Core App Shell — Layout Engine

Architectural Foundation: Mantine AppShell · @mantine/hooks

Description: Configuration-driven layout engine wrapping Mantine's AppShell, providing three layout variants (header-first, sidebar-first, top-nav), double sidebar support, responsive mobile drawers, and state persistence via Context API.

Package: @repo/ui · Module Path: @repo/ui/components > Dependencies: React 18+, Mantine v8 (AppShell), @mantine/hooks

---

Table of Contents

• Overview
• Architecture
  • Composition Model
  • File Structure
• API Reference
  • CoreAppShellConfig
  • Layout Variants
  • Features
  • Dimensions
  • Slots
  • Context API
• Usage Examples
  • Minimal Setup
  • Header-First with Utility Bar
  • Double Sidebar (Rail + Panel)
  • Interactive Config Builder
• CorePageContainer
• Design Decisions & Caveats

---

Overview

The Core App Shell is a configuration-driven layout engine that wraps Mantine's AppShell component. It provides a single <CoreAppShell> component that renders enterprise-grade application frames — complete with headers, sidebars, aside panels, utility bars, and footers — controlled entirely through a declarative config object and slot-based content injection.

Key capabilities:

• Three layout variants — header-first, sidebar-first, and top-nav — covering the most common enterprise SaaS patterns
• Double sidebar — Google-style rail + contextual panel navigation
• Smart defaults — Slots auto-detect presence; no explicit feature flags needed for basic layouts
• Responsive out-of-the-box — Mobile drawer, desktop collapse, and mini-sidebar are all built-in
• State persistence — Optional localStorage-backed sidebar state via @mantine/hooks
• Context API — All layout toggle methods (toggleMobile, toggleDesktop, setSidebarVariant, etc.) are available to any descendant component via useCoreAppShell()

---

Architecture

Composition Model

The layout engine uses a Provider → Inner composition pattern:

CoreAppShell (Public API)
  └── CoreAppShellProvider (Context — state management)
        └── CoreAppShellInner (Layout rendering — consumes context)
              └── Mantine <AppShell> (CSS Grid engine)
                    ├── AppShell.Header    ← slots.utilityBar + slots.header
                    ├── AppShell.Navbar    ← slots.sidebar | slots.sidebarRail + slots.sidebarPanel
                    ├── AppShell.Main      ← children
                    ├── AppShell.Aside     ← slots.aside
                    └── AppShell.Footer    ← slots.footer

The outer CoreAppShell is a thin wrapper that instantiates the provider and passes config down. The inner component subscribes to context and derives all layout calculations (navbar width, header height, collapse states) from the live config + user interactions.

File Structure

packages/ui/src/components/core-app-shell/
├── types.ts                       # All TypeScript interfaces and union types
├── core-app-shell-context.tsx     # Context provider + useCoreAppShell hook
├── core-app-shell.tsx             # Main component (Public API + Inner renderer)
├── core-page-container.tsx        # Companion page-level content wrapper
└── index.ts                       # Barrel exports

Source: packages/ui/src/components/core-app-shell/

---

API Reference

CoreAppShellConfig

The top-level configuration object that controls the entire layout:

interface CoreAppShellConfig {
  variant: LayoutVariant;
  dimensions?: CoreAppShellDimensions;
  features?: CoreAppShellFeatures;
}

Property	Type	Required	Description
variant	LayoutVariant	✅	Determines the structural layout mode
dimensions	CoreAppShellDimensions	—	Override default pixel dimensions
features	CoreAppShellFeatures	—	Toggle optional layout regions and behaviors

---

Layout Variants

type LayoutVariant = 'header-first' | 'sidebar-first' | 'top-nav';

Variant	Mantine layout	Visual Description
header-first	default	Header spans the full viewport width. Sidebar and aside sit below the header, stretching to the bottom of the screen. Footer is inset between the sidebar and aside. This is the most common enterprise/dashboard pattern (e.g., Azure Portal, Jira).
sidebar-first	alt	Sidebar spans the full viewport height. Header sits to the right of the sidebar. Produces a "desktop application" feel (e.g., VS Code, Slack). Footer spans full width beneath the sidebar.
top-nav	default	Header-only layout with no visible desktop sidebar. The sidebar is hidden on desktop but remains accessible as a mobile drawer on small screens. Ideal for documentation sites or marketing pages.

IMPORTANT

When variant is set to top-nav, the desktop navbar is visually hidden via collapsed.desktop: true and width 0. However, the <AppShell.Navbar> DOM element remains mounted with responsive width props so the mobile drawer continues to function. This is an intentional design choice to avoid conditional DOM removal.

