feat(editor): board shell with iframe frame and selection overlay

React Flow board (pan/zoom + frame drag are pure editor-side transforms
— zero canvas-protocol traffic, <16ms budget) hosting one iframe frame
node on the adapter origin. The frame waits for runtime.ready
(queue-drain) behind an explicit 'Starting preview…' skeleton, then
requests a single Element via render-frame (core-runner-protocol
schema) plus geometry; agent-reported geometry stays frame-local and
click reports drive store selection. The selection ring renders as an
editor-side overlay from reported geometry — chrome never inside the
customer's document (ADR-028). Stories + jsdom component tests for
board/frame/overlay; Storybook stories glob extended to
packages/editor (verified via static build).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016j8z4VHjedXDTjEDNg7qHK

packages/editor/src/canvas-protocol/scripted-agent.mock.ts

@@ -19,6 +19,25 @@ export type PostedMessage = {
   targetOrigin: string;
 };
 
+/**
+ * Script one agent envelope onto the REAL window (jsdom) — for component
+ * tests where the canvas client listens on the default editor window.
+ * `MessageEvent` carries the given origin explicitly; `source` stays
+ * `null`, which the client tolerates (it cannot know the source when the
+ * scripted agent is not a window).
+ */
+export function postAgentEnvelopeToWindow(
+  message: CanvasAgentMessage,
+  origin: string,
+): void {
+  window.dispatchEvent(
+    new MessageEvent("message", {
+      data: { protocolVersion: PROTOCOL_VERSION, message },
+      origin,
+    }),
+  );
+}
+
 type PostOverrides = {
   /** Origin the event claims to come from. Defaults to the double's origin. */
   origin?: string;

packages/editor/src/ui/components/editor-board.stories.tsx

@@ -0,0 +1,49 @@
+import type { Meta, StoryObj } from "@storybook/react";
+import { useEditorStore } from "../../store/editor-store";
+import { EditorBoard } from "./editor-board";
+
+/**
+ * The infinite board (ADR-028): scroll pans, pinch zooms, the frame drags
+ * by its name tab — all pure React Flow transforms, zero canvas-protocol
+ * traffic. The frame hosts the adapter origin in an iframe; without a live
+ * adapter it stays in its honest "Starting preview…" state.
+ */
+const ADAPTER_ORIGIN = "https://adapter.veect.localhost:5199";
+
+const meta = {
+  title: "Editor/EditorBoard",
+  component: EditorBoard,
+  tags: ["autodocs"],
+  args: { adapterOrigin: ADAPTER_ORIGIN },
+  decorators: [
+    (Story) => (
+      <div style={{ width: "100%", height: 600 }}>
+        <Story />
+      </div>
+    ),
+  ],
+} satisfies Meta<typeof EditorBoard>;
+export default meta;
+
+type Story = StoryObj<typeof meta>;
+
+export const WithFrame: Story = {
+  decorators: [
+    (Story) => {
+      useEditorStore.setState({
+        registry: [{ id: "button", name: "Button" }],
+        selectedNodeId: null,
+      });
+      return <Story />;
+    },
+  ],
+};
+
+export const EmptyRegistry: Story = {
+  decorators: [
+    (Story) => {
+      useEditorStore.setState({ registry: [], selectedNodeId: null });
+      return <Story />;
+    },
+  ],
+};

