diff --git a/crates/chattyness-user-ui/src/components/avatar.rs b/crates/chattyness-user-ui/src/components/avatar.rs
index 369297b..dd0adea 100644
--- a/crates/chattyness-user-ui/src/components/avatar.rs
+++ b/crates/chattyness-user-ui/src/components/avatar.rs
@@ -27,7 +27,7 @@ use super::canvas_utils::normalize_asset_path;
 /// Screen boundaries for visual clamping in screen space.
 ///
 /// Used by Avatar for clamping avatar positions and bubble positions.
-#[derive(Clone, Copy, Debug)]
+#[derive(Clone, Copy, Debug, PartialEq)]
 pub struct ScreenBounds {
     /// Left edge of drawable area (= offset_x)
     pub min_x: f64,
@@ -82,7 +82,7 @@ impl ScreenBounds {
 /// Transform parameters for converting scene coordinates to screen coordinates.
 ///
 /// Used by Avatar and LoosePropCanvas to position elements on screen.
-#[derive(Clone, Copy, Debug)]
+#[derive(Clone, Copy, Debug, PartialEq)]
 pub struct SceneTransform {
     /// X scale factor (screen pixels per scene unit)
     pub scale_x: f64,
diff --git a/crates/chattyness-user-ui/src/components/scene_viewer.rs b/crates/chattyness-user-ui/src/components/scene_viewer.rs
index bcf1e6a..504c0a5 100644
--- a/crates/chattyness-user-ui/src/components/scene_viewer.rs
+++ b/crates/chattyness-user-ui/src/components/scene_viewer.rs
@@ -444,16 +444,17 @@ pub fn RealmSceneViewer(
 
     let text_em_size = Signal::derive(move || settings.get().text_em_size);
 
-    // Compute SceneTransform once for all avatars and props
-    let scene_transform = Signal::derive(move || SceneTransform {
+    // Compute SceneTransform once for all avatars and props (memoized)
+    let scene_transform: Signal<SceneTransform> = Memo::new(move |_| SceneTransform {
         scale_x: scale_x.get(),
         scale_y: scale_y.get(),
         offset_x: offset_x.get(),
         offset_y: offset_y.get(),
-    });
+    })
+    .into();
 
-    // Compute ScreenBounds once for all avatars (for clamping)
-    let screen_bounds = Signal::derive(move || {
+    // Compute ScreenBounds once for all avatars (memoized for clamping)
+    let screen_bounds: Signal<ScreenBounds> = Memo::new(move |_| {
         let t = scene_transform.get();
         ScreenBounds::from_transform(
             scene_width_f,
@@ -463,7 +464,8 @@ pub fn RealmSceneViewer(
             t.offset_x,
             t.offset_y,
         )
-    });
+    })
+    .into();
 
     let members_by_key = Signal::derive(move || {
         sorted_members.get().into_iter().enumerate()