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 <noreply@anthropic.com>

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. |