Surface Extend: a planar surface's straight edges pushed out (FusionExtendCommand)

Kernel extend(body, edges, distance) moves the picked straight edges of a
planar surface outward in its plane, with neighbours meeting them. Doc
feature SurfaceExtend, engine FusionExtendCommand. Tests: 10x10 extended
by 5 past one edge gives 150, past two gives 225; the engine patch, trim,
extend and thicken gives 240.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/doc/src/assembly.rs

@@ -261,7 +261,7 @@ impl FeatureKind {
             | FeatureKind::Thicken { .. }
             | FeatureKind::Import { .. }
             | FeatureKind::MeshImport { .. } => {}
-            FeatureKind::Patch { edges, .. } => edges.iter_mut().for_each(pt),
+            FeatureKind::Patch { edges, .. } | FeatureKind::SurfaceExtend { edges, .. } => edges.iter_mut().for_each(pt),
             FeatureKind::SurfaceTrim { plane, tool, keep, .. } => {
                 map_plane_ref(m, plane);
                 if let Some(t) = tool {

crates/doc/src/document.rs

@@ -634,6 +634,12 @@ pub enum FeatureKind {
         #[serde(default, skip_serializing_if = "Vec::is_empty")]
         targets: Vec<String>,
     },
+    /// A planar surface body extended outward by `distance` past the edges through `edges`.
+    SurfaceExtend {
+        body: String,
+        edges: Vec<Vec3>,
+        distance: String,
+    },
     /// A surface body trimmed by a plane, or by a face of a body (`tool`), keeping the side of
     /// `keep`.
     SurfaceTrim {
@@ -887,6 +893,7 @@ impl FeatureKind {
             FeatureKind::Stitch { .. } => "StitchFeature",
             FeatureKind::Thicken { .. } => "ThickenFeature",
             FeatureKind::SurfaceTrim { .. } => "TrimFeature",
+            FeatureKind::SurfaceExtend { .. } => "ExtendFeature",
             FeatureKind::Import { .. } => "BaseFeature",
             FeatureKind::MeshImport { .. } => "MeshFeature",
         }
@@ -945,6 +952,7 @@ impl FeatureKind {
             FeatureKind::Stitch { .. } => "Stitch",
             FeatureKind::Thicken { .. } => "Thicken",
             FeatureKind::SurfaceTrim { .. } => "Trim",
+            FeatureKind::SurfaceExtend { .. } => "Extend",
             FeatureKind::Import { .. } => "Import",
             FeatureKind::MeshImport { .. } => "Mesh",
         }
@@ -1086,6 +1094,7 @@ impl FeatureKind {
             FeatureKind::Stitch { tolerance, .. } => v.push(tolerance),
             FeatureKind::Thicken { thickness, .. } => v.push(thickness),
             FeatureKind::SurfaceTrim { plane, .. } => plane_exprs(plane, &mut v),
+            FeatureKind::SurfaceExtend { distance, .. } => v.push(distance),
             FeatureKind::Patch { .. } => {}
             FeatureKind::Import { .. } | FeatureKind::MeshImport { .. } => {}
         }

crates/doc/src/eval.rs

@@ -1916,9 +1916,11 @@ fn eval_feature(doc: &Document, vals: &BTreeMap<String, Value>, f: &Feature, st:
         FeatureKind::Boss { .. } | FeatureKind::Lip { .. } | FeatureKind::SnapFit { .. } | FeatureKind::Rest { .. } => {
             more::plastic_eval(doc, vals, f, st)
         }
-        FeatureKind::Patch { .. } | FeatureKind::Stitch { .. } | FeatureKind::Thicken { .. } | FeatureKind::SurfaceTrim { .. } => {
-            surface::eval(doc, vals, f, st)
-        }
+        FeatureKind::Patch { .. }
+        | FeatureKind::Stitch { .. }
+        | FeatureKind::Thicken { .. }
+        | FeatureKind::SurfaceTrim { .. }
+        | FeatureKind::SurfaceExtend { .. } => surface::eval(doc, vals, f, st),
         FeatureKind::Emboss { .. }
         | FeatureKind::Rib { .. }
         | FeatureKind::ReplaceFace { .. }

crates/doc/src/eval_surface.rs

@@ -74,6 +74,16 @@ pub(super) fn eval(doc: &Document, vals: &BTreeMap<String, Value>, f: &Feature,
             }
             Ok(())
         }
+        FeatureKind::SurfaceExtend { body, edges, distance } => {
+            let d = val(vals, distance, Kind::Length)?;
+            let i = st.bodies.iter().position(|b| &b.name == body).ok_or_else(|| DocError::Unknown(format!("body `{body}`")))?;
+            let Some(mb) = st.bodies.get(i).cloned() else { return Err(DocError::Invalid("body".into())) };
+            let out = kernel::extend(&mb.body, edges, d)?;
+            if let Some(slot) = st.bodies.get_mut(i) {
+                *slot = ModelBody::new(mb.name, out, mb.feature);
+            }
+            Ok(())
+        }
         _ => Err(DocError::Invalid("not a surface feature".into())),
     }
 }

crates/doc/src/params.rs

@@ -226,6 +226,7 @@ impl FeatureKind {
             FeatureKind::Stitch { tolerance, .. } => v.push(("Tolerance", tolerance, L)),
             FeatureKind::Thicken { thickness, .. } => v.push(("Thickness", thickness, L)),
             FeatureKind::SurfaceTrim { plane, .. } => plane_inputs_mut(plane, &mut v),
+            FeatureKind::SurfaceExtend { distance, .. } => v.push(("Distance", distance, L)),
             FeatureKind::Patch { .. } => {}
             FeatureKind::Combine { .. }
             | FeatureKind::SheetBase { .. }