMesh(old), EntityType::PolygonMesh(new)) => validate_polygon_mesh(Some(old), new)?,
         (EntityType::PolyfaceMesh(old), EntityType::PolyfaceMesh(new)) => validate_polyface_mesh(Some(old), new)?,
         (EntityType::Mesh(old), EntityType::Mesh(new)) => validate_mesh(Some(old), new)?,
+        (EntityType::Helix(old), EntityType::Helix(new)) => validate_helix(Some(old), new)?,
         (EntityType::MLine(old), EntityType::MLine(new)) => validate_mline(Some(old), new)?,
         (EntityType::Leader(old), EntityType::Leader(new)) => validate_leader(Some(old), new)?,
         (EntityType::AttributeDefinition(old), EntityType::AttributeDefinition(new)) => {
@@ -1879,6 +1919,7 @@ mod tests {
                         | "PolygonMesh"
                         | "PolyfaceMesh"
                         | "Mesh"
+                        | "Helix"
                 )
             {
                 assert!(
@@ -2134,6 +2175,14 @@ mod tests {
                 "Mesh.faces".to_owned(),
                 "Mesh.edges".to_owned(),
                 "Mesh.override_option".to_owned(),
+                "Helix.axis_base_point".to_owned(),
+                "Helix.start_point".to_owned(),
+                "Helix.axis_vector".to_owned(),
+                "Helix.radius".to_owned(),
+                "Helix.turns".to_owned(),
+                "Helix.turn_height".to_owned(),
+                "Helix.handedness".to_owned(),
+                "Helix.constraint".to_owned(),
             ])
         );
     }

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

@@ -7,13 +7,13 @@ 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 **30 of 43** canvas kinds: 29
+v7. The Python feature has explicit writes for **31 of 43** canvas kinds: 30
 are creatable and `Insert` remains update-only. This is **not** 30 completed
 kinds: Tolerance, Shape, AttributeEntity, Hatch, MLine, Dimension, MultiLeader, Table, PolygonMesh, PolyfaceMesh and Mesh pass every completion gate.
 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
-`acadrust` revision `7ea4247`. Leader is mapped and integration-tested but blocked at W by three acadrust persistence gaps (see the ledger). The other 13 canvas kinds have only `layer`
+`acadrust` revision `7ea4247`. Leader is mapped and integration-tested but blocked at W by three acadrust persistence gaps (see the ledger). Leader and Helix are mapped and integration-tested but blocked at W by acadrust persistence gaps (see the ledger). The other 12 canvas kinds have only `layer`
 writes through the document model. All 43 have raw typed snapshots. There are
 three internal records and two opaque fallbacks outside the 43 canvas kinds.
 
@@ -123,7 +123,7 @@ The last five may require new engine capabilities rather than only Python conver
 
 ## Handoff start point
 
-Continue with **Helix** (queue item 9). Leader is done except for its W
+Continue with **RasterImage** (queue item 10). Leader is done except for its W
 gate; when the engine writes DXF group 340, reads group 213 and the DWG
 R2010+ text-size question is decided, flip the canary assertions in
 `staged_python_leader_lifecycle_over_real_ipc` and mark it `Complete`.
@@ -163,3 +163,4 @@ exact queue above and update statuses with evidence after each increment.
 - Completed `MultiLeader`. The adapter generator now converts `Color`, `LineWeight`, mixed unit/payload enums, fixed float arrays and bitflags-2 newtypes, and a `keep_types` override lets a hand-written setter reuse generated converters (used for the merge-style `context` patch). `Leader.override_color` became writable through the same `Color` form; neither file format stores it. `staged_python_multileader_lifecycle_over_real_ipc` passes the full gate with DWG and DXF reopen. The queue now continues with `Table`.
 - Completed `Table`. The generator now handles tuples and `usize`; the host keeps DXF cell merge dimensions in step with `merged_ranges`. `staged_python_table_lifecycle_over_real_ipc` passes the full gate with DWG and DXF reopen. The queue now continues with `PolygonMesh`.
 - Completed `PolygonMesh`, `PolyfaceMesh` and `Mesh` (queue items 6-8) with one shared `run_mesh_lifecycle` test driver and per-kind host validation. The generator now omits a sub-record's own `EntityCommon` from the scripted form. All three pass the full gate including DWG and DXF reopen with re-edit. The queue now continues with `Helix`.
+- Mapped `Helix` with a host-rebuilt spline. `run_mesh_lifecycle` gained per-format DXF expectations so an engine gap is pinned by a canary instead of hidden. All gates pass except W for `handedness` in DXF (reader ignores boolean group 290). The queue now continues with `RasterImage`.

