diff --git a/craft/src/panels/history/HistoryModal.tsx b/craft/src/panels/history/HistoryModal.tsx
index 1bf1bc4..503b25b 100644
--- a/craft/src/panels/history/HistoryModal.tsx
+++ b/craft/src/panels/history/HistoryModal.tsx
@@ -66,6 +66,9 @@ export function useRestoreSnapshot() {
   }, [actions]);
 
   const restoreSite = useCallback((snapshot: Snapshot, at: string): boolean => {
+    // #57: a restore while a master zone is open would load page content into
+    // the zone (or strand it); Done first.
+    if (pagesRef.current.isEditingGlobal) { notify({ kind: 'error', message: 'Click Done on the global section you are editing before restoring a version.' }); return false; }
     const valid = validateSnapshot(snapshot);
     if (!valid.ok) { notify({ kind: 'error', message: valid.reason }); return false; }
     const snapPages = snapshotToPages(snapshot);
@@ -93,6 +96,7 @@ export function useRestoreSnapshot() {
   }, [extras, updateDesign, markDirty, notify, putOnCanvas]);
 
   const restorePage = useCallback((snapshot: Snapshot, pageIndex: number, at: string): boolean => {
+    if (pagesRef.current.isEditingGlobal) { notify({ kind: 'error', message: 'Click Done on the global section you are editing before restoring a version.' }); return false; }
     const valid = validateSnapshot(snapshot);
     if (!valid.ok) { notify({ kind: 'error', message: valid.reason }); return false; }
     const snapPage = snapshotToPages(snapshot)[pageIndex];
@@ -124,6 +128,7 @@ interface Pending { id: string; mode: Mode; snapshot: Snapshot; at: string }
 export const HistoryModal: React.FC<{ open: boolean; onClose: () => void }> = ({ open, onClose }) => {
   const { listHistory, getSnapshot } = useHistoryApi();
   const { restoreSite, restorePage } = useRestoreSnapshot();
+  const { isEditingGlobal } = usePages();
   const { notify } = useNotices();
   const [items, setItems] = useState<HistoryItem[] | null>(null);
   const [loading, setLoading] = useState(false);
@@ -197,6 +202,7 @@ export const HistoryModal: React.FC<{ open: boolean; onClose: () => void }> = ({
           </button>
         </div>
         <div className="wsb-history-body">
+          {isEditingGlobal && <p className="wsb-history-empty" role="status">Click Done on the global section you are editing before restoring a version.</p>}
           {loading && <p className="wsb-history-empty">Loading...</p>}
           {!loading && items && items.length === 0 && <p className="wsb-history-empty">No earlier versions yet. One is kept each time you save.</p>}
           {days.map((g) => (
@@ -210,8 +216,8 @@ export const HistoryModal: React.FC<{ open: boolean; onClose: () => void }> = ({
                       <span className="wsb-history-time" title={fmtExact(it.at)}>{relativeTime(it.at)}</span>
                       <span className="wsb-history-actions">
                         <button type="button" disabled={busyId === it.id} onClick={() => begin(it, 'preview')}>Preview</button>
-                        <button type="button" disabled={busyId === it.id} onClick={() => begin(it, 'restore-page')}>Restore one page…</button>
-                        <button type="button" disabled={busyId === it.id} onClick={() => begin(it, 'restore-site')}>Restore site…</button>
+                        <button type="button" disabled={busyId === it.id || isEditingGlobal} onClick={() => begin(it, 'restore-page')}>Restore one page…</button>
+                        <button type="button" disabled={busyId === it.id || isEditingGlobal} onClick={() => begin(it, 'restore-site')}>Restore site…</button>
                       </span>
                     </div>
                     {pending && pending.id === it.id && (
diff --git a/craft/src/panels/right/SiteDesignPanel.reset.test.tsx b/craft/src/panels/right/SiteDesignPanel.reset.test.tsx
index 7a3b185..7bcf70e 100644
--- a/craft/src/panels/right/SiteDesignPanel.reset.test.tsx
+++ b/craft/src/panels/right/SiteDesignPanel.reset.test.tsx
@@ -16,14 +16,16 @@ import { act } from 'react-dom/test-utils';
  * for a real-provider test.
  * ---------------------------------------------------------------------- */
 