packages/editor/src/ui/components/editor-board.test.tsx

@@ -0,0 +1,115 @@
+import { describe, it, expect, beforeEach, vi } from "vitest";
+import { act } from "react";
+import { fireEvent, render, screen } from "@testing-library/react";
+import { postAgentEnvelopeToWindow } from "@/canvas-protocol/scripted-agent.mock";
+import { useEditorStore } from "@/store/editor-store";
+import { mockReactFlow } from "./react-flow.mock";
+import { EditorBoard } from "./editor-board";
+
+const ADAPTER_ORIGIN = "https://adapter.veect.test:5199";
+
+mockReactFlow();
+
+function renderBoard() {
+  return render(
+    <div style={{ width: "1200px", height: "800px" }}>
+      <EditorBoard adapterOrigin={ADAPTER_ORIGIN} />
+    </div>,
+  );
+}
+
+beforeEach(() => {
+  useEditorStore.setState({ registry: [], selectedNodeId: null });
+});
+
+describe("EditorBoard — empty registry", () => {
+  it("renders an empty board: canvas present, no frame", () => {
+    const { container } = renderBoard();
+    expect(screen.getByTestId("editor-board")).toBeInTheDocument();
+    expect(container.querySelector(".react-flow")).not.toBeNull();
+    expect(container.querySelector("iframe")).toBeNull();
+  });
+});
+
+describe("EditorBoard — one frame from the registry", () => {
+  beforeEach(() => {
+    useEditorStore.setState({
+      registry: [
+        { id: "button", name: "Button" },
+        { id: "card", name: "Card" },
+      ],
+      selectedNodeId: null,
+    });
+  });
+
+  it("hosts one iframe frame node for the FIRST discovered component", async () => {
+    renderBoard();
+    const iframe = (await screen.findByTitle(
+      "Button frame",
+    )) as HTMLIFrameElement;
+    expect(iframe).toHaveAttribute("src", ADAPTER_ORIGIN);
+    // walking-skeleton scope: a single frame — the second registry entry
+    // does not get a frame.
+    expect(screen.queryByTitle("Card frame")).not.toBeInTheDocument();
+    expect(screen.getByText("Button")).toBeInTheDocument();
+  });
+
+  it("marks the frame node draggable by its handle only", async () => {
+    const { container } = renderBoard();
+    await screen.findByTitle("Button frame");
+    expect(container.querySelector(".frame-drag-handle")).not.toBeNull();
+  });
+
+  it("clears the selection on pane click — editor-side, no protocol traffic", async () => {
+    const { container } = renderBoard();
+    const iframe = (await screen.findByTitle(
+      "Button frame",
+    )) as HTMLIFrameElement;
+    const post = vi.spyOn(iframe.contentWindow!, "postMessage");
+    act(() => useEditorStore.getState().select("el-1"));
+
+    const pane = container.querySelector(".react-flow__pane");
+    expect(pane).not.toBeNull();
+    fireEvent.click(pane!);
+
+    expect(useEditorStore.getState().selectedNodeId).toBeNull();
+    expect(post).not.toHaveBeenCalled();
+  });
+
+  it("pan/zoom gestures on the pane produce zero canvas-protocol traffic (<16 ms budget, ADR-028)", async () => {
+    const { container } = renderBoard();
+    const iframe = (await screen.findByTitle(
+      "Button frame",
+    )) as HTMLIFrameElement;
+    const post = vi.spyOn(iframe.contentWindow!, "postMessage");
+    // Drain the ready handshake first so the assertion below isolates the
+    // gesture path.
+    act(() =>
+      postAgentEnvelopeToWindow({ type: "runtime.ready" }, ADAPTER_ORIGIN),
+    );
+    expect(post).toHaveBeenCalledTimes(2);
+    post.mockClear();
+
+    const pane = container.querySelector(".react-flow__pane")!;
+    fireEvent.wheel(pane, { deltaY: -120 }); // panOnScroll
+    fireEvent.wheel(pane, { deltaY: 80, ctrlKey: true }); // zoomOnPinch
+    // (Empty-pane mouse-drag panning can't be simulated in jsdom — it
+    // refuses MouseEvent's `view` member — but frame dragging is the same
+    // structural path: a pure rerender, proven protocol-silent in
+    // frame-node.test.tsx.)
+
+    expect(post).not.toHaveBeenCalled();
+  });
+
+  it("resyncs the board when the registry changes", async () => {
+    renderBoard();
+    await screen.findByTitle("Button frame");
+
+    act(() =>
+      useEditorStore.getState().setRegistry([{ id: "badge", name: "Badge" }]),
+    );
+
+    expect(await screen.findByTitle("Badge frame")).toBeInTheDocument();
+    expect(screen.queryByTitle("Button frame")).not.toBeInTheDocument();
+  });
+});

