From 541c459adcfb14eefc908eb90056028e8b56f110 Mon Sep 17 00:00:00 2001
From: Patrick <Patrick@ShowYou.us>
Date: Sat, 23 Aug 2025 00:14:56 +0200
Subject: [PATCH 01/25] add universal load to /streaming/server test

---
 .../kit/test/apps/basics/src/routes/streaming/server/+page.js  | 3 +++
 1 file changed, 3 insertions(+)
 create mode 100644 packages/kit/test/apps/basics/src/routes/streaming/server/+page.js

diff --git a/packages/kit/test/apps/basics/src/routes/streaming/server/+page.js b/packages/kit/test/apps/basics/src/routes/streaming/server/+page.js
new file mode 100644
index 000000000000..a5673a92a7b2
--- /dev/null
+++ b/packages/kit/test/apps/basics/src/routes/streaming/server/+page.js
@@ -0,0 +1,3 @@
+export function load({ data }) {
+	return { ...data };
+}

From a175295c3771150799ccdd1ba4771e4d45d98862 Mon Sep 17 00:00:00 2001
From: Patrick <Patrick@ShowYou.us>
Date: Sat, 23 Aug 2025 00:17:01 +0200
Subject: [PATCH 02/25] revert #14268

---
 .../kit/src/runtime/server/page/load_data.js  | 42 ++++---------------
 1 file changed, 7 insertions(+), 35 deletions(-)

diff --git a/packages/kit/src/runtime/server/page/load_data.js b/packages/kit/src/runtime/server/page/load_data.js
index 8d06de88038e..9eacf46b7b22 100644
--- a/packages/kit/src/runtime/server/page/load_data.js
+++ b/packages/kit/src/runtime/server/page/load_data.js
@@ -1,12 +1,11 @@
+import { merge_tracing, with_request_store } from '@sveltejs/kit/internal/server';
 import { DEV } from 'esm-env';
-import * as devalue from 'devalue';
 import { disable_search, make_trackable } from '../../../utils/url.js';
 import { validate_depends, validate_load_response } from '../../shared.js';
-import { with_request_store, merge_tracing } from '@sveltejs/kit/internal/server';
 import { record_span } from '../../telemetry/record_span.js';
-import { clarify_devalue_error, get_node_type } from '../utils.js';
 import { base64_encode, text_decoder } from '../../utils.js';
 import { NULL_BODY_STATUS } from '../constants.js';
+import { get_node_type } from '../utils.js';
 
 /**
  * Calls the user's server `load` function.
@@ -234,38 +233,11 @@ export async function load_data({
 		},
 		fn: async (current) => {
 			const traced_event = merge_tracing(event, current);
-			return await with_request_store({ event: traced_event, state: event_state }, () => {
-				/** @type {Record<string, any> | null} */
-				let data = null;
-
-				return load.call(null, {
+			return await with_request_store({ event: traced_event, state: event_state }, () =>
+				load.call(null, {
 					url: event.url,
 					params: event.params,
-					get data() {
-						if (data === null && server_data_node?.data != null) {
-							/** @type {Record<string, (value: any) => any>} */
-							const reducers = {};
-
-							/** @type {Record<string, (value: any) => any>} */
-							const revivers = {};
-
-							for (const key in event_state.transport) {
-								reducers[key] = event_state.transport[key].encode;
-								revivers[key] = event_state.transport[key].decode;
-							}
-
-							// run it through devalue so that the developer can't accidentally mutate it
-							try {
-								data = devalue.parse(devalue.stringify(server_data_node.data, reducers), revivers);
-							} catch (e) {
-								// @ts-expect-error
-								e.path = e.path.slice(1);
-								throw new Error(clarify_devalue_error(event, /** @type {any} */ (e)));
-							}
-						}
-
-						return data;
-					},
+					data: server_data_node?.data ?? null,
 					route: event.route,
 					fetch: create_universal_fetch(event, state, fetched, csr, resolve_opts),
 					setHeaders: event.setHeaders,
@@ -273,8 +245,8 @@ export async function load_data({
 					parent,
 					untrack: (fn) => fn(),
 					tracing: traced_event.tracing
-				});
-			});
+				})
+			);
 		}
 	});
 