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: **30 of 43 canvas kinds have explicit geometry writes** (29 creatable, plus update-only `Insert`), **11 kinds are complete**, and 13 remain layer-only. `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: **31 of 43 canvas kinds have explicit geometry writes** (30 creatable, plus update-only `Insert`), **11 kinds are complete**, and 12 remain layer-only. `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.
 
@@ -36,7 +36,7 @@ Completion gate codes: **C** = create through Python document model; **R** = rea
 | PolygonMesh | **Complete** | Writable: `flags`, `m_vertex_count`, `n_vertex_count`, `m_smooth_density`, `n_smooth_density`, `smooth_type`, `elevation`, `normal`, `vertices` (each `{location, flags}`; a vertex's own common data is not scripted and defaults). Host validation requires M and N of at least 2, exactly M×N vertices, non-negative densities, finite elevation and locations, and a nonzero normal, so inconsistent counts are refused before any mutation. `staged_python_polygon_mesh_lifecycle_over_real_ipc` (shared `run_mesh_lifecycle`) passes C/R/E/D/U/I/W/V/P: a 3×3 grid, a vertex move plus density and cubic smoothing in one transaction, canvas wires, seven rejection cases plus an atomic rollback, DWG and DXF reopen with re-edit, and three-step undo/redo. |
 | PolyfaceMesh | **Complete** | Writable: `elevation`, `flags`, `normal`, `start_width`, `end_width`, `smooth_surface`, `thickness`, `vertices` (location, flags, bulge, widths, tangent, id) and `faces` (four indices, flags, optional colour). `seqend_handle` is read-only and preserved. Host validation requires at least 3 finite vertices and 1 face, every face index within the vertex count (a negative index hides that edge, 0 marks an unused corner), at least 3 indices per face, and finite widths, thickness and elevation. `staged_python_polyface_mesh_lifecycle_over_real_ipc` passes the full gate: two triangles, a vertex move plus a new vertex and a hidden-edge face in one transaction, canvas wires, six rejection cases plus an atomic rollback, DWG and DXF reopen with re-edit, and three-step undo/redo. |
 | Mesh | **Complete** | Writable: `blend_crease`, `subdivision_level`, `vertices`, `faces`, `edges` (start, end, optional crease), `override_option`; `version` is read-only. Host validation requires at least 3 finite vertices, faces of at least 3 in-range indices, edges with distinct in-range endpoints and a finite non-negative crease, and a non-negative subdivision level, so out-of-range topology is rejected before mutation. `staged_python_mesh_lifecycle_over_real_ipc` passes the full gate: a quad with a creased edge, an added vertex and triangle plus subdivision level 1 in one transaction, canvas wires, seven rejection cases plus an atomic rollback, DWG and DXF reopen with re-edit, and three-step undo/redo. |
-| Helix | Layer-only | Requires valid derived-spline fixture. |
+| Helix | **Integration-tested / blocked at W by acadrust (DXF handedness)** | Writable generating parameters: `axis_base_point`, `start_point`, `axis_vector`, `radius` (the top radius; the base radius is the start point's distance from the axis), `turns`, `turn_height`, `handedness`, `constraint`. Read-only: `spline`, `major_version`, `maintenance_version`. The host rebuilds the derived NURBS spline with OCS's own helix builder on every scripted create or parameter edit (`normalize_scripted_helix`), so the spline always matches the parameters. Host validation requires finite positive radius, turns and turn height, a nonzero axis and a start point off the axis. `staged_python_helix_lifecycle_over_real_ipc` (shared `run_mesh_lifecycle`) passes C/R/E/D/U/I/V/P: creation with a derived spline ending at z = turns × turn height, a turns and handedness edit that regenerates it, canvas wires, seven rejection cases plus an atomic rollback, DWG reopen and re-edit, DXF reopen and re-edit, and three-step undo/redo. **W blocker (engine, pinned by a canary assertion):** the DXF reader parses boolean group 290 as an `i16` and never applies it, so a clockwise helix reopens counter-clockwise from DXF while DWG keeps it. Not `Complete` until the reader is fixed. |
 | RasterImage | Layer-only | Requires image definition and file fixture. |
 | Wipeout | Layer-only | Requires clip and image-definition fixture. |
 | Underlay | Layer-only | Requires external definition/file fixture. |

