From 0813d0f730301c6645c779f4743da9704d474463 Mon Sep 17 00:00:00 2001
From: Chew Tee Ming <chew.tee.ming@nindatech.com>
Date: Tue, 19 Aug 2025 17:35:58 +0800
Subject: [PATCH 01/11] add test

---
 .../src/routes/serialization-stream/+page.server.ts   |  7 +++++++
 .../src/routes/serialization-stream/+page.svelte      | 11 +++++++++++
 packages/kit/test/apps/basics/test/test.js            |  7 +++++++
 3 files changed, 25 insertions(+)
 create mode 100644 packages/kit/test/apps/basics/src/routes/serialization-stream/+page.server.ts
 create mode 100644 packages/kit/test/apps/basics/src/routes/serialization-stream/+page.svelte

diff --git a/packages/kit/test/apps/basics/src/routes/serialization-stream/+page.server.ts b/packages/kit/test/apps/basics/src/routes/serialization-stream/+page.server.ts
new file mode 100644
index 000000000000..9484424e9d2d
--- /dev/null
+++ b/packages/kit/test/apps/basics/src/routes/serialization-stream/+page.server.ts
@@ -0,0 +1,7 @@
+import { Foo } from '$lib';
+
+export const load = () => {
+	return {
+		foo: Promise.resolve(new Foo("It works"))
+	};
+};
diff --git a/packages/kit/test/apps/basics/src/routes/serialization-stream/+page.svelte b/packages/kit/test/apps/basics/src/routes/serialization-stream/+page.svelte
new file mode 100644
index 000000000000..75c6a2f7a800
--- /dev/null
+++ b/packages/kit/test/apps/basics/src/routes/serialization-stream/+page.svelte
@@ -0,0 +1,11 @@
+<script>
+	export let data;
+</script>
+
+<h1>
+	{#await data.foo}
+		Loading...
+	{:then result}
+		{result.bar()}
+	{/await}
+</h1>
diff --git a/packages/kit/test/apps/basics/test/test.js b/packages/kit/test/apps/basics/test/test.js
index 55db0bf20db6..a91cd0362ffe 100644
--- a/packages/kit/test/apps/basics/test/test.js
+++ b/packages/kit/test/apps/basics/test/test.js
@@ -1560,6 +1560,13 @@ test.describe('Serialization', () => {
 		await page.click('button');
 		await expect(page.locator('h1')).toHaveText('It works!');
 	});
+
+	test('works with streaming', async ({ page, javaScriptEnabled }) => {
+		test.skip(!javaScriptEnabled, 'skip when JavaScript is disabled');
+
+		await page.goto('/serialization-stream');
+		await expect(page.locator('h1', { hasText: 'It works!'})).toBeVisible();
+	});
 });
 
 test.describe('getRequestEvent', () => {

From 76fd22bc7ce55eee1cf80e05375300580984f40b Mon Sep 17 00:00:00 2001
From: Chew Tee Ming <chew.tee.ming@nindatech.com>
Date: Wed, 20 Aug 2025 10:37:05 +0800
Subject: [PATCH 02/11] add test for single apps

---
 .../{+page.server.ts => +page.server.js}              |  2 +-
 packages/kit/test/apps/basics/test/test.js            |  2 +-
 packages/kit/test/apps/options-2/src/hooks.js         |  9 +++++++++
 packages/kit/test/apps/options-2/src/lib/index.js     |  9 +++++++++
 .../src/routes/serialization-stream/+page.server.js   |  7 +++++++
 .../src/routes/serialization-stream/+page.svelte      | 11 +++++++++++
 packages/kit/test/apps/options-2/test/test.js         |  5 +++++
 7 files changed, 43 insertions(+), 2 deletions(-)
 rename packages/kit/test/apps/basics/src/routes/serialization-stream/{+page.server.ts => +page.server.js} (62%)
 create mode 100644 packages/kit/test/apps/options-2/src/hooks.js
 create mode 100644 packages/kit/test/apps/options-2/src/lib/index.js
 create mode 100644 packages/kit/test/apps/options-2/src/routes/serialization-stream/+page.server.js
 create mode 100644 packages/kit/test/apps/options-2/src/routes/serialization-stream/+page.svelte

diff --git a/packages/kit/test/apps/basics/src/routes/serialization-stream/+page.server.ts b/packages/kit/test/apps/basics/src/routes/serialization-stream/+page.server.js
similarity index 62%
rename from packages/kit/test/apps/basics/src/routes/serialization-stream/+page.server.ts
rename to packages/kit/test/apps/basics/src/routes/serialization-stream/+page.server.js
index 9484424e9d2d..957f34dc1b76 100644
--- a/packages/kit/test/apps/basics/src/routes/serialization-stream/+page.server.ts
+++ b/packages/kit/test/apps/basics/src/routes/serialization-stream/+page.server.js
@@ -2,6 +2,6 @@ import { Foo } from '$lib';
 
