Block saving invalid brushes

crates/editor/src/scene/scene_io.rs

@@ -404,6 +404,9 @@ fn format_actor_validation(err: ActorValidationError) -> String {
         ActorValidationError::BrushHasModelRef => {
             "Save failed: Brush actor cannot have ModelRef".into()
         }
+        ActorValidationError::InvalidBrushGeometry(message) => {
+            format!("Save failed: invalid brush geometry: {message}")
+        }
         ActorValidationError::StaticMeshMissingPrimitive => {
             "Save failed: StaticMesh actor requires Primitive or StaticMeshRenderer with a mesh slot"
                 .into()

crates/shared/src/actor.rs

@@ -4,9 +4,9 @@ use bevy::ecs::world::EntityRef;
 use bevy::prelude::*;
 
 use crate::{
-    ActorKind, BrushDesc, LevelObject, LightDesc, ModelRef, ObjectiveMarker, PlayerSpawn,
-    PostProcessVolumeDesc, PrefabInstance, PrefabRef, Primitive, StaticMeshRenderer, TeamSpawn,
-    TriggerVolume, WeaponSpawn,
+    brush_math::validate_brush, ActorKind, BrushDesc, LevelObject, LightDesc, ModelRef,
+    ObjectiveMarker, PlayerSpawn, PostProcessVolumeDesc, PrefabInstance, PrefabRef, Primitive,
+    StaticMeshRenderer, TeamSpawn, TriggerVolume, WeaponSpawn,
 };
 
 /// One-shot deterministic kind from authoring components (scene migration only).
@@ -59,6 +59,7 @@ pub enum ActorValidationError {
     BrushHasStaticMeshRenderer,
     BrushHasLight,
     BrushHasModelRef,
+    InvalidBrushGeometry(String),
     StaticMeshMissingPrimitive,
     StaticMeshHasLight,
     StaticMeshHasModelRef,
@@ -99,9 +100,9 @@ pub fn validate_actor(entity: EntityRef<'_>) -> Result<(), ActorValidationError>
 
     match kind {
         ActorKind::Brush => {
-            if entity.get::<BrushDesc>().is_none() {
+            let Some(brush) = entity.get::<BrushDesc>() else {
                 return Err(ActorValidationError::BrushMissingDesc);
-            }
+            };
             if entity.get::<Primitive>().is_some() {
                 return Err(ActorValidationError::BrushHasPrimitive);
             }
@@ -114,6 +115,18 @@ pub fn validate_actor(entity: EntityRef<'_>) -> Result<(), ActorValidationError>
             if entity.get::<ModelRef>().is_some() {
                 return Err(ActorValidationError::BrushHasModelRef);
             }
+            let report = validate_brush(brush);
+            if !report.is_valid() {
+                let message = report
+                    .diagnostics
+                    .into_iter()
+                    .find(|diagnostic| {
+                        diagnostic.severity == crate::brush_math::BrushDiagnosticSeverity::Error
+                    })
+                    .map(|diagnostic| diagnostic.message)
+                    .unwrap_or_else(|| "Brush geometry is invalid.".to_string());
+                return Err(ActorValidationError::InvalidBrushGeometry(message));
+            }
         }
         ActorKind::StaticMesh => {
             let has_static_mesh_renderer = entity
@@ -262,6 +275,20 @@ mod tests {
         );
     }
 
+    #[test]
+    fn validate_brush_rejects_invalid_geometry() {
+        let mut world = World::new();
+        let mut brush = BrushDesc::default();
+        brush.faces[0].vertices.clear();
+        let e = level_entity(&mut world, (ActorKind::Brush, brush));
+        assert_eq!(
+            validate_actor(world.entity(e)),
+            Err(ActorValidationError::InvalidBrushGeometry(
+                "Face has fewer than three vertices.".into()
+            ))
+        );
+    }
+
     #[test]
     fn validate_post_process_volume_ok() {
         let mut world = World::new();

docs/editor/brushes.md

@@ -10,6 +10,7 @@ Brushes are persisted blockout geometry stored as `ActorKind::Brush + BrushDesc`
 - Brush actors validate separately from primitives and imported/static mesh actors.
 - The Actor Inspector Add Component shelf can add a **Brush** component. The Brush card exposes kind, face count, shadow flags, and cube reset.
 - The Brush card runs shared validation and reports invalid faces inline. Fatal geometry errors prevent hydration; warnings call out authoring issues that can still render. **Reset Cube Brush** is the MVP repair path.
+- Scene save runs the same fatal brush validation and blocks writing unrecoverable invalid brush geometry.
 - Draw Brush mode (`B`, toolbar pencil, or command `brush.draw`) creates additive prism brushes from snapped floor points. LMB places points, Backspace removes the last point, Enter commits through undo history, and Esc/right-click cancels without scene mutation.
 
 ## Element Modes