---

Features

interface CoreAppShellFeatures {
  desktopCollapseVariant?: DesktopCollapseVariant;
  withUtilityBar?: boolean;
  withAside?: boolean;
  withFooter?: boolean;
  withDoubleSidebar?: boolean;
  persistState?: boolean;
  zIndex?: number;
  disabled?: boolean;
}

Property	Type	Default	Description
desktopCollapseVariant	'hide' | 'mini'	'hide'	hide: Sidebar slides out completely (collapsed width = 0). mini: Sidebar shrinks to sidebarMiniWidth showing only icons.
withUtilityBar	boolean	Auto-detected	Show the utility bar above the header. If omitted, the bar renders when a utilityBar slot is provided. Set explicitly to false to suppress.
withAside	boolean	Auto-detected	Show the right-hand aside panel. Same auto-detection logic as withUtilityBar.
withFooter	boolean	Auto-detected	Show the bottom footer. Same auto-detection logic.
withDoubleSidebar	boolean	false	Enable the Rail + Panel double sidebar mode. When true, the navbar renders sidebarRail and sidebarPanel slots instead of the single sidebar slot.
persistState	boolean	true (implied)	Persist sidebar variant (expanded/mini/hidden) to localStorage via useLocalStorage. Set to false for demos or ephemeral layouts.
zIndex	number	200	Base z-index passed to Mantine's AppShell.
disabled	boolean	false	Disables the AppShell layout entirely (renders children without structural chrome).

TIP

Smart defaults: You rarely need to set withUtilityBar, withAside, or withFooter explicitly. The engine auto-detects presence by checking if the corresponding slot is provided and truthy. Only set them to false when you want to suppress a slot that is being passed.

---

Dimensions

interface CoreAppShellDimensions {
  utilityBarHeight?: number | string;
  headerHeight?: number | string;
  sidebarWidth?: number | string;
  sidebarMiniWidth?: number | string;
  sidebarRailWidth?: number | string;
  asideWidth?: number | string;
}

Property	Type	Default	Description
utilityBarHeight	number | string	32	Height of the utility bar strip above the header
headerHeight	number | string	60	Height of the main header
sidebarWidth	number | string	260	Width of the expanded sidebar
sidebarMiniWidth	number | string	80	Width of the sidebar in mini collapse mode
sidebarRailWidth	number | string	54	Width of the icon rail in double-sidebar mode
asideWidth	number | string	260	Width of the right-hand aside panel

NOTE

All dimension values accept both pixel numbers (e.g., 260) and CSS strings (e.g., '20rem'). When both headerHeight and utilityBarHeight are numbers, they are summed directly. When either is a string, the engine wraps them in a calc() expression automatically.

---

Slots

Content is injected via the slots prop — a flat object of named ReactNode values:

interface CoreAppShellSlots {
  utilityBar?: ReactNode;
  header?: ReactNode;
  sidebar?: ReactNode;
  sidebarMobile?: ReactNode;
  sidebarRail?: ReactNode;
  sidebarPanel?: ReactNode;
  aside?: ReactNode;
  footer?: ReactNode;
}

Slot	Location	Notes
utilityBar	Above the header, hidden on mobile (display: none below sm)	Typically used for environment banners, announcements, or top-level links.
header	Main application header	Must contain its own <Burger> for mobile toggle (use useCoreAppShell() context).
sidebar	Desktop navbar body (single-sidebar mode)	Ignored when withDoubleSidebar is true — use sidebarRail + sidebarPanel instead.
sidebarMobile	Mobile drawer content	Falls back to sidebar if not provided. Use this to render a simplified mobile-specific navigation.
sidebarRail	Narrow icon rail (double-sidebar mode)	Only rendered when withDoubleSidebar is true. Separated from sidebarPanel by a 1px border.
sidebarPanel	Contextual panel beside the rail (double-sidebar mode)	Collapsible via toggleNavbarPanel(). Only rendered when withDoubleSidebar is true and navbarPanelOpened is true.
aside	Right-hand panel	Collapsible via toggleAside(). Only rendered when withAside is enabled.
footer	Bottom application footer	In header-first mode, the footer is inset between sidebar and aside. In sidebar-first mode, it spans the full width.