 export const load = () => {
 	return {
-		foo: Promise.resolve(new Foo("It works"))
+		foo: Promise.resolve(new Foo('It works'))
 	};
 };
diff --git a/packages/kit/test/apps/basics/test/test.js b/packages/kit/test/apps/basics/test/test.js
index a91cd0362ffe..ac9755b2c741 100644
--- a/packages/kit/test/apps/basics/test/test.js
+++ b/packages/kit/test/apps/basics/test/test.js
@@ -1565,7 +1565,7 @@ test.describe('Serialization', () => {
 		test.skip(!javaScriptEnabled, 'skip when JavaScript is disabled');
 
 		await page.goto('/serialization-stream');
-		await expect(page.locator('h1', { hasText: 'It works!'})).toBeVisible();
+		await expect(page.locator('h1', { hasText: 'It works!' })).toBeVisible();
 	});
 });
 
diff --git a/packages/kit/test/apps/options-2/src/hooks.js b/packages/kit/test/apps/options-2/src/hooks.js
new file mode 100644
index 000000000000..f611d294bd35
--- /dev/null
+++ b/packages/kit/test/apps/options-2/src/hooks.js
@@ -0,0 +1,9 @@
+import { Foo } from "$lib";
+
+/** @type {import("@sveltejs/kit").Transport} */
+export const transport = {
+	Foo: {
+		encode: (value) => value instanceof Foo && [value.message],
+		decode: ([message]) => new Foo(message)
+	}
+};
diff --git a/packages/kit/test/apps/options-2/src/lib/index.js b/packages/kit/test/apps/options-2/src/lib/index.js
new file mode 100644
index 000000000000..f9917fd877e2
--- /dev/null
+++ b/packages/kit/test/apps/options-2/src/lib/index.js
@@ -0,0 +1,9 @@
+export class Foo {
+	constructor(message) {
+		this.message = message;
+	}
+
+	bar() {
+		return this.message + '!';
+	}
+}
diff --git a/packages/kit/test/apps/options-2/src/routes/serialization-stream/+page.server.js b/packages/kit/test/apps/options-2/src/routes/serialization-stream/+page.server.js
new file mode 100644
index 000000000000..957f34dc1b76
--- /dev/null
+++ b/packages/kit/test/apps/options-2/src/routes/serialization-stream/+page.server.js
@@ -0,0 +1,7 @@
+import { Foo } from '$lib';
+
+export const load = () => {
+	return {
+		foo: Promise.resolve(new Foo('It works'))
+	};
+};
diff --git a/packages/kit/test/apps/options-2/src/routes/serialization-stream/+page.svelte b/packages/kit/test/apps/options-2/src/routes/serialization-stream/+page.svelte
new file mode 100644
index 000000000000..75c6a2f7a800
--- /dev/null
+++ b/packages/kit/test/apps/options-2/src/routes/serialization-stream/+page.svelte
@@ -0,0 +1,11 @@
+<script>
+	export let data;
+</script>
+
+<h1>
+	{#await data.foo}
+		Loading...
+	{:then result}
+		{result.bar()}
+	{/await}
+</h1>
diff --git a/packages/kit/test/apps/options-2/test/test.js b/packages/kit/test/apps/options-2/test/test.js
index 4af842e6f7ee..f3df40146a8d 100644
--- a/packages/kit/test/apps/options-2/test/test.js
+++ b/packages/kit/test/apps/options-2/test/test.js
@@ -190,4 +190,9 @@ test.describe("bundleStrategy: 'single'", () => {
 		await page.goto('/basepath/deserialize');
 		await expect(page.locator('p')).toHaveText('Hello world!');
 	});
+
+	test('serialization works with streaming', async ({ page }) => {
+		await page.goto('/basepath/serialization-stream');
+		await expect(page.locator('h1', { hasText: 'It works!' })).toBeVisible();
+	});
 });

From 2bb66479da53bccff22e6557235262210a38b05f Mon Sep 17 00:00:00 2001
From: Chew Tee Ming <chew.tee.ming@nindatech.com>
Date: Wed, 20 Aug 2025 14:07:29 +0800
Subject: [PATCH 03/11] wrap statement in app import