packages/editor/src/ui/components/editor-board.tsx

@@ -0,0 +1,101 @@
+"use client";
+
+import { useCallback, useEffect, useMemo, useState } from "react";
+import {
+  applyNodeChanges,
+  Background,
+  BackgroundVariant,
+  ReactFlow,
+  type Node,
+  type NodeChange,
+  type NodeTypes,
+} from "@xyflow/react";
+import "@xyflow/react/dist/style.css";
+import { useEditorStore } from "../../store/editor-store";
+import { FrameNode, type FrameNodeData } from "./frame-node";
+
+/**
+ * The board shell (ADR-028): an infinite React Flow canvas whose frames are
+ * iframe containers. Pan/zoom and frame dragging are pure React Flow
+ * transforms on those containers — zero canvas-protocol traffic on drag
+ * (<16 ms/frame budget); only the frame's name tab drags
+ * (`dragHandle: ".frame-drag-handle"`).
+ *
+ * Walking-skeleton scope: one frame, rendering the FIRST discovered
+ * registry component from the editor store. An empty registry renders an
+ * empty board. Pane clicks clear the selection editor-side.
+ */
+type BoardNode = Node<FrameNodeData, "frame">;
+
+const nodeTypes: NodeTypes = { frame: FrameNode };
+
+export type EditorBoardProps = {
+  /** The adapter's origin — pinned targetOrigin for every frame's canvas protocol. */
+  adapterOrigin: string;
+};
+
+export function EditorBoard({ adapterOrigin }: EditorBoardProps) {
+  const registry = useEditorStore((s) => s.registry);
+  const select = useEditorStore((s) => s.select);
+  const component = registry[0];
+
+  const initialNodes = useMemo<BoardNode[]>(
+    () =>
+      component === undefined
+        ? []
+        : [
+            {
+              id: `frame:${component.id}`,
+              type: "frame",
+              position: { x: 0, y: 0 },
+              data: {
+                frame: {
+                  name: component.name,
+                  componentId: component.id,
+                  adapterOrigin,
+                },
+              },
+              dragHandle: ".frame-drag-handle",
+            },
+          ],
+    [component, adapterOrigin],
+  );
+
+  const [nodes, setNodes] = useState<BoardNode[]>(initialNodes);
+
+  // Resync when the registry (or adapter origin) changes.
+  useEffect(() => setNodes(initialNodes), [initialNodes]);
+
+  const onNodesChange = useCallback(
+    (changes: NodeChange<BoardNode>[]) =>
+      setNodes((current) => applyNodeChanges(changes, current)),
+    [],
+  );
+
+  return (
+    <div
+      data-testid="editor-board"
+      style={{ position: "relative", width: "100%", height: "100%" }}
+    >
+      <ReactFlow
+        nodes={nodes}
+        edges={[]}
+        nodeTypes={nodeTypes}
+        onNodesChange={onNodesChange}
+        onPaneClick={() => select(null)}
+        fitView
+        fitViewOptions={{ padding: 0.18, maxZoom: 1 }}
+        minZoom={0.08}
+        maxZoom={2.5}
+        panOnScroll
+        zoomOnScroll={false}
+        zoomOnPinch
+        panOnDrag={[0, 1]}
+        nodesFocusable={false}
+        deleteKeyCode={null}
+      >
+        <Background variant={BackgroundVariant.Dots} gap={26} size={1} />
+      </ReactFlow>
+    </div>
+  );
+}

packages/editor/src/ui/components/frame-node.stories.tsx

@@ -0,0 +1,62 @@
+import type { Meta, StoryObj } from "@storybook/react";
+import { PROTOCOL_VERSION } from "@repo/core-runner-protocol";
+import type { CanvasAgentMessage } from "../../canvas-protocol/messages";
+import { FrameNode } from "./frame-node";
+
+/**
+ * One frame hosting the runner adapter's origin through a sandboxed
+ * cross-origin iframe (ADR-028). Storybook has no live adapter, so the
+ * frame shows its honest cold-start state — the explicit
+ * "Starting preview…" skeleton, never presented as the real render. The
+ * scripted story below plays the agent side of the canvas protocol to
+ * drive the ready → geometry → click selection round-trip.
+ */
+const ADAPTER_ORIGIN = "https://adapter.veect.localhost:5199";
+
+function agentSays(message: CanvasAgentMessage) {
+  window.dispatchEvent(
+    new MessageEvent("message", {
+      data: { protocolVersion: PROTOCOL_VERSION, message },
+      origin: ADAPTER_ORIGIN,
+    }),
+  );
+}
+
+const meta = {
+  title: "Editor/FrameNode",
+  component: FrameNode,
+  tags: ["autodocs"],
+} satisfies Meta<typeof FrameNode>;
+export default meta;
+
+type Story = StoryObj<typeof meta>;
+
+export const StartingPreview: Story = {
+  args: {
+    data: {
+      frame: {
+        name: "Button",
+        componentId: "button",
+        adapterOrigin: ADAPTER_ORIGIN,
+        width: 640,
+        height: 400,
+      },
+    },
+  },
+};
+
+export const SelectionRoundTrip: Story = {
+  args: StartingPreview.args,
+  play: async () => {
+    // Scripted agent: runtime.ready → geometry.report → click.target.
+    await new Promise((resolve) => setTimeout(resolve, 100));
+    agentSays({ type: "runtime.ready" });
+    agentSays({
+      type: "geometry.report",
+      targets: [
+        { nodeId: "el-1", rect: { x: 48, y: 40, width: 320, height: 72 } },
+      ],
+    });
+    agentSays({ type: "click.target", nodeId: "el-1" });
+  },
+};

