diff --git a/frontend/apps/artcraft/app/src/pages/PageImageTo3DObject/ImageTo3DStore.ts b/frontend/apps/artcraft/app/src/pages/PageImageTo3DObject/ImageTo3DStore.ts
index b38348ea84..ca1dfaf42e 100644
--- a/frontend/apps/artcraft/app/src/pages/PageImageTo3DObject/ImageTo3DStore.ts
+++ b/frontend/apps/artcraft/app/src/pages/PageImageTo3DObject/ImageTo3DStore.ts
@@ -2,145 +2,7 @@ import { create } from "zustand";
 import { listen } from "@tauri-apps/api/event";
 import { MediaFilesApi, MediaUploadApi } from "@storyteller/api";
 import { v4 as uuidv4 } from "uuid";
-import * as THREE from "three";
-import { GLTFLoader } from "three/examples/jsm/loaders/GLTFLoader.js";
-
-// Offscreen thumbnail capture function - produces a square image
-async function captureModelThumbnail(modelUrl: string): Promise<string | null> {
-  return new Promise((resolve) => {
-    try {
-      // Square dimensions for thumbnail
-      const size = 512;
-      const fov = 50;
-
-      const scene = new THREE.Scene();
-      scene.background = new THREE.Color(0x282828);
-
-      const camera = new THREE.PerspectiveCamera(fov, 1, 0.1, 1000); // Aspect ratio 1 for square
-
-      const renderer = new THREE.WebGLRenderer({
-        antialias: true,
-        alpha: false,
-        preserveDrawingBuffer: true,
-      });
-      renderer.setSize(size, size);
-      renderer.setPixelRatio(1);
-
-      // Add lights
-      const ambientLight = new THREE.AmbientLight(0xffffff, 2);
-      scene.add(ambientLight);
-
-      const hemisphereLight = new THREE.HemisphereLight(
-        0xffffff,
-        0x888888,
-        1.2,
-      );
-      scene.add(hemisphereLight);
-
-      const keyLight = new THREE.DirectionalLight(0xffffff, 2);
-      keyLight.position.set(2, 10, 8);
-      scene.add(keyLight);
-
-      const fillLight = new THREE.DirectionalLight(0xffffff, 1.2);
-      fillLight.position.set(-6, 6, -4);
-      scene.add(fillLight);
-
-      const frontLight = new THREE.DirectionalLight(0xffffff, 1);
-      frontLight.position.set(0, 4, 10);
-      scene.add(frontLight);
-
-      const loader = new GLTFLoader();
-      // Without anonymous CORS the GLTF + textures taint the WebGL canvas, so
-      // toDataURL() below throws a SecurityError and the thumbnail is lost.
-      loader.setCrossOrigin("anonymous");
-      loader.load(
-        modelUrl,
-        (gltf) => {
-          const model = gltf.scene;
-
-          const box = new THREE.Box3().setFromObject(model);
-          const modelSize = box.getSize(new THREE.Vector3());
-
-          const maxDim = Math.max(modelSize.x, modelSize.y, modelSize.z);
-          const scale = 2 / maxDim;
-          model.scale.multiplyScalar(scale);
-
-          const scaledBox = new THREE.Box3().setFromObject(model);
-          const scaledCenter = scaledBox.getCenter(new THREE.Vector3());
-          const scaledSize = scaledBox.getSize(new THREE.Vector3());
-
-          model.position.x = -scaledCenter.x;
-          model.position.z = -scaledCenter.z;
-          model.position.y = -scaledBox.min.y;
-
-          scene.add(model);
-
-          // Calculate camera distance to fit model in view with padding
-          const modelHeight = scaledSize.y;
-          const maxModelDim = Math.max(
-            scaledSize.x,
-            scaledSize.y,
-            scaledSize.z,
-          );
-
-          // Calculate distance needed to fit the model based on FOV
-          // For a 45-degree camera angle, we view from a diagonal
-          const fovRad = (fov * Math.PI) / 180;
-          const fitDistance = maxModelDim / 2 / Math.tan(fovRad / 2);
-
-          // Add some padding (1.3x) and account for diagonal viewing angle
-          const cameraDistance = fitDistance * 1.3;
-
-          // Position camera at 45-degree angle
-          const angle = Math.PI / 4; // 45 degrees
-          camera.position.set(
-            Math.sin(angle) * cameraDistance,
-            modelHeight * 0.5 + cameraDistance * 0.4,
-            Math.cos(angle) * cameraDistance,
-          );
-          camera.lookAt(0, modelHeight * 0.4, 0);
-
-          // Render and capture
-          renderer.render(scene, camera);
-          let dataUrl: string | null = null;
-          try {
-            dataUrl = renderer.domElement.toDataURL("image/png");
-          } catch (err) {
-            // A tainted canvas (CORS) throws SecurityError here. Log so the
-            // failure is diagnosable instead of silently producing no thumbnail.
-            console.warn(
-              "[captureModelThumbnail] toDataURL failed (likely CORS taint):",
-              err,
-            );
-          }
-
-          // Cleanup
-          renderer.dispose();
-          scene.clear();
-
-          resolve(dataUrl);
-        },
-        undefined,
-        (error) => {
-          console.error("[captureModelThumbnail] Error loading model:", error);
-          renderer.dispose();
-          scene.clear();
-          resolve(null);
-        },
-      );
-
-      // Timeout after 30 seconds
-      setTimeout(() => {
-        renderer.dispose();
-        scene.clear();
-        resolve(null);
-      }, 30000);
-    } catch (error) {
-      console.error("[captureModelThumbnail] Error:", error);
-      resolve(null);
-    }
-  });
-}
+import { captureModelThumbnail } from "./captureModelThumbnail";
 
