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 <[email protected]>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/engine/src/schema.rs

@@ -124,10 +124,14 @@ pub enum Collection {
     SolvedStep,
     /// A body of the open design.
     Body,
-    /// A datum plane or axis.
+    /// A datum plane, axis or point.
     Datum,
     /// A datum plane.
     DatumPlane,
+    /// A datum axis.
+    DatumAxis,
+    /// A datum point.
+    DatumPoint,
     Partition,
 }
 
@@ -151,6 +155,8 @@ impl Collection {
             Collection::Body => "body",
             Collection::Datum => "datum",
             Collection::DatumPlane => "datum plane",
+            Collection::DatumAxis => "datum axis",
+            Collection::DatumPoint => "datum point",
             Collection::Partition => "partition",
         }
     }
@@ -178,6 +184,8 @@ impl Session {
             Collection::Body => Box::new(self.design.iter().flat_map(|d| d.bodies.iter().map(|b| b.name.as_str()))),
             Collection::Datum => Box::new(m.datums().keys().map(String::as_str)),
             Collection::DatumPlane => Box::new(m.datums().iter().filter(|(_, d)| d.plane().is_some()).map(|(n, _)| n.as_str())),
+            Collection::DatumAxis => Box::new(m.datums().iter().filter(|(_, d)| d.axis().is_some()).map(|(n, _)| n.as_str())),
+            Collection::DatumPoint => Box::new(m.datums().iter().filter(|(_, d)| d.point().is_some()).map(|(n, _)| n.as_str())),
             Collection::Partition => Box::new(m.partitions().iter().map(|p| p.name.as_str())),
         };
         names.take(MAX_NAMES).map(str::to_string).collect()