packages/editor/src/ui/components/frame-node.test.tsx

@@ -0,0 +1,197 @@
+import { describe, it, expect, beforeEach, vi } from "vitest";
+import { act } from "react";
+import { render, screen } from "@testing-library/react";
+import { postAgentEnvelopeToWindow } from "@/canvas-protocol/scripted-agent.mock";
+import { useEditorStore } from "@/store/editor-store";
+import { FrameNode, type FrameNodeData } from "./frame-node";
+
+const ADAPTER_ORIGIN = "https://adapter.veect.test:5199";
+const EVIL_ORIGIN = "https://evil.example.com";
+
+const data: FrameNodeData = {
+  frame: {
+    name: "Button",
+    componentId: "button",
+    adapterOrigin: ADAPTER_ORIGIN,
+    width: 640,
+    height: 480,
+  },
+};
+
+function getIframe(): HTMLIFrameElement {
+  return screen.getByTitle("Button frame") as HTMLIFrameElement;
+}
+
+function spyOnAgentWindow() {
+  const contentWindow = getIframe().contentWindow;
+  if (contentWindow === null) throw new Error("iframe has no contentWindow");
+  return vi.spyOn(contentWindow, "postMessage");
+}
+
+function agentSays(message: Parameters<typeof postAgentEnvelopeToWindow>[0]) {
+  act(() => postAgentEnvelopeToWindow(message, ADAPTER_ORIGIN));
+}
+
+beforeEach(() => {
+  useEditorStore.setState({ registry: [], selectedNodeId: null });
+});
+
+describe("FrameNode — cold start", () => {
+  it("hosts the adapter origin in a sandboxed iframe with a drag-handle tab", () => {
+    render(<FrameNode data={data} />);
+    const iframe = getIframe();
+    expect(iframe).toHaveAttribute("src", ADAPTER_ORIGIN);
+    expect(iframe).toHaveAttribute(
+      "sandbox",
+      "allow-scripts allow-same-origin",
+    );
+    expect(screen.getByTitle("Drag to move")).toHaveClass("frame-drag-handle");
+    expect(screen.getByText("Button")).toBeInTheDocument();
+  });
+
+  it('shows the explicit "Starting preview…" skeleton until runtime.ready (ADR-028)', () => {
+    render(<FrameNode data={data} />);
+    expect(screen.getByText("Starting preview…")).toBeInTheDocument();
+  });
+
+  it("sends nothing before runtime.ready — queue-drain semantics", () => {
+    render(<FrameNode data={data} />);
+    const post = spyOnAgentWindow();
+    expect(post).not.toHaveBeenCalled();
+  });
+});
+
+describe("FrameNode — runtime.ready", () => {
+  it("requests a single Element via render-frame (default props) then geometry, pinned to the adapter origin", () => {
+    render(<FrameNode data={data} />);
+    const post = spyOnAgentWindow();
+
+    agentSays({ type: "runtime.ready" });
+
+    expect(post).toHaveBeenCalledTimes(2);
+    expect(post).toHaveBeenNthCalledWith(
+      1,
+      {
+        protocolVersion: "0",
+        message: { type: "render-frame", componentId: "button" },
+      },
+      ADAPTER_ORIGIN,
+    );
+    expect(post).toHaveBeenNthCalledWith(
+      2,
+      {
+        protocolVersion: "0",
+        message: { type: "geometry.request" },
+      },
+      ADAPTER_ORIGIN,
+    );
+    expect(screen.queryByText("Starting preview…")).not.toBeInTheDocument();
+  });
+
+  it("ignores runtime.ready from a wrong origin — still starting, nothing sent", () => {
+    render(<FrameNode data={data} />);
+    const post = spyOnAgentWindow();
+
+    act(() =>
+      postAgentEnvelopeToWindow({ type: "runtime.ready" }, EVIL_ORIGIN),
+    );
+
+    expect(post).not.toHaveBeenCalled();
