diff --git a/craft/src/panels/sitesmith/SitesmithModal.tsx b/craft/src/panels/sitesmith/SitesmithModal.tsx
index 6f3ea80..6bb9ac7 100644
--- a/craft/src/panels/sitesmith/SitesmithModal.tsx
+++ b/craft/src/panels/sitesmith/SitesmithModal.tsx
@@ -11,6 +11,7 @@ import { MessageList } from './MessageList';
 import { ChatInput } from './ChatInput';
 import { WorkingIndicator } from './WorkingIndicator';
 import { SitesmithResponse } from '../../types/sitesmith';
+import { Modal } from '../../ui/Modal';
 
 interface Props {
   onClose: () => void;
@@ -39,7 +40,6 @@ export const SitesmithModal: React.FC<Props> = ({ onClose, target }) => {
 
   const canChat = summary && (summary.status === 'OK_BONUS' || summary.status === 'OK_MONTHLY');
 
-  const overlay: React.CSSProperties = { position: 'fixed', inset: 0, background: 'rgba(0,0,0,0.8)', zIndex: 9000, display: 'flex', alignItems: 'center', justifyContent: 'center' };
   const panel:   React.CSSProperties = { background: '#0f0f17', border: '1px solid #27272a', borderRadius: 12, width: 'min(720px, 90vw)', maxHeight: '90vh', display: 'flex', flexDirection: 'column' };
   const header:  React.CSSProperties = { display: 'flex', alignItems: 'center', padding: '14px 18px', borderBottom: '1px solid #27272a', gap: 8 };
   const body:    React.CSSProperties = { flex: 1, padding: '14px 18px', overflowY: 'auto', display: 'flex', flexDirection: 'column' };
@@ -93,7 +93,14 @@ export const SitesmithModal: React.FC<Props> = ({ onClose, target }) => {
   };
 
   return (
-    <div role="dialog" aria-modal="true" style={overlay}>
+    <Modal
+      open
+      onClose={onClose}
+      closeOnEscape={false}
+      closeOnBackdropClick={false}
+      backdropStyle={{ backgroundColor: 'rgba(0,0,0,0.8)', zIndex: 9000 }}
+      backdropProps={{ role: 'dialog', 'aria-modal': true }}
+    >
       <div style={panel}>
         <div style={header}>
           <div style={{ fontWeight: 600, color: '#fff' }}>✨ Sitesmith</div>
@@ -166,6 +173,6 @@ export const SitesmithModal: React.FC<Props> = ({ onClose, target }) => {
           onCancel={() => setPendingReplace(null)}
         />
       </div>
-    </div>
+    </Modal>
   );
 };
diff --git a/craft/src/panels/topbar/HeadCodeModal.tsx b/craft/src/panels/topbar/HeadCodeModal.tsx
index 7030649..d84f528 100644
--- a/craft/src/panels/topbar/HeadCodeModal.tsx
+++ b/craft/src/panels/topbar/HeadCodeModal.tsx
@@ -1,5 +1,6 @@
-import React, { useEffect } from 'react';
+import React from 'react';
 import { useSiteDesign } from '../../state/SiteDesignContext';
+import { Modal } from '../../ui/Modal';
 
 interface HeadCodeModalProps {
   open: boolean;
@@ -9,19 +10,8 @@ interface HeadCodeModalProps {
 export const HeadCodeModal: React.FC<HeadCodeModalProps> = ({ open, onClose }) => {
   const { design, updateDesign } = useSiteDesign();
 
-  useEffect(() => {
-    if (!open) return;
-    const handler = (e: KeyboardEvent) => {
-      if (e.key === 'Escape') onClose();
-    };
-    window.addEventListener('keydown', handler);
-    return () => window.removeEventListener('keydown', handler);
-  }, [open, onClose]);
-
-  if (!open) return null;
-
   return (
-    <div style={backdropStyle} onClick={onClose}>
+    <Modal open={open} onClose={onClose}>
       <div style={modalStyle} onClick={(e) => e.stopPropagation()}>
         {/* Header */}
         <div style={modalHeaderStyle}>
@@ -92,25 +82,12 @@ export const HeadCodeModal: React.FC<HeadCodeModalProps> = ({ open, onClose }) =
           </button>
         </div>
       </div>
-    </div>
+    </Modal>
   );
 };
 
