model: face splits along datum planes (#508)

A datum plane a split uses is in use, as one a partition cuts by.

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

crates/model/src/lib.rs

@@ -85,7 +85,7 @@ pub use steps::{
 };
 pub use tie::Tie;
 pub use units::UnitSystem;
-pub use virtual_faces::{FaceMerge, Stitch};
+pub use virtual_faces::{FaceMerge, FaceSplit, Stitch};
 
 /// The largest node or element label. Nastran's GRID and element ids stop at 99 999 999 (eight
 /// digits in a small field), the tightest of the three formats.
@@ -180,6 +180,9 @@ pub struct Model {
     /// Stitches of imported surfaces, in the order they apply.
     #[serde(skip_serializing_if = "Vec::is_empty")]
     stitches: Vec<Stitch>,
+    /// Face splits along datum planes, in the order they apply (after the merges).
+    #[serde(skip_serializing_if = "Vec::is_empty")]
+    face_splits: Vec<FaceSplit>,
 }
 
 /// A [`Model`] as stored, before it is checked.
@@ -236,6 +239,8 @@ struct ModelData {
     face_merges: Vec<FaceMerge>,
     #[serde(default)]
     stitches: Vec<Stitch>,
+    #[serde(default)]
+    face_splits: Vec<FaceSplit>,
 }
 
 impl TryFrom<ModelData> for Model {
@@ -331,6 +336,9 @@ impl TryFrom<ModelData> for Model {
         for v in d.stitches {
             m.add_stitch(v)?;
         }
+        for v in d.face_splits {
+            m.add_face_split(v)?;
+        }
         Ok(m)
     }
 }
@@ -465,6 +473,7 @@ impl Model {
             mesh_plans: self.mesh_plans.clone(),
             face_merges: self.face_merges.clone(),
             stitches: self.stitches.clone(),
+            face_splits: self.face_splits.clone(),
         }
     }
 
@@ -515,7 +524,7 @@ impl Model {
     }
 
     /// Counts of each kind of definition, for summaries.
-    pub fn definition_counts(&self) -> [(&'static str, usize); 18] {
+    pub fn definition_counts(&self) -> [(&'static str, usize); 19] {
         [
             ("sets", self.sets.len()),
             ("materials", self.materials.len()),
@@ -535,6 +544,7 @@ impl Model {
             ("seeds", self.seeds.len()),
             ("face_merges", self.face_merges.len()),
             ("stitches", self.stitches.len()),
+            ("face_splits", self.face_splits.len()),
         ]
     }
 }