+    expect(screen.getByText("Starting preview…")).toBeInTheDocument();
+  });
+});
+
+describe("FrameNode — selection round-trip from reported geometry", () => {
+  it("click report selects in the store and the overlay renders at the reported rect", () => {
+    render(<FrameNode data={data} />);
+    agentSays({ type: "runtime.ready" });
+    agentSays({
+      type: "geometry.report",
+      targets: [
+        { nodeId: "el-1", rect: { x: 16, y: 32, width: 240, height: 56 } },
+      ],
+    });
+
+    expect(screen.queryByTestId("selection-overlay")).not.toBeInTheDocument();
+
+    agentSays({ type: "click.target", nodeId: "el-1" });
+
+    expect(useEditorStore.getState().selectedNodeId).toBe("el-1");
+    expect(screen.getByTestId("selection-overlay")).toHaveStyle({
+      left: "16px",
+      top: "32px",
+      width: "240px",
+      height: "56px",
+    });
+  });
+
+  it("background click deselects and hides the overlay", () => {
+    render(<FrameNode data={data} />);
+    agentSays({ type: "runtime.ready" });
+    agentSays({
+      type: "geometry.report",
+      targets: [
+        { nodeId: "el-1", rect: { x: 0, y: 0, width: 10, height: 10 } },
+      ],
+    });
+    agentSays({ type: "click.target", nodeId: "el-1" });
+    expect(screen.getByTestId("selection-overlay")).toBeInTheDocument();
+
+    agentSays({ type: "click.target", nodeId: null });
+
+    expect(useEditorStore.getState().selectedNodeId).toBeNull();
+    expect(screen.queryByTestId("selection-overlay")).not.toBeInTheDocument();
+  });
+
+  it("no overlay when the selected node has no reported geometry yet", () => {
+    render(<FrameNode data={data} />);
+    agentSays({ type: "runtime.ready" });
+    agentSays({ type: "click.target", nodeId: "el-unmeasured" });
+    expect(useEditorStore.getState().selectedNodeId).toBe("el-unmeasured");
+    expect(screen.queryByTestId("selection-overlay")).not.toBeInTheDocument();
+  });
+});
+
+describe("FrameNode — drag path stays off the protocol", () => {
+  it("rerendering (as frame drag does) produces zero protocol traffic", () => {
+    const { rerender } = render(<FrameNode data={data} />);
+    const post = spyOnAgentWindow();
+    agentSays({ type: "runtime.ready" });
+    expect(post).toHaveBeenCalledTimes(2);
+
+    // React Flow drag rerenders the node with fresh props; data values
+    // are unchanged, so the canvas client must not be recreated and no
+    // message may be sent (<16 ms/frame budget, ADR-028).
+    rerender(<FrameNode data={{ frame: { ...data.frame } }} />);
+    rerender(<FrameNode data={{ frame: { ...data.frame } }} />);
+
+    expect(post).toHaveBeenCalledTimes(2);
+  });
+
+  it("stops listening on unmount — late agent messages no longer reach the store", () => {
+    const { unmount } = render(<FrameNode data={data} />);
+    agentSays({ type: "runtime.ready" });
+    unmount();
+
+    agentSays({ type: "click.target", nodeId: "el-late" });
+
+    expect(useEditorStore.getState().selectedNodeId).toBeNull();
+  });
+});
+
+describe("FrameNode — defaults", () => {
+  it("falls back to the 800x600 default viewport", () => {
+    render(
+      <FrameNode
+        data={{
+          frame: {
+            name: "Card",
+            componentId: "card",
+            adapterOrigin: ADAPTER_ORIGIN,
+          },
+        }}
+      />,
+    );
+    expect(screen.getByText(/800 × 600/)).toBeInTheDocument();
+  });
+});