-const replaceAllPages = vi.fn();
+// Real contract: true when replaced, false when refused (a global-section master is open).
+const replaceAllPages = vi.fn((_pages: { name: string; tree: any }[]) => true);
+let mockEditingGlobal = false;
 const setHeader = vi.fn();
 const setFooter = vi.fn();
 const resetToDefaults = vi.fn();
 let mockSiteDomain = 'example.com';
 
 vi.mock('../../state/PageContext', () => ({
-  usePages: () => ({ replaceAllPages, setHeader, setFooter, pages: [], siteDesign: {} }),
+  usePages: () => ({ replaceAllPages, setHeader, setFooter, pages: [], siteDesign: {}, isEditingGlobal: mockEditingGlobal }),
 }));
 vi.mock('../../state/SiteDesignContext', () => ({
   useSiteDesign: () => ({ design: {}, updateDesign: vi.fn(), resetToDefaults }),
@@ -210,4 +212,24 @@ describe('Reset Entire Site -- guard + wiring (mocked hooks)', () => {
     expect(container.textContent).toContain('Danger zone');
     unmount();
   });
+  test('#57: refused while a global-section master is open (button disabled AND handler guarded)', () => {
+    mockSiteDomain = 'example.com';
+    mockEditingGlobal = true;
+    replaceAllPages.mockClear(); setHeader.mockClear(); setFooter.mockClear(); resetToDefaults.mockClear();
+    try {
+      render();
+      act(() => { (container.querySelector('[data-action="open-site-reset"]') as HTMLButtonElement).click(); });
+      const input = container.querySelector('[data-testid="site-reset-domain"]') as HTMLInputElement;
+      act(() => { setInputValue(input, 'example.com'); });
+      const confirm = container.querySelector('[data-action="confirm-site-reset"]') as HTMLButtonElement;
+      expect(confirm.disabled).toBe(true);
+      act(() => { invokeReactOnClick(confirm); });
+      expect(replaceAllPages).not.toHaveBeenCalled();
+      expect(setHeader).not.toHaveBeenCalled();
+      expect(setFooter).not.toHaveBeenCalled();
+      expect(resetToDefaults).not.toHaveBeenCalled();
+    } finally {
+      mockEditingGlobal = false;
+    }
+  });
 });
diff --git a/craft/src/panels/right/SiteDesignPanel.tsx b/craft/src/panels/right/SiteDesignPanel.tsx
index 672b75b..efa7311 100644
--- a/craft/src/panels/right/SiteDesignPanel.tsx
+++ b/craft/src/panels/right/SiteDesignPanel.tsx
@@ -205,7 +205,7 @@ export function siteResetConfirmMatches(typed: string, domain: string): boolean
 
 export const SiteDesignPanel: React.FC = () => {
   const { design, updateDesign, resetToDefaults } = useSiteDesign();
-  const { replaceAllPages, setHeader, setFooter } = usePages();
+  const { replaceAllPages, setHeader, setFooter, isEditingGlobal } = usePages();
   const { whpConfig } = useEditorConfig();
   const { armForceEmptyNextSave } = useSaveGuard();
   // Standalone mode (no WHP_CONFIG) has no site domain to confirm against --
@@ -223,11 +223,13 @@ export const SiteDesignPanel: React.FC = () => {
     // `disabled` attribute were ever bypassed (a synthetic click, or a
     // future refactor that drops it).
     if (!siteResetConfirmMatches(siteResetTyped, siteDomain)) return;
+    // #57: never wipe the site out from under an open global-section master.
+    if (isEditingGlobal) return;
 
