Engine: geometry.datum.point; planes and axes through datum points; datum edits and cascading delete

A datum point by coordinates, at a mesh vertex, a fraction along a
design edge, at a face's centre, or where a datum axis crosses a datum
plane. Datum planes take three datum points or a normal to a datum axis;
axes take two datum points. geometry.datum.edit, .axis.edit and
.point.edit redefine a datum of their kind (partitions cut again);
geometry.datum.delete with cascade also deletes the partitions that cut
by it. The ribbon shows Datum Plane, Datum Axis, Datum Point and
Partition, each with its own icon; edit and delete leave the ribbon
(still commands, claimed by their entries).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

docs/features.md

@@ -6,7 +6,7 @@ Every entry is a toolbar button. **Ready** entries run their command; **coming s
 shown greyed with the roadmap milestone that brings them (ROADMAP.md). Scripts, the command line,
 the control channel and AI agents over MCP (docs/mcp.md) run the same commands.
 
-62 ready, 41 coming soon.
+64 ready, 41 coming soon.
 
 ## Geometry
 
@@ -17,8 +17,10 @@ the control channel and AI agents over MCP (docs/mcp.md) run the same commands.
 | Inspect | Bodies — List the open design's bodies, volumes and named faces | ready | `geometry.bodies` |
 | Inspect | Tessellate — Tessellate a body into a face-tagged boundary surface | ready | `geometry.tessellate` |
 | Inspect | Check Surface — Weld, closed, manifold, orientation and self-intersection checks; feature edges | ready | `mesh.surface.check` |
-| Prepare | Datum Plane — Datum planes (principal plane and offset, three points, point and normal) and axes | ready | `geometry.datum`, `geometry.datum.axis`, `geometry.datum.delete` |
-| Prepare | Partition — Cut bodies into cells by a datum plane; the two faces of each cut are paired by name | ready | `geometry.partition`, `geometry.partition.delete` |
+| Prepare | Datum Plane — A datum plane: principal plane and offset, three points or datum points, point and normal, normal to an axis | ready | `geometry.datum`, (`geometry.datum.edit`), (`geometry.datum.delete`) |
+| Prepare | Datum Axis — A datum axis: principal axis, two points or datum points, point and direction | ready | `geometry.datum.axis`, (`geometry.datum.axis.edit`) |
+| Prepare | Datum Point — A datum point: coordinates, a mesh vertex, along an edge, a face's centre, an axis through a plane | ready | `geometry.datum.point`, (`geometry.datum.point.edit`) |
+| Prepare | Partition — Cut bodies into cells by a datum plane; the two faces of each cut are paired by name | ready | `geometry.partition`, (`geometry.partition.delete`) |
 | Prepare | Midsurface — Extract midsurfaces of thin parts for shell meshes | coming soon (M8) |  |
 
 ## Mesh