packages/editor/src/ui/components/frame-node.tsx

@@ -0,0 +1,142 @@
+"use client";
+
+import { useEffect, useRef, useState } from "react";
+import { createCanvasClient } from "../../canvas-protocol/canvas-client";
+import type { GeometryTarget } from "../../canvas-protocol/messages";
+import { useEditorStore } from "../../store/editor-store";
+import { SelectionOverlay } from "./selection-overlay";
+
+/**
+ * One frame on the board: a cross-origin iframe hosting the runner
+ * adapter's origin (ADR-028). The frame speaks the canvas protocol through
+ * `createCanvasClient` — `targetOrigin` pinned both directions — and:
+ *
+ *   - waits for `runtime.ready` before requesting anything (queue-drain,
+ *     spec §9), showing an explicit "Starting preview…" skeleton until then
+ *     (never presented as the real render);
+ *   - then asks the adapter to render a single Element — the discovered
+ *     component with default props — via `render-frame`
+ *     (`@repo/core-runner-protocol` schema) and requests geometry;
+ *   - keeps agent-reported geometry as frame-local state (the store holds
+ *     registry + selection ONLY) and feeds click-target reports into the
+ *     store's selection;
+ *   - renders the selection ring as an editor-side overlay from that
+ *     reported geometry.
+ *
+ * Dragging the frame only rerenders with a new position — the canvas
+ * client is keyed on `adapterOrigin`/`componentId`, so drag/pan/zoom
+ * produce zero protocol round-trips (<16 ms/frame budget, ADR-028).
+ * Only the name tab (`.frame-drag-handle`) drags, so pointer events inside
+ * the iframe stay with the customer's document.
+ */
+export type FrameDescriptor = {
+  /** Display name on the frame's drag-handle tab. */
+  name: string;
+  /** Registry id of the discovered component this frame renders. */
+  componentId: string;
+  /** The adapter's origin — pinned targetOrigin for the canvas protocol. */
+  adapterOrigin: string;
+  /** Viewport size of the frame; defaults to 800x600. */
+  width?: number;
+  height?: number;
+};
+
+export type FrameNodeData = {
+  frame: FrameDescriptor;
+};
+
+export const DEFAULT_FRAME_WIDTH = 800;
+export const DEFAULT_FRAME_HEIGHT = 600;
+
+export function FrameNode({ data }: { data: FrameNodeData }) {
+  const { frame } = data;
+  const width = frame.width ?? DEFAULT_FRAME_WIDTH;
+  const height = frame.height ?? DEFAULT_FRAME_HEIGHT;
+
+  const iframeRef = useRef<HTMLIFrameElement | null>(null);
+  const [ready, setReady] = useState(false);
+  const [targets, setTargets] = useState<readonly GeometryTarget[]>([]);
+  const selectedNodeId = useEditorStore((s) => s.selectedNodeId);
+  const select = useEditorStore((s) => s.select);
+
+  useEffect(() => {
+    const client = createCanvasClient({
+      adapterOrigin: frame.adapterOrigin,
+      getAgentWindow: () => iframeRef.current?.contentWindow ?? null,
+      handlers: {
+        onRuntimeReady: () => {
+          setReady(true);
+          client.renderFrame(frame.componentId);
+          client.requestGeometry();
+        },
+        onGeometry: setTargets,
+        onClick: select,
+      },
+    });
+    client.start();
+    return () => client.stop();
+  }, [frame.adapterOrigin, frame.componentId, select]);
+
+  const selectedRect =
+    targets.find((target) => target.nodeId === selectedNodeId)?.rect ?? null;
+
+  return (
+    <div style={{ width }}>
+      <div
+        className="frame-drag-handle"
+        title="Drag to move"
+        style={{
+          cursor: "grab",
+          userSelect: "none",
+          whiteSpace: "nowrap",
+          fontFamily: "ui-monospace, monospace",
+          fontSize: 12,
+          padding: "2px 0 6px",
+          color: "var(--veect-text-muted, #6b7280)",
+        }}
+      >
+        {frame.name}{" "}
+        <span style={{ fontSize: 10.5, opacity: 0.7 }}>
+          {frame.componentId} · {width} × {height}
+        </span>
+      </div>
+      <div
+        style={{
+          position: "relative",
+          width,
+          height,
+          background: "var(--veect-frame-bg, #ffffff)",
+          border: "1px solid var(--veect-line, #e5e7eb)",
+          borderRadius: 4,
+          overflow: "hidden",
+        }}
+      >
+        <iframe
+          ref={iframeRef}
+          src={frame.adapterOrigin}
+          title={`${frame.name} frame`}
+          sandbox="allow-scripts allow-same-origin"
+          style={{ width: "100%", height: "100%", border: 0, display: "block" }}
+        />
+        {!ready && (
+          <div
+            style={{
+              position: "absolute",
+              inset: 0,
+              display: "flex",
+              alignItems: "center",
+              justifyContent: "center",
+              background: "var(--veect-frame-bg, #ffffff)",
+              color: "var(--veect-text-muted, #6b7280)",
+              fontFamily: "ui-monospace, monospace",
+              fontSize: 12,
+            }}
+          >
+            Starting preview…
+          </div>
+        )}
+        <SelectionOverlay rect={selectedRect} />
+      </div>
+    </div>
+  );
+}

