From e651b4cd63c3bd64a8739c9f60c6dfa437f19b4b Mon Sep 17 00:00:00 2001
From: Ruben Fiszel <ruben@windmill.dev>
Date: Fri, 11 Sep 2026 13:14:09 +0200
Subject: [PATCH] perf: lazy-load the low-code runtime on public app pages
 (#11087)

* perf: lazy-load the low-code runtime on public app pages

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018bSzETfUb23CRRMEJdwqeS

* perf: fetch the low-code runtime alongside the app payload

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018bSzETfUb23CRRMEJdwqeS

---------

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
---
 frontend/src/lib/components/DiffDrawer.svelte |  2 +-
 frontend/src/lib/components/FlowViewer.svelte |  3 +-
 .../lib/components/LocalDraftBanner.svelte    |  8 +--
 frontend/src/lib/components/Login.svelte      | 16 +++---
 .../components/WorkspaceItemDiffViewer.svelte |  3 +-
 .../apps/editor/DeploymentHistory.svelte      |  2 +-
 .../components/apps/editor/PublicApp.svelte   | 57 +++++++++++--------
 .../apps/editor/PublicAppFrame.svelte         |  9 ++-
 .../components/apps/editor/loadAppPreview.ts  | 12 ++++
 .../components/raw_apps/rawAppDiffUtils.ts    |  3 +-
 frontend/src/lib/navigation.ts                |  2 +-
 frontend/src/lib/sharedUtils.ts               |  5 +-
 frontend/src/lib/svelte5UtilsKit.svelte.ts    |  9 +--
 frontend/src/lib/utils.ts                     | 27 +--------
 frontend/src/lib/utils/capitalize.ts          |  3 +
 frontend/src/lib/utils/orderedYaml.ts         | 23 ++++++++
 frontend/src/lib/utils/serializeParam.ts      | 12 ++++
 frontend/vite.config.js                       | 49 +++++++++++++++-
 18 files changed, 161 insertions(+), 84 deletions(-)
 create mode 100644 frontend/src/lib/components/apps/editor/loadAppPreview.ts
 create mode 100644 frontend/src/lib/utils/capitalize.ts
 create mode 100644 frontend/src/lib/utils/orderedYaml.ts
 create mode 100644 frontend/src/lib/utils/serializeParam.ts

diff --git a/frontend/src/lib/components/DiffDrawer.svelte b/frontend/src/lib/components/DiffDrawer.svelte
index 25e94a8efe..d70046d62a 100644
--- a/frontend/src/lib/components/DiffDrawer.svelte
+++ b/frontend/src/lib/components/DiffDrawer.svelte
@@ -7,10 +7,10 @@
 	import {
 		cleanValueProperties,
 		orderedJsonStringify,
-		orderedYamlStringify,
 		replaceFalseWithUndefined,
 		type Value
 	} from '$lib/utils'
+	import { orderedYamlStringify } from '$lib/utils/orderedYaml'
 	import type { Script } from '$lib/gen'
 
 	type DiffData = {
diff --git a/frontend/src/lib/components/FlowViewer.svelte b/frontend/src/lib/components/FlowViewer.svelte
index 1e321584e3..03baebb501 100644
--- a/frontend/src/lib/components/FlowViewer.svelte
+++ b/frontend/src/lib/components/FlowViewer.svelte
@@ -5,7 +5,8 @@
 	import SchemaViewer from './SchemaViewer.svelte'
 	import FlowGraphViewer from './FlowGraphViewer.svelte'
 	import { Loader2 } from 'lucide-svelte'
-	import { orderedYamlStringify, cleanValueProperties, replaceFalseWithUndefined } from '$lib/utils'
+	import { cleanValueProperties, replaceFalseWithUndefined } from '$lib/utils'
+	import { orderedYamlStringify } from '$lib/utils/orderedYaml'
 	import { workspaceStore } from '$lib/stores'
 	import { watch } from 'runed'
 