---
 packages/kit/src/runtime/app/forms.js         |  2 +-
 packages/kit/src/runtime/client/bundle.js     |  2 ++
 .../kit/src/runtime/server/page/render.js     | 27 ++++++++++++++++---
 3 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/packages/kit/src/runtime/app/forms.js b/packages/kit/src/runtime/app/forms.js
index f4d0a352f628..1142609fe859 100644
--- a/packages/kit/src/runtime/app/forms.js
+++ b/packages/kit/src/runtime/app/forms.js
@@ -33,7 +33,7 @@ export function deserialize(result) {
 
 	if (parsed.data) {
 		// the decoders should never be initialised at the top-level because `app`
-		// will not initialised yet if `kit.output.bundleStrategy` is 'single' or 'inline'
+		// will not be initialised yet if `kit.output.bundleStrategy` is 'single' or 'inline'
 		parsed.data = devalue.parse(parsed.data, BROWSER ? client_app.decoders : server_app.decoders);
 	}
 
diff --git a/packages/kit/src/runtime/client/bundle.js b/packages/kit/src/runtime/client/bundle.js
index 7a915d3110a4..f375d02e8355 100644
--- a/packages/kit/src/runtime/client/bundle.js
+++ b/packages/kit/src/runtime/client/bundle.js
@@ -13,3 +13,5 @@ import * as app from '__sveltekit/manifest';
 export function start(element, options) {
 	void kit.start(app, element, options);
 }
+
+export { app };
diff --git a/packages/kit/src/runtime/server/page/render.js b/packages/kit/src/runtime/server/page/render.js
index 0d22352839bf..f871737f57cd 100644
--- a/packages/kit/src/runtime/server/page/render.js
+++ b/packages/kit/src/runtime/server/page/render.js
@@ -297,7 +297,9 @@ export async function render_response({
 		options,
 		branch.map((b) => b.server_data),
 		csp,
-		global
+		global,
+		client,
+		prefixed
 	);
 
 	if (page_config.ssr && page_config.csr) {
@@ -622,14 +624,18 @@ export async function render_response({
  * @param {Array<import('types').ServerDataNode | null>} nodes
  * @param {import('./csp.js').Csp} csp
  * @param {string} global
+ * @param {NonNullable<import('types').BuildData["client"]>} client
+ * @param {(path: string) => string} prefixed
  * @returns {{ data: string, chunks: AsyncIterable<string> | null }}
  */
-function get_data(event, event_state, options, nodes, csp, global) {
+function get_data(event, event_state, options, nodes, csp, global, client, prefixed) {
 	let promise_id = 1;
 	let count = 0;
 
 	const { iterator, push, done } = create_async_iterator();
 
+	const app = client.inline ? `__sveltekit_${options.version_hash}.app.app` : 'app';
+
 	/** @param {any} thing */
 	function replacer(thing) {
 		if (typeof thing?.then === 'function') {
@@ -665,7 +671,20 @@ function get_data(event, event_state, options, nodes, csp, global) {
 						}
 
 						const nonce = csp.script_needs_nonce ? ` nonce="${csp.nonce}"` : '';
-						push(`<script${nonce}>${global}.resolve(${str})</script>\n`);
+						const code = `${global}.resolve(${str})`;
+						if (!client.inline && str.includes("app.decode('")) {
+							if (client.app) {
+								push(
+									`<script${nonce}>import(${prefixed(client.app)}).then((app)=>{${code}})</script>\n`
+								);
+							} else {
+								push(
+									`<script${nonce}>import(${prefixed(client.start)}).then(({app})=>{${code}})</script>\n`
+								);
+							}
+						} else {
+							push(`<script${nonce}>${code}</script>\n`);
+						}
 						if (count === 0) done();
 					}
 				);
@@ -675,7 +694,7 @@ function get_data(event, event_state, options, nodes, csp, global) {
 			for (const key in options.hooks.transport) {
 				const encoded = options.hooks.transport[key].encode(thing);
 				if (encoded) {
-					return `app.decode('${key}', ${devalue.uneval(encoded, replacer)})`;
+					return `${app}.decode('${key}', ${devalue.uneval(encoded, replacer)})`;
 				}
 			}
 		}

From 926a55ecab7e209007bcbb461aa765a38f00eec7 Mon Sep 17 00:00:00 2001
From: Chew Tee Ming <chew.tee.ming@nindatech.com>
Date: Wed, 20 Aug 2025 14:07:39 +0800
Subject: [PATCH 04/11] add test for inlined apps