packages/editor/src/ui/components/react-flow.mock.ts

@@ -0,0 +1,86 @@
+/**
+ * jsdom shims React Flow needs to render in component tests, adapted from
+ * the official React Flow testing guide
+ * (https://reactflow.dev/learn/advanced-use/testing). jsdom implements
+ * neither `ResizeObserver` nor `DOMMatrixReadOnly`, and its elements have
+ * no layout, so `offsetWidth`/`offsetHeight` fall back to inline styles.
+ *
+ * Call `mockReactFlow()` once per test file (module scope or `beforeAll`)
+ * before rendering a board. Idempotent.
+ */
+let initialized = false;
+
+export function mockReactFlow(): void {
+  if (initialized) return;
+  initialized = true;
+
+  class ResizeObserverMock {
+    private readonly callback: ResizeObserverCallback;
+
+    constructor(callback: ResizeObserverCallback) {
+      this.callback = callback;
+    }
+
+    observe(target: Element): void {
+      const width = (target as HTMLElement).offsetWidth || 1;
+      const height = (target as HTMLElement).offsetHeight || 1;
+      const contentRect = {
+        x: 0,
+        y: 0,
+        top: 0,
+        left: 0,
+        right: width,
+        bottom: height,
+        width,
+        height,
+        toJSON: () => ({ width, height }),
+      } as DOMRectReadOnly;
+      this.callback(
+        [{ target, contentRect } as ResizeObserverEntry],
+        this as unknown as ResizeObserver,
+      );
+    }
+
+    unobserve(): void {
+      // jsdom shim — nothing to release.
+    }
+
+    disconnect(): void {
+      // jsdom shim — nothing to release.
+    }
+  }
+  globalThis.ResizeObserver =
+    ResizeObserverMock as unknown as typeof ResizeObserver;
+
+  class DOMMatrixReadOnlyMock {
+    readonly m22: number;
+
+    constructor(transform?: string) {
+      const scale = transform?.match(/scale\(([\d.]+)\)/)?.[1];
+      this.m22 = scale === undefined ? 1 : Number(scale);
+    }
+  }
+  globalThis.DOMMatrixReadOnly =
+    DOMMatrixReadOnlyMock as unknown as typeof DOMMatrixReadOnly;
+
+  Object.defineProperties(globalThis.HTMLElement.prototype, {
+    offsetHeight: {
+      configurable: true,
+      get(this: HTMLElement) {
+        return Number.parseFloat(this.style.height) || 1;
+      },
+    },
+    offsetWidth: {
+      configurable: true,
+      get(this: HTMLElement) {
+        return Number.parseFloat(this.style.width) || 1;
+      },
+    },
+  });
+
+  (
+    globalThis.SVGElement.prototype as SVGElement & {
+      getBBox: () => DOMRect;
+    }
+  ).getBBox = () => ({ x: 0, y: 0, width: 0, height: 0 }) as DOMRect;
+}