     // The user explicitly confirmed wiping the site, so the next save must
     // be allowed to replace the saved site with an empty one.
+    if (!replaceAllPages([{ name: 'Home', tree: BLANK_PAGE_TREE }])) return;
     armForceEmptyNextSave();
-    replaceAllPages([{ name: 'Home', tree: BLANK_PAGE_TREE }]);
     setHeader(BLANK_HEADER_TREE);
     setFooter(BLANK_FOOTER_TREE);
     resetToDefaults();
@@ -499,7 +501,7 @@ export const SiteDesignPanel: React.FC = () => {
               <div style={{ display: 'flex', gap: 6, marginTop: 8 }}>
                 <button
                   data-action="confirm-site-reset"
-                  disabled={!siteResetConfirmMatches(siteResetTyped, siteDomain)}
+                  disabled={isEditingGlobal || !siteResetConfirmMatches(siteResetTyped, siteDomain)}
                   onClick={handleResetSite}
                   style={{
                     flex: 1, padding: '7px 10px', fontSize: 11, fontWeight: 600,
diff --git a/craft/src/panels/topbar/TemplateModal.tsx b/craft/src/panels/topbar/TemplateModal.tsx
index 392fec5..7c3a9cb 100644
--- a/craft/src/panels/topbar/TemplateModal.tsx
+++ b/craft/src/panels/topbar/TemplateModal.tsx
@@ -47,7 +47,7 @@ const CATEGORY_COLORS: Record<TemplateCategory, string> = {
 
 export const TemplateModal: React.FC<TemplateModalProps> = ({ open, onClose }) => {
   const { actions, query } = useEditor();
-  const { pages, addPage, switchPage, deletePage, editHeader, editFooter } = usePages();
+  const { pages, addPage, switchPage, deletePage, editHeader, editFooter, isEditingGlobal } = usePages();
   const { updateDesign } = useSiteDesign();
   const { armForceEmptyNextSave } = useSaveGuard();
 
@@ -180,6 +180,10 @@ export const TemplateModal: React.FC<TemplateModalProps> = ({ open, onClose }) =
   // while the sequence is still mutating a canvas the dialog just tore down.
   const handleLoad = useCallback(async () => {
     if (!confirmTemplate) return;
+    // #57: the live canvas is a global-section master. Clearing it and
+    // switching away would commit the template's first section as the new
+    // master and rewrite every instance on the site with it.
+    if (isEditingGlobal) { setConfirmTemplate(null); return; }
     setLoading(true);
 
     const tpl = confirmTemplate;
@@ -245,7 +249,7 @@ export const TemplateModal: React.FC<TemplateModalProps> = ({ open, onClose }) =
       if (mountedRef.current) setLoading(false);
       onClose();
     }
-  }, [confirmTemplate, applyDesign, pages, addPage, switchPage, deletePage, updateDesign, addTemplateComponents, clearCanvas, applyHeaderFooter, wait, onClose, armForceEmptyNextSave]);
+  }, [confirmTemplate, isEditingGlobal, applyDesign, pages, addPage, switchPage, deletePage, updateDesign, addTemplateComponents, clearCanvas, applyHeaderFooter, wait, onClose, armForceEmptyNextSave]);
 
   // Mobile-A2: portaled to `document.body` -- TopBar.tsx mounts this modal
   // as a child of `.topbar`, which (as a flex item with its own z-index)
@@ -306,6 +310,12 @@ export const TemplateModal: React.FC<TemplateModalProps> = ({ open, onClose }) =
           ))}
         </div>
 