diff --git a/frontend/src/lib/components/LocalDraftBanner.svelte b/frontend/src/lib/components/LocalDraftBanner.svelte
index dff131b281..af2787222e 100644
--- a/frontend/src/lib/components/LocalDraftBanner.svelte
+++ b/frontend/src/lib/components/LocalDraftBanner.svelte
@@ -2,12 +2,8 @@
 	import { Button } from '$lib/components/common'
 	import DiffDrawer from '$lib/components/DiffDrawer.svelte'
 	import { classes } from '$lib/components/common/alert/model'
-	import {
-		cleanValueProperties,
-		orderedYamlStringify,
-		replaceFalseWithUndefined,
-		type Value
-	} from '$lib/utils'
+	import { cleanValueProperties, replaceFalseWithUndefined, type Value } from '$lib/utils'
+	import { orderedYamlStringify } from '$lib/utils/orderedYaml'
 	import { AlertCircle, Diff } from 'lucide-svelte'
 	import { twMerge } from 'tailwind-merge'
 	import { fade } from 'svelte/transition'
diff --git a/frontend/src/lib/components/Login.svelte b/frontend/src/lib/components/Login.svelte
index 0307643a08..e4b73478aa 100644
--- a/frontend/src/lib/components/Login.svelte
+++ b/frontend/src/lib/components/Login.svelte
@@ -16,15 +16,13 @@
 
 <script lang="ts">
 	import { goto } from '$lib/navigation'
-	import {
-		Auth0Icon,
-		GithubIcon,
-		GitlabIcon,
-		GoogleIcon,
-		MicrosoftIcon,
-		NextcloudIcon,
-		OktaIcon
-	} from '$lib/components/icons'
+	import Auth0Icon from '$lib/components/icons/Auth0Icon.svelte'
+	import GithubIcon from '$lib/components/icons/GithubIcon.svelte'
+	import GitlabIcon from '$lib/components/icons/GitlabIcon.svelte'
+	import GoogleIcon from '$lib/components/icons/GoogleIcon.svelte'
+	import MicrosoftIcon from '$lib/components/icons/MicrosoftIcon.svelte'
+	import NextcloudIcon from '$lib/components/icons/NextcloudIcon.svelte'
+	import OktaIcon from '$lib/components/icons/OktaIcon.svelte'
 	import PocketIdIcon from '$lib/components/icons/PocketIdIcon.svelte'
 
 	import { OauthService, UserService, WorkspaceService } from '$lib/gen'
diff --git a/frontend/src/lib/components/WorkspaceItemDiffViewer.svelte b/frontend/src/lib/components/WorkspaceItemDiffViewer.svelte
index 77aae182fa..cd0622959c 100644
--- a/frontend/src/lib/components/WorkspaceItemDiffViewer.svelte
+++ b/frontend/src/lib/components/WorkspaceItemDiffViewer.svelte
@@ -24,7 +24,8 @@ doesn't reflow the parent.
 	import RawAppFileDiff from './raw_apps/RawAppFileDiff.svelte'
 	import type { RawAppFileItem } from './raw_apps/rawAppDiffUtils'
 	import { Loader2 } from 'lucide-svelte'
-	import { cleanValueProperties, orderedYamlStringify, replaceFalseWithUndefined } from '$lib/utils'
+	import { cleanValueProperties, replaceFalseWithUndefined } from '$lib/utils'
+	import { orderedYamlStringify } from '$lib/utils/orderedYaml'
 	import { scriptLangToEditorLang } from '$lib/scripts'
 