 /* ---------- Styles ---------- */
 
-const backdropStyle: React.CSSProperties = {
-  position: 'fixed',
-  top: 0,
-  left: 0,
-  right: 0,
-  bottom: 0,
-  backgroundColor: 'rgba(0, 0, 0, 0.65)',
-  display: 'flex',
-  alignItems: 'center',
-  justifyContent: 'center',
-  zIndex: 10000,
-};
-
 const modalStyle: React.CSSProperties = {
   width: '90vw',
   maxWidth: 700,
diff --git a/craft/src/panels/topbar/TemplateModal.tsx b/craft/src/panels/topbar/TemplateModal.tsx
index 0577843..93b2227 100644
--- a/craft/src/panels/topbar/TemplateModal.tsx
+++ b/craft/src/panels/topbar/TemplateModal.tsx
@@ -10,6 +10,7 @@ import {
 } from '../../templates';
 import { componentResolver } from '../../components/resolver';
 import { clickableProps } from '../../utils/a11y';
+import { Modal } from '../../ui/Modal';
 
 // ---------------------------------------------------------------------------
 // Types
@@ -60,18 +61,15 @@ export const TemplateModal: React.FC<TemplateModalProps> = ({ open, onClose }) =
     };
   }, []);
 
-  // Close on Escape key
-  useEffect(() => {
-    if (!open) return;
-    const handler = (e: KeyboardEvent) => {
-      if (e.key === 'Escape') {
-        if (confirmTemplate) setConfirmTemplate(null);
-        else onClose();
-      }
-    };
-    document.addEventListener('keydown', handler);
-    return () => document.removeEventListener('keydown', handler);
-  }, [open, confirmTemplate, onClose]);
+  // Escape / backdrop-click close the confirmation dialog first if it's open,
+  // otherwise close the modal. Passed to <Modal> below, which handles the
+  // Escape listener and the backdrop-click detection itself; the header's own
+  // close button (X) below still uses the raw `onClose` prop directly, so it
+  // always fully closes the modal even mid-confirmation (unchanged behavior).
+  const handleModalClose = useCallback(() => {
+    if (confirmTemplate) setConfirmTemplate(null);
+    else onClose();
+  }, [confirmTemplate, onClose]);
 
   // Filter templates by category
   const filtered = useMemo(() => {
@@ -236,24 +234,8 @@ export const TemplateModal: React.FC<TemplateModalProps> = ({ open, onClose }) =
     }
   }, [confirmTemplate, applyDesign, pages, addPage, switchPage, deletePage, updateDesign, addTemplateComponents, clearCanvas, applyHeaderFooter, wait, onClose]);
 
-  // Close on backdrop click
-  const handleBackdropClick = useCallback(
-    (e: React.MouseEvent) => {
-      if (e.target === e.currentTarget) {
-        if (confirmTemplate) {
-          setConfirmTemplate(null);
-        } else {
-          onClose();
-        }
-      }
-    },
-    [confirmTemplate, onClose],
-  );
-
-  if (!open) return null;
-
   return (
-    <div style={backdropStyle} onClick={handleBackdropClick}>
+    <Modal open={open} onClose={handleModalClose}>
       <div style={modalStyle}>
         {/* Header */}
         <div style={modalHeaderStyle}>
@@ -377,7 +359,7 @@ export const TemplateModal: React.FC<TemplateModalProps> = ({ open, onClose }) =
           </div>
         )}
       </div>
-    </div>
+    </Modal>
   );
 };
 
@@ -473,19 +455,6 @@ const TemplateCard: React.FC<{
 // Styles
 // ---------------------------------------------------------------------------
 
