diff --git a/packages/block-editor/package.json b/packages/block-editor/package.json
index fe223019..1447852b 100644
--- a/packages/block-editor/package.json
+++ b/packages/block-editor/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@wrnexus/block-editor",
-  "version": "0.1.5",
+  "version": "0.1.6",
   "type": "module",
   "description": "Hydrated accessible editor runtime for WRNexus block documents.",
   "exports": {
diff --git a/packages/block-editor/src/canvas.ts b/packages/block-editor/src/canvas.ts
new file mode 100644
index 00000000..64540284
--- /dev/null
+++ b/packages/block-editor/src/canvas.ts
@@ -0,0 +1,51 @@
+import type { BlockNode } from "@wrnexus/blocks";
+import { mountBlockEditor, type MountedEditor, type MountEditorOptions } from "./runtime.ts";
+
+/** Annotates an editor-only rendered document; never changes the canonical tree. */
+export function mountBlockCanvas(root: HTMLElement, tree: BlockNode, options: MountEditorOptions): MountedEditor {
+  const elements = new Map([...root.querySelectorAll<HTMLElement>("[data-block-id]")].map(element => [element.dataset.blockId!, element]));
+  const cleanup: Array<() => void> = [];
+  const visit = (node: BlockNode, parent?: BlockNode, slot?: string) => {
+    const element = elements.get(node.id);
+    if (element) {
+      const old = ["data-block-parent", "data-block-slot", "data-block-type", "draggable"].map(name => [name, element.getAttribute(name)] as const);
+      cleanup.push(() => { for (const [name, value] of old) value === null ? element.removeAttribute(name) : element.setAttribute(name, value); });
+      element.setAttribute("draggable", "false");
+      if (parent && slot !== undefined) {
+        element.dataset.blockParent = parent.id;
+        element.dataset.blockSlot = slot;
+        element.dataset.blockType = node.type;
+        const handle = root.ownerDocument.createElement("button");
+        handle.type = "button";
+        handle.dataset.blockHandle = "";
+        handle.className = "wrn-canvas-drag-handle";
+        handle.setAttribute("aria-label", `Move ${node.type}`);
+        handle.style.touchAction = "none";
+        handle.textContent = "⋮⋮";
+        element.prepend(handle);
+        cleanup.push(() => handle.remove());
+      }
+      for (const [name, children] of Object.entries(node.slots)) {
+        if (children.length) continue;
+        const target = root.ownerDocument.createElement("div");
+        target.dataset.blockParent = node.id;
+        target.dataset.blockSlotTarget = name;
+        target.className = "wrn-canvas-empty-slot";
+        target.textContent = `Drop blocks in ${name}`;
+        // Root is a presentation table; keep editor decorations in a valid cell.
+        const container = element.tagName === "TABLE" ? element.querySelector("td") : element;
+        if (container) { container.append(target); cleanup.push(() => target.remove()); }
+      }
+    }
+    for (const [name, children] of Object.entries(node.slots)) for (const child of children) visit(child, node, name);
+  };
+  visit(tree);
+  let mounted: MountedEditor;
+  try { mounted = mountBlockEditor(root, options); }
+  catch (error) { cleanup.reverse().forEach(fn => fn()); throw error; }
+  let destroyed = false;
+  return {
+    refresh: () => { if (!destroyed) mounted.refresh(); },
+    destroy() { if (destroyed) return; destroyed = true; mounted.destroy(); cleanup.reverse().forEach(fn => fn()); },
+  };
+}
diff --git a/packages/block-editor/src/index.ts b/packages/block-editor/src/index.ts
index 0395521a..5b490bea 100644
--- a/packages/block-editor/src/index.ts
+++ b/packages/block-editor/src/index.ts
@@ -1,3 +1,4 @@
 export * from "./state.ts";
 export * from "./runtime.ts";
 export * from "./unsaved.ts";
+export * from "./canvas.ts";
diff --git a/packages/block-editor/test/canvas.test.ts b/packages/block-editor/test/canvas.test.ts
new file mode 100644
index 00000000..6dbddcb1
--- /dev/null
+++ b/packages/block-editor/test/canvas.test.ts
@@ -0,0 +1,37 @@
+import { expect, test } from "bun:test";
+import { readFileSync } from "node:fs";
+import { Window } from "happy-dom";
+
+const code = new Bun.Transpiler({ loader: "ts" }).transformSync(readFileSync(new URL("../src/canvas.ts", import.meta.url), "utf8"))
+  .replace(/^import .*;\s*$/gm, "").replace("export function mountBlockCanvas", "function mountBlockCanvas");
+
+test("canvas annotates exact node locations and cleans editor decorations without changing content", () => {
+  const window = new Window();
+  const root = window.document.body;
+  root.innerHTML = '<table data-block-id="root"><tbody><tr><td data-block-id="column" draggable="true"><table></table></td></tr></tbody></table>';
+  const original = root.innerHTML;
+  const tree = { id: "root", type: "layout.email-document", slots: { content: [{ id: "column", type: "layout.column", slots: { content: [] } }] } };
+  const before = JSON.stringify(tree);
+  let destroyed = 0;
+  const mount = new Function("mountBlockEditor", code + ";return mountBlockCanvas;")(() => ({ destroy: () => destroyed++, refresh() {} }));
+  const mounted = mount(root, tree, {});
+  const column = root.querySelector('[data-block-id="column"]')!;
+  expect(column.getAttribute("data-block-parent")).toBe("root");
+  expect(column.getAttribute("data-block-slot")).toBe("content");
+  expect(column.getAttribute("draggable")).toBe("false");
+  expect(root.querySelectorAll("[data-block-handle]")).toHaveLength(1);
+  expect(root.querySelector("[data-block-slot-target]")?.getAttribute("data-block-parent")).toBe("column");
+  expect(JSON.stringify(tree)).toBe(before);
+  mounted.destroy(); mounted.destroy();
+  expect(destroyed).toBe(1);
+  expect(root.innerHTML).toBe(original);
+});
+
+test("failed canvas mounting rolls back annotations", () => {
+  const root = new Window().document.body;
+  root.innerHTML = '<div data-block-id="root"><div data-block-id="child">Content</div></div>';
+  const before = root.innerHTML;
+  const mount = new Function("mountBlockEditor", code + ";return mountBlockCanvas;")(() => { throw new Error("backend unavailable"); });
+  expect(() => mount(root, { id: "root", type: "root", slots: { content: [{ id: "child", type: "text", slots: {} }] } }, {})).toThrow("backend unavailable");
+  expect(root.innerHTML).toBe(before);
+});