---
 packages/kit/test/apps/options-3/package.json | 23 ++++++++++++++++++
 .../test/apps/options-3/playwright.config.js  |  1 +
 packages/kit/test/apps/options-3/src/app.html | 11 +++++++++
 packages/kit/test/apps/options-3/src/hooks.js |  9 +++++++
 .../kit/test/apps/options-3/src/lib/index.js  |  9 +++++++
 .../apps/options-3/src/routes/+layout.svelte  |  7 ++++++
 .../serialization-stream/+page.server.js      |  7 ++++++
 .../routes/serialization-stream/+page.svelte  | 11 +++++++++
 .../kit/test/apps/options-3/svelte.config.js  | 10 ++++++++
 packages/kit/test/apps/options-3/test/test.js | 18 ++++++++++++++
 .../kit/test/apps/options-3/tsconfig.json     |  8 +++++++
 .../kit/test/apps/options-3/vite.config.js    | 18 ++++++++++++++
 pnpm-lock.yaml                                | 24 +++++++++++++++++++
 13 files changed, 156 insertions(+)
 create mode 100644 packages/kit/test/apps/options-3/package.json
 create mode 100644 packages/kit/test/apps/options-3/playwright.config.js
 create mode 100644 packages/kit/test/apps/options-3/src/app.html
 create mode 100644 packages/kit/test/apps/options-3/src/hooks.js
 create mode 100644 packages/kit/test/apps/options-3/src/lib/index.js
 create mode 100644 packages/kit/test/apps/options-3/src/routes/+layout.svelte
 create mode 100644 packages/kit/test/apps/options-3/src/routes/serialization-stream/+page.server.js
 create mode 100644 packages/kit/test/apps/options-3/src/routes/serialization-stream/+page.svelte
 create mode 100644 packages/kit/test/apps/options-3/svelte.config.js
 create mode 100644 packages/kit/test/apps/options-3/test/test.js
 create mode 100644 packages/kit/test/apps/options-3/tsconfig.json
 create mode 100644 packages/kit/test/apps/options-3/vite.config.js