+        {isEditingGlobal && (
+          <div role="status" className="template-modal-global-notice" style={{ margin: '0 20px', padding: '10px 12px', borderRadius: 6, background: 'rgba(245,158,11,0.12)', border: '1px solid rgba(245,158,11,0.4)', color: '#fbbf24', fontSize: 12 }}>
+            Click Done on the global section you are editing before loading a template.
+          </div>
+        )}
+
         {/* Template Grid */}
         <div style={gridContainerStyle}>
           <div style={gridStyle}>
@@ -313,7 +323,7 @@ export const TemplateModal: React.FC<TemplateModalProps> = ({ open, onClose }) =
               <TemplateCard
                 key={tpl.id}
                 template={tpl}
-                onSelect={() => setConfirmTemplate(tpl)}
+                onSelect={() => { if (!isEditingGlobal) setConfirmTemplate(tpl); }}
               />
             ))}
             {filtered.length === 0 && (
diff --git a/craft/src/panels/topbar/TopBar.test.tsx b/craft/src/panels/topbar/TopBar.test.tsx
index e91d488..e35174f 100644
--- a/craft/src/panels/topbar/TopBar.test.tsx
+++ b/craft/src/panels/topbar/TopBar.test.tsx
@@ -34,13 +34,14 @@ import { act } from 'react-dom/test-utils';
 
 // #54: what the pre-publish checks see. Default (no pages) means no checks, so
 // every pre-existing test publishes directly.
-const checkFixture: { pages: any[]; liveState: string; activePageId: string; footerState: string | null } = { pages: [], liveState: '{}', activePageId: 'home', footerState: null };
+const checkFixture: { pages: any[]; liveState: string; activePageId: string; footerState: string | null; editingGlobal?: boolean } = { pages: [], liveState: '{}', activePageId: 'home', footerState: null };
 vi.mock('../../state/PageContext', () => ({
   usePages: () => ({
     pages: checkFixture.pages,
     headerPage: { id: '__header__', name: 'Header', slug: '__header__', craftState: null },
     footerPage: { id: '__footer__', name: 'Footer', slug: '__footer__', craftState: checkFixture.footerState },
     activePageId: checkFixture.activePageId,
+    isEditingGlobal: !!checkFixture.editingGlobal,
     switchPage: vi.fn(),
   }),
 }));
@@ -146,6 +147,7 @@ afterEach(() => {
   checkFixture.liveState = '{}';
   checkFixture.activePageId = 'home';
   checkFixture.footerState = null;
+  checkFixture.editingGlobal = false;
   openPaletteMock.mockReset();
 });
 
@@ -344,6 +346,18 @@ describe('TopBar search button (#49 integration)', () => {
   });
 });
 
+describe('TopBar Templates while a global-section master is open (#57)', () => {
+  test('the Templates button is disabled (and enabled otherwise)', () => {
+    render();
+    expect(container.querySelector<HTMLButtonElement>('button[aria-label="Templates"]')!.disabled).toBe(false);
+    act(() => { root.unmount(); });
+    container.remove();
+    checkFixture.editingGlobal = true;
+    render();
+    expect(container.querySelector<HTMLButtonElement>('button[aria-label="Templates"]')!.disabled).toBe(true);
+  });
+});
+
 describe('TopBar slow publish', () => {
   test('after 30s the button reads "Still publishing..." instead of failing', async () => {
     vi.useFakeTimers();
diff --git a/craft/src/panels/topbar/TopBar.tsx b/craft/src/panels/topbar/TopBar.tsx
index d0f5ea6..11a11a3 100644
--- a/craft/src/panels/topbar/TopBar.tsx
+++ b/craft/src/panels/topbar/TopBar.tsx
@@ -46,7 +46,7 @@ export const TopBar: React.FC<TopBarProps> = ({ showGuides, onToggleGuides }) =>
     neverSaved,
   } = useSaveGuard();
   const canSave = loadState === 'loaded';
-  const { headerPage, footerPage, pages, activePageId } = usePages();
+  const { headerPage, footerPage, pages, activePageId, isEditingGlobal } = usePages();
   const { design } = useSiteDesign();
 
