Merge PR #442: cut mesh-import wire-set memory ~35% (#358)

entity_wires() returns the memoized Arc instead of a per-call deep copy;
MESH entities over 50k vertices ship no per-vertex snap/key tables
(matching PolyfaceMesh/PolygonMesh); the Face3D/other render split
caches a None marker and uses the base set directly when there is no
Face3D wire; test fix for the depth-map BlockCache::build signature.

Reviewed: correctness sound — wire AABB comes from entity_aabb (not
key_vertices) so large meshes stay selectable; snap consumers are
empty-guarded; the Arc/strong_count reasoning for try_resident_patch
holds. One consistent pre-existing quirk noted (auto_fit_viewport
centroid excludes tableless meshes, as Poly*Mesh already do).

src/scene/mod.rs

@@ -1069,9 +1069,15 @@ pub struct Scene {
     /// [`WIRE_CONTENT_GEN`] id. `split_face3d_wires` is an O(N) per-wire
     /// handle lookup + clone that otherwise re-runs every frame. A map, not a
     /// slot: a paper frame walks several sources (sheet + viewports).
+    ///
+    /// `None` for the second element means "no Face3D wire in this set — use
+    /// the base set itself". The base `Arc` is deliberately NOT stored here:
+    /// `try_resident_patch` can only move a resident set out for an
+    /// incremental patch while its `Arc` is uniquely held, so pinning it in
+    /// this cache would silently force a full rebuild on every edit (#358).
     #[allow(clippy::type_complexity)]
     split_cache:
-        RefCell<HashMap<u64, (Arc<Vec<WireModel>>, Arc<Vec<WireModel>>)>>,
+        RefCell<HashMap<u64, (Arc<Vec<WireModel>>, Option<Arc<Vec<WireModel>>>)>>,
     /// Cached `selected ∪ hover` handle set for the GPU xray overlay, keyed by
     /// `selection_generation`. Rebuilt only when the selection changes so
     /// `build_primitive` doesn't clone the set every frame.
@@ -2870,9 +2876,9 @@ impl Scene {
     /// Collect closed polygon outlines (world XY) from the current layout.
     pub fn closed_outlines(&self) -> Vec<Vec<[f32; 2]>> {
         self.entity_wires()
-            .into_iter()
+            .iter()
             .filter_map(|wire| {
-                let pts = wire.points;
+                let pts = &wire.points;
                 if pts.len() < 4 {
                     return None;
                 }
@@ -2891,7 +2897,7 @@ impl Scene {
                 // boundary commands) see one vertex per corner — not the doubled
                 // ring that otherwise shows two grips at every corner.
                 let mut ring: Vec<[f32; 2]> = Vec::with_capacity(pts.len());
-                for p in &pts {
+                for p in pts {
                     if !p[0].is_finite() || !p[1].is_finite() {
                         continue;
                     }
@@ -3361,8 +3367,12 @@ impl Scene {
     }
 
     /// Build WireModels from all document entities + optional preview wire.
-    pub fn entity_wires(&self) -> Vec<WireModel> {
-        (*self.entity_wires_arc()).clone()
+    ///
+    /// Returns the memoized set by `Arc` — callers only ever iterate it, and
+    /// the previous per-call deep clone was a full copy of every wire buffer
+    /// (hundreds of MB on large mesh imports, #358).
+    pub fn entity_wires(&self) -> Arc<Vec<WireModel>> {
+        self.entity_wires_arc()
     }
 
     /// Per-entity normalized draw-order depth, keyed by entity handle value.

src/scene/view/render.rs

@@ -1251,9 +1251,18 @@ impl Scene {
         // each frame — for every source, since all ids are stable now.
         let (face3d_wires, other_arc) = {
             let cached = { self.split_cache.borrow().get(&wire_content_id).cloned() };
-            cached.unwrap_or_else(|| {
-                let (f, o) = split_face3d_wires(&base_arc, &self.document);
-                let (fa, oa) = (Arc::new(f), Arc::new(o));
+            let (fa, oa) = cached.unwrap_or_else(|| {
+                // No Face3D wire at all (pure 2-D drawings, mesh imports):
+                // "others" would be a wire-for-wire copy of the base set —
+                // mark it `None` and use the base set directly instead of
+                // duplicating it (#358). The base Arc itself must not be
+                // stored in the cache (see the `split_cache` field docs).
+                let (fa, oa) = if base_arc.iter().any(|w| is_face3d_wire(w, &self.document)) {
+                    let (f, o) = split_face3d_wires(&base_arc, &self.document);
+                    (Arc::new(f), Some(Arc::new(o)))
+                } else {
+                    (Arc::new(Vec::new()), None)
+                };
                 let mut c = self.split_cache.borrow_mut();
                 // Ids change on rebuild, so old keys die naturally; the cap
                 // just bounds pathological churn.
@@ -1262,7 +1271,8 @@ impl Scene {
                 }
                 c.insert(wire_content_id, (fa.clone(), oa.clone()));
                 (fa, oa)
-            })
+            });
+            (fa, oa.unwrap_or_else(|| Arc::clone(&base_arc)))
         };
         // Base wire set — the cached `other` Arc directly, never cloned to
         // append overlays. Preview / interim wires ride in their own small
@@ -1569,9 +1579,19 @@ pub(crate) fn resolve_pattern(
     (pat_len, pat)
 }
 
+/// Whether a wire belongs to a Face3D entity, by document handle lookup —
+/// so no changes to WireModel are needed.
+fn is_face3d_wire(w: &WireModel, document: &acadrust::CadDocument) -> bool {
+    w.name
+        .parse::<u64>()
+        .ok()
+        .and_then(|v| document.get_entity(Handle::new(v)))
+        .map(|e| matches!(e, EntityType::Face3D(_)))
+        .unwrap_or(false)
+}
+
 /// Partition a wire list into (face3d_wires, other_wires).
 ///
-/// Uses a document handle lookup so no changes to WireModel are needed.
 /// O(N) per geometry epoch — acceptable since it runs once per epoch.
 fn split_face3d_wires(
     wires: &[WireModel],
@@ -1580,14 +1600,7 @@ fn split_face3d_wires(
     let mut face3d = Vec::new();
     let mut others = Vec::new();
     for w in wires {
-        let is_face3d = w
-            .name
-            .parse::<u64>()
-            .ok()
-            .and_then(|v| document.get_entity(Handle::new(v)))
-            .map(|e| matches!(e, EntityType::Face3D(_)))
-            .unwrap_or(false);
-        if is_face3d {
+        if is_face3d_wire(w, document) {
             face3d.push(w.clone());
         } else {
             others.push(w.clone());