feat(renderer): Zen mode (Esc exits, hides chrome)

src/renderer/components/layout/AppShell.tsx

@@ -11,13 +11,43 @@ import { ResizablePanelGroup, ResizablePanel, ResizableHandle } from '@/componen
 import { useFileShortcuts } from '@/hooks/use-file-shortcuts';
 import { useRestoreLastFolder } from '@/hooks/use-restore-last-folder';
 import { useRegisterMenuCommands, useBridgeNativeMenu } from '@/lib/commands/register-menu-commands';
+import { useZenMode } from '@/hooks/use-zen-mode';
 
 export function AppShell() {
   useFileShortcuts();
   useRestoreLastFolder();
   useRegisterMenuCommands();
   useBridgeNativeMenu();
+  useZenMode();
   const { sidebarVisible, previewVisible, paneSizes, setPaneSizes } = useAppStore();
+  const zenMode = useAppStore((s) => s.zenMode);
+
+  if (zenMode) {
+    return (
+      <main className="h-screen w-screen overflow-hidden bg-background">
+        <ResizablePanelGroup
+          direction="horizontal"
+          onLayout={(sizes) => setPaneSizes({ sidebar: 0, editor: sizes[0], preview: sizes[1] })}
+        >
+          <ResizablePanel defaultSize={previewVisible ? 50 : 100} minSize={20}>
+            <section className="h-full bg-background">
+              <EditorPane />
+            </section>
+          </ResizablePanel>
+          {previewVisible && (
+            <>
+              <ResizableHandle />
+              <ResizablePanel defaultSize={50} minSize={20}>
+                <section className="h-full border-l border-border bg-card/10">
+                  <PreviewPane />
+                </section>
+              </ResizablePanel>
+            </>
+          )}
+        </ResizablePanelGroup>
+      </main>
+    );
+  }
 
   return (
     <div className="flex h-screen flex-col bg-background text-foreground">

src/renderer/hooks/use-zen-mode.ts

@@ -0,0 +1,22 @@
+import { useEffect } from 'react';
+import { useAppStore } from '@/stores/app-store';
+
+/**
+ * Mounts a global keydown listener that exits zen mode when the user
+ * presses Escape. Should be called once at the App root.
+ */
+export function useZenMode() {
+  const zenMode = useAppStore((s) => s.zenMode);
+  const setZenMode = useAppStore((s) => s.setZenMode);
+
+  useEffect(() => {
+    if (!zenMode) return;
+    const handler = (e: KeyboardEvent) => {
+      if (e.key === 'Escape') {
+        setZenMode(false);
+      }
+    };
+    window.addEventListener('keydown', handler);
+    return () => window.removeEventListener('keydown', handler);
+  }, [zenMode, setZenMode]);
+}

tests/unit/hooks/use-zen-mode.test.ts

@@ -0,0 +1,31 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+import { renderHook } from '@testing-library/react';
+import { useZenMode } from '@/hooks/use-zen-mode';
+import { useAppStore } from '@/stores/app-store';
+
+describe('useZenMode', () => {
+  beforeEach(() => {
+    localStorage.clear();
+    useAppStore.setState({ ...useAppStore.getInitialState(), zenMode: true });
+  });
+
+  it('attaches a keydown listener that exits zen mode on Escape', () => {
+    renderHook(() => useZenMode());
+    expect(useAppStore.getState().zenMode).toBe(true);
+
+    // Simulate Escape keydown
+    const event = new KeyboardEvent('keydown', { key: 'Escape' });
+    window.dispatchEvent(event);
+
+    expect(useAppStore.getState().zenMode).toBe(false);
+  });
+
+  it('does nothing if zen mode is already off', () => {
+    useAppStore.setState({ ...useAppStore.getInitialState(), zenMode: false });
+    const setZenMode = vi.fn();
+    useAppStore.setState({ setZenMode });
+    renderHook(() => useZenMode());
+    // No Escape dispatched; setZenMode should not be called
+    expect(setZenMode).not.toHaveBeenCalled();
+  });
+});