 export interface PendingExternalImage {
   url: string;
diff --git a/frontend/apps/artcraft/app/src/pages/PageImageTo3DObject/captureModelThumbnail.spec.ts b/frontend/apps/artcraft/app/src/pages/PageImageTo3DObject/captureModelThumbnail.spec.ts
new file mode 100644
index 0000000000..b6345a6884
--- /dev/null
+++ b/frontend/apps/artcraft/app/src/pages/PageImageTo3DObject/captureModelThumbnail.spec.ts
@@ -0,0 +1,106 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import * as THREE from "three";
+import { captureModelThumbnail } from "./captureModelThumbnail";
+
+const { renderers, pendingLoads } = vi.hoisted(() => ({
+  renderers: [] as Array<{
+    dispose: ReturnType<typeof vi.fn>;
+    forceContextLoss: ReturnType<typeof vi.fn>;
+  }>,
+  pendingLoads: [] as Array<{
+    onLoad: (gltf: { scene: THREE.Object3D }) => void;
+    onError: (error: unknown) => void;
+  }>,
+}));
+
+// jsdom has no WebGL; only the teardown calls matter here.
+vi.mock("three", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("three")>();
+  class WebGLRenderer {
+    domElement = { toDataURL: () => "data:image/png;base64,AAAA" };
+    dispose = vi.fn();
+    forceContextLoss = vi.fn();
+    constructor() {
+      renderers.push(this);
+    }
+    setSize() {}
+    setPixelRatio() {}
+    render() {}
+  }
+  return { ...actual, WebGLRenderer };
+});
+
+// Loads stay pending until a test settles them.
+vi.mock("three/examples/jsm/loaders/GLTFLoader.js", () => ({
+  GLTFLoader: class {
+    setCrossOrigin() {}
+    load(
+      _url: string,
+      onLoad: (gltf: { scene: THREE.Object3D }) => void,
+      _onProgress: unknown,
+      onError: (error: unknown) => void,
+    ) {
+      pendingLoads.push({ onLoad, onError });
+    }
+  },
+}));
+
+describe("captureModelThumbnail", () => {
+  beforeEach(() => {
+    renderers.length = 0;
+    pendingLoads.length = 0;
+    vi.useFakeTimers();
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it("returns the frame and frees the model, renderer and context once", async () => {
+    const { model, onDispose } = trackedModel();
+    const capture = captureModelThumbnail("model.glb");
+
+    pendingLoads[0].onLoad({ scene: model });
+    const dataUrl = await capture;
+    vi.runAllTimers();
+
+    expect(dataUrl).toMatch(/^data:image\/png/);
+    expect(onDispose).toHaveBeenCalledTimes(1);
+    expect(renderers[0].dispose).toHaveBeenCalledTimes(1);
+    expect(renderers[0].forceContextLoss).toHaveBeenCalledTimes(1);
+  });
+
+  it("frees the renderer and context when the model fails to load", async () => {
+    const capture = captureModelThumbnail("missing.glb");
+    vi.spyOn(console, "error").mockImplementation(() => undefined);
+
+    pendingLoads[0].onError(new Error("404"));
+
+    expect(await capture).toBeNull();
+    expect(renderers[0].dispose).toHaveBeenCalledTimes(1);
+    expect(renderers[0].forceContextLoss).toHaveBeenCalledTimes(1);
+  });
+
+  it("gives up after the timeout and frees a model that loads later", async () => {
+    const capture = captureModelThumbnail("slow.glb");
+
+    vi.advanceTimersByTime(30000);
+    expect(await capture).toBeNull();
+    expect(renderers[0].forceContextLoss).toHaveBeenCalledTimes(1);
+
+    const { model, onDispose } = trackedModel();
+    pendingLoads[0].onLoad({ scene: model });
+
+    expect(onDispose).toHaveBeenCalledTimes(1);
+    expect(renderers[0].dispose).toHaveBeenCalledTimes(1);
+  });
+});
+
+function trackedModel() {
+  const geometry = new THREE.BoxGeometry();
+  const onDispose = vi.fn();
+  geometry.addEventListener("dispose", onDispose);
+  const model = new THREE.Group();
+  model.add(new THREE.Mesh(geometry));
+  return { model, onDispose };
+}
diff --git a/frontend/apps/artcraft/app/src/pages/PageImageTo3DObject/captureModelThumbnail.ts b/frontend/apps/artcraft/app/src/pages/PageImageTo3DObject/captureModelThumbnail.ts
new file mode 100644
index 0000000000..d67d863d19
--- /dev/null
+++ b/frontend/apps/artcraft/app/src/pages/PageImageTo3DObject/captureModelThumbnail.ts
@@ -0,0 +1,160 @@
+import * as THREE from "three";
+import { GLTFLoader } from "three/examples/jsm/loaders/GLTFLoader.js";
+import { disposeObject3D } from "@storyteller/ui-viewer-3d";
+
+const THUMBNAIL_SIZE = 512;
+const FOV = 50;
+const LOAD_TIMEOUT_MS = 30000;
+
+// Offscreen thumbnail capture: loads the model into a throwaway renderer,
+// renders one square frame and returns it as a PNG data URL (null on
+// failure or timeout). The renderer, its WebGL context and the model are
+// freed exactly once, whichever of load, error or timeout comes first.
+export async function captureModelThumbnail(
+  modelUrl: string,
+): Promise<string | null> {
+  return new Promise((resolve) => {
+    try {
+      const scene = new THREE.Scene();
+      scene.background = new THREE.Color(0x282828);
+
+      const camera = new THREE.PerspectiveCamera(FOV, 1, 0.1, 1000); // Aspect ratio 1 for square
+
+      const renderer = new THREE.WebGLRenderer({
+        antialias: true,
+        alpha: false,
+        preserveDrawingBuffer: true,
+      });
+      renderer.setSize(THUMBNAIL_SIZE, THUMBNAIL_SIZE);
+      renderer.setPixelRatio(1);
+
+      addLights(scene);
+
+      let done = false;
+      const finish = (dataUrl: string | null) => {
+        if (done) return;
+        done = true;
+        clearTimeout(timeout);
+        disposeObject3D(scene);
+        renderer.dispose();
+        // The renderer's canvas is never attached, so nothing else can use
+        // this context; release it now instead of at garbage collection.
+        renderer.forceContextLoss();
+        resolve(dataUrl);
+      };
+
+      const timeout = setTimeout(() => finish(null), LOAD_TIMEOUT_MS);
+
+      const loader = new GLTFLoader();
+      // Without anonymous CORS the GLTF + textures taint the WebGL canvas, so
+      // toDataURL() below throws a SecurityError and the thumbnail is lost.
+      loader.setCrossOrigin("anonymous");
+      loader.load(
+        modelUrl,
+        (gltf) => {
+          // Timed out already: the renderer is gone, just free the model.
+          if (done) {
+            disposeObject3D(gltf.scene);
+            return;
+          }
+          const model = gltf.scene;
+          const modelHeight = fitModel(model);
+          scene.add(model);
+          frameCamera(camera, model, modelHeight);
+
+          // Render and capture
+          renderer.render(scene, camera);
+          let dataUrl: string | null = null;
+          try {
+            dataUrl = renderer.domElement.toDataURL("image/png");
+          } catch (err) {
+            // A tainted canvas (CORS) throws SecurityError here. Log so the
+            // failure is diagnosable instead of silently producing no thumbnail.
+            console.warn(
+              "[captureModelThumbnail] toDataURL failed (likely CORS taint):",
+              err,
+            );
+          }
+          finish(dataUrl);
+        },
+        undefined,
+        (error) => {
+          console.error("[captureModelThumbnail] Error loading model:", error);
+          finish(null);
+        },
+      );
+    } catch (error) {
+      console.error("[captureModelThumbnail] Error:", error);
+      resolve(null);
+    }
+  });
+}
+
+// Scale the model to a 2-unit max dimension and stand it centered on the
+// origin. Returns its scaled height.
+function fitModel(model: THREE.Object3D): number {
+  const box = new THREE.Box3().setFromObject(model);
+  const modelSize = box.getSize(new THREE.Vector3());
+
+  const maxDim = Math.max(modelSize.x, modelSize.y, modelSize.z);
+  const scale = 2 / maxDim;
+  model.scale.multiplyScalar(scale);
+
+  const scaledBox = new THREE.Box3().setFromObject(model);
+  const scaledCenter = scaledBox.getCenter(new THREE.Vector3());
+
+  model.position.x = -scaledCenter.x;
+  model.position.z = -scaledCenter.z;
+  model.position.y = -scaledBox.min.y;
+
+  return scaledBox.getSize(new THREE.Vector3()).y;
+}
+
+// Place the camera on a 45-degree diagonal, far enough to fit the model.
+function frameCamera(
+  camera: THREE.PerspectiveCamera,
+  model: THREE.Object3D,
+  modelHeight: number,
+): void {
+  const scaledSize = new THREE.Box3()
+    .setFromObject(model)
+    .getSize(new THREE.Vector3());
+  const maxModelDim = Math.max(scaledSize.x, scaledSize.y, scaledSize.z);
+
+  // Calculate distance needed to fit the model based on FOV
+  // For a 45-degree camera angle, we view from a diagonal
+  const fovRad = (FOV * Math.PI) / 180;
+  const fitDistance = maxModelDim / 2 / Math.tan(fovRad / 2);
+
+  // Add some padding (1.3x) and account for diagonal viewing angle
+  const cameraDistance = fitDistance * 1.3;
+
+  // Position camera at 45-degree angle
+  const angle = Math.PI / 4; // 45 degrees
+  camera.position.set(
+    Math.sin(angle) * cameraDistance,
+    modelHeight * 0.5 + cameraDistance * 0.4,
+    Math.cos(angle) * cameraDistance,
+  );
+  camera.lookAt(0, modelHeight * 0.4, 0);
+}
+
+function addLights(scene: THREE.Scene): void {
+  const ambientLight = new THREE.AmbientLight(0xffffff, 2);
+  scene.add(ambientLight);
+
+  const hemisphereLight = new THREE.HemisphereLight(0xffffff, 0x888888, 1.2);
+  scene.add(hemisphereLight);
+
+  const keyLight = new THREE.DirectionalLight(0xffffff, 2);
+  keyLight.position.set(2, 10, 8);
+  scene.add(keyLight);
+
+  const fillLight = new THREE.DirectionalLight(0xffffff, 1.2);
+  fillLight.position.set(-6, 6, -4);
+  scene.add(fillLight);
+
+  const frontLight = new THREE.DirectionalLight(0xffffff, 1);
+  frontLight.position.set(0, 4, 10);
+  scene.add(frontLight);
+}
diff --git a/frontend/libs/components/pagedraw/src/lib/components/Model3DOverlay.tsx b/frontend/libs/components/pagedraw/src/lib/components/Model3DOverlay.tsx
index d0a1b29278..12b5f28ed3 100644
--- a/frontend/libs/components/pagedraw/src/lib/components/Model3DOverlay.tsx
+++ b/frontend/libs/components/pagedraw/src/lib/components/Model3DOverlay.tsx
@@ -3,6 +3,7 @@ import * as THREE from "three";
 import { OrbitControls } from "three/examples/jsm/controls/OrbitControls.js";
 import { GLTFLoader } from "three/examples/jsm/loaders/GLTFLoader.js";
 import Konva from "konva";
+import { disposeObject3D } from "@storyteller/ui-viewer-3d";
 import { Node } from "../Node";
 import {
   Model3DParams,
@@ -226,11 +227,17 @@ export const Model3DOverlay = React.forwardRef<Model3DOverlayHandle, Model3DOver
       front.position.set(0, 4, 10);
       scene.add(front);
 
-      // Load model
+      // Load model. Set by cleanup: a model that finishes loading after the
+      // overlay closed or switched models is freed instead of added.
+      let cancelled = false;
       const loader = new GLTFLoader();
       loader.load(
         node.modelUrl!,
         (gltf) => {
+          if (cancelled) {
+            disposeObject3D(gltf.scene);
+            return;
+          }
           const model = gltf.scene;
 
           // Auto-fit + apply user scale
@@ -261,18 +268,15 @@ export const Model3DOverlay = React.forwardRef<Model3DOverlayHandle, Model3DOver
       animate();
 