diff --git a/packages/kit/test/apps/options-3/package.json b/packages/kit/test/apps/options-3/package.json
new file mode 100644
index 000000000000..78543175148f
--- /dev/null
+++ b/packages/kit/test/apps/options-3/package.json
@@ -0,0 +1,23 @@
+{
+	"name": "test-options-3",
+	"private": true,
+	"version": "0.0.1",
+	"scripts": {
+		"dev": "vite dev",
+		"build": "vite build",
+		"preview": "vite preview",
+		"prepare": "svelte-kit sync",
+		"check": "svelte-kit sync && tsc && svelte-check",
+		"test": "playwright test"
+	},
+	"devDependencies": {
+		"@sveltejs/adapter-node": "workspace:^",
+		"@sveltejs/kit": "workspace:^",
+		"@sveltejs/vite-plugin-svelte": "catalog:",
+		"svelte": "^5.35.5",
+		"svelte-check": "^4.1.1",
+		"typescript": "^5.5.4",
+		"vite": "catalog:"
+	},
+	"type": "module"
+}
diff --git a/packages/kit/test/apps/options-3/playwright.config.js b/packages/kit/test/apps/options-3/playwright.config.js
new file mode 100644
index 000000000000..33d36b651014
--- /dev/null
+++ b/packages/kit/test/apps/options-3/playwright.config.js
@@ -0,0 +1 @@
+export { config as default } from '../../utils.js';
diff --git a/packages/kit/test/apps/options-3/src/app.html b/packages/kit/test/apps/options-3/src/app.html
new file mode 100644
index 000000000000..b8ba4699b2ba
--- /dev/null
+++ b/packages/kit/test/apps/options-3/src/app.html
@@ -0,0 +1,11 @@
+<!doctype html>
+<html lang="en">
+	<head>
+		<meta charset="utf-8" />
+		<meta name="viewport" content="width=device-width, initial-scale=1" />
+		%sveltekit.head%
+	</head>
+	<body>
+		<div style="display: contents">%sveltekit.body%</div>
+	</body>
+</html>
diff --git a/packages/kit/test/apps/options-3/src/hooks.js b/packages/kit/test/apps/options-3/src/hooks.js
new file mode 100644
index 000000000000..f611d294bd35
--- /dev/null
+++ b/packages/kit/test/apps/options-3/src/hooks.js
@@ -0,0 +1,9 @@
+import { Foo } from "$lib";
+
+/** @type {import("@sveltejs/kit").Transport} */
+export const transport = {
+	Foo: {
+		encode: (value) => value instanceof Foo && [value.message],
+		decode: ([message]) => new Foo(message)
+	}
+};
diff --git a/packages/kit/test/apps/options-3/src/lib/index.js b/packages/kit/test/apps/options-3/src/lib/index.js
new file mode 100644
index 000000000000..f9917fd877e2
--- /dev/null
+++ b/packages/kit/test/apps/options-3/src/lib/index.js
@@ -0,0 +1,9 @@
+export class Foo {
+	constructor(message) {
+		this.message = message;
+	}
+
+	bar() {
+		return this.message + '!';
+	}
+}
diff --git a/packages/kit/test/apps/options-3/src/routes/+layout.svelte b/packages/kit/test/apps/options-3/src/routes/+layout.svelte
new file mode 100644
index 000000000000..5e1f1fed86c2
--- /dev/null
+++ b/packages/kit/test/apps/options-3/src/routes/+layout.svelte
@@ -0,0 +1,7 @@
+<script>
+	import { setup } from '../../../../setup.js';
+
+	setup();
+</script>
+
+<slot />
diff --git a/packages/kit/test/apps/options-3/src/routes/serialization-stream/+page.server.js b/packages/kit/test/apps/options-3/src/routes/serialization-stream/+page.server.js
new file mode 100644
index 000000000000..957f34dc1b76
--- /dev/null
+++ b/packages/kit/test/apps/options-3/src/routes/serialization-stream/+page.server.js
@@ -0,0 +1,7 @@
+import { Foo } from '$lib';
+
+export const load = () => {
+	return {
+		foo: Promise.resolve(new Foo('It works'))
+	};
+};
diff --git a/packages/kit/test/apps/options-3/src/routes/serialization-stream/+page.svelte b/packages/kit/test/apps/options-3/src/routes/serialization-stream/+page.svelte
new file mode 100644
index 000000000000..75c6a2f7a800
--- /dev/null
+++ b/packages/kit/test/apps/options-3/src/routes/serialization-stream/+page.svelte
@@ -0,0 +1,11 @@
+<script>
+	export let data;
+</script>
+
+<h1>
+	{#await data.foo}
+		Loading...
+	{:then result}
+		{result.bar()}
+	{/await}
+</h1>
diff --git a/packages/kit/test/apps/options-3/svelte.config.js b/packages/kit/test/apps/options-3/svelte.config.js
new file mode 100644
index 000000000000..bcfcfccabb1f
--- /dev/null
+++ b/packages/kit/test/apps/options-3/svelte.config.js
@@ -0,0 +1,10 @@
+/** @type {import('@sveltejs/kit').Config} */
+const config = {
+	kit: {
+		output: {
+			bundleStrategy: 'inline'
+		}
+	}
+};
+
+export default config;
diff --git a/packages/kit/test/apps/options-3/test/test.js b/packages/kit/test/apps/options-3/test/test.js
new file mode 100644
index 000000000000..69a753c4bafd
--- /dev/null
+++ b/packages/kit/test/apps/options-3/test/test.js
@@ -0,0 +1,18 @@
+import path from 'node:path';
+import process from 'node:process';
+import { fileURLToPath } from 'node:url';
+import { expect } from '@playwright/test';
+import { test } from '../../../utils.js';
+
+/** @typedef {import('@playwright/test').Response} Response */
+
+test.describe.configure({ mode: 'parallel' });
+
+test.describe("bundleStrategy: 'inline'", () => {
+	test.skip(({ javaScriptEnabled }) => !javaScriptEnabled || !!process.env.DEV);
+
+	test('serialization works with streaming', async ({ page }) => {
+		await page.goto('/serialization-stream');
+		await expect(page.locator('h1', { hasText: 'It works!' })).toBeVisible();
+	});
+});
diff --git a/packages/kit/test/apps/options-3/tsconfig.json b/packages/kit/test/apps/options-3/tsconfig.json
new file mode 100644
index 000000000000..b1096bf168cd
--- /dev/null
+++ b/packages/kit/test/apps/options-3/tsconfig.json
@@ -0,0 +1,8 @@
+{
+	"compilerOptions": {
+		"allowJs": true,
+		"checkJs": true,
+		"noEmit": true
+	},
+	"extends": "./.svelte-kit/tsconfig.json"
+}
diff --git a/packages/kit/test/apps/options-3/vite.config.js b/packages/kit/test/apps/options-3/vite.config.js
new file mode 100644
index 000000000000..69200cdb7cd8
--- /dev/null
+++ b/packages/kit/test/apps/options-3/vite.config.js
@@ -0,0 +1,18 @@
+import * as path from 'node:path';
+import { sveltekit } from '@sveltejs/kit/vite';
+
+/** @type {import('vite').UserConfig} */
+const config = {
+	build: {
+		minify: false
+	},
+	clearScreen: false,
+	plugins: [sveltekit()],
+	server: {
+		fs: {
+			allow: [path.resolve('../../../src')]
+		}
+	}
+};
+
+export default config;
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 643098904aaa..13b5d6dd4927 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -714,6 +714,30 @@ importers:
         specifier: 'catalog:'
         version: 6.3.5(@types/node@18.19.119)(jiti@2.4.2)(lightningcss@1.30.1)(yaml@2.8.0)
 