---

Context API

The useCoreAppShell() hook provides access to all layout state and toggle methods from any descendant component:

import { useCoreAppShell } from '@repo/ui/components';

Property / Method	Type	Description
mobileOpened	boolean	Whether the mobile drawer is currently open
desktopOpened	boolean	Whether the desktop sidebar is expanded (only applies when desktopCollapseVariant is 'hide')
sidebarVariant	SidebarVariant	Current sidebar mode: 'expanded' | 'mini' | 'hidden'
asideOpened	boolean	Whether the aside panel is currently visible
navbarPanelOpened	boolean	Whether the secondary panel in double-sidebar mode is expanded
config	CoreAppShellConfig	Read-only access to the current layout configuration
toggleMobile()	() => void	Toggle the mobile drawer open/closed
toggleDesktop()	() => void	Toggle the desktop sidebar open/closed
toggleAside()	() => void	Toggle the aside panel visibility
toggleNavbarPanel()	() => void	Toggle the double-sidebar panel open/closed
setSidebarVariant()	(variant: SidebarVariant) => void	Programmatically set the sidebar to 'expanded', 'mini', or 'hidden'

WARNING

useCoreAppShell() must be called from within a <CoreAppShell> subtree. Calling it outside the provider will throw: "useCoreAppShell must be used within CoreAppShellProvider". If you need context access in the header slot, pass a component (not inline JSX) so it mounts inside the provider tree.

---

Usage Examples

Minimal Setup

The simplest possible layout — a header and sidebar with all defaults:

import { CoreAppShell, CoreAppShellConfig, useCoreAppShell } from '@repo/ui/components';
import { Group, Text, Box, Stack, Button, Burger } from '@repo/ui/components';

function MyHeader() {
  const { mobileOpened, toggleMobile } = useCoreAppShell();
  return (
    <Group h="100%" px="md">
      <Burger opened={mobileOpened} onClick={toggleMobile} hiddenFrom="sm" size="sm" />
      <Text fw={700}>My Application</Text>
    </Group>
  );
}

const config: CoreAppShellConfig = {
  variant: 'header-first',
};

function App() {
  return (
    <CoreAppShell
      config={config}
      slots={{
        header: <MyHeader />,
        sidebar: (
          <Stack p="md" gap="xs">
            <Button variant="subtle" fullWidth>
              Dashboard
            </Button>
            <Button variant="subtle" fullWidth>
              Settings
            </Button>
          </Stack>
        ),
      }}
    >
      <Text>Main content area</Text>
    </CoreAppShell>
  );
}

---

Header-First with Utility Bar

A full enterprise layout with utility bar, aside, and footer:

import { CoreAppShell, CoreAppShellConfig, useCoreAppShell } from '@repo/ui/components';
import { Group, Text, Box, Burger } from '@repo/ui/components';

function AppHeader() {
  const { mobileOpened, toggleMobile } = useCoreAppShell();
  return (
    <Group h="100%" px="md" justify="space-between">
      <Group>
        <Burger opened={mobileOpened} onClick={toggleMobile} hiddenFrom="sm" size="sm" />
        <Text fw={700} size="lg">
          Enterprise Dashboard
        </Text>
      </Group>
    </Group>
  );
}

const config: CoreAppShellConfig = {
  variant: 'header-first',
  features: {
    desktopCollapseVariant: 'hide',
    persistState: true,
  },
  dimensions: {
    headerHeight: 60,
    utilityBarHeight: 32,
    sidebarWidth: 280,
    asideWidth: 300,
  },
};

function App() {
  return (
    <CoreAppShell
      config={config}
      slots={{
        utilityBar: (
          <Group h="100%" px="md" justify="flex-end">
            <Text size="xs">v2.4.1 · Production</Text>
          </Group>
        ),
        header: <AppHeader />,
        sidebar: <MySidebar />,
        aside: <MyAside />,
        footer: (
          <Group h="100%" px="md">
            <Text size="sm">© 2026 Acme Corp</Text>
          </Group>
        ),
      }}
    >
      <MyPageContent />
    </CoreAppShell>
  );
}

---

Double Sidebar (Rail + Panel)

Google-style navigation with an icon rail and a collapsible contextual panel:

import { CoreAppShell, CoreAppShellConfig, useCoreAppShell } from '@repo/ui/components';
import { Stack, Box, Text, Burger, Group } from '@repo/ui/components';
import { Home, Settings, BarChart2 } from 'lucide-react';

function AppHeader() {
  const { mobileOpened, toggleMobile } = useCoreAppShell();
  return (
    <Group h="100%" px="md">
      <Burger opened={mobileOpened} onClick={toggleMobile} hiddenFrom="sm" size="sm" />
      <Text fw={700}>Admin Panel</Text>
    </Group>
  );
}

const config: CoreAppShellConfig = {
  variant: 'sidebar-first',
  features: {
    withDoubleSidebar: true,
  },
  dimensions: {
    sidebarRailWidth: 54,
    sidebarWidth: 260,
  },
};

function App() {
  return (
    <CoreAppShell
      config={config}
      slots={{
        header: <AppHeader />,
        sidebarRail: (
          <Stack align="center" gap="lg" pt="md">
            <Home size={24} />
            <BarChart2 size={24} />
            <Settings size={24} />
          </Stack>
        ),
        sidebarPanel: (
          <Box p="md">
            <Text fw={700} mb="sm">
              Navigation
            </Text>
            {/* Contextual links based on active rail icon */}
          </Box>
        ),
        sidebarMobile: (
          <Box p="md">
            <Text fw={700}>Mobile Nav</Text>
            {/* Simplified mobile navigation */}
          </Box>
        ),
      }}
    >
      <Text>Main content</Text>
    </CoreAppShell>
  );
}