       return () => {
+        cancelled = true;
         if (animFrameRef.current) cancelAnimationFrame(animFrameRef.current);
         controls.dispose();
-        scene.traverse((obj) => {
-          if (obj instanceof THREE.Mesh) {
-            obj.geometry?.dispose();
-            const mats = Array.isArray(obj.material)
-              ? obj.material
-              : [obj.material];
-            mats.forEach((m) => m?.dispose());
-          }
-        });
+        disposeObject3D(scene);
         renderer.dispose();
+        // A model change re-runs this effect on the same canvas, which hands
+        // the next renderer this same context, so only force the loss once
+        // the canvas has left the DOM (the overlay closed).
+        if (!canvas.isConnected) renderer.forceContextLoss();
       };
       // eslint-disable-next-line react-hooks/exhaustive-deps
     }, [node.modelUrl]);
diff --git a/frontend/libs/components/pagedraw/src/lib/utilities/render3DModel.spec.ts b/frontend/libs/components/pagedraw/src/lib/utilities/render3DModel.spec.ts
new file mode 100644
index 0000000000..a2d6141fd8
--- /dev/null
+++ b/frontend/libs/components/pagedraw/src/lib/utilities/render3DModel.spec.ts
@@ -0,0 +1,82 @@
+import * as THREE from "three";
+import {
+  DEFAULT_MODEL3D_PARAMS,
+  render3DModelToDataUrl,
+} from "./render3DModel";
+
+const { renderers, gltfOutcome } = vi.hoisted(() => ({
+  renderers: [] as FakeRenderer[],
+  gltfOutcome: { scene: undefined as unknown, error: undefined as unknown },
+}));
+
+type FakeRenderer = {
+  dispose: ReturnType<typeof vi.fn>;
+  forceContextLoss: ReturnType<typeof vi.fn>;
+};
+
+// jsdom has no WebGL; only the teardown calls matter here.
+vi.mock("three", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("three")>();
+  class WebGLRenderer {
+    domElement = { toDataURL: () => "data:image/png;base64,AAAA" };
+    dispose = vi.fn();
+    forceContextLoss = vi.fn();
+    constructor() {
+      renderers.push(this);
+    }
+    setClearColor() {}
+    setSize() {}
+    render() {}
+  }
+  return { ...actual, WebGLRenderer };
+});
+
+vi.mock("three/examples/jsm/loaders/GLTFLoader.js", () => ({
+  GLTFLoader: class {
+    load(
+      _url: string,
+      onLoad: (gltf: { scene: unknown }) => void,
+      _onProgress: unknown,
+      onError: (error: unknown) => void,
+    ) {
+      if (gltfOutcome.error) onError(gltfOutcome.error);
+      else onLoad({ scene: gltfOutcome.scene });
+    }
+  },
+}));
+
+describe("render3DModelToDataUrl", () => {
+  beforeEach(() => {
+    renderers.length = 0;
+    gltfOutcome.scene = undefined;
+    gltfOutcome.error = undefined;
+  });
+
+  it("frees the model and the renderer's context after rendering", async () => {
+    const geometry = new THREE.BoxGeometry();
+    const onDispose = vi.fn();
+    geometry.addEventListener("dispose", onDispose);
+    gltfOutcome.scene = new THREE.Mesh(geometry);
+
+    const dataUrl = await render3DModelToDataUrl(
+      "model.glb",
+      DEFAULT_MODEL3D_PARAMS,
+    );
+
+    expect(dataUrl).toMatch(/^data:image\/png/);
+    expect(onDispose).toHaveBeenCalledTimes(1);
+    expect(renderers[0].dispose).toHaveBeenCalledTimes(1);
+    expect(renderers[0].forceContextLoss).toHaveBeenCalledTimes(1);
+  });
+
+  it("frees the renderer's context when the model fails to load", async () => {
+    gltfOutcome.error = new Error("404");
+
+    await expect(
+      render3DModelToDataUrl("missing.glb", DEFAULT_MODEL3D_PARAMS),
+    ).rejects.toThrow("404");
+
+    expect(renderers[0].dispose).toHaveBeenCalledTimes(1);
+    expect(renderers[0].forceContextLoss).toHaveBeenCalledTimes(1);
+  });
+});
diff --git a/frontend/libs/components/pagedraw/src/lib/utilities/render3DModel.ts b/frontend/libs/components/pagedraw/src/lib/utilities/render3DModel.ts
index 5906c1243e..c804b5f57c 100644
--- a/frontend/libs/components/pagedraw/src/lib/utilities/render3DModel.ts
+++ b/frontend/libs/components/pagedraw/src/lib/utilities/render3DModel.ts
@@ -1,5 +1,6 @@
 import * as THREE from "three";
 import { GLTFLoader } from "three/examples/jsm/loaders/GLTFLoader.js";
+import { disposeObject3D } from "@storyteller/ui-viewer-3d";
 
 export interface Model3DParams {
   cameraPosition: { x: number; y: number; z: number };
@@ -76,18 +77,16 @@ function normalizeAndPlaceModel(
   model.position.y = -scaledBox.min.y;
 }
 
+// The renderer and its canvas are throwaway, so free the scene and then the
+// context itself; otherwise each render holds a WebGL context until the
+// canvas is garbage collected.
 function disposeScene(
   scene: THREE.Scene,
   renderer: THREE.WebGLRenderer,
 ): void {
-  scene.traverse((obj) => {
-    if (obj instanceof THREE.Mesh) {
-      obj.geometry?.dispose();
-      const mats = Array.isArray(obj.material) ? obj.material : [obj.material];
-      mats.forEach((m) => m?.dispose());
-    }
-  });
+  disposeObject3D(scene);
   renderer.dispose();
+  renderer.forceContextLoss();
 }
 
 export async function render3DModelToDataUrl(
diff --git a/frontend/libs/components/pagedraw/tsconfig.lib.json b/frontend/libs/components/pagedraw/tsconfig.lib.json
index 2d93887a85..835b56cfde 100644
--- a/frontend/libs/components/pagedraw/tsconfig.lib.json
+++ b/frontend/libs/components/pagedraw/tsconfig.lib.json
@@ -88,6 +88,9 @@
     },
     {
       "path": "../modal/tsconfig.lib.json"
+    },
+    {
+      "path": "../viewer-3d/tsconfig.lib.json"
     }
   ]
 }
diff --git a/frontend/libs/components/pagescene/src/lib/engine/editor.ts b/frontend/libs/components/pagescene/src/lib/engine/editor.ts
index 96af58ca37..075cb39d43 100644
--- a/frontend/libs/components/pagescene/src/lib/engine/editor.ts
+++ b/frontend/libs/components/pagescene/src/lib/engine/editor.ts
@@ -1127,11 +1127,27 @@ class Editor {
 
     this.bus.emit(new SceneLoadedEvent(false));
     this.stopRenderLoop();
+    this.viewport.dispose();
+
+    // Free the scene's GPU resources. EngineProvider serialized the scene
+    // before calling us, and the next mount builds a fresh Editor, so
+    // nothing reads this scene again. The gizmo's dispose also removes its
+    // pointer listeners from the canvas.
+    this.entranceAnimator.clear();
+    this.gizmo.control?.dispose();
+    this.activeScene.dispose();
 
     // Fix: dispose 3D contexts
     this.renderer?.dispose();
     this.postProcessing.dispose();
     this.rawRenderer?.dispose();
+    // dispose() leaves the GL objects themselves (render targets, programs)
+    // in the context. Leaving the page detaches the canvases, and the
+    // context then lingers until garbage collection, two per visit. A
+    // scene change keeps the canvases mounted and the next Editor reuses
+    // their contexts, so only release a context whose canvas is gone.
+    releaseContextIfDetached(this.renderer);
+    releaseContextIfDetached(this.rawRenderer);
 
     this.isMounted = false;
     this.bus.emit(new EngineInitializedEvent(false));
@@ -1145,4 +1161,10 @@ class Editor {
   }
 }
 
+function releaseContextIfDetached(renderer: THREE.WebGLRenderer | undefined) {
+  if (renderer && !renderer.domElement.isConnected) {
+    renderer.forceContextLoss();
+  }
+}
+
 export default Editor;
diff --git a/frontend/libs/components/pagescene/src/lib/engine/editor/ViewportController.spec.ts b/frontend/libs/components/pagescene/src/lib/engine/editor/ViewportController.spec.ts
new file mode 100644
index 0000000000..7aca5291ad
--- /dev/null
+++ b/frontend/libs/components/pagescene/src/lib/engine/editor/ViewportController.spec.ts
@@ -0,0 +1,38 @@
+import { ViewportController } from "./ViewportController";
+
+describe("ViewportController", () => {
+  it("stops observing the container on dispose", () => {
+    const observers = stubResizeObserver();
+    const renderScene = vi.fn();
+    const viewport = new ViewportController({
+      getCamera: () => null,
+      getRenderCamera: () => null,
+      getRenderer: () => ({ setSize: vi.fn(), setPixelRatio: vi.fn() }) as never,
+      getRenderAspectRatio: () => 1,
+      resizePostProcessing: vi.fn(),
+      renderScene,
+    });
+    viewport.container = document.createElement("div");
+
+    viewport.setupResizeObserver();
+    viewport.dispose();
+
+    expect(observers[0].disconnect).toHaveBeenCalledTimes(1);
+  });
+});
+
+// jsdom has no ResizeObserver; record each one the controller creates.
+function stubResizeObserver() {
+  const observers: Array<{ disconnect: ReturnType<typeof vi.fn> }> = [];
+  vi.stubGlobal(
+    "ResizeObserver",
+    class {
+      disconnect = vi.fn();
+      constructor() {
+        observers.push(this);
+      }
+      observe() {}
+    },
+  );
+  return observers;
+}
diff --git a/frontend/libs/components/pagescene/src/lib/engine/editor/ViewportController.ts b/frontend/libs/components/pagescene/src/lib/engine/editor/ViewportController.ts
index e23a3184a2..a2ff8280a4 100644
--- a/frontend/libs/components/pagescene/src/lib/engine/editor/ViewportController.ts
+++ b/frontend/libs/components/pagescene/src/lib/engine/editor/ViewportController.ts
@@ -100,4 +100,12 @@ export class ViewportController {
     });
     this.observer.observe(this.container);
   }
+
+  // Stop observing on unmount. The container can outlive this editor (a
+  // scene change keeps it mounted), and a live observer would keep
+  // re-rendering the dead editor's scene on every resize.
+  dispose() {
+    this.observer?.disconnect();
+    this.observer = undefined;
+  }
 }
diff --git a/frontend/libs/components/pagescene/src/lib/engine/helper.ts b/frontend/libs/components/pagescene/src/lib/engine/helper.ts
index b90ef1d826..8df19a90fa 100644
--- a/frontend/libs/components/pagescene/src/lib/engine/helper.ts
+++ b/frontend/libs/components/pagescene/src/lib/engine/helper.ts
@@ -148,45 +148,11 @@ function removeObject3D(object3D) {
       return;
     }
 