docs/plugin-host-model.md

@@ -35,7 +35,7 @@ attached attribute and sequence records. Those fields report `transaction_geomet
 catalog. All 43 canvas kinds also support nonempty `layer` changes through
 the same undoable transaction; internal and opaque variants remain read-only
 through the document model. The adapter accepts only `layer` patches for
-canvas kinds outside its 30 geometry converters. Other writable properties
+canvas kinds outside its 31 geometry converters. Other writable properties
 still report `type_conversion_only`; broader CAD range and cross-property
 checks remain outstanding.
 The host's `entity_snapshot` helper serializes any typed entity as a detached
@@ -91,7 +91,7 @@ Input tokens are bound to the drawing tab that requested the pick. Polling a
 token from another tab returns no result and does not consume it.
 
 Python `doc.entities[handle]` returns a descriptor for every entity. For kinds
-outside the 30-kind generated schema it contains only handle, kind, and layer;
+outside the 31-kind generated schema it contains only handle, kind, and layer;
 `layer` is editable on canvas kinds. `doc.coverage()` enumerates the
 catalog; `doc.coverage("Line")` and `line.coverage` return one entry. For
 covered kinds, the coverage object lists actual readable and editable

plugins/opencad-python/README.md

@@ -94,7 +94,7 @@ The host-owned catalog classifies all 48 entity variants and tracks every
 traced field, including fields marked `unmapped`. Query it with
 `doc.coverage()` or `doc.coverage("Line")`; each row includes source field,
 type, access, and current validation status. Geometry edits remain limited to
-the 30 mapped kinds.
+the 31 mapped kinds.
 For any entity, `entity.snapshot` returns a detached dictionary of its raw
 CAD fields, including `snapshot["common"]` and kind-specific nested values.
 It can inspect an unmapped kind; editing the dictionary does

plugins/opencad-python/entity_manifest.json

@@ -29,7 +29,8 @@
     "Table",
     "PolygonMesh",
     "PolyfaceMesh",
-    "Mesh"
+    "Mesh",
+    "Helix"
   ],
   "manual_kinds": ["Dimension"],
   "base_fields": ["handle", "layer", "owner_handle"],
@@ -331,6 +332,14 @@
         "faces": { "required": true },
         "version": { "read_only": true }
       }
+    },
+    "Helix": {
+      "fields": {
+        "start_point": { "required": true },
+        "spline": { "read_only": true, "_comment": "Derived by the host from the generating parameters." },
+        "major_version": { "read_only": true },
+        "maintenance_version": { "read_only": true }
+      }
     }
   }
 }

plugins/opencad-python/src/ocs_module.rs

@@ -4756,7 +4756,7 @@ mod tests {
                 );
             }
         }
-        assert_eq!(emitted.len(), 30);
+        assert_eq!(emitted.len(), 31);
     }
 