 	interface Props {
diff --git a/frontend/src/lib/components/apps/editor/DeploymentHistory.svelte b/frontend/src/lib/components/apps/editor/DeploymentHistory.svelte
index 4ae67dbb0e..614d1f4fa4 100644
--- a/frontend/src/lib/components/apps/editor/DeploymentHistory.svelte
+++ b/frontend/src/lib/components/apps/editor/DeploymentHistory.svelte
@@ -9,10 +9,10 @@
 		cleanValueProperties,
 		displayDate,
 		emptyString,
-		orderedYamlStringify,
 		replaceFalseWithUndefined,
 		type Value
 	} from '$lib/utils'
+	import { orderedYamlStringify } from '$lib/utils/orderedYaml'
 	import { AppService, type AppWithLastVersion, type AppHistory } from '$lib/gen'
 	import { workspaceStore } from '$lib/stores'
 	import { Skeleton } from '$lib/components/common'
diff --git a/frontend/src/lib/components/apps/editor/PublicApp.svelte b/frontend/src/lib/components/apps/editor/PublicApp.svelte
index 6523f13ffa..f807520c27 100644
--- a/frontend/src/lib/components/apps/editor/PublicApp.svelte
+++ b/frontend/src/lib/components/apps/editor/PublicApp.svelte
@@ -6,8 +6,9 @@
 	import { page } from '$app/state'
 	import Login from '$lib/components/Login.svelte'
 	import { isCloudHosted } from '$lib/cloud'
-	import { Alert, Skeleton } from '$lib/components/common'
-	import { WindmillIcon } from '$lib/components/icons'
+	import Alert from '$lib/components/common/alert/Alert.svelte'
+	import Skeleton from '$lib/components/common/skeleton/Skeleton.svelte'
+	import WindmillIcon from '$lib/components/icons/WindmillIcon.svelte'
 	import { getContext, onMount, setContext } from 'svelte'
 	import {
 		EMBED_NAV_CONTEXT_KEY,
@@ -18,7 +19,7 @@
 	import { UserService, type AppWithLastVersion, type GlobalWhoamiResponse } from '$lib/gen'
 	import { urlParamsToObject } from '$lib/utils'
 	import { goto } from '$app/navigation'
-	import AppPreview from './AppPreview.svelte'
+	import { loadAppPreview } from './loadAppPreview'
 	import RawAppPreview from '$lib/components/raw_apps/RawAppPreview.svelte'
 	import type { Runnable } from '$lib/components/raw_apps/rawAppPolicy'
 	import { twMerge } from 'tailwind-merge'
@@ -188,27 +189,35 @@
 				)}
 				style={app?.value?.['css']?.['app']?.['viewer']?.style}
 			>
-				<AppPreview
-					noBackend={false}
-					{hideRefreshBar}
-					context={{
-						email: $userStore?.email,
-						name: $userStore?.name,
-						groups: $userStore?.groups,
-						username: $userStore?.username,
-						query: urlParamsToObject(page.url.searchParams, { stripReserved: true }),
-						hash: page.url.hash.substring(1)
-					}}
-					workspace={effectiveWorkspace}
-					summary={app.summary}
-					app={app.value}
-					appPath={app.path}
-					{breakpoint}
-					policy={app.policy}
-					isEditor={false}
-					replaceStateFn={(path) => goto(path)}
-					gotoFn={(path, opt) => (embedNav ? embedNav.navigateTop(path) : goto(path, opt))}
-				/>
+				{#await loadAppPreview()}
+					<Skeleton layout={[[4], 0.5, [50]]} />
+				{:then Module}
+					<Module.default
+						noBackend={false}
+						{hideRefreshBar}
+						context={{
+							email: $userStore?.email,
+							name: $userStore?.name,
+							groups: $userStore?.groups,
+							username: $userStore?.username,
+							query: urlParamsToObject(page.url.searchParams, { stripReserved: true }),
+							hash: page.url.hash.substring(1)
+						}}
+						workspace={effectiveWorkspace}
+						summary={app.summary}
+						app={app.value}
+						appPath={app.path}
+						{breakpoint}
+						policy={app.policy}
+						isEditor={false}
+						replaceStateFn={(path) => goto(path)}
+						gotoFn={(path, opt) => (embedNav ? embedNav.navigateTop(path) : goto(path, opt))}
+					/>
+				{:catch}
+					<div class="px-4 mt-20 w-full">
+						<Alert type="error" title="Could not load the app">Reload the page to try again.</Alert>
+					</div>
+				{/await}
 			</div>
 		{/if}
 	{/key}
diff --git a/frontend/src/lib/components/apps/editor/PublicAppFrame.svelte b/frontend/src/lib/components/apps/editor/PublicAppFrame.svelte
index dbe8f8d503..e994767488 100644
--- a/frontend/src/lib/components/apps/editor/PublicAppFrame.svelte
+++ b/frontend/src/lib/components/apps/editor/PublicAppFrame.svelte
@@ -26,12 +26,14 @@
 	import { OpenAPI, UserService } from '$lib/gen'
 	import { page } from '$app/state'
 	import { onDestroy, onMount, setContext, type Snippet } from 'svelte'
-	import { Alert, Skeleton } from '$lib/components/common'
+	import Alert from '$lib/components/common/alert/Alert.svelte'
+	import Skeleton from '$lib/components/common/skeleton/Skeleton.svelte'
 	import { base } from '$app/paths'
 	import { goto } from '$app/navigation'
 	import Login from '$lib/components/Login.svelte'
 	import { WINDMILL_RESERVED_QUERY_PARAMS } from '$lib/utils'
 	import { EMBED_NAV_CONTEXT_KEY, type EmbedNav } from '../types'
+	import { loadAppPreview } from './loadAppPreview'
 	import RawAppSdkConsent from '$lib/components/raw_apps/RawAppSdkConsent.svelte'
 	import { hasStoredSdkConsent, storeSdkConsent } from '$lib/components/raw_apps/sdkScopes'
 