-    // Finally remove the object from the scene
+    // Finally remove the object from the scene and free its GPU resources.
+    // Undo re-loads deleted objects from a snapshot (DeleteAction), so
+    // nothing reuses this instance.
     this.scene.scene.remove(obj);
-
-    obj.traverse(child => {
-      (child as THREE.Mesh)?.geometry?.dispose()
-      // eslint-disable-next-line @typescript-eslint/no-explicit-any
-      const childTexture = (child as any).texture;
-      if (Array.isArray(childTexture)) {
-        childTexture.forEach(mat => mat.dispose());
-      } else if (childTexture) {
-        childTexture.dispose();
-      }
-
-      const childMaterial = (child as THREE.Mesh).material;
-      if (Array.isArray(childMaterial)) {
-        childMaterial.forEach(mat => mat.dispose());
-      } else if (childMaterial) {
-        childMaterial.dispose();
-      }
-    })
-
-    // eslint-disable-next-line @typescript-eslint/no-explicit-any
-    const objTexture = (obj as any).texture;
-    if (Array.isArray(objTexture)) {
-      objTexture.forEach(mat => mat.dispose());
-    } else if (objTexture) {
-      objTexture.dispose();
-    }
-
-    const objMaterial = (obj as THREE.Mesh).material;
-    if (Array.isArray(objMaterial)) {
-      objMaterial.forEach(mat => mat.dispose());
-    } else if (objMaterial) {
-      objMaterial.dispose();
-    }
-
-    if ((obj as THREE.Mesh).geometry) {
-      (obj as THREE.Mesh).geometry.dispose()
-    }
+    this.scene.disposeObject(obj);
 
     this.deps.bus.emit(new ObjectRemovedEvent(uuid));
     this.deps.clearSelected();
diff --git a/frontend/libs/components/pagescene/src/lib/engine/scene.spec.ts b/frontend/libs/components/pagescene/src/lib/engine/scene.spec.ts
new file mode 100644
index 0000000000..37b9731f6b
--- /dev/null
+++ b/frontend/libs/components/pagescene/src/lib/engine/scene.spec.ts
@@ -0,0 +1,167 @@
+import * as THREE from "three";
+import Scene from "./scene";
+
+// Scene imports Spark for splat loading; none of these tests load one.
+vi.mock("@sparkjsdev/spark", async () => {
+  const { Object3D } = await import("three");
+  return {
+    SplatMesh: class extends Object3D {},
+    SparkRenderer: class extends Object3D {},
+  };
+});
+
+// The Addons barrel pulls in a lottie canvas module jsdom cannot run; Scene
+// only needs these two names from it.
+vi.mock("three/examples/jsm/Addons.js", async () => {
+  const { Mesh } = await import("three");
+  return { MMDAnimationHelper: class {}, Water: class extends Mesh {} };
+});
+
+describe("Scene disposal", () => {
+  describe("disposeObject", () => {
+    it("frees the object's GPU resources", () => {
+      const scene = makeScene();
+      const geometry = new THREE.BoxGeometry();
+      const onDispose = vi.fn();
+      geometry.addEventListener("dispose", onDispose);
+
+      scene.disposeObject(new THREE.Mesh(geometry));
+
+      expect(onDispose).toHaveBeenCalledTimes(1);
+    });
+
+    it("stops shader ticks for disposed water but keeps the rest", () => {
+      const scene = makeScene();
+      const water = waterLikeMesh();
+      const otherWater = waterLikeMesh();
+      scene.shader_objects = [water, otherWater] as never;
+      const group = new THREE.Group();
+      group.add(water);
+
+      scene.disposeObject(group);
+
+      expect(scene.shader_objects).toEqual([otherWater]);
+    });
+
+    it("stops and forgets the video behind a video plane", () => {
+      const scene = makeScene();
+      const video = stubbedVideo();
+      const otherVideo = stubbedVideo();
+      scene.video_planes = [video, otherVideo];
+      const plane = new THREE.Mesh(
+        new THREE.PlaneGeometry(),
+        new THREE.MeshBasicMaterial({ map: new THREE.VideoTexture(video) }),
+      );
+
+      scene.disposeObject(plane);
+
+      expect(video.pause).toHaveBeenCalled();
+      expect(video.load).toHaveBeenCalled();
+      expect(video.hasAttribute("src")).toBe(false);
+      expect(scene.video_planes).toEqual([otherVideo]);
+      expect(otherVideo.pause).not.toHaveBeenCalled();
+    });
+
+    it("removes MMD meshes from the animation helper", () => {
+      const scene = makeScene();
+      const mmd = new THREE.SkinnedMesh();
+      const other = new THREE.SkinnedMesh();
+      const remove = vi.fn();
+      scene.helper = { meshes: [mmd, other], remove } as never;
+
+      scene.disposeObject(mmd);
+
+      expect(remove).toHaveBeenCalledTimes(1);
+      expect(remove).toHaveBeenCalledWith(mmd);
+    });
+  });
+
+  describe("disposeContents", () => {
+    it("empties the scene and frees every child", () => {
+      const scene = makeScene();
+      const geometries = [new THREE.BoxGeometry(), new THREE.SphereGeometry()];
+      const disposed = new Set<THREE.BufferGeometry>();
+      for (const geometry of geometries) {
+        geometry.addEventListener("dispose", () => disposed.add(geometry));
+        scene.scene.add(new THREE.Mesh(geometry));
+      }
+      const child = scene.scene.children[0];
+      scene.hot_items = [child];
+
+      scene.disposeContents();
+
+      expect(scene.scene.children).toHaveLength(0);
+      expect(child.parent).toBeNull();
+      expect(scene.hot_items).toEqual([]);
+      expect(disposed).toEqual(new Set(geometries));
+    });
+
+    it("leaves the background for the skybox to replace", () => {
+      const scene = makeScene();
+      const background = new THREE.CubeTexture();
+      const onDispose = vi.fn();
+      background.addEventListener("dispose", onDispose);
+      scene.scene.background = background;
+
+      scene.disposeContents();
+
+      expect(scene.scene.background).toBe(background);
+      expect(onDispose).not.toHaveBeenCalled();
+    });
+  });
+
+  it("dispose frees the contents and the background", () => {
+    const scene = makeScene();
+    const geometry = new THREE.BoxGeometry();
+    const background = new THREE.CubeTexture();
+    const disposed = new Set<unknown>();
+    geometry.addEventListener("dispose", () => disposed.add(geometry));
+    background.addEventListener("dispose", () => disposed.add(background));
+    scene.scene.add(new THREE.Mesh(geometry));
+    scene.scene.background = background;
+
+    scene.dispose();
+
+    expect(disposed).toEqual(new Set([geometry, background]));
+    expect(scene.scene.children).toHaveLength(0);
+    expect(scene.scene.background).toBeNull();
+  });
+
+  it("disposeBackground frees a texture background", () => {
+    const scene = makeScene();
+    const background = new THREE.CubeTexture();
+    const onDispose = vi.fn();
+    background.addEventListener("dispose", onDispose);
+    scene.scene.background = background;
+
+    scene.disposeBackground();
+
+    expect(onDispose).toHaveBeenCalledTimes(1);
+  });
+});
+
+function makeScene(): Scene {
+  return new Scene("test", "::CAM::", () => undefined, 1, {
+    getCameras: () => [],
+    getSelectedCameraId: () => "main",
+    fetchAsset: () => Promise.reject(new Error("no network in tests")),
+    getMediaUrlByToken: () => Promise.reject(new Error("no network in tests")),
+  });
+}
+
+// Scene only tracks Water instances by identity; a plain mesh stands in.
+function waterLikeMesh(): THREE.Mesh {
+  return new THREE.Mesh(
+    new THREE.PlaneGeometry(),
+    new THREE.MeshBasicMaterial(),
+  );
+}
+
+// jsdom does not implement media playback, so stub the calls stopVideo makes.
+function stubbedVideo(): HTMLVideoElement {
+  const video = document.createElement("video");
+  video.src = "https://example.invalid/clip.mp4";
+  video.pause = vi.fn();
+  video.load = vi.fn();
+  return video;
+}
diff --git a/frontend/libs/components/pagescene/src/lib/engine/scene.ts b/frontend/libs/components/pagescene/src/lib/engine/scene.ts
index cf5972e565..83fbae813d 100644
--- a/frontend/libs/components/pagescene/src/lib/engine/scene.ts
+++ b/frontend/libs/components/pagescene/src/lib/engine/scene.ts
@@ -13,6 +13,10 @@ import type { Camera } from "@storyteller/common";
 import toast from "react-hot-toast";
 import { SplatMesh } from "@sparkjsdev/spark";
 import { ensureInternalBbox } from "./internalBbox";
+import {
+  collectObjectTextures,
+  disposeObject3D,
+} from "@storyteller/ui-viewer-3d";
 
 // Capabilities Scene needs from outside its own state. Editor wires
 // these in inline at construction (Phase 2 idiom — same shape as
@@ -134,16 +138,64 @@ class Scene {
   }
 
   clear() {
-    this.scene.children = [];
-    // hot_items held detached keyframe-point refs across reloads; reset it
-    // so it never carries stale objects from a previous scene.
-    this.hot_items = [];
+    this.disposeContents();
     this._createGrid();
     this._create_base_lighting();
     this._create_skybox();
     this._create_camera_obj();
   }
 