packages/editor/src/ui/components/selection-overlay.stories.tsx

@@ -0,0 +1,44 @@
+import type { Meta, StoryObj } from "@storybook/react";
+import { SelectionOverlay } from "./selection-overlay";
+
+/**
+ * Editor-side selection chrome (ADR-028): the ring is positioned from
+ * agent-reported geometry and never renders inside the customer's iframe
+ * document. The gray box below stands in for a frame's iframe viewport.
+ */
+const meta = {
+  title: "Editor/SelectionOverlay",
+  component: SelectionOverlay,
+  tags: ["autodocs"],
+  decorators: [
+    (Story) => (
+      <div
+        style={{
+          position: "relative",
+          width: 480,
+          height: 240,
+          background: "#f3f4f6",
+          border: "1px solid #e5e7eb",
+          borderRadius: 4,
+        }}
+      >
+        <Story />
+      </div>
+    ),
+  ],
+} satisfies Meta<typeof SelectionOverlay>;
+export default meta;
+
+type Story = StoryObj<typeof meta>;
+
+export const Selected: Story = {
+  args: { rect: { x: 48, y: 64, width: 240, height: 56 } },
+};
+
+export const FullBleedElement: Story = {
+  args: { rect: { x: 0, y: 0, width: 480, height: 240 } },
+};
+
+export const NoSelection: Story = {
+  args: { rect: null },
+};

packages/editor/src/ui/components/selection-overlay.test.tsx

@@ -0,0 +1,31 @@
+import { describe, it, expect } from "vitest";
+import { render, screen } from "@testing-library/react";
+import { SelectionOverlay } from "./selection-overlay";
+
+describe("SelectionOverlay", () => {
+  it("renders nothing when rect is null (no selection)", () => {
+    render(<SelectionOverlay rect={null} />);
+    expect(screen.queryByTestId("selection-overlay")).not.toBeInTheDocument();
+  });
+
+  it("positions the ring from the agent-reported rect", () => {
+    render(
+      <SelectionOverlay rect={{ x: 24, y: 12, width: 320, height: 48 }} />,
+    );
+    const overlay = screen.getByTestId("selection-overlay");
+    expect(overlay).toHaveStyle({
+      position: "absolute",
+      left: "24px",
+      top: "12px",
+      width: "320px",
+      height: "48px",
+    });
+  });
+
+  it("is chrome, not content: hidden from a11y and inert to pointers (ADR-028)", () => {
+    render(<SelectionOverlay rect={{ x: 0, y: 0, width: 10, height: 10 }} />);
+    const overlay = screen.getByTestId("selection-overlay");
+    expect(overlay).toHaveAttribute("aria-hidden", "true");
+    expect(overlay).toHaveStyle({ pointerEvents: "none" });
+  });
+});

packages/editor/src/ui/components/selection-overlay.tsx

@@ -0,0 +1,36 @@
+import type { Rect } from "../../canvas-protocol/messages";
+
+/**
+ * Editor-side selection ring, positioned from agent-reported geometry
+ * (ADR-028): chrome never renders inside the customer's iframe document.
+ * The overlay lives in the frame node's coordinate space (the iframe's
+ * top-left is the origin), so React Flow's pan/zoom transform carries it
+ * along with the iframe for free — no protocol traffic on drag.
+ */
+export type SelectionOverlayProps = {
+  /** Bounding rect of the selected node, in iframe CSS pixels; `null` hides the ring. */
+  rect: Rect | null;
+};
+
+export function SelectionOverlay({ rect }: SelectionOverlayProps) {
+  if (rect === null) return null;
+  return (
+    <div
+      data-testid="selection-overlay"
+      aria-hidden="true"
+      style={{
+        position: "absolute",
+        left: rect.x,
+        top: rect.y,
+        width: rect.width,
+        height: rect.height,
+        pointerEvents: "none",
+        boxSizing: "border-box",
+        border: "1.5px solid var(--veect-accent, #4f46e5)",
+        borderRadius: 2,
+        boxShadow:
+          "0 0 0 3px var(--veect-accent-soft, rgba(79, 70, 229, 0.18))",
+      }}
+    />
+  );
+}

packages/editor/src/ui/index.ts

@@ -1,5 +1,15 @@
 // Public UI surface of @repo/editor: apps import components/hooks from
-// `@repo/editor/ui` and contracts from `@repo/editor`. The React Flow
-// board, iframe frame node, and selection overlay land here with the
-// board-shell slice.
+// `@repo/editor/ui` and contracts from `@repo/editor`.
 export { useEditorStore, type EditorStoreState } from "../store/editor-store";
+export { EditorBoard, type EditorBoardProps } from "./components/editor-board";
+export {
+  FrameNode,
+  type FrameNodeData,
+  type FrameDescriptor,
+  DEFAULT_FRAME_WIDTH,
+  DEFAULT_FRAME_HEIGHT,
+} from "./components/frame-node";
+export {
+  SelectionOverlay,
+  type SelectionOverlayProps,
+} from "./components/selection-overlay";