   const [saving, setSaving] = useState(false);
@@ -372,10 +372,10 @@ export const TopBar: React.FC<TopBarProps> = ({ showGuides, onToggleGuides }) =>
     { id: 'site.save', title: 'Save', group: 'site', shortcut: 'mod+s', allowWhileTyping: true, when: () => canSave, run: () => handleSave() },
     ...(isWHP ? [{ id: 'site.publish', title: 'Publish', group: 'site' as const, shortcut: 'mod+shift+p', allowWhileTyping: true, when: () => canSave, run: () => handlePublish() }] : []),
     { id: 'site.preview', title: 'Preview', group: 'site', shortcut: 'mod+p', allowWhileTyping: true, run: () => handlePreview() },
-    { id: 'site.templates', title: 'Templates', group: 'site', when: () => canSave, run: ({ openTemplates }) => openTemplates() },
+    { id: 'site.templates', title: 'Templates', group: 'site', when: () => canSave && !isEditingGlobal, run: ({ openTemplates }) => openTemplates() },
     { id: 'site.head-code', title: 'Custom head code', group: 'site', when: () => canSave, run: ({ openHeadCode }) => openHeadCode() },
     { id: 'site.report-issue', title: 'Report an issue', group: 'site', run: () => setReportOpen(true) },
-  ], [canSave, isWHP, handleSave, handlePublish, handlePreview]);
+  ], [canSave, isEditingGlobal, isWHP, handleSave, handlePublish, handlePreview]);
 
   // Phase A: at ≤768px the topbar collapses to only the essentials --
   // back arrow, Undo/Redo, Save (+Publish) -- with Templates, Sitesmith,
@@ -468,6 +468,7 @@ export const TopBar: React.FC<TopBarProps> = ({ showGuides, onToggleGuides }) =>
           onPreview={handlePreview}
           sitesmithNode={<SitesmithButton onClick={() => openSitesmith()} disabled={!canSave} />}
           editingDisabled={!canSave}
+          templatesDisabled={isEditingGlobal}
         />
 
         <TemplateModal open={templateModalOpen} onClose={() => setTemplateModalOpen(false)} />
@@ -531,7 +532,7 @@ export const TopBar: React.FC<TopBarProps> = ({ showGuides, onToggleGuides }) =>
           <i className="fa fa-repeat" />
         </button>
         <span className="topbar-divider" />
-        <button className="topbar-btn" disabled={!canSave} title="Templates" aria-label="Templates" onClick={() => setTemplateModalOpen(true)}>
+        <button className="topbar-btn" disabled={!canSave || isEditingGlobal} title={isEditingGlobal ? 'Click Done on the global section first' : 'Templates'} aria-label="Templates" onClick={() => setTemplateModalOpen(true)}>
           <i className="fa fa-th-large" /> Templates
         </button>
         <button
diff --git a/craft/src/panels/topbar/TopBarOverflowMenu.tsx b/craft/src/panels/topbar/TopBarOverflowMenu.tsx
index 85e60ca..9659f7a 100644
--- a/craft/src/panels/topbar/TopBarOverflowMenu.tsx
+++ b/craft/src/panels/topbar/TopBarOverflowMenu.tsx
@@ -17,6 +17,8 @@ export interface TopBarOverflowMenuProps {
   sitesmithNode: React.ReactNode;
   /** Canvas-changing items (Templates, Head Code) are disabled until the site has loaded. */
   editingDisabled?: boolean;
+  /** #57: Templates replace the site; refused while a global-section master is open. */
+  templatesDisabled?: boolean;
 }
 
 /**
@@ -37,6 +39,7 @@ export const TopBarOverflowMenu: React.FC<TopBarOverflowMenuProps> = ({
   onPreview,
   sitesmithNode,
   editingDisabled,
+  templatesDisabled,
 }) => {
   const { device, setDevice: onDeviceChange } = useDevice();
   const menuRef = useRef<HTMLDivElement>(null);
@@ -85,7 +88,7 @@ export const TopBarOverflowMenu: React.FC<TopBarOverflowMenuProps> = ({
         </div>
       </div>
 