+  // Remove everything from the scene and free its GPU resources. The
+  // background is left in place: _create_skybox frees it when it is
+  // replaced, and teardown frees it through disposeBackground.
+  disposeContents() {
+    this.disposeObject(this.scene);
+    this.scene.clear();
+    // hot_items held detached keyframe-point refs across reloads; reset it
+    // so it never carries stale objects from a previous scene.
+    this.hot_items = [];
+  }
+
+  // Free an object tree that has left the scene for good: its GPU
+  // resources, plus its entries in the per-object registries (Water
+  // shaders ticked every frame, video elements, MMD animation).
+  disposeObject(root: THREE.Object3D) {
+    const inTree = new Set<THREE.Object3D>();
+    root.traverse((child) => inTree.add(child));
+    this.shader_objects = this.shader_objects.filter(
+      (water) => !inTree.has(water),
+    );
+    for (const mesh of [...(this.helper?.meshes ?? [])]) {
+      if (inTree.has(mesh)) this.helper.remove(mesh);
+    }
+
+    const videos = new Set<HTMLVideoElement>();
+    for (const texture of collectObjectTextures(root)) {
+      if (texture instanceof THREE.VideoTexture) videos.add(texture.image);
+    }
+    for (const video of videos) stopVideo(video);
+    this.video_planes = this.video_planes.filter(
+      (video) => !videos.has(video),
+    );
+
+    disposeObject3D(root);
+  }
+
+  // Final teardown when the owning Editor unmounts: free the contents and
+  // the background. The Scene is not used again — every mount builds a new
+  // Editor, and EngineProvider serializes the scene before unmounting.
+  dispose() {
+    this.disposeContents();
+    this.disposeBackground();
+    this.scene.background = null;
+  }
+
+  disposeBackground() {
+    if (this.scene.background instanceof THREE.Texture) {
+      this.scene.background.dispose();
+    }
+  }
+
   async instantiate(
     name: string,
     pos: THREE.Vector3 = new THREE.Vector3(0, 0, 0),
@@ -1118,6 +1170,9 @@ class Scene {
   // default skybox.
   _create_skybox() {
     const loader = new THREE.CubeTextureLoader();
+    // Every branch below replaces the background, so free the cube texture
+    // being replaced (skybox switches and New Scene used to leak it).
+    this.disposeBackground();
 
     // Theme-aware: in light mode, use a near-white background for better contrast with UI
     try {
@@ -1272,4 +1327,12 @@ class Scene {
 
 }
 
+// Pausing alone keeps the decoder and buffered media alive; dropping the
+// source and reloading is what releases them.
+function stopVideo(video: HTMLVideoElement) {
+  video.pause();
+  video.removeAttribute("src");
+  video.load();
+}
+
 export default Scene;
diff --git a/frontend/libs/components/pagescene/src/lib/proxy/storyteller_proxy_scene.spec.ts b/frontend/libs/components/pagescene/src/lib/proxy/storyteller_proxy_scene.spec.ts
new file mode 100644
index 0000000000..fbb7123613
--- /dev/null
+++ b/frontend/libs/components/pagescene/src/lib/proxy/storyteller_proxy_scene.spec.ts
@@ -0,0 +1,91 @@
+import * as THREE from "three";
+import Scene from "../engine/scene";
+import type { LoadTicket } from "../engine/save_manager";
+import { StoryTellerProxyScene } from "./storyteller_proxy_scene";
+
+vi.mock("@sparkjsdev/spark", async () => {
+  const { Object3D } = await import("three");
+  return {
+    SplatMesh: class extends Object3D {},
+    SparkRenderer: class extends Object3D {},
+  };
+});
+
+// The Addons barrel pulls in a lottie canvas module jsdom cannot run.
+vi.mock("three/examples/jsm/Addons.js", async () => {
+  const { Mesh } = await import("three");
+  return { MMDAnimationHelper: class {}, Water: class extends Mesh {} };
+});
+
+const BOX_JSON = {
+  media_file_token: "Parim",
+  object_name: "Box",
+  object_user_data_name: "Box",
+  object_uuid: "box-uuid",
+  position: new THREE.Vector3(),
+  rotation: new THREE.Vector3(),
+  scale: new THREE.Vector3(1, 1, 1),
+  color: "#FFFFFF",
+  metalness: 0,
+  shininess: 0.5,
+  specular: 0,
+  locked: false,
+  visible: true,
+  media_file_type: "none",
+  user_data: { shapeKey: "Box" },
+};
+
+describe("loadFromSceneJson", () => {
+  it("removes and frees objects that finish after the load is cancelled", async () => {
+    const scene = makeScene();
+    const proxy = new StoryTellerProxyScene(2, scene);
+    const ticket = makeTicket();
+    const onDispose = vi.fn();
+    const addListener = trackFirstMeshGeometry(scene, onDispose);
+
+    const load = proxy.loadFromSceneJson([BOX_JSON] as never, "m_1", 2, ticket);
+    // The box is created before the loader's first await on its tasks;
+    // cancel while that await is pending, as a newer load or an unmount
+    // would.
+    addListener();
+    ticket.cancelled = true;
+    await load;
+
+    expect(scene.scene.getObjectByProperty("name", "Box")).toBeUndefined();
+    expect(onDispose).toHaveBeenCalledTimes(1);
+  });
+
+  it("keeps the loaded objects when the load is not cancelled", async () => {
+    const scene = makeScene();
+    const proxy = new StoryTellerProxyScene(2, scene);
+
+    await proxy.loadFromSceneJson([BOX_JSON] as never, "m_1", 2, makeTicket());
+
+    expect(scene.get_object_by_uuid("box-uuid")).toBeDefined();
+  });
+});
+
+function makeScene(): Scene {
+  return new Scene("test", "::CAM::", () => undefined, 2, {
+    getCameras: () => [],
+    getSelectedCameraId: () => "main",
+    fetchAsset: () => Promise.reject(new Error("no network in tests")),
+    getMediaUrlByToken: () => Promise.reject(new Error("no network in tests")),
+  });
+}
+
+function makeTicket(): LoadTicket {
+  return { cancelled: false, signal: new AbortController().signal };
+}
+
+// Returns a function that, once the load has created its box, subscribes
+// `onDispose` to that box's geometry.
+function trackFirstMeshGeometry(
+  scene: Scene,
+  onDispose: () => void,
+): () => void {
+  return () => {
+    const box = scene.scene.getObjectByProperty("name", "Box") as THREE.Mesh;
+    box.geometry.addEventListener("dispose", onDispose);
+  };
+}
diff --git a/frontend/libs/components/pagescene/src/lib/proxy/storyteller_proxy_scene.ts b/frontend/libs/components/pagescene/src/lib/proxy/storyteller_proxy_scene.ts
index 225a7d790e..4debc117f4 100644
--- a/frontend/libs/components/pagescene/src/lib/proxy/storyteller_proxy_scene.ts
+++ b/frontend/libs/components/pagescene/src/lib/proxy/storyteller_proxy_scene.ts
@@ -128,9 +128,9 @@ export class StoryTellerProxyScene {
   ) {
     if (scene_json == null || this.scene == null) return;
 
-    while (this.scene.scene.children.length > 0) {
-      this.scene.scene.remove(this.scene.scene.children[0]);
-    }
+    // Free the outgoing scene before loading over it; removing the
+    // children alone left all of their GPU resources allocated.
+    this.scene.disposeContents();
 
     // Warm Scene's URL cache up front so per-asset loadObject() calls
     // never hit the network for token→URL resolution. One batch call
@@ -229,7 +229,10 @@ export class StoryTellerProxyScene {
     );
 
     const settled = await Promise.allSettled(tasks);
-    if (ticket?.cancelled) return;
+    if (ticket?.cancelled) {
+      this.discardLoadedObjects(settled);
+      return;
+    }
 
     // Synchronous transform-application pass. We walk results in
     // original JSON order to preserve scene.children insertion
@@ -295,4 +298,21 @@ export class StoryTellerProxyScene {
     this.scene._createGrid();
     this.scene.updateSkybox(skybox_media_id);
   }
+
+  // A cancelled load has still added whatever finished loading to the
+  // scene. Take those objects back out and free them, or they would leak
+  // and, when a newer load superseded this one, show up in its scene.
+  // Lights are skipped: Scene tracks its base lights in fields that a
+  // newer load may have re-pointed at them.
+  private discardLoadedObjects(
+    settled: PromiseSettledResult<{ obj: THREE.Object3D | undefined }>[],
+  ) {
+    for (const result of settled) {
+      if (result.status !== "fulfilled") continue;
+      const { obj } = result.value;
+      if (!obj || obj instanceof THREE.Light) continue;
+      obj.removeFromParent();
+      this.scene.disposeObject(obj);
+    }
+  }
 }
diff --git a/frontend/libs/components/pagescene/tsconfig.lib.json b/frontend/libs/components/pagescene/tsconfig.lib.json
index f7a21e4eb9..28460cea8e 100644
--- a/frontend/libs/components/pagescene/tsconfig.lib.json
+++ b/frontend/libs/components/pagescene/tsconfig.lib.json
@@ -124,6 +124,9 @@
     },
     {
       "path": "../../icons/tsconfig.lib.json"
+    },
+    {
+      "path": "../viewer-3d/tsconfig.lib.json"
     }
   ]
 }
diff --git a/frontend/libs/components/upload-modal/src/lib/UploadModal3D/UploadFiles3D.tsx b/frontend/libs/components/upload-modal/src/lib/UploadModal3D/UploadFiles3D.tsx
index 58c3b74552..dd2efe88ae 100644
--- a/frontend/libs/components/upload-modal/src/lib/UploadModal3D/UploadFiles3D.tsx
+++ b/frontend/libs/components/upload-modal/src/lib/UploadModal3D/UploadFiles3D.tsx
@@ -160,12 +160,13 @@ export const UploadFiles3D = ({
     });
   };
 
+  // Tears down the current preview: stops its loop, cancels in-flight
+  // loads and frees its scene and renderer (see loadPreviewOnCanvas).
+  const disposePreviewRef = useRef<(() => void) | null>(null);
   const disposeRenderer = () => {
-    if (rendererRef.current) {
-      rendererRef.current.setAnimationLoop(null);
-      rendererRef.current.dispose();
-      rendererRef.current = null;
-    }
+    disposePreviewRef.current?.();
+    disposePreviewRef.current = null;
+    rendererRef.current = null;
   };
 
