Add friction, collision callbacks and slope-aware physics APIs

Engine/apps/editor/src/agent_tools.rs

@@ -204,7 +204,7 @@ impl EditorApp {
                             {
                                 if !matches!(
                                     k.as_str(),
-                                    "color" | "anchored" | "can_touch" | "can_collide"
+                                    "color" | "anchored" | "can_touch" | "can_collide" | "friction"
                                 ) {
                                     return Err(format!("unknown part attribute: {k}"));
                                 }

Engine/apps/editor/src/main.rs

@@ -2909,7 +2909,7 @@ impl EditorViewer<'_> {
             attributes.color = color;
             attributes_changed |= ui
                 .checkbox(&mut attributes.can_touch, "Can touch")
-                .on_hover_text("Reserved for touch events. Does not affect solid collisions.")
+                .on_hover_text("Enables clicks, taps and collision event subscriptions. Does not affect solid response.")
                 .changed();
             attributes_changed |= ui
                 .checkbox(&mut attributes.can_collide, "Can collide")
@@ -2921,6 +2921,14 @@ impl EditorViewer<'_> {
                     "Prevents gravity and collision response from moving this primitive in Play.",
                 )
                 .changed();
+            attributes_changed |= ui
+                .add(
+                    egui::DragValue::new(&mut attributes.friction)
+                        .range(0.0..=10.0)
+                        .speed(0.01)
+                        .prefix("Friction: "),
+                )
+                .changed();
             ui.label(format!(
                 "Parent: {}",
                 snapshot

Engine/apps/luau-host/src/main.rs

@@ -72,6 +72,9 @@ fn run() -> Result<(), Box<dyn std::error::Error>> {
             if let Some(error) = response.get("error").and_then(serde_json::Value::as_str) {
                 return Err(mlua::Error::external(error.to_owned()));
             }
+            if response["result"].is_null() {
+                return Ok(Value::Nil);
+            }
             lua.to_value_with(
                 &response["result"],
                 mlua::SerializeOptions::new().serialize_none_to_null(false),