@@ -420,7 +422,8 @@
 		if (unsandboxed || isRaw) {
 			// Render the app directly on this origin: same-origin when unsandboxed
 			// (the default), or a single opaque bundle iframe when it's a sandboxed
-			// raw app.
+			// raw app. A low-code app's runtime downloads alongside the app payload.
+			if (!isRaw) loadAppPreview().catch(() => {})
 			onViewerReady?.(undefined, requestTokenRefresh)
 		} else {
 			// Sandboxed low-code: hand the scoped token to the opaque viewer iframe.
@@ -529,6 +532,8 @@
 
 	onMount(() => {
 		if (isViewer) {
+			// Only a sandboxed low-code app is ever framed as a viewer.
+			loadAppPreview().catch(() => {})
 			window.addEventListener('message', handleViewerMessage)
 			installHashRelay()
 			// Announce readiness so the embedder sends us the token.
diff --git a/frontend/src/lib/components/apps/editor/loadAppPreview.ts b/frontend/src/lib/components/apps/editor/loadAppPreview.ts
new file mode 100644
index 0000000000..57e82e09f8
--- /dev/null
+++ b/frontend/src/lib/components/apps/editor/loadAppPreview.ts
@@ -0,0 +1,12 @@
+// AppPreview must stay a dynamic import: it statically reaches every low-code component
+// (and through them monaco, ag-grid, chart.js...), none of which a raw app renders.
+// assertLeanPublicAppRoutes in vite.config.js fails the build if that regresses.
+let pending: Promise<typeof import('./AppPreview.svelte')> | undefined
+
+export function loadAppPreview() {
+	pending ??= import('./AppPreview.svelte').catch((e) => {
+		console.error('Could not load the low-code app viewer', e)
+		throw e
+	})
+	return pending
+}
diff --git a/frontend/src/lib/components/raw_apps/rawAppDiffUtils.ts b/frontend/src/lib/components/raw_apps/rawAppDiffUtils.ts
index 444e03a0a3..6a18a28e46 100644
--- a/frontend/src/lib/components/raw_apps/rawAppDiffUtils.ts
+++ b/frontend/src/lib/components/raw_apps/rawAppDiffUtils.ts
@@ -1,5 +1,6 @@
 import { extToLang } from '$lib/editorLangUtils'
-import { cleanValueProperties, orderedYamlStringify, replaceFalseWithUndefined } from '$lib/utils'
+import { cleanValueProperties, replaceFalseWithUndefined } from '$lib/utils'
+import { orderedYamlStringify } from '$lib/utils/orderedYaml'
 
 // A raw app rendered as a *folder of files* for diffing. Each entry is one
 // virtual file: real `files` keep their natural path, runnables become
diff --git a/frontend/src/lib/navigation.ts b/frontend/src/lib/navigation.ts
index d0c2bae4e7..db8b9f3a80 100644
--- a/frontend/src/lib/navigation.ts
+++ b/frontend/src/lib/navigation.ts
@@ -1,6 +1,6 @@
 import { goto as svelteGoto } from '$app/navigation'
 import { base as svelteBase } from '$app/paths'
-import { serializeParam } from '$lib/svelte5UtilsKit.svelte'
+import { serializeParam } from '$lib/utils/serializeParam'
 
 export function goto(path: string, options = {}) {
 	if (svelteBase == '' || path.startsWith('?')) {
diff --git a/frontend/src/lib/sharedUtils.ts b/frontend/src/lib/sharedUtils.ts
index da903dba58..d47d1881c3 100644
--- a/frontend/src/lib/sharedUtils.ts
+++ b/frontend/src/lib/sharedUtils.ts
@@ -2,7 +2,4 @@ export { updatePolicy } from './components/apps/editor/appPolicy'
 export { genWmillTs } from './components/raw_apps/utils'
 export { updateRawAppPolicy } from './components/raw_apps/rawAppPolicy'
 export * as wmillTsRaw from './rawAppWmillTs?raw'
-
-export function capitalize(word: string): string {
-	return word ? word.charAt(0).toUpperCase() + word.slice(1) : ''
-}
+export { capitalize } from './utils/capitalize'
diff --git a/frontend/src/lib/svelte5UtilsKit.svelte.ts b/frontend/src/lib/svelte5UtilsKit.svelte.ts
index 139d6985df..7b6420ab7e 100644
--- a/frontend/src/lib/svelte5UtilsKit.svelte.ts
+++ b/frontend/src/lib/svelte5UtilsKit.svelte.ts
@@ -2,20 +2,13 @@
 // This file should only be imported in SvelteKit apps as it depends on $app/environment
 
 import { z } from 'zod'
+import { serializeParam } from '$lib/utils/serializeParam'
 
 export type SearchParamsResult<S extends z.ZodType> =
 	S extends z.ZodObject<infer Shape>
 		? { -readonly [K in keyof Shape]: z.infer<Shape[K]> } & Record<string, unknown>
 		: z.infer<S> & Record<string, unknown>
 