+  packages/kit/test/apps/options-3:
+    devDependencies:
+      '@sveltejs/adapter-node':
+        specifier: workspace:^
+        version: link:../../../../adapter-node
+      '@sveltejs/kit':
+        specifier: workspace:^
+        version: link:../../..
+      '@sveltejs/vite-plugin-svelte':
+        specifier: 'catalog:'
+        version: 6.0.0-next.3(svelte@5.35.5)(vite@6.3.5(@types/node@18.19.119)(jiti@2.4.2)(lightningcss@1.30.1)(yaml@2.8.0))
+      svelte:
+        specifier: ^5.35.5
+        version: 5.35.5
+      svelte-check:
+        specifier: ^4.1.1
+        version: 4.1.1(picomatch@4.0.3)(svelte@5.35.5)(typescript@5.8.3)
+      typescript:
+        specifier: ^5.5.4
+        version: 5.8.3
+      vite:
+        specifier: 'catalog:'
+        version: 6.3.5(@types/node@18.19.119)(jiti@2.4.2)(lightningcss@1.30.1)(yaml@2.8.0)
+
   packages/kit/test/apps/prerendered-app-error-pages:
     devDependencies:
       '@sveltejs/kit':

From 2b4d59b4a638601b082b65e213b338aea32587c8 Mon Sep 17 00:00:00 2001
From: Chew Tee Ming <chew.tee.ming@nindatech.com>
Date: Wed, 20 Aug 2025 14:19:50 +0800
Subject: [PATCH 05/11] format

---
 packages/kit/test/apps/options-2/src/hooks.js | 2 +-
 packages/kit/test/apps/options-3/src/hooks.js | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/kit/test/apps/options-2/src/hooks.js b/packages/kit/test/apps/options-2/src/hooks.js
index f611d294bd35..238cc7744f2c 100644
--- a/packages/kit/test/apps/options-2/src/hooks.js
+++ b/packages/kit/test/apps/options-2/src/hooks.js
@@ -1,4 +1,4 @@
-import { Foo } from "$lib";
+import { Foo } from '$lib';
 
 /** @type {import("@sveltejs/kit").Transport} */
 export const transport = {
diff --git a/packages/kit/test/apps/options-3/src/hooks.js b/packages/kit/test/apps/options-3/src/hooks.js
index f611d294bd35..238cc7744f2c 100644
--- a/packages/kit/test/apps/options-3/src/hooks.js
+++ b/packages/kit/test/apps/options-3/src/hooks.js
@@ -1,4 +1,4 @@
-import { Foo } from "$lib";
+import { Foo } from '$lib';
 
 /** @type {import("@sveltejs/kit").Transport} */
 export const transport = {

From b65e18c9ea6cde12ea005d8fafc70376424a31fc Mon Sep 17 00:00:00 2001
From: Chew Tee Ming <chew.tee.ming@nindatech.com>
Date: Wed, 20 Aug 2025 14:25:58 +0800
Subject: [PATCH 06/11] changeset

---
 .changeset/brown-seals-rhyme.md | 5 +++++
 1 file changed, 5 insertions(+)
 create mode 100644 .changeset/brown-seals-rhyme.md

diff --git a/.changeset/brown-seals-rhyme.md b/.changeset/brown-seals-rhyme.md
new file mode 100644
index 000000000000..ecdcb7b1f756
--- /dev/null
+++ b/.changeset/brown-seals-rhyme.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: correctly decode custom types streamed from a server load function

From 2ef8eac642e49dbf1320824672168d2e2f2dee15 Mon Sep 17 00:00:00 2001
From: Tee Ming <chewteeming01@gmail.com>
Date: Wed, 20 Aug 2025 22:27:57 +0800
Subject: [PATCH 07/11] fix lint errors

---
 packages/kit/test/apps/options-3/test/test.js | 2 --
 1 file changed, 2 deletions(-)

diff --git a/packages/kit/test/apps/options-3/test/test.js b/packages/kit/test/apps/options-3/test/test.js
index 69a753c4bafd..b85f5c61265b 100644
--- a/packages/kit/test/apps/options-3/test/test.js
+++ b/packages/kit/test/apps/options-3/test/test.js
@@ -1,6 +1,4 @@
-import path from 'node:path';
 import process from 'node:process';
-import { fileURLToPath } from 'node:url';
 import { expect } from '@playwright/test';
 import { test } from '../../../utils.js';
 