   // Normalize an FBX to GLB in the background. Completion swaps the entry's
@@ -237,7 +238,7 @@ export const UploadFiles3D = ({
       return;
     }
 
-    const { renderer, camera, selectAnimation, setSkeletonVisible, cancel } =
+    const { renderer, camera, selectAnimation, setSkeletonVisible, dispose } =
       loadPreviewOnCanvas({
         file: currentFile,
         canvas: canvasRef.current,
@@ -250,17 +251,15 @@ export const UploadFiles3D = ({
         },
       });
     rendererRef.current = renderer;
+    disposePreviewRef.current = dispose;
     cameraRef.current = camera;
     selectAnimationRef.current = selectAnimation;
     setSkeletonVisibleRef.current = setSkeletonVisible;
 
-    return () => {
-      // Cancel BEFORE disposing: an in-flight load's callbacks must not
-      // render on the disposed renderer or write into the next preview's
-      // status/animation/rig state (or its thumbnail).
-      cancel();
-      disposeRenderer();
-    };
+    // dispose() cancels first: an in-flight load's callbacks must not
+    // render on the disposed renderer or write into the next preview's
+    // status/animation/rig state (or its thumbnail).
+    return disposeRenderer;
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [previewIndex, filesVersion]);
 
diff --git a/frontend/libs/components/upload-modal/src/lib/UploadModal3D/utilities/loadPreviewOnCanvas.spec.ts b/frontend/libs/components/upload-modal/src/lib/UploadModal3D/utilities/loadPreviewOnCanvas.spec.ts
new file mode 100644
index 0000000000..4e97bd7981
--- /dev/null
+++ b/frontend/libs/components/upload-modal/src/lib/UploadModal3D/utilities/loadPreviewOnCanvas.spec.ts
@@ -0,0 +1,124 @@
+import * as THREE from "three";
+import { loadPreviewOnCanvas } from "./loadPreviewOnCanvas";
+
+const { renderers, pendingGltfLoads } = vi.hoisted(() => ({
+  renderers: [] as Array<{
+    dispose: ReturnType<typeof vi.fn>;
+    forceContextLoss: ReturnType<typeof vi.fn>;
+    setAnimationLoop: ReturnType<typeof vi.fn>;
+  }>,
+  pendingGltfLoads: [] as Array<(gltf: { scene: unknown }) => void>,
+}));
+
+// jsdom has no WebGL; only the lifecycle calls matter here.
+vi.mock("three", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("three")>();
+  class WebGLRenderer {
+    dispose = vi.fn();
+    forceContextLoss = vi.fn();
+    setAnimationLoop = vi.fn();
+    constructor() {
+      renderers.push(this);
+    }
+    setSize() {}
+    render() {}
+  }
+  return { ...actual, WebGLRenderer };
+});
+
+// Loads stay pending until a test resolves them, to model a load that
+// finishes after the preview was superseded.
+vi.mock("three/addons/loaders/GLTFLoader.js", () => ({
+  GLTFLoader: class {
+    load(_url: string, onLoad: (gltf: { scene: unknown }) => void) {
+      pendingGltfLoads.push(onLoad);
+    }
+  },
+}));
+
+vi.mock("@sparkjsdev/spark", async () => {
+  const { Object3D } = await import("three");
+  return {
+    SplatFileType: { SPZ: "spz" },
+    SplatMesh: class extends Object3D {},
+    SparkRenderer: class extends Object3D {},
+  };
+});
+
+describe("loadPreviewOnCanvas dispose", () => {
+  beforeEach(() => {
+    renderers.length = 0;
+    pendingGltfLoads.length = 0;
+    vi.stubGlobal("URL", {
+      ...URL,
+      createObjectURL: vi.fn(() => "blob:preview"),
+      revokeObjectURL: vi.fn(),
+    });
+  });
+
+  it("stops the loop, frees the renderer and revokes the blob URL", () => {
+    const canvas = attachedCanvas();
+    const preview = loadPreviewOnCanvas({
+      file: new File([], "model.glb"),
+      canvas,
+      statusCallback: vi.fn(),
+    });
+
+    preview.dispose();
+
+    const renderer = renderers[0];
+    expect(renderer.setAnimationLoop).toHaveBeenLastCalledWith(null);
+    expect(renderer.dispose).toHaveBeenCalledTimes(1);
+    expect(URL.revokeObjectURL).toHaveBeenCalledWith("blob:preview");
+  });
+
+  it("keeps the context while the canvas is reused for the next file", () => {
+    const preview = loadPreviewOnCanvas({
+      file: new File([], "model.glb"),
+      canvas: attachedCanvas(),
+      statusCallback: vi.fn(),
+    });
+
+    preview.dispose();
+
+    expect(renderers[0].forceContextLoss).not.toHaveBeenCalled();
+  });
+
+  it("releases the context once the canvas has left the DOM", () => {
+    const canvas = attachedCanvas();
+    const preview = loadPreviewOnCanvas({
+      file: new File([], "model.glb"),
+      canvas,
+      statusCallback: vi.fn(),
+    });
+
+    canvas.remove();
+    preview.dispose();
+
+    expect(renderers[0].forceContextLoss).toHaveBeenCalledTimes(1);
+  });
+
+  it("ignores a model that finishes loading after dispose", () => {
+    const statusCallback = vi.fn();
+    const preview = loadPreviewOnCanvas({
+      file: new File([], "model.glb"),
+      canvas: attachedCanvas(),
+      statusCallback,
+    });
+
+    preview.dispose();
+    const lateModel = new THREE.Group();
+    lateModel.add(new THREE.Mesh(new THREE.BoxGeometry()));
+    pendingGltfLoads[0]({ scene: lateModel });
+
+    expect(lateModel.children).toHaveLength(1);
+    expect(statusCallback).not.toHaveBeenCalled();
+  });
+});
+
+function attachedCanvas(): HTMLCanvasElement {
+  const canvas = document.createElement("canvas");
+  canvas.getContext = vi.fn(() => null) as never;
+  document.body.appendChild(canvas);
+  return canvas;
+}
diff --git a/frontend/libs/components/upload-modal/src/lib/UploadModal3D/utilities/loadPreviewOnCanvas.ts b/frontend/libs/components/upload-modal/src/lib/UploadModal3D/utilities/loadPreviewOnCanvas.ts
index b1eba45872..d3209c218f 100644
--- a/frontend/libs/components/upload-modal/src/lib/UploadModal3D/utilities/loadPreviewOnCanvas.ts
+++ b/frontend/libs/components/upload-modal/src/lib/UploadModal3D/utilities/loadPreviewOnCanvas.ts
@@ -3,10 +3,12 @@ import { GLTFLoader } from "three/addons/loaders/GLTFLoader.js";
 import { FontLoader } from "three/addons/loaders/FontLoader.js";
 import { TextGeometry } from "three/addons/geometries/TextGeometry.js";
 import { SplatFileType, SplatMesh } from "@sparkjsdev/spark";
-import { NodeHierarchyHelper } from "@storyteller/ui-viewer-3d";
+import { NodeHierarchyHelper, disposeObject3D } from "@storyteller/ui-viewer-3d";
 
 interface LoaderInterface {
   file: File;
+  // Blob URL for `file`, revoked when the preview is disposed.
+  fileUrl: string;
   camera: THREE.PerspectiveCamera;
   scene: THREE.Scene;
   renderer: THREE.WebGLRenderer;
@@ -31,9 +33,10 @@ interface PreviewReturn {
   // Show/hide the skeleton overlay (rigged GLBs only; no-op otherwise).
   // Defaults visible for mesh-less models so there's something to see.
   setSkeletonVisible: (visible: boolean) => void;
-  // Call when a newer preview supersedes this one (effect cleanup): any
-  // still-in-flight load's callbacks become no-ops.
-  cancel: () => void;
+  // Call when a newer preview supersedes this one or the preview goes away
+  // (effect cleanup): in-flight loads become no-ops, the animation loop
+  // stops, and the scene, renderer and blob URL are freed.
+  dispose: () => void;
 }
 
 export const loadPreviewOnCanvas = ({
@@ -83,6 +86,7 @@ export const loadPreviewOnCanvas = ({
   scene.add(light);
 
   let splatMesh: SplatMesh | null = null;
+  const fileUrl = URL.createObjectURL(file);
 
   // Supersession flag: each preview invocation owns one. The effect that
   // created this preview flips it in its cleanup, and every async loader
@@ -90,9 +94,6 @@ export const loadPreviewOnCanvas = ({
   // renderer, write status/animation/rig state into the NEXT preview, or
   // trigger a thumbnail snapshot of the wrong model.
   let cancelled = false;
-  const cancel = () => {
-    cancelled = true;
-  };
   const isCancelled = () => cancelled;
 
   // Animation playback state for GLBs with baked clips. The mixer is rooted
@@ -143,6 +144,7 @@ export const loadPreviewOnCanvas = ({
   if (file.name.endsWith(".glb")) {
     glbLoader({
       file,
+      fileUrl,
       scene,
       camera,
       renderer,
@@ -181,7 +183,15 @@ export const loadPreviewOnCanvas = ({
       },
     });
   } else if (file.name.endsWith(".pmd")) {
-    pmdLoader({ file, scene, camera, renderer, statusCallback, isCancelled });
+    pmdLoader({
+      file,
+      fileUrl,
+      scene,
+      camera,
+      renderer,
+      statusCallback,
+      isCancelled,
+    });
   } else if (
     file.name.endsWith(".png") ||
     file.name.endsWith(".jpg") ||
@@ -190,6 +200,7 @@ export const loadPreviewOnCanvas = ({
   ) {
     imagePlaneLoader({
       file,
+      fileUrl,
       scene,
       camera,
       renderer,
@@ -242,11 +253,26 @@ export const loadPreviewOnCanvas = ({
   };
   renderer.setAnimationLoop(animate);
 