-      <button type="button" className="topbar-overflow-item" role="menuitem" disabled={editingDisabled} onClick={runAndClose(onOpenTemplates)}>
+      <button type="button" className="topbar-overflow-item" role="menuitem" disabled={editingDisabled || templatesDisabled} onClick={runAndClose(onOpenTemplates)}>
         <i className="fa fa-th-large" aria-hidden="true" /> Templates
       </button>
       <button type="button" className="topbar-overflow-item" role="menuitem" onClick={runAndClose(onPreview)}>
diff --git a/craft/src/state/GlobalSectionsContext.test.tsx b/craft/src/state/GlobalSectionsContext.test.tsx
index ca08456..fd0a159 100644
--- a/craft/src/state/GlobalSectionsContext.test.tsx
+++ b/craft/src/state/GlobalSectionsContext.test.tsx
@@ -19,6 +19,8 @@ import { ContextMenu } from '../panels/context-menu/ContextMenu';
 import { SectionLibraryModal, openSectionLibrary, closeSectionLibrary } from '../panels/sections/SectionLibraryModal';
 import { Canvas } from '../editor/Canvas';
 import { useApplyAiResponse } from '../utils/apply-ai-response';
+import { TemplateModal } from '../panels/topbar/TemplateModal';
+import { HistoryModal } from '../panels/history/HistoryModal';
 
 /**
  * #57 global sections against the REAL Craft editor + PageProvider +
@@ -441,6 +443,77 @@ describe('#57 global sections', () => {
     expect(h!.getSerialized()).toContain('AI takeover');
   });
 