From 8ef5668b90285f85ae4ea4409f4930ec416ada10 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 20 Aug 2025 14:59:30 -0400
Subject: [PATCH 08/11] fix

---
 packages/kit/src/runtime/server/page/render.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/kit/src/runtime/server/page/render.js b/packages/kit/src/runtime/server/page/render.js
index f871737f57cd..1d5c489a2a85 100644
--- a/packages/kit/src/runtime/server/page/render.js
+++ b/packages/kit/src/runtime/server/page/render.js
@@ -675,11 +675,11 @@ function get_data(event, event_state, options, nodes, csp, global, client, prefi
 						if (!client.inline && str.includes("app.decode('")) {
 							if (client.app) {
 								push(
-									`<script${nonce}>import(${prefixed(client.app)}).then((app)=>{${code}})</script>\n`
+									`<script${nonce}>import(${s(prefixed(client.app))}).then((app)=>{${code}})</script>\n`
 								);
 							} else {
 								push(
-									`<script${nonce}>import(${prefixed(client.start)}).then(({app})=>{${code}})</script>\n`
+									`<script${nonce}>import(${s(prefixed(client.start))}).then(({app})=>{${code}})</script>\n`
 								);
 							}
 						} else {

From f4ec516e397de8732c6d892eb32b2faf869b3469 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 20 Aug 2025 15:20:20 -0400
Subject: [PATCH 09/11] leaner payloads

---
 .../kit/src/runtime/server/page/render.js     | 35 ++++++++++---------
 1 file changed, 18 insertions(+), 17 deletions(-)

diff --git a/packages/kit/src/runtime/server/page/render.js b/packages/kit/src/runtime/server/page/render.js
index 1d5c489a2a85..8d16cce996d8 100644
--- a/packages/kit/src/runtime/server/page/render.js
+++ b/packages/kit/src/runtime/server/page/render.js
@@ -368,9 +368,21 @@ export async function render_response({
 							deferred.set(id, { fulfil, reject });
 						})`);
 
+			let prelude = `const [data, error] = fn();`;
+
+			if (client.app) {
+				prelude = `const app = await import(${s(prefixed(client.app))})
+							const [data, error] = fn(app);`;
+			} else {
+				prelude = `const { app } = await import(${s(prefixed(client.start))})
+							const [data, error] = fn(app);`;
+			}
+
 			// When resolving, the id might not yet be available due to the data
 			// be evaluated upon init of kit, so we use a timeout to retry
-			properties.push(`resolve: ({ id, data, error }) => {
+			properties.push(`resolve: async (id, fn) => {
+							${prelude}
+
 							const try_to_resolve = () => {
 								if (!deferred.has(id)) {
 									setTimeout(try_to_resolve, 0);
@@ -658,7 +670,7 @@ function get_data(event, event_state, options, nodes, csp, global, client, prefi
 
 						let str;
 						try {
-							str = devalue.uneval({ id, data, error }, replacer);
+							str = devalue.uneval([data], replacer);
 						} catch {
 							error = await handle_error_and_jsonify(
 								event,
@@ -667,24 +679,13 @@ function get_data(event, event_state, options, nodes, csp, global, client, prefi
 								new Error(`Failed to serialize promise while rendering ${event.route.id}`)
 							);
 							data = undefined;
-							str = devalue.uneval({ id, data, error }, replacer);
+							str = devalue.uneval([null, error], replacer);
 						}
 
 						const nonce = csp.script_needs_nonce ? ` nonce="${csp.nonce}"` : '';
-						const code = `${global}.resolve(${str})`;
-						if (!client.inline && str.includes("app.decode('")) {
-							if (client.app) {
-								push(
-									`<script${nonce}>import(${s(prefixed(client.app))}).then((app)=>{${code}})</script>\n`
-								);
-							} else {
-								push(
-									`<script${nonce}>import(${s(prefixed(client.start))}).then(({app})=>{${code}})</script>\n`
-								);
-							}
-						} else {
-							push(`<script${nonce}>${code}</script>\n`);
-						}
+						push(
+							`<script${nonce}>${global}.resolve(${id}, ${str.includes('app.decode') ? `(app) => ${str}` : `() => ${str}`})</script>\n`
+						);
 						if (count === 0) done();
 					}
 				);