-/** Serialize a value to a URL search param string. Primitives are written as-is; anything else is JSON. */
-export function serializeParam(value: unknown): string {
-	if (typeof value === 'string') return value
-	if (typeof value === 'number') return String(value)
-	if (typeof value === 'boolean') return String(value)
-	return JSON.stringify(value)
-}
-
 /** Parse a raw string from the URL back to a typed value guided by the zod field schema. */
 function deserializeParam(raw: string, fieldSchema: z.ZodType): unknown {
 	// Unwrap nullable / optional / default wrappers to get the inner type
diff --git a/frontend/src/lib/utils.ts b/frontend/src/lib/utils.ts
index 55fba3fb13..635fc6f14e 100644
--- a/frontend/src/lib/utils.ts
+++ b/frontend/src/lib/utils.ts
@@ -7,7 +7,6 @@
 // import { get } from 'svelte/store'
 
 import { deepEqual } from 'fast-equals'
-import YAML from 'yaml'
 import { type UserExt } from './stores'
 import { sendUserToast } from './toast'
 import type { CompletedJob, Job, RunnableKind, Script, ScriptLang, Retry } from './gen'
@@ -815,7 +814,8 @@ export function addDeterminant(word: string): string {
 	return (/^[aeiou]/i.test(word) ? 'an ' : 'a ') + word
 }
 
-export { capitalize } from './sharedUtils'
+// Not from './sharedUtils': that module drags the app policy code into every page.
+export { capitalize } from './utils/capitalize'
 
 export function addWhitespaceBeforeCapitals(word?: string): string {
 	if (!word) {
@@ -1483,27 +1483,6 @@ export function orderedJsonStringify(obj: any, space?: string | number) {
 	return JSON.stringify(obj, (Array.from(allKeys) as string[]).sort(), space)
 }
 
-function sortObjectKeys(obj: any): any {
-	if (obj && typeof obj === 'object' && !Array.isArray(obj)) {
-		const sortedObj: any = {}
-		Object.keys(obj)
-			.sort()
-			.forEach((key) => {
-				sortedObj[key] = sortObjectKeys(obj[key])
-			})
-		return sortedObj
-	} else if (Array.isArray(obj)) {
-		return obj.map((item) => sortObjectKeys(item))
-	} else {
-		return obj
-	}
-}
-
-export function orderedYamlStringify(obj: any) {
-	const sortedObj = sortObjectKeys(obj)
-	return YAML.stringify(sortedObj)
-}
-
 function evalJs(expr: string) {
 	let template = `
 return function (fields) {
@@ -2039,7 +2018,7 @@ import tokensFile from './assets/tokens/tokens.json'
 import githubDarkTokens from './assets/tokens/githubDark.json'
 import { darkModeName, lightModeName } from './assets/tokens/colorTokensConfig'
 import BarsStaggered from './components/icons/BarsStaggered.svelte'
-import { GitIcon } from './components/icons'
+import GitIcon from './components/icons/GitIcon.svelte'
 import { Bot, Code, Package } from 'lucide-svelte'
 import type { DbInput } from './components/dbTypes'
 export function getCssColor(
diff --git a/frontend/src/lib/utils/capitalize.ts b/frontend/src/lib/utils/capitalize.ts
new file mode 100644
index 0000000000..ff0e4381e6
--- /dev/null
+++ b/frontend/src/lib/utils/capitalize.ts
@@ -0,0 +1,3 @@
+export function capitalize(word: string): string {
+	return word ? word.charAt(0).toUpperCase() + word.slice(1) : ''
+}
diff --git a/frontend/src/lib/utils/orderedYaml.ts b/frontend/src/lib/utils/orderedYaml.ts
new file mode 100644
index 0000000000..3765d47f6f
--- /dev/null
+++ b/frontend/src/lib/utils/orderedYaml.ts
@@ -0,0 +1,23 @@
+// Kept out of $lib/utils, which every page loads: `yaml` is only needed by the diff views.
+import YAML from 'yaml'
+
+function sortObjectKeys(obj: any): any {
+	if (obj && typeof obj === 'object' && !Array.isArray(obj)) {
+		const sortedObj: any = {}
+		Object.keys(obj)
+			.sort()
+			.forEach((key) => {
+				sortedObj[key] = sortObjectKeys(obj[key])
+			})
+		return sortedObj
+	} else if (Array.isArray(obj)) {
+		return obj.map((item) => sortObjectKeys(item))
+	} else {
+		return obj
+	}
+}
+
+export function orderedYamlStringify(obj: any) {
+	const sortedObj = sortObjectKeys(obj)
+	return YAML.stringify(sortedObj)
+}
diff --git a/frontend/src/lib/utils/serializeParam.ts b/frontend/src/lib/utils/serializeParam.ts
new file mode 100644
index 0000000000..c9397ffde8
--- /dev/null
+++ b/frontend/src/lib/utils/serializeParam.ts
@@ -0,0 +1,12 @@
+// A leaf on purpose. navigation.ts (loaded by nearly every page) must not pull in zod
+// through svelte5UtilsKit, and svelte5UtilsKit must not import navigation.ts: the
+// sharedUtils declaration build type-checks it via utils.ts -> stores.ts ->
+// dbManagerDrawerModel, where $app/* does not resolve.
+
+/** Serialize a value to a URL search param string. Primitives are written as-is; anything else is JSON. */
+export function serializeParam(value: unknown): string {
+	if (typeof value === 'string') return value
+	if (typeof value === 'number') return String(value)
+	if (typeof value === 'boolean') return String(value)
+	return JSON.stringify(value)
+}
diff --git a/frontend/vite.config.js b/frontend/vite.config.js
index 732eec8687..6cda86a381 100644
--- a/frontend/vite.config.js
+++ b/frontend/vite.config.js
@@ -73,6 +73,52 @@ function assertAcyclicChunks() {
 	}
 }
 