-  return { renderer, camera, selectAnimation, setSkeletonVisible, cancel };
+  // The canvas is reused for the next file's preview, which hands that
+  // renderer this same WebGL context, so the context loss is forced only
+  // once the canvas has left the DOM (the modal closed).
+  const dispose = () => {
+    cancelled = true;
+    renderer.setAnimationLoop(null);
+    disposeObject3D(scene);
+    // A splat still decoding when the preview was superseded never made it
+    // into the scene.
+    if (splatMesh && !splatMesh.parent) splatMesh.dispose();
+    URL.revokeObjectURL(fileUrl);
+    renderer.dispose();
+    if (!canvas.isConnected) renderer.forceContextLoss();
+  };
+
+  return { renderer, camera, selectAnimation, setSkeletonVisible, dispose };
 };
 
 const glbLoader = ({
-  file,
+  fileUrl,
   camera,
   scene,
   renderer,
@@ -257,7 +283,7 @@ const glbLoader = ({
 }: LoaderInterface) => {
   const loader = new GLTFLoader();
   loader.load(
-    URL.createObjectURL(file),
+    fileUrl,
     (data) => {
       if (isCancelled?.()) return;
       // Inspect BEFORE re-parenting (the loop below moves children out of
@@ -403,7 +429,7 @@ const pmdLoader = ({
 };
 
 const imagePlaneLoader = ({
-  file,
+  fileUrl,
   scene,
   statusCallback,
   isCancelled,
@@ -411,7 +437,7 @@ const imagePlaneLoader = ({
   const geometry = new THREE.PlaneGeometry(1, 1);
   const loader = new THREE.TextureLoader();
   const texture = loader.load(
-    URL.createObjectURL(file),
+    fileUrl,
     undefined,
     undefined,
     (loaderError) => {
diff --git a/frontend/libs/components/upload-modal/src/lib/UploadModalSplat/UploadFilesSplat.tsx b/frontend/libs/components/upload-modal/src/lib/UploadModalSplat/UploadFilesSplat.tsx
index ad5dd639ae..dbf4020293 100644
--- a/frontend/libs/components/upload-modal/src/lib/UploadModalSplat/UploadFilesSplat.tsx
+++ b/frontend/libs/components/upload-modal/src/lib/UploadModalSplat/UploadFilesSplat.tsx
@@ -92,12 +92,13 @@ export const UploadFilesSplat = ({
   const [overallProgress, setOverallProgress] = useState<{ current: number; total: number } | null>(null);
   const [selectionError, setSelectionError] = useState<string | undefined>();
 
+  // Tears down the current preview: stops its loop, cancels in-flight
+  // loads and frees its scene and renderer (see loadPreviewOnCanvas).
+  const disposePreviewRef = useRef<(() => void) | null>(null);
   const disposeRenderer = () => {
-    if (rendererRef.current) {
-      rendererRef.current.setAnimationLoop(null);
-      rendererRef.current.dispose();
-      rendererRef.current = null;
-    }
+    disposePreviewRef.current?.();
+    disposePreviewRef.current = null;
+    rendererRef.current = null;
   };
 
   useEffect(() => {
@@ -107,12 +108,13 @@ export const UploadFilesSplat = ({
     disposeRenderer();
     setPreviewStatus({ type: "init" });
 
-    const { renderer, camera } = loadPreviewOnCanvas({
+    const { renderer, camera, dispose } = loadPreviewOnCanvas({
       file: currentFile,
       canvas: canvasRef.current,
       statusCallback: setPreviewStatus,
     });
     rendererRef.current = renderer;
+    disposePreviewRef.current = dispose;
     cameraRef.current = camera;
 
     return disposeRenderer;
diff --git a/frontend/libs/components/viewer-3d/src/index.ts b/frontend/libs/components/viewer-3d/src/index.ts
index c52bc6084f..fcbaf013bb 100644
--- a/frontend/libs/components/viewer-3d/src/index.ts
+++ b/frontend/libs/components/viewer-3d/src/index.ts
@@ -1,3 +1,4 @@
 