     #[cfg(feature = "experimental-host-model")]

src/app/plugin_host.rs

@@ -158,6 +158,13 @@ impl<'a> HostSession<'a> {
         if let EntityType::Dimension(dimension) = entity {
             crate::entities::dimension::normalize_scripted_dimension(dimension);
         }
+        if let EntityType::Helix(new) = entity {
+            let old = match old {
+                Some(EntityType::Helix(old)) => Some(old),
+                _ => None,
+            };
+            crate::entities::helix::normalize_scripted_helix(old, new)?;
+        }
         if let EntityType::Table(new) = entity {
             let old = match old {
                 Some(EntityType::Table(old)) => Some(old),
@@ -3112,6 +3119,10 @@ mod tests {
         expect_created: &'static str,
         expect_edited: &'static str,
         expect_reedited: &'static str,
+        /// Digest a DXF reopen yields when the engine loses a field (empty:
+        /// same as DWG). A canary that fails once the engine round-trips it.
+        expect_edited_dxf: &'static str,
+        expect_reedited_dxf: &'static str,
     }
 
     fn run_mesh_lifecycle(case: &MeshCase) {
@@ -3172,13 +3183,18 @@ mod tests {
         let dxf = crate::io::load_bytes("mesh.dxf", acadrust::DxfWriter::new(host.document()).write_to_vec().unwrap()).unwrap();
         let mut gaps = Vec::new();
         for (format, document) in [("DWG", &dwg), ("DXF", &dxf)] {
+            let expected_digest = if format == "DXF" && !case.expect_edited_dxf.is_empty() {
+                case.expect_edited_dxf
+            } else {
+                case.expect_edited
+            };
             match document.get_entity(handle) {
-                Some(entity) if (case.digest)(entity) == case.expect_edited => {}
+                Some(entity) if (case.digest)(entity) == expected_digest => {}
                 Some(entity) => gaps.push(format!("{format}: {}", (case.digest)(entity))),
                 None => gaps.push(format!("{format}: entity missing")),
             }
         }
-        assert!(gaps.is_empty(), "persistence gaps (expected {}): {gaps:#?}", case.expect_edited);
+        assert!(gaps.is_empty(), "persistence gaps (expected {} / DXF {:?}): {gaps:#?}", case.expect_edited, case.expect_edited_dxf);
         for (name, mut document) in [("mesh-reedit.dwg", dwg), ("mesh-reedit.dxf", dxf)] {
             let before = document.get_entity(handle).unwrap().clone();
             let mut after = before.clone();
@@ -3192,7 +3208,12 @@ mod tests {
                 acadrust::DxfWriter::new(&document).write_to_vec().unwrap()
             };
             let reopened = crate::io::load_bytes(name, bytes).unwrap();
-            assert_eq!((case.digest)(reopened.get_entity(handle).unwrap()), case.expect_reedited, "{name}");
+            let expected_digest = if name.ends_with("dxf") && !case.expect_reedited_dxf.is_empty() {
+                case.expect_reedited_dxf
+            } else {
+                case.expect_reedited
+            };
+            assert_eq!((case.digest)(reopened.get_entity(handle).unwrap()), expected_digest, "{name}");
         }
 
         dispatch(&mut host, &format!("PY_EVAL ocs.active_document.delete_entity({})", handle.value()));
@@ -3252,6 +3273,8 @@ mod tests {
             expect_created: "3x3 v9 z0 d0/0 NoSmooth",
             expect_edited: "3x3 v9 z2.5 d6/6 Cubic",
             expect_reedited: "3x3 v9 z2.5 d6/6 Cubic",
+            expect_edited_dxf: "",
+            expect_reedited_dxf: "",
         });
     }
 
@@ -3293,6 +3316,8 @@ mod tests {
             expect_created: "v4 f2 z0 last Some((1, 3, 4))",
             expect_edited: "v5 f3 z3 last Some((3, -4, 5))",
             expect_reedited: "v5 f3 z3 last Some((3, -4, 5))",
+            expect_edited_dxf: "",
+            expect_reedited_dxf: "",
         });
     }
 