-const backdropStyle: React.CSSProperties = {
-  position: 'fixed',
-  top: 0,
-  left: 0,
-  right: 0,
-  bottom: 0,
-  backgroundColor: 'rgba(0, 0, 0, 0.65)',
-  display: 'flex',
-  alignItems: 'center',
-  justifyContent: 'center',
-  zIndex: 10000,
-};
-
 const modalStyle: React.CSSProperties = {
   width: '90vw',
   maxWidth: 900,
diff --git a/craft/src/ui/Modal.test.tsx b/craft/src/ui/Modal.test.tsx
new file mode 100644
index 0000000..47fa5b7
--- /dev/null
+++ b/craft/src/ui/Modal.test.tsx
@@ -0,0 +1,96 @@
+import { describe, test, expect, vi, afterEach } from 'vitest';
+import React from 'react';
+import { createRoot, Root } from 'react-dom/client';
+import { act } from 'react-dom/test-utils';
+import { Modal } from './Modal';
+
+/* ---------- DOM test harness (no @testing-library/react in this repo, see
+   src/ui/AssetPicker.test.tsx for the same pattern: react-dom/client +
+   react-dom/test-utils `act`, both transitive deps of react-dom already). ---------- */
+let container: HTMLDivElement;
+let root: Root;
+
+function render(ui: React.ReactElement) {
+  container = document.createElement('div');
+  document.body.appendChild(container);
+  act(() => {
+    root = createRoot(container);
+    root.render(ui);
+  });
+}
+
+function unmount() {
+  act(() => { root.unmount(); });
+  container.remove();
+}
+
+function pressEscape() {
+  act(() => {
+    window.dispatchEvent(new KeyboardEvent('keydown', { key: 'Escape', bubbles: true }));
+  });
+}
+
+function click(el: Element | null) {
+  if (!el) throw new Error('element not found');
+  act(() => { (el as HTMLElement).dispatchEvent(new MouseEvent('click', { bubbles: true })); });
+}
+
+afterEach(() => {
+  if (container) unmount();
+  document.body.style.overflow = '';
+});
+
+describe('Modal', () => {
+  test('renders children when open', () => {
+    render(<Modal open onClose={vi.fn()}><div data-testid="body">hello</div></Modal>);
+    expect(container.querySelector('[data-testid="body"]')?.textContent).toBe('hello');
+  });
+
+  test('renders nothing when closed', () => {
+    render(<Modal open={false} onClose={vi.fn()}><div data-testid="body">hello</div></Modal>);
+    expect(container.querySelector('[data-testid="body"]')).toBeNull();
+  });
+
+  test('Escape calls onClose by default', () => {
+    const onClose = vi.fn();
+    render(<Modal open onClose={onClose}><div>body</div></Modal>);
+    pressEscape();
+    expect(onClose).toHaveBeenCalledTimes(1);
+  });
+
+  test('Escape does not call onClose when closeOnEscape is false', () => {
+    const onClose = vi.fn();
+    render(<Modal open onClose={onClose} closeOnEscape={false}><div>body</div></Modal>);
+    pressEscape();
+    expect(onClose).not.toHaveBeenCalled();
+  });
+
+  test('clicking the backdrop calls onClose by default', () => {
+    const onClose = vi.fn();
+    render(<Modal open onClose={onClose}><div data-testid="body">body</div></Modal>);
+    // The backdrop is the outermost rendered element.
+    click(container.firstElementChild);
+    expect(onClose).toHaveBeenCalledTimes(1);
+  });
+
+  test('clicking inside the content does not call onClose', () => {
+    const onClose = vi.fn();
+    render(<Modal open onClose={onClose}><div data-testid="body">body</div></Modal>);
+    click(container.querySelector('[data-testid="body"]'));
+    expect(onClose).not.toHaveBeenCalled();
+  });
+
+  test('clicking the backdrop does not call onClose when closeOnBackdropClick is false', () => {
+    const onClose = vi.fn();
+    render(<Modal open onClose={onClose} closeOnBackdropClick={false}><div>body</div></Modal>);
+    click(container.firstElementChild);
+    expect(onClose).not.toHaveBeenCalled();
+  });
+
+  test('locks body scroll while open and restores it on close', () => {