From e856b3ff31e9326e3399c78000d52379ce58b18a Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 20 Aug 2025 15:32:27 -0400
Subject: [PATCH 10/11] fix

---
 .../kit/src/runtime/server/page/render.js     | 35 ++++++++++---------
 1 file changed, 18 insertions(+), 17 deletions(-)

diff --git a/packages/kit/src/runtime/server/page/render.js b/packages/kit/src/runtime/server/page/render.js
index 8d16cce996d8..1cec01233e71 100644
--- a/packages/kit/src/runtime/server/page/render.js
+++ b/packages/kit/src/runtime/server/page/render.js
@@ -297,9 +297,7 @@ export async function render_response({
 		options,
 		branch.map((b) => b.server_data),
 		csp,
-		global,
-		client,
-		prefixed
+		global
 	);
 
 	if (page_config.ssr && page_config.csr) {
@@ -368,16 +366,23 @@ export async function render_response({
 							deferred.set(id, { fulfil, reject });
 						})`);
 
-			let prelude = `const [data, error] = fn();`;
+			let app_declaration = '';
 
-			if (client.app) {
-				prelude = `const app = await import(${s(prefixed(client.app))})
-							const [data, error] = fn(app);`;
-			} else {
-				prelude = `const { app } = await import(${s(prefixed(client.start))})
-							const [data, error] = fn(app);`;
+			if (Object.keys(options.hooks.transport).length > 0) {
+				if (client.inline) {
+					app_declaration = `const app = __sveltekit_${options.version_hash}.app.app;`;
+				} else if (client.app) {
+					app_declaration = `const app = await import(${s(prefixed(client.app))});`;
+				} else {
+					app_declaration = `const { app } = await import(${s(prefixed(client.start))});`;
+				}
 			}
 
+			const prelude = app_declaration
+				? `${app_declaration}
+							const [data, error] = fn(app);`
+				: `const [data, error] = fn();`;
+
 			// When resolving, the id might not yet be available due to the data
 			// be evaluated upon init of kit, so we use a timeout to retry
 			properties.push(`resolve: async (id, fn) => {
@@ -636,18 +641,14 @@ export async function render_response({
  * @param {Array<import('types').ServerDataNode | null>} nodes
  * @param {import('./csp.js').Csp} csp
  * @param {string} global
- * @param {NonNullable<import('types').BuildData["client"]>} client
- * @param {(path: string) => string} prefixed
  * @returns {{ data: string, chunks: AsyncIterable<string> | null }}
  */
-function get_data(event, event_state, options, nodes, csp, global, client, prefixed) {
+function get_data(event, event_state, options, nodes, csp, global) {
 	let promise_id = 1;
 	let count = 0;
 
 	const { iterator, push, done } = create_async_iterator();
 
-	const app = client.inline ? `__sveltekit_${options.version_hash}.app.app` : 'app';
-
 	/** @param {any} thing */
 	function replacer(thing) {
 		if (typeof thing?.then === 'function') {
@@ -670,7 +671,7 @@ function get_data(event, event_state, options, nodes, csp, global, client, prefi
 
 						let str;
 						try {
-							str = devalue.uneval([data], replacer);
+							str = devalue.uneval(error ? [, error] : [data], replacer);
 						} catch {
 							error = await handle_error_and_jsonify(
 								event,
@@ -695,7 +696,7 @@ function get_data(event, event_state, options, nodes, csp, global, client, prefi
 			for (const key in options.hooks.transport) {
 				const encoded = options.hooks.transport[key].encode(thing);
 				if (encoded) {
-					return `${app}.decode('${key}', ${devalue.uneval(encoded, replacer)})`;
+					return `app.decode('${key}', ${devalue.uneval(encoded, replacer)})`;
 				}
 			}
 		}

From 23af149ced7d1f5cae5bde800a199f63aa16343c Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 20 Aug 2025 15:39:41 -0400
Subject: [PATCH 11/11] tweak

---
 packages/kit/src/runtime/server/page/render.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/kit/src/runtime/server/page/render.js b/packages/kit/src/runtime/server/page/render.js
index 1cec01233e71..bb55ce707613 100644
--- a/packages/kit/src/runtime/server/page/render.js
+++ b/packages/kit/src/runtime/server/page/render.js
@@ -680,7 +680,7 @@ function get_data(event, event_state, options, nodes, csp, global) {
 								new Error(`Failed to serialize promise while rendering ${event.route.id}`)
 							);
 							data = undefined;
-							str = devalue.uneval([null, error], replacer);
+							str = devalue.uneval([, error], replacer);
 						}
 
 						const nonce = csp.script_needs_nonce ? ` nonce="${csp.nonce}"` : '';