@@ -3333,6 +3358,47 @@ mod tests {
             expect_created: "v4 f1 e1 sub0 crease Some(1.5)",
             expect_edited: "v5 f2 e1 sub1 crease Some(1.5)",
             expect_reedited: "v5 f2 e1 sub1 crease Some(1.5)",
+            expect_edited_dxf: "",
+            expect_reedited_dxf: "",
+        });
+    }
+
+    #[test]
+    fn staged_python_helix_lifecycle_over_real_ipc() {
+        run_mesh_lifecycle(&MeshCase {
+            create: concat!(
+                "doc.create_entity('Helix', axis_base_point=P(0.0, 0.0, 0.0), axis_vector=P(0.0, 0.0, 1.0),\n",
+                "    start_point=P(5.0, 0.0, 0.0), radius=5.0, turns=3.0, turn_height=2.0)\n"),
+            edit: concat!(
+                "helix = doc.entities[HANDLE]\n",
+                "with doc.transaction('Edit helix'):\n",
+                "    helix.turns = 5.0\n",
+                "    helix.handedness = False\n",
+                "doc.selection = [helix]\n"),
+            rejects: &[
+                ("'radius':0.0", "greater than zero"),
+                ("'turns':-1.0", "greater than zero"),
+                ("'turn_height':float('nan')", "greater than zero"),
+                ("'axis_vector':{'x':0.0,'y':0.0,'z':0.0}", "nonzero"),
+                ("'start_point':{'x':0.0,'y':0.0,'z':3.0}", "on the axis"),
+                ("'spline':{}", "read-only"),
+                ("'major_version':1", "read-only"),
+            ],
+            is_kind: |entity| matches!(entity, EntityType::Helix(_)),
+            digest: |entity| match entity {
+                EntityType::Helix(h) => format!("r{} t{} h{} endz{:.1} ccw{} cp{}", h.radius, h.turns, h.turn_height,
+                    h.spline.control_points.last().map_or(f64::NAN, |p| p.z), h.handedness,
+                    !h.spline.control_points.is_empty()),
+                _ => "wrong kind".into(),
+            },
+            reedit: |entity| if let EntityType::Helix(h) = entity { h.turns = 6.0; },
+            expect_created: "r5 t3 h2 endz6.0 ccwtrue cptrue",
+            expect_edited: "r5 t5 h2 endz10.0 ccwfalse cptrue",
+            expect_reedited: "r5 t6 h2 endz10.0 ccwfalse cptrue",
+            // BLOCKER: the DXF reader parses boolean group 290 as an i16 and
+            // never applies it, so handedness always reopens counter-clockwise.
+            expect_edited_dxf: "r5 t5 h2 endz10.0 ccwtrue cptrue",
+            expect_reedited_dxf: "r5 t6 h2 endz10.0 ccwtrue cptrue",
         });
     }
 

src/entities/helix.rs

@@ -602,3 +602,28 @@ mod tests {
         }
     }
 }
+
+/// Rebuild the derived spline after a scripted create or edit of the
+/// generating parameters. `radius` is the top radius; the base radius is the
+/// start point's distance from the axis.
+pub(crate) fn normalize_scripted_helix(old: Option<&Helix>, new: &mut Helix) -> Result<(), String> {
+    let unchanged = old.is_some_and(|old| {
+        old.axis_base_point == new.axis_base_point
+            && old.start_point == new.start_point
+            && old.axis_vector == new.axis_vector
+            && old.radius.to_bits() == new.radius.to_bits()
+            && old.turns.to_bits() == new.turns.to_bits()
+            && old.turn_height.to_bits() == new.turn_height.to_bits()
+            && old.handedness == new.handedness
+            && old.constraint == new.constraint
+    });
+    if unchanged {
+        return Ok(());
+    }
+    let top = new.radius;
+    if rebuild(new, top) {
+        Ok(())
+    } else {
+        Err("Helix parameters do not define a valid curve".into())
+    }
+}