test(ConfirmDialog): add 6 WCAG accessibility tests

Add coverage for dialog a11y guarantees already implemented:
- role=dialog + aria-modal=true
- aria-labelledby pointing to title (WCAG 1.3.1)
- Escape → onCancel, Enter → onConfirm (WCAG 2.1.1)
- Focus moves to first button on open (WCAG 2.4.3)
- Backdrop click → onCancel
- aria-label on backdrop (WCAG 4.1.2)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

canvas/src/components/__tests__/ConfirmDialog.test.tsx

@@ -1,12 +1,114 @@
 // @vitest-environment jsdom
-import { describe, it, expect, vi, afterEach } from "vitest";
-import { render, screen, fireEvent, cleanup } from "@testing-library/react";
+import { describe, it, expect, vi, afterEach, beforeEach } from "vitest";
+import { render, screen, fireEvent, cleanup, act } from "@testing-library/react";
 import { ConfirmDialog } from "../ConfirmDialog";
 
 afterEach(() => {
   cleanup();
 });
 
+describe("ConfirmDialog — WCAG dialog accessibility", () => {
+  it("dialog has role=dialog and aria-modal=true", () => {
+    render(
+      <ConfirmDialog
+        open
+        title="Are you sure?"
+        message="This action cannot be undone."
+        onConfirm={vi.fn()}
+        onCancel={vi.fn()}
+      />
+    );
+    const dialog = screen.getByRole("dialog");
+    expect(dialog).toBeTruthy();
+    expect(dialog.getAttribute("aria-modal")).toBe("true");
+  });
+
+  it("dialog has aria-labelledby pointing to the title", () => {
+    render(
+      <ConfirmDialog
+        open
+        title="Delete workspace"
+        message="This will permanently delete the workspace."
+        onConfirm={vi.fn()}
+        onCancel={vi.fn()}
+      />
+    );
+    const dialog = screen.getByRole("dialog");
+    const labelledBy = dialog.getAttribute("aria-labelledby");
+    expect(labelledBy).toBeTruthy();
+    const titleEl = document.getElementById(labelledBy!);
+    expect(titleEl?.textContent?.trim()).toBe("Delete workspace");
+  });
+
+  it("Escape key invokes onCancel", () => {
+    const onCancel = vi.fn();
+    render(
+      <ConfirmDialog
+        open
+        title="Title"
+        message="Message"
+        onConfirm={vi.fn()}
+        onCancel={onCancel}
+      />
+    );
+    fireEvent.keyDown(window, { key: "Escape" });
+    expect(onCancel).toHaveBeenCalledTimes(1);
+  });
+
+  it("Enter key invokes onConfirm", () => {
+    const onConfirm = vi.fn();
+    render(
+      <ConfirmDialog
+        open
+        title="Title"
+        message="Message"
+        onConfirm={onConfirm}
+        onCancel={vi.fn()}
+      />
+    );
+    fireEvent.keyDown(window, { key: "Enter" });
+    expect(onConfirm).toHaveBeenCalledTimes(1);
+  });
+
+  it("moves focus to the first button when dialog opens (WCAG 2.4.3)", async () => {
+    const onConfirm = vi.fn();
+    render(
+      <ConfirmDialog
+        open
+        title="Title"
+        message="Message"
+        onConfirm={onConfirm}
+        onCancel={vi.fn()}
+      />
+    );
+    // Flush requestAnimationFrame so ConfirmDialog's internal rAF focus fires
+    await act(async () => {
+      await new Promise((r) => requestAnimationFrame(() => requestAnimationFrame(r)));
+    });
+    const firstButton = screen.getAllByRole("button")[0];
+    expect(document.activeElement).toBe(firstButton);
+  });
+});
+
+describe("ConfirmDialog — backdrop", () => {
+  it("backdrop click invokes onCancel", () => {
+    const onCancel = vi.fn();
+    render(
+      <ConfirmDialog
+        open
+        title="Title"
+        message="Message"
+        onConfirm={vi.fn()}
+        onCancel={onCancel}
+      />
+    );
+    const backdrop = document.querySelector('[aria-label="Dismiss dialog"]') as HTMLElement;
+    expect(backdrop).toBeTruthy();
+    fireEvent.click(backdrop);
+    expect(onCancel).toHaveBeenCalledTimes(1);
+  });
+});
+
 describe("ConfirmDialog singleButton prop", () => {
   it("renders Cancel button by default", () => {
     render(