+  test('Templates are refused while a master is open: master and instances untouched', async () => {
+    mount(<TemplateModal open onClose={() => {}} />);
+    const sec = addPromo();
+    let libraryId = '';
+    h!.act(() => { libraryId = globals.makeGlobal(sec, 'Promo')!; });
+    h!.act(() => { pages.editGlobal(libraryId); });
+    await flush();
+    const zoneBefore = h!.getSerialized();
+    expect(document.body.textContent).toContain('Click Done on the global section');
+    const card = document.body.querySelector<HTMLElement>('[role="button"][tabindex="0"]');
+    expect(card).not.toBeNull();
+    h!.act(() => { card!.click(); });
+    // No confirm dialog -> nothing can be applied to the zone.
+    expect(Array.from(document.body.querySelectorAll('button')).some((b) => b.textContent === 'Load Template')).toBe(false);
+    expect(h!.getSerialized()).toBe(zoneBefore);
+    expect(lib()[libraryId].rev).toBe(1);
+  });
+
+  test('Sitesmith site-scope replace is refused while a master is open', async () => {
+    mount();
+    const sec = addPromo();
+    let libraryId = '';
+    h!.act(() => { libraryId = globals.makeGlobal(sec, 'Promo')!; });
+    h!.act(() => { pages.editGlobal(libraryId); });
+    await flush();
+    const before = pages.pages.map((p) => p.craftState);
+    let r: any;
+    const tree = { type: { resolvedName: 'Container' }, props: {}, nodes: [{ type: { resolvedName: 'Heading' }, props: { text: 'AI site' } }] } as any;
+    await h!.act(async () => { r = await applyAi({ type: 'replace', scope: 'site', pages: [{ name: 'Home', tree }], header: { tree } } as any); });
+    await flush();
+    expect(r.ok).toBe(false);
+    expect(r.message).toMatch(/global section/i);
+    expect(pages.isEditingGlobal).toBe(true);
+    expect(pages.pages.map((p) => p.craftState)).toEqual(before);
+    expect(JSON.stringify(pages.headerPage.craftState ?? '')).not.toContain('AI site');
+    expect(lib()[libraryId].rev).toBe(1);
+  });
+
+  test('history Restore (site and one page) is refused while a master is open; Preview stays available', async () => {
+    const snap = {
+      pages_craft_state: [{ id: 'home', name: 'Home', slug: 'index', craftState: JSON.stringify({ ROOT: { type: { resolvedName: 'Container' }, isCanvas: true, props: {}, displayName: 'Container', custom: {}, hidden: false, nodes: [], linkedNodes: {}, parent: null } }) }],
+    };
+    vi.stubGlobal('fetch', vi.fn(async (url: string) => {
+      const u = String(url);
+      const body = u.includes('history_list')
+        ? { success: true, items: [{ id: 'v1', kind: 'save', at: '2026-10-07T17:15:01.042Z', size: 1 }] }
+        : { success: true, project: snap };
+      return { ok: true, status: 200, headers: { get: () => 'application/json' }, json: async () => body, text: async () => '' } as any;
+    }));
+    h = renderEditorHarness({
+      onRender: RenderNode,
+      wrap: (tree) => (
+        <EditorConfigProvider config={WHP_CFG}><SaveGuardProvider><NoticeProvider><ProjectExtrasProvider><SiteDesignProvider>{tree}</SiteDesignProvider></ProjectExtrasProvider></NoticeProvider></SaveGuardProvider></EditorConfigProvider>
+      ),
+    });
+    h.mountChild(<PageProvider><GlobalSectionsProvider><Probe /><HistoryModal open onClose={() => {}} /></GlobalSectionsProvider></PageProvider>);
+    h.act(() => { guard.setLoadState('loaded'); });
+    const sec = addPromo();
+    let libraryId = '';
+    h!.act(() => { libraryId = globals.makeGlobal(sec, 'Promo')!; });
+    h!.act(() => { pages.editGlobal(libraryId); });
+    await flush();
+    await flush();
+    const buttons = () => Array.from(document.body.querySelectorAll<HTMLButtonElement>('.wsb-history-row button'));
+    const byText = (t: string) => buttons().find((b) => b.textContent === t)!;
+    expect(byText('Preview').disabled).toBe(false);
+    expect(byText('Restore site…').disabled).toBe(true);
+    expect(byText('Restore one page…').disabled).toBe(true);
+    expect(document.body.textContent).toContain('Click Done on the global section');
+  });
+
   test('remove is refused while instances exist, allowed once none are left', () => {
     mount();
     const sec = addPromo();
diff --git a/craft/src/state/PageContext.tsx b/craft/src/state/PageContext.tsx
index 3b8ad16..8bec861 100644
--- a/craft/src/state/PageContext.tsx
+++ b/craft/src/state/PageContext.tsx
@@ -97,7 +97,8 @@ interface PageContextValue {
    */
   setActivePageIdDirect: (pageId: string) => void;
   /** AI helpers — replace entire site or page with a new tree */
-  replaceAllPages: (pages: { name: string; tree: SerializedTreeNode }[]) => void;
+  /** False (nothing replaced) while a global-section master is open (#57). */
+  replaceAllPages: (pages: { name: string; tree: SerializedTreeNode }[]) => boolean;
   /** False (nothing changed) while a global-section master is on the canvas (#57). */
   replaceCurrentPage: (page: { name: string; tree: SerializedTreeNode }) => boolean;
   setHeader: (tree: SerializedTreeNode) => void;
@@ -283,7 +284,7 @@ const PageContext = createContext<PageContextValue>({
   setFooterCraftState: () => {},
   setPagesCraftState: () => {},
   setActivePageIdDirect: () => {},
-  replaceAllPages: () => {},
+  replaceAllPages: () => false,
   replaceCurrentPage: () => false,
   setHeader: () => {},
   setFooter: () => {},
@@ -897,8 +898,12 @@ export const PageProvider: React.FC<{ children: ReactNode }> = ({ children }) =>
    * Stores each page's serialized state without touching the live canvas
    * (the canvas still shows the currently active page — call switchPage() if needed).
    */
-  const replaceAllPages = useCallback((newPages: { name: string; tree: SerializedTreeNode }[]) => {
-    if (newPages.length === 0) return;
+  const replaceAllPages = useCallback((newPages: { name: string; tree: SerializedTreeNode }[]): boolean => {
+    if (newPages.length === 0) return false;
+    // #57: leaving a master zone without committing it would silently drop
+    // the master edits (and strand the zone's return target). Refuse; the
+    // caller tells the user to click Done first.
+    if (isGlobalZoneId(activePageIdRef.current)) return false;
     // Track slugs as they're assigned so later pages dedupe against earlier
     // ones in the same batch (e.g. the AI generating two "About" pages).
     const seenSlugs: string[] = [];
@@ -921,6 +926,7 @@ export const PageProvider: React.FC<{ children: ReactNode }> = ({ children }) =>
     setActivePageId(built[0].id);
     activePageIdRef.current = built[0].id;
     loadState(firstState, EMPTY_CANVAS);
+    return true;
   }, [loadState]);
 