 export * from './lib/viewer-3d';
 export * from './lib/NodeHierarchyHelper';
+export * from './lib/disposeObject3D';
diff --git a/frontend/libs/components/viewer-3d/src/lib/disposeObject3D.spec.ts b/frontend/libs/components/viewer-3d/src/lib/disposeObject3D.spec.ts
new file mode 100644
index 0000000000..0a1066c30e
--- /dev/null
+++ b/frontend/libs/components/viewer-3d/src/lib/disposeObject3D.spec.ts
@@ -0,0 +1,160 @@
+import * as THREE from "three";
+import { SparkRenderer, SplatMesh } from "@sparkjsdev/spark";
+import { disposeObject3D } from "./disposeObject3D";
+
+// A real SplatMesh / SparkRenderer needs Spark's WASM decoder and a WebGL
+// renderer; only `instanceof` and the dispose() calls matter here.
+vi.mock("@sparkjsdev/spark", async () => {
+  const { Object3D } = await import("three");
+  const accumulator = () => ({ splats: { dispose: vi.fn() } });
+  return {
+    SplatMesh: class extends Object3D {
+      dispose = vi.fn();
+    },
+    SparkRenderer: class extends Object3D {
+      defaultView = { dispose: vi.fn() };
+      active = accumulator();
+      freeAccumulators = [accumulator(), accumulator()];
+    },
+  };
+});
+
+describe("disposeObject3D", () => {
+  it("disposes nested geometries, materials and their textures", () => {
+    const map = new THREE.Texture();
+    const normalMap = new THREE.Texture();
+    const material = new THREE.MeshStandardMaterial({ map, normalMap });
+    const geometry = new THREE.BoxGeometry();
+    const root = new THREE.Group();
+    const child = new THREE.Group();
+    child.add(new THREE.Mesh(geometry, material));
+    root.add(child);
+
+    const disposed = trackDisposals([map, normalMap, material, geometry]);
+    disposeObject3D(root);
+
+    expect(disposed).toEqual(new Set([map, normalMap, material, geometry]));
+  });
+
+  it("disposes every material of a multi-material mesh", () => {
+    const first = new THREE.MeshBasicMaterial({ map: new THREE.Texture() });
+    const second = new THREE.MeshBasicMaterial();
+    const mesh = new THREE.Mesh(new THREE.BoxGeometry(), [first, second]);
+
+    const disposed = trackDisposals([first, second, first.map!]);
+    disposeObject3D(mesh);
+
+    expect(disposed).toEqual(new Set([first, second, first.map]));
+  });
+
+  it("disposes a material shared by several meshes once", () => {
+    const material = new THREE.MeshBasicMaterial();
+    const root = new THREE.Group();
+    root.add(new THREE.Mesh(new THREE.BoxGeometry(), material));
+    root.add(new THREE.Mesh(new THREE.BoxGeometry(), material));
+
+    const onDispose = vi.fn();
+    material.addEventListener("dispose", onDispose);
+    disposeObject3D(root);
+
+    expect(onDispose).toHaveBeenCalledTimes(1);
+  });
+
+  it("disposes skinned mesh skeletons", () => {
+    const bone = new THREE.Bone();
+    const skeleton = new THREE.Skeleton([bone]);
+    const mesh = new THREE.SkinnedMesh(
+      new THREE.BoxGeometry(),
+      new THREE.MeshBasicMaterial(),
+    );
+    mesh.add(bone);
+    mesh.bind(skeleton);
+    const dispose = vi.spyOn(skeleton, "dispose");
+
+    disposeObject3D(mesh);
+
+    expect(dispose).toHaveBeenCalledTimes(1);
+  });
+
+  it("frees splat buffers", () => {
+    const splat = new SplatMesh();
+    const root = new THREE.Group();
+    root.add(splat);
+
+    disposeObject3D(root);
+
+    expect(splat.dispose).toHaveBeenCalledTimes(1);
+  });
+
+  it("frees a SparkRenderer's viewpoint and accumulators", () => {
+    const spark = new SparkRenderer({} as never);
+    const root = new THREE.Group();
+    root.add(spark);
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const { freeAccumulators } = spark as any;
+
+    disposeObject3D(root);
+
+    expect(spark.defaultView.dispose).toHaveBeenCalledTimes(1);
+    expect(spark.active.splats.dispose).toHaveBeenCalledTimes(1);
+    for (const accumulator of freeAccumulators) {
+      expect(accumulator.splats.dispose).toHaveBeenCalledTimes(1);
+    }
+  });
+
+  it("disposes textures held in ShaderMaterial uniforms", () => {
+    const normals = new THREE.Texture();
+    const mirror = new THREE.WebGLRenderTarget(4, 4).texture;
+    const layers = [new THREE.Texture(), new THREE.Texture()];
+    const material = new THREE.ShaderMaterial({
+      uniforms: {
+        normalSampler: { value: normals },
+        mirrorSampler: { value: mirror },
+        layerSamplers: { value: layers },
+        size: { value: 1.0 },
+      },
+    });
+    const mesh = new THREE.Mesh(new THREE.PlaneGeometry(), material);
+
+    const disposed = trackDisposals([normals, mirror, ...layers]);
+    disposeObject3D(mesh);
+
+    expect(disposed).toEqual(new Set([normals, mirror, ...layers]));
+  });
+
+  it("disposes a texture shared by a property and a uniform once", () => {
+    const video = new THREE.Texture();
+    const material = new THREE.ShaderMaterial({
+      uniforms: { map: { value: video } },
+    });
+    // ChromaKeyMaterial keeps its VideoTexture both here and in a uniform.
+    (material as unknown as { texture: THREE.Texture }).texture = video;
+    const mesh = new THREE.Mesh(new THREE.PlaneGeometry(), material);
+
+    const onDispose = vi.fn();
+    video.addEventListener("dispose", onDispose);
+    disposeObject3D(mesh);
+
+    expect(onDispose).toHaveBeenCalledTimes(1);
+  });
+
+  it("skips objects without geometry or material", () => {
+    const root = new THREE.Group();
+    root.add(new THREE.DirectionalLight());
+    root.add(new THREE.PerspectiveCamera());
+
+    expect(() => disposeObject3D(root)).not.toThrow();
+  });
+});
+
+// Records which resources dispatched their "dispose" event.
+function trackDisposals(
+  resources: Array<THREE.Texture | THREE.Material | THREE.BufferGeometry>,
+): Set<unknown> {
+  const disposed = new Set<unknown>();
+  for (const resource of resources) {
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    (resource as any).addEventListener("dispose", () => disposed.add(resource));
+  }
+  return disposed;
+}
diff --git a/frontend/libs/components/viewer-3d/src/lib/disposeObject3D.ts b/frontend/libs/components/viewer-3d/src/lib/disposeObject3D.ts
new file mode 100644
index 0000000000..e468c5e5b1
--- /dev/null
+++ b/frontend/libs/components/viewer-3d/src/lib/disposeObject3D.ts
@@ -0,0 +1,93 @@
+import * as THREE from "three";
+import { SparkRenderer, SplatMesh } from "@sparkjsdev/spark";
+
+// Free the GPU resources held by an object tree that is leaving the scene
+// for good: geometries, materials, the textures those materials reference
+// (Material.dispose() does not free its maps), skeleton bone textures and
+// Spark splat buffers. Call it after the tree has been removed.
+//
+// Textures are found both as material properties (map, normalMap, ...) and
+// as ShaderMaterial uniforms (Water's normal and mirror samplers, Spark's
+// splat textures). Water keeps its mirror render target in a closure, so
+// only that target's color texture can be reached; its framebuffer and depth
+// buffer stay allocated.
+//
+// Geometry, material and texture disposal is safe even if one of them is
+// shared with an object that stays — three.js re-uploads it the next time
+// it renders. Splat buffers are not re-creatable, but every SplatMesh owns
+// its own (scene.ts builds one per load), and undo re-loads deleted
+// objects from their snapshot rather than reusing the instance.
+export function disposeObject3D(root: THREE.Object3D): void {
+  root.traverse((child) => {
+    if (child instanceof SplatMesh) child.dispose();
+    if (child instanceof SparkRenderer) disposeSparkRenderer(child);
+    if (child instanceof THREE.SkinnedMesh) child.skeleton?.dispose();
+    (child as Partial<THREE.Mesh>).geometry?.dispose();
+  });
+
+  const materials = collectMaterials(root);
+  const textures = collectMaterialTextures(materials);
+  for (const material of materials) material.dispose();
+  for (const texture of textures) texture.dispose();
+}
+
+// Every texture the tree's materials reference, as material properties or
+// ShaderMaterial uniforms, deduplicated.
+export function collectObjectTextures(
+  root: THREE.Object3D,
+): Set<THREE.Texture> {
+  return collectMaterialTextures(collectMaterials(root));
+}
+
+// A SparkRenderer is added to the scene automatically the first time a
+// splat renders. Its viewpoint render targets and splat accumulators are
+// not reachable from its material, so free them explicitly. The viewpoint
+// goes first: disposing it returns its accumulators to the free list.
+function disposeSparkRenderer(spark: SparkRenderer): void {
+  spark.defaultView.dispose();
+  spark.active.splats.dispose();
+  const { freeAccumulators } = spark as unknown as {
+    freeAccumulators: SparkRenderer["active"][];
+  };
+  for (const accumulator of freeAccumulators) accumulator.splats.dispose();
+}
+
+function collectMaterials(root: THREE.Object3D): Set<THREE.Material> {
+  const materials = new Set<THREE.Material>();
+  root.traverse((child) => {
+    const { material } = child as Partial<THREE.Mesh>;
+    const childMaterials = Array.isArray(material) ? material : [material];
+    for (const childMaterial of childMaterials) {
+      if (childMaterial) materials.add(childMaterial);
+    }
+  });
+  return materials;
+}
+
+function collectMaterialTextures(
+  materials: Iterable<THREE.Material>,
+): Set<THREE.Texture> {
+  const textures = new Set<THREE.Texture>();
+  for (const material of materials) {
+    addTextures(Object.values(material), textures);
+    if (material instanceof THREE.ShaderMaterial) {
+      addTextures(
+        Object.values(material.uniforms).map((uniform) => uniform?.value),
+        textures,
+      );
+    }
+  }
+  return textures;
+}
+
+function addTextures(values: unknown[], into: Set<THREE.Texture>): void {
+  for (const value of values) {
+    if (value instanceof THREE.Texture) {
+      into.add(value);
+    } else if (Array.isArray(value)) {
+      for (const item of value) {
+        if (item instanceof THREE.Texture) into.add(item);
+      }
+    }
+  }
+}
diff --git a/frontend/libs/components/viewer-3d/src/lib/viewer-3d.spec.tsx b/frontend/libs/components/viewer-3d/src/lib/viewer-3d.spec.tsx
index c449c2683a..aac63e3f3b 100644
--- a/frontend/libs/components/viewer-3d/src/lib/viewer-3d.spec.tsx
+++ b/frontend/libs/components/viewer-3d/src/lib/viewer-3d.spec.tsx
@@ -2,11 +2,23 @@ import { render } from '@testing-library/react';
 
 import StorytellerUiViewer3d from './viewer-3d';
 
+// jsdom has no ResizeObserver; the viewer only needs it to exist.
+vi.stubGlobal(
+  'ResizeObserver',
+  class {
+    observe() {}
+    disconnect() {}
+  },
+);
+
 describe('StorytellerUiViewer3d', () => {
-  
   it('should render successfully', () => {
     const { baseElement } = render(<StorytellerUiViewer3d />);
     expect(baseElement).toBeTruthy();
   });
-  
+
+  it('unmounts cleanly before the scene ever initialized', () => {
+    const { unmount } = render(<StorytellerUiViewer3d />);
+    expect(() => unmount()).not.toThrow();
+  });
 });
diff --git a/frontend/libs/components/viewer-3d/src/lib/viewer-3d.tsx b/frontend/libs/components/viewer-3d/src/lib/viewer-3d.tsx
index a67043cc22..0ddde8f2ce 100644
--- a/frontend/libs/components/viewer-3d/src/lib/viewer-3d.tsx
+++ b/frontend/libs/components/viewer-3d/src/lib/viewer-3d.tsx
@@ -9,6 +9,7 @@ import {
   NodeHierarchyHelper,
   createRigHelper,
 } from "./NodeHierarchyHelper";
+import { disposeObject3D } from "./disposeObject3D";
 
 // Dropdown value for the "no animation" choice (models rest in their bind /
 // T-pose). Clip values are their stringified index.
@@ -277,20 +278,14 @@ export function Viewer3D({
       ) {
         container.removeChild(rendererRef.current.domElement);
       }
-      rendererRef.current?.dispose();
       controlsRef.current?.dispose();
-
-      if (cubeRef.current) {
-        const cube = cubeRef.current;
-        if (cube.geometry) cube.geometry.dispose();
-        if (cube.material) {
-          if (Array.isArray(cube.material)) {
-            cube.material.forEach((m) => m.dispose());
-          } else {
-            cube.material.dispose();
-          }
-        }
-      }
+      // Free everything still in the scene (placeholder cube, grid, any
+      // model, Spark's auto-added splat renderer), then the context itself.
+      // The canvas is ours and already detached, so forcing the context
+      // loss frees it now instead of whenever the canvas is collected.
+      if (sceneRef.current) disposeObject3D(sceneRef.current);
+      rendererRef.current?.dispose();
+      rendererRef.current?.forceContextLoss();
     };
   }, []);
 
@@ -407,11 +402,19 @@ export function Viewer3D({
     const SPLAT_EXTENSIONS = ["spz", "ply", "splat", "ksplat"];
     const GLTF_EXTENSIONS = ["glb", "gltf", ""];
 
+    // Set by this effect's cleanup. A model that finishes loading after the
+    // URL changed or the viewer unmounted is freed instead of shown.
+    let cancelled = false;
+
     if (SPLAT_EXTENSIONS.includes(urlExtension)) {
       console.log(`[Viewer3D] splat format detected (.${urlExtension})`);
       new SplatMesh({
         url: modelUrl,
         onLoad: (mesh) => {
+          if (cancelled) {
+            mesh.dispose();
+            return;
+          }
           mesh.rotation.z = Math.PI;
           mesh.position.y = 1;
           scene.add(mesh);
@@ -450,6 +453,10 @@ export function Viewer3D({
       loader.load(
         modelUrl,
         (gltf) => {
+          if (cancelled) {
+            disposeObject3D(gltf.scene);
+            return;
+          }
           console.log("[Viewer3D] Model loaded successfully");
           const model = gltf.scene;
           onModelLoaded(model);
@@ -503,10 +510,12 @@ export function Viewer3D({
     }
 
     return () => {
+      cancelled = true;
       stopAnimations();
       removeSkeletonHelper();
-      if (loadedModelRef.current && sceneRef.current) {
-        sceneRef.current.remove(loadedModelRef.current);
+      if (loadedModelRef.current) {
+        loadedModelRef.current.removeFromParent();
+        disposeObject3D(loadedModelRef.current);
         loadedModelRef.current = null;
       }
     };