diff --git a/tests/e2e/transform-foundation.e2e.ts b/tests/e2e/transform-foundation.e2e.ts
new file mode 100644
index 00000000..bdfa856d
--- /dev/null
+++ b/tests/e2e/transform-foundation.e2e.ts
@@ -0,0 +1,228 @@
+import { expect, test } from "@playwright/test";
+
+import { createModelInstance } from "../../src/assets/model-instances";
+import { createProjectAssetStorageKey, type ModelAssetRecord } from "../../src/assets/project-assets";
+import { createBoxBrush } from "../../src/document/brushes";
+import { createEmptySceneDocument } from "../../src/document/scene-document";
+import { createPlayerStartEntity } from "../../src/entities/entity-instances";
+import {
+  clickViewport,
+  getEditorStoreSnapshot,
+  getViewportCanvas,
+  replaceSceneDocument
+} from "./viewport-test-helpers";
+
+const modelAsset = {
+  id: "asset-model-transform-e2e",
+  kind: "model",
+  sourceName: "transform-fixture.glb",
+  mimeType: "model/gltf-binary",
+  storageKey: createProjectAssetStorageKey("asset-model-transform-e2e"),
+  byteLength: 72,
+  metadata: {
+    kind: "model",
+    format: "glb",
+    sceneName: "Transform Fixture",
+    nodeCount: 1,
+    meshCount: 1,
+    materialNames: [],
+    textureNames: [],
+    animationNames: [],
+    boundingBox: {
+      min: {
+        x: -0.5,
+        y: 0,
+        z: -0.5
+      },
+      max: {
+        x: 0.5,
+        y: 1,
+        z: 0.5
+      },
+      size: {
+        x: 1,
+        y: 1,
+        z: 1
+      }
+    },
+    warnings: []
+  }
+} satisfies ModelAssetRecord;
+
+async function seedTransformScene(page: Parameters<typeof test>[0]["page"]) {
+  const brush = createBoxBrush({
+    id: "brush-transform-main",
+    name: "Brush Transform Fixture",
+    center: {
+      x: 0,
+      y: 1,
+      z: 0
+    }
+  });
+  const playerStart = createPlayerStartEntity({
+    id: "entity-player-start-transform",
+    name: "Player Start Fixture",
+    position: {
+      x: 4,
+      y: 0,
+      z: -4
+    },
+    yawDegrees: 0
+  });
+  const modelInstance = createModelInstance({
+    id: "model-instance-transform-main",
+    assetId: modelAsset.id,
+    name: "Model Transform Fixture",
+    position: {
+      x: -4,
+      y: 0,
+      z: 4
+    }
+  });
+
+  await replaceSceneDocument(page, {
+    ...createEmptySceneDocument({ name: "Transform Foundation Fixture" }),
+    brushes: {
+      [brush.id]: brush
+    },
+    assets: {
+      [modelAsset.id]: modelAsset
+    },
+    entities: {
+      [playerStart.id]: playerStart
+    },
+    modelInstances: {
+      [modelInstance.id]: modelInstance
+    }
+  });
+
+  return {
+    brush,
+    playerStart,
+    modelInstance
+  };
+}
+
+async function getViewportCenter(page: Parameters<typeof test>[0]["page"], panelId: "topLeft" | "topRight" | "bottomLeft" | "bottomRight") {
+  const viewportCanvas = getViewportCanvas(page, panelId);
+  const bounds = await viewportCanvas.boundingBox();
+
+  if (bounds === null) {
+    throw new Error(`Viewport ${panelId} is not visible.`);
+  }
+
+  return {
+    x: bounds.x + bounds.width * 0.5,
+    y: bounds.y + bounds.height * 0.5
+  };
+}
+
+async function commitKeyboardMove(
+  page: Parameters<typeof test>[0]["page"],
+  panelId: "topLeft" | "topRight" | "bottomLeft" | "bottomRight",
+  delta: { x: number; y: number },
+  axisConstraint?: "x" | "y" | "z"
+) {
+  const center = await getViewportCenter(page, panelId);
+
+  await page.mouse.move(center.x, center.y);
+  await page.keyboard.press("g");
+
+  if (axisConstraint !== undefined) {
+    await page.keyboard.press(axisConstraint);
+  }
+
+  await page.mouse.move(center.x + delta.x, center.y + delta.y);
+  await page.mouse.click(center.x + delta.x, center.y + delta.y);
+}
+