+/**
+ * Fail the build if a public app URL statically loads the low-code runtime or monaco.
+ *
+ * These pages also serve raw apps, which only need a small shell around their bundle's
+ * iframe. One static import of AppPreview (or of anything reaching monaco) makes every
+ * public app page preload ~650 chunks instead of ~55. See loadAppPreview.ts.
+ */
+function assertLeanPublicAppRoutes() {
+	// Route directories, so +page.js counts as well as +page.svelte.
+	const routes = ['/src/routes/public/[workspace]/[...secret]/', '/src/routes/a/[...path]/']
+	const forbidden = [
+		'/src/lib/components/apps/editor/AppPreview.svelte',
+		'/node_modules/monaco-editor/'
+	]
+	return {
+		name: 'wm-assert-lean-public-app-routes',
+		generateBundle(_options, bundle) {
+			const chunks = Object.entries(bundle).filter(([, c]) => c.type === 'chunk')
+			if (!chunks.some(([file]) => file.startsWith('_app/immutable/'))) return
+			const idsOf = (c) => c.moduleIds ?? Object.keys(c.modules ?? {})
+			for (const route of routes) {
+				const starts = chunks
+					.filter(([, c]) => idsOf(c).some((id) => id.includes(route)))
+					.map(([file]) => file)
+				if (!starts.length)
+					this.error(`No chunk contains ${route}; update assertLeanPublicAppRoutes`)
+				const seen = new Set(starts)
+				const queue = [...starts]
+				while (queue.length) {
+					const chunk = bundle[queue.shift()]
+					if (!chunk) continue
+					const hit = idsOf(chunk).find((id) => forbidden.some((f) => id.includes(f)))
+					if (hit) {
+						this.error(`${route} statically loads ${hit}; import it lazily (see loadAppPreview.ts)`)
+					}
+					for (const dep of chunk.imports ?? []) {
+						if (seen.has(dep)) continue
+						seen.add(dep)
+						queue.push(dep)
+					}
+				}
+			}
+		}
+	}
+}
+
 const remoteUrl =
 	process.env.REMOTE ??
 	(process.env.BACKEND_PORT
@@ -188,7 +234,8 @@ const config = {
 		sveltekit(),
 		...(process.env.HTTPS === 'true' ? [mkcert()] : []),
 		plugin,
-		assertAcyclicChunks()
+		assertAcyclicChunks(),
+		assertLeanPublicAppRoutes()
 	],
 	define: { __pkg__: version },
 	optimizeDeps: {