Route-level code splitting for faster mobile first paint (#106)

The whole app shipped in one 578 KB chunk, so a phone on cell data
downloaded and parsed everything — the canvas editor, gestures, geometry,
every page — before the login screen could paint.

- Lazy-load the heavy/deep routes via React.lazy: the editor (its
  GardenCanvas + use-gesture + geometry are the biggest surface), the
  public garden view, plants, settings, register. Login and the gardens
  list stay eager (entry points — no fallback flash on landing). AppShell
  wraps <Outlet> in a Suspense boundary.
- One `vendor` manualChunk for all node_modules so the rarely-changing
  libraries cache across app deploys while the tiny app chunk churns.
  Kept as a SINGLE chunk deliberately: splitting react-dom/scheduler into
  their own chunk reorders module init across chunk boundaries and breaks
  React 19 at load ("Cannot set 'Activity' of undefined") — verified that
  failure and backed it out.

Result: app entry chunk 578 KB → 39 KB; vendor 421 KB (cached); the editor
(43 KB) + canvas (17 KB) only download when you open a garden. No more
>500 KB chunk warning.

Verified live against the embedded binary: /gardens loads with only
index+vendor; opening a garden lazy-fetches the editor chunk and renders;
console clean; the embed serves the hashed split chunks + SPA fallback fine.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01H3zbym8Doka2d7D48maSgZ

web/src/components/layout/AppShell.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useState } from 'react'
+import { Suspense, useEffect, useState } from 'react'
 import { Link, Outlet, useMatchRoute, useNavigate, useRouterState } from '@tanstack/react-router'
 import { Toaster } from '@/components/ui/toast'
 import { useLogout, useMe } from '@/lib/auth'
@@ -93,7 +93,10 @@ export function AppShell() {
           showBottomNav && 'pb-[calc(3.5rem+env(safe-area-inset-bottom))] md:pb-6',
         )}
       >
-        <Outlet />
+        {/* Boundary for the lazily-loaded routes (see router.tsx). */}
+        <Suspense fallback={<p className="p-6 text-sm text-muted">Loading…</p>}>
+          <Outlet />
+        </Suspense>
       </main>
 
       {showBottomNav && <BottomNav sections={visibleSections} />}

web/src/router.tsx

@@ -1,3 +1,4 @@
+import { lazy } from 'react'
 import {
   createRootRouteWithContext,
   createRoute,
@@ -9,13 +10,27 @@ import { AppShell } from '@/components/layout/AppShell'
 import { NotFound } from '@/components/NotFound'
 import { RouteError } from '@/components/RouteError'
 import { LoginPage } from '@/pages/LoginPage'
-import { RegisterPage } from '@/pages/RegisterPage'
 import { GardensPage } from '@/pages/GardensPage'
-import { GardenEditorPage } from '@/pages/GardenEditorPage'
-import { PublicGardenPage } from '@/pages/PublicGardenPage'
-import { PlantsPage } from '@/pages/PlantsPage'
-import { SettingsPage } from '@/pages/SettingsPage'
 import { meQueryOptions } from '@/lib/auth'
+
+// Code-split the heavier / deeper routes so a phone on cell data doesn't download
+// the whole app (notably the canvas editor with its gesture + geometry deps)
+// before the first screen paints. Login and the gardens list — the entry points —
+// stay eager to avoid a fallback flash on landing; AppShell wraps the Outlet in a
+// Suspense boundary for the rest.
+const GardenEditorPage = lazy(() =>
+  import('@/pages/GardenEditorPage').then((m) => ({ default: m.GardenEditorPage })),
+)
+const PublicGardenPage = lazy(() =>
+  import('@/pages/PublicGardenPage').then((m) => ({ default: m.PublicGardenPage })),
+)
+const PlantsPage = lazy(() => import('@/pages/PlantsPage').then((m) => ({ default: m.PlantsPage })))
+const SettingsPage = lazy(() =>
+  import('@/pages/SettingsPage').then((m) => ({ default: m.SettingsPage })),
+)
+const RegisterPage = lazy(() =>
+  import('@/pages/RegisterPage').then((m) => ({ default: m.RegisterPage })),
+)
 import { queryClient } from '@/lib/queryClient'
 import { safeRedirectPath } from '@/lib/redirect'
 import { getLastGardenId } from '@/lib/lastGarden'

web/vite.config.ts

@@ -29,6 +29,20 @@ export default defineConfig(({ mode }) => {
     build: {
       outDir: 'dist',
       sourcemap: true,
+      rollupOptions: {
+        output: {
+          // One vendor chunk for ALL node_modules: it's rarely-changing, so it
+          // caches across app deploys while the tiny app chunk churns. Kept as a
+          // SINGLE chunk on purpose — splitting react-dom/scheduler into their own
+          // chunk reorders their module init across chunk boundaries and breaks
+          // React 19 at load ("Cannot set 'Activity' of undefined"). The heavy
+          // routes are code-split separately via React.lazy (router.tsx), which is
+          // where the real first-paint win is.
+          manualChunks(id) {
+            return id.includes('node_modules') ? 'vendor' : undefined
+          },
+        },
+      },
     },
   }
 })