+    render(<Modal open onClose={vi.fn()}><div>body</div></Modal>);
+    expect(document.body.style.overflow).toBe('hidden');
+    act(() => { root.render(<Modal open={false} onClose={vi.fn()}><div>body</div></Modal>); });
+    expect(document.body.style.overflow).toBe('');
+  });
+});
diff --git a/craft/src/ui/Modal.tsx b/craft/src/ui/Modal.tsx
new file mode 100644
index 0000000..9c4be30
--- /dev/null
+++ b/craft/src/ui/Modal.tsx
@@ -0,0 +1,94 @@
+import React, { useEffect } from 'react';
+
+export interface ModalProps {
+  open: boolean;
+  onClose: () => void;
+  title?: string;
+  children: React.ReactNode;
+  width?: number | string;
+  /** Override the backdrop's own inline styles (e.g. a different overlay
+   *  opacity/z-index). Merged on top of the shared defaults. */
+  backdropStyle?: React.CSSProperties;
+  /** Escape key closes the modal. Default true — set false to preserve a
+   *  modal that never handled Escape before this component existed. */
+  closeOnEscape?: boolean;
+  /** Clicking the backdrop (outside the modal content) closes the modal.
+   *  Default true — set false to preserve a modal that never handled
+   *  backdrop clicks before this component existed. */
+  closeOnBackdropClick?: boolean;
+  /** Extra attributes spread onto the backdrop div (e.g. role="dialog",
+   *  aria-modal) for a modal that previously set those directly. */
+  backdropProps?: React.HTMLAttributes<HTMLDivElement>;
+}
+
+const defaultBackdropStyle: React.CSSProperties = {
+  position: 'fixed',
+  top: 0,
+  left: 0,
+  right: 0,
+  bottom: 0,
+  backgroundColor: 'rgba(0, 0, 0, 0.65)',
+  display: 'flex',
+  alignItems: 'center',
+  justifyContent: 'center',
+  zIndex: 10000,
+};
+
+/* ---------- Shared modal chrome ----------
+   Backdrop + centered panel wrapper + Escape-to-close + scroll-lock, extracted
+   from TemplateModal / HeadCodeModal / SitesmithModal (task E4.3). Each
+   modal's own content — including its own header, close button, and panel
+   styling (background, radius, shadow, dimensions) — stays in that modal's
+   own file and is passed in as `children`, since those visuals differ across
+   the three. `closeOnEscape` / `closeOnBackdropClick` default to true (the
+   behavior TemplateModal and HeadCodeModal already had); SitesmithModal had
+   neither before this extraction, so it opts out of both to keep its exact
+   prior behavior. */
+export const Modal: React.FC<ModalProps> = ({
+  open,
+  onClose,
+  title,
+  children,
+  width,
+  backdropStyle,
+  closeOnEscape = true,
+  closeOnBackdropClick = true,
+  backdropProps,
+}) => {
+  useEffect(() => {
+    if (!open || !closeOnEscape) return;
+    const handler = (e: KeyboardEvent) => {
+      if (e.key === 'Escape') onClose();
+    };
+    window.addEventListener('keydown', handler);
+    return () => window.removeEventListener('keydown', handler);
+  }, [open, closeOnEscape, onClose]);
+
+  useEffect(() => {
+    if (!open) return;
+    const prevOverflow = document.body.style.overflow;
+    document.body.style.overflow = 'hidden';
+    return () => {
+      document.body.style.overflow = prevOverflow;
+    };
+  }, [open]);
+
+  if (!open) return null;
+
+  return (
+    <div
+      {...backdropProps}
+      style={backdropStyle ? { ...defaultBackdropStyle, ...backdropStyle } : defaultBackdropStyle}
+      onClick={(e) => {
+        if (closeOnBackdropClick && e.target === e.currentTarget) onClose();
+      }}
+    >
+      <div style={width !== undefined ? { width } : undefined}>
+        {title !== undefined && (
+          <div style={{ fontSize: 15, fontWeight: 600, marginBottom: 8 }}>{title}</div>
+        )}
+        {children}
+      </div>
+    </div>
+  );
+};