NOTE

When withDoubleSidebar is true, the sidebar slot is ignored on desktop. The navbar renders sidebarRail (fixed-width icon column) and sidebarPanel (collapsible contextual panel) side-by-side. On mobile, sidebarMobile takes priority, falling back to sidebar if not provided.

---

Interactive Config Builder

The showcase demo at apps/showcase/src/pages/showcase-original/shell-demo/ demonstrates a live, interactive config builder where every feature toggle and variant switch updates the layout in real-time. The key pattern is managing config state externally and passing it as a prop:

import { useState, useMemo } from 'react';
import { CoreAppShell, CoreAppShellConfig, LayoutVariant, DesktopCollapseVariant } from '@repo/ui/components';

function ShellDemo() {
  const [layoutVariant, setLayoutVariant] = useState<LayoutVariant>('header-first');
  const [collapseVariant, setCollapseVariant] = useState<DesktopCollapseVariant>('hide');
  const [withDoubleSidebar, setWithDoubleSidebar] = useState(false);

  const config: CoreAppShellConfig = useMemo(
    () => ({
      variant: layoutVariant,
      features: {
        desktopCollapseVariant: collapseVariant,
        withDoubleSidebar,
        persistState: false,
      },
    }),
    [layoutVariant, collapseVariant, withDoubleSidebar],
  );

  return (
    <CoreAppShell config={config} slots={{ header: <MyHeader />, sidebar: <MySidebar /> }}>
      {/* Config controls live here — they can use useCoreAppShell() for toggle methods */}
    </CoreAppShell>
  );
}

---

CorePageContainer

A companion component for structuring page-level content within the <AppShell.Main> area. It provides a sticky page header and a contained, padded content region.

import { CorePageContainer } from '@repo/ui/components';

Props

interface CorePageContainerProps extends ContainerProps {
  headerSlot?: ReactNode;
  children: ReactNode;
  stickyHeader?: boolean;
}

Prop	Type	Default	Description
headerSlot	ReactNode	—	Page-level header content (title, breadcrumbs, action buttons). Rendered above the main content with a bottom border.
stickyHeader	boolean	false	When true, the page header sticks to the top of the scroll area, offset by the AppShell header height via var(--app-shell-header-offset).
px	MantineSpacing	'md'	Horizontal padding for both the header and content areas
py	MantineSpacing	'md'	Vertical padding for both the header and content areas
...rest	ContainerProps	—	All other Mantine Container props are forwarded to the content region

Usage

<CoreAppShell config={config} slots={slots}>
  <CorePageContainer
    stickyHeader
    headerSlot={
      <Group justify="space-between">
        <Text component="h1" size="xl" fw={700}>
          Users
        </Text>
        <Button>Add User</Button>
      </Group>
    }
  >
    <UserTable />
  </CorePageContainer>
</CoreAppShell>

---

Design Decisions & Caveats

Mobile Navbar Lifecycle

The <AppShell.Navbar> DOM element is always mounted, even when the layout variant is top-nav. The desktop content is hidden via visibleFrom="sm" and mobile content via hiddenFrom="sm". This ensures Mantine's native drawer engine works correctly on mobile without conditional DOM removal breaking the transition animations.

Footer Positioning in header-first Mode

In header-first mode, the footer is inset between the sidebar and aside using CSS custom properties:

left: var(--app-shell-navbar-offset, 0px);
right: var(--app-shell-aside-offset, 0px);

In sidebar-first mode, the footer spans the full viewport width (left: 0; right: 0).

Z-Index Strategy

Element	header-first	sidebar-first
AppShell (base)	200 (default)	200 (default)
Navbar	105	100
Aside	105	100
Footer	100	100

The elevated 105 z-index for navbar/aside in header-first mode ensures they render above the footer, which is positioned at 100.

Sidebar Width Calculation

The navbar width is dynamically computed based on multiple state variables:

navbarWidth.sm =
  isTopNav                    → 0
  isDoubleSidebar + panelOpen → sidebarWidth
  isDoubleSidebar + panelClosed → sidebarRailWidth
  sidebarVariant === 'mini'   → sidebarMiniWidth
  default                     → sidebarWidth

On mobile and xs breakpoints, the width is always 100% and sidebarWidth respectively, regardless of variant.