   /**
diff --git a/craft/src/utils/apply-ai-response.ts b/craft/src/utils/apply-ai-response.ts
index 0fe283e..2c92686 100644
--- a/craft/src/utils/apply-ai-response.ts
+++ b/craft/src/utils/apply-ai-response.ts
@@ -58,7 +58,14 @@ export function useApplyAiResponse() {
 
     if (resp.type === 'replace') {
       if (resp.scope === 'site') {
-        pages.replaceAllPages(resp.pages.map((p) => ({ name: p.name, tree: p.tree })));
+        if (!pages.replaceAllPages(resp.pages.map((p) => ({ name: p.name, tree: p.tree })))) {
+          return {
+            ok: false,
+            message: pages.isEditingGlobal
+              ? 'You are editing a global section. Click Done, then ask again to replace the site.'
+              : 'Nothing to apply.',
+          };
+        }
         if (resp.header) pages.setHeader(resp.header.tree);
         if (resp.footer) pages.setFooter(resp.footer.tree);
         return { ok: true };
diff --git a/craft/src/utils/sandboxed-preview.test.ts b/craft/src/utils/sandboxed-preview.test.ts
index b6a64a8..ba82475 100644
--- a/craft/src/utils/sandboxed-preview.test.ts
+++ b/craft/src/utils/sandboxed-preview.test.ts
@@ -1,6 +1,4 @@
 import { describe, expect, test, vi } from 'vitest';
-import { readdirSync, readFileSync, statSync } from 'node:fs';
-import { join } from 'node:path';
 import { openSandboxedPreview, PREVIEW_SANDBOX } from './sandboxed-preview';
 
 /** A real (detached) document standing in for the about:blank popup. */
@@ -52,16 +50,12 @@ describe('openSandboxedPreview (customer head code never runs in the panel origi
 });
 
 describe('no same-origin path for composed-page HTML remains in the source', () => {
-  const root = join(__dirname, '..');
-  const files: string[] = [];
-  const walk = (dir: string) => {
-    for (const name of readdirSync(dir)) {
-      const p = join(dir, name);
-      if (statSync(p).isDirectory()) walk(p);
-      else if (/\.(ts|tsx)$/.test(name) && !/\.test\.(ts|tsx)$/.test(name) && !p.includes('test-utils')) files.push(p);
-    }
-  };
-  walk(root);
+  // Every non-test source file under src/, as raw text (Vite glob; no @types/node here).
+  const sources = import.meta.glob(['../**/*.{ts,tsx}', '!../**/*.test.{ts,tsx}', '!../test-utils/**'], { query: '?raw', import: 'default', eager: true }) as Record<string, string>;
+  const files = Object.keys(sources);
+  const readFileSync = (f: string, _enc: string) => sources[f];
+  const root = '..';
+  expect(files.length).toBeGreaterThan(100);
 
   test('nothing builds a text/html blob, document.writes, or opens a blob: URL', () => {
     const offenders = files.filter((f) => {