+test("viewport picking defaults to whole-brush selection and axis-constrained brush move commits through the shared transform session", async ({ page }) => {
+  await page.goto("/");
+  await page.evaluate((storageKey) => {
+    window.localStorage.removeItem(storageKey);
+  }, "webeditor3d.scene-document-draft");
+  await page.reload();
+
+  const fixtures = await seedTransformScene(page);
+
+  await page.getByTestId("viewport-layout-quad").click();
+  await clickViewport(page, "topRight");
+
+  const selectedSnapshot = await getEditorStoreSnapshot(page);
+  expect(selectedSnapshot.selection).toEqual({
+    kind: "brushes",
+    ids: [fixtures.brush.id]
+  });
+
+  await commitKeyboardMove(page, "topRight", { x: 160, y: 0 }, "x");
+
+  const movedSnapshot = await getEditorStoreSnapshot(page);
+  expect(movedSnapshot.viewportTransientState.transformSession).toEqual({
+    kind: "none"
+  });
+  expect(movedSnapshot.document.brushes[fixtures.brush.id].center.y).toBe(fixtures.brush.center.y);
+  expect(movedSnapshot.document.brushes[fixtures.brush.id].center.z).toBe(fixtures.brush.center.z);
+  expect(movedSnapshot.document.brushes[fixtures.brush.id].center.x).not.toBe(fixtures.brush.center.x);
+});
+
+test("keyboard move commits an entity translation through the shared transform controller", async ({ page }) => {
+  await page.goto("/");
+  await page.evaluate((storageKey) => {
+    window.localStorage.removeItem(storageKey);
+  }, "webeditor3d.scene-document-draft");
+  await page.reload();
+
+  const fixtures = await seedTransformScene(page);
+
+  await page.getByRole("button", { name: fixtures.playerStart.name as string }).click();
+  await commitKeyboardMove(page, "topLeft", { x: 100, y: -60 });
+
+  const snapshot = await getEditorStoreSnapshot(page);
+  expect(snapshot.viewportTransientState.transformSession).toEqual({
+    kind: "none"
+  });
+  expect(snapshot.document.entities[fixtures.playerStart.id].position).not.toEqual(fixtures.playerStart.position);
+});
+
+test("escape cancels an active entity transform session without committing preview changes", async ({ page }) => {
+  await page.goto("/");
+  await page.evaluate((storageKey) => {
+    window.localStorage.removeItem(storageKey);
+  }, "webeditor3d.scene-document-draft");
+  await page.reload();
+
+  const fixtures = await seedTransformScene(page);
+
+  await page.getByRole("button", { name: fixtures.playerStart.name as string }).click();
+
+  const center = await getViewportCenter(page, "topLeft");
+  await page.mouse.move(center.x, center.y);
+  await page.keyboard.press("g");
+  await page.mouse.move(center.x + 140, center.y + 40);
+  await page.keyboard.press("Escape");
+
+  const snapshot = await getEditorStoreSnapshot(page);
+  expect(snapshot.viewportTransientState.transformSession).toEqual({
+    kind: "none"
+  });
+  expect(snapshot.document.entities[fixtures.playerStart.id].position).toEqual(fixtures.playerStart.position);
+});
+
+test("keyboard move commits a model instance translation through the shared transform controller", async ({ page }) => {
+  await page.goto("/");
+  await page.evaluate((storageKey) => {
+    window.localStorage.removeItem(storageKey);
+  }, "webeditor3d.scene-document-draft");
+  await page.reload();
+
+  const fixtures = await seedTransformScene(page);
+
+  await page.getByRole("button", { name: fixtures.modelInstance.name as string }).click();
+  await commitKeyboardMove(page, "topLeft", { x: -120, y: 80 });
+
+  const snapshot = await getEditorStoreSnapshot(page);
+  expect(snapshot.viewportTransientState.transformSession).toEqual({
+    kind: "none"
+  });
+  expect(snapshot.document.modelInstances[fixtures.modelInstance.id].position).not.toEqual(fixtures.modelInstance.position);
+});