From 663f72811751e7bc76c4a68656d71f17d970b9ab Mon Sep 17 00:00:00 2001
From: Patrick <Patrick@ShowYou.us>
Date: Sat, 23 Aug 2025 00:21:54 +0200
Subject: [PATCH 03/25] server data serializer

---
 packages/kit/src/runtime/server/data/index.js |  15 +-
 .../runtime/server/page/data_serializer.js    | 207 ++++++++++++++++++
 packages/kit/src/runtime/server/page/index.js |  43 ++--
 .../kit/src/runtime/server/page/render.js     | 127 ++---------
 .../runtime/server/page/respond_with_error.js |  12 +-
 .../kit/src/runtime/server/page/types.d.ts    |  22 +-
 packages/kit/src/runtime/server/respond.js    |  54 ++---
 7 files changed, 314 insertions(+), 166 deletions(-)
 create mode 100644 packages/kit/src/runtime/server/page/data_serializer.js

diff --git a/packages/kit/src/runtime/server/data/index.js b/packages/kit/src/runtime/server/data/index.js
index 37fc409ab42d..b5aa34e3f5da 100644
--- a/packages/kit/src/runtime/server/data/index.js
+++ b/packages/kit/src/runtime/server/data/index.js
@@ -1,13 +1,14 @@
 import { text } from '@sveltejs/kit';
-import { HttpError, SvelteKitError, Redirect } from '@sveltejs/kit/internal';
+import { HttpError, Redirect, SvelteKitError } from '@sveltejs/kit/internal';
+import * as devalue from 'devalue';
 import { normalize_error } from '../../../utils/error.js';
 import { once } from '../../../utils/functions.js';
-import { load_server_data } from '../page/load_data.js';
-import { clarify_devalue_error, handle_error_and_jsonify, serialize_uses } from '../utils.js';
-import { normalize_path } from '../../../utils/url.js';
-import * as devalue from 'devalue';
 import { create_async_iterator } from '../../../utils/streaming.js';
+import { normalize_path } from '../../../utils/url.js';
 import { text_encoder } from '../../utils.js';
+import { server_data_serializer_json } from '../page/data_serializer.js';
+import { load_server_data } from '../page/load_data.js';
+import { clarify_devalue_error, handle_error_and_jsonify, serialize_uses } from '../utils.js';
 
 /**
  * @param {import('@sveltejs/kit').RequestEvent} event
@@ -120,7 +121,9 @@ export async function render_data(
 			)
 		);
 
-		const { data, chunks } = get_data_json(event, event_state, options, nodes);
+		const data_serializer = server_data_serializer_json(event, event_state, options);
+		for (let i = 0; i < nodes.length; i++) data_serializer.serialize(i, nodes[i]);
+		const { data, chunks } = data_serializer.get_data();
 
 		if (!chunks) {
 			// use a normal JSON response where possible, so we get `content-length`
diff --git a/packages/kit/src/runtime/server/page/data_serializer.js b/packages/kit/src/runtime/server/page/data_serializer.js
new file mode 100644
index 000000000000..663726587402
--- /dev/null
+++ b/packages/kit/src/runtime/server/page/data_serializer.js
@@ -0,0 +1,207 @@
+import * as devalue from 'devalue';
+import { create_async_iterator } from '../../../utils/streaming.js';
+import { clarify_devalue_error, handle_error_and_jsonify, serialize_uses } from '../utils.js';
+
+/**
+ * If the serialized data contains promises, `chunks` will be an
+ * async iterable containing their resolutions
+ * @param {import('@sveltejs/kit').RequestEvent} event
+ * @param {import('types').RequestState} event_state
+ * @param {import('types').SSROptions} options
+ * @returns {import('./types.js').ServerDataSerializer}
+ */
+export function server_data_serializer(event, event_state, options) {
+	let promise_id = 1;
+	let count = 0;
+
+	const { iterator, push, done } = create_async_iterator();
+	const global_placeholder = `__GLOBAL__${Math.random().toString(36).slice(2)}__`;
+
+	/** @type {(info: { global: string; nonce: string; }) => void} */
+	let set_info;
+	const info = /** @type {Promise<{ global: string; nonce: string }>} */ new Promise(
+		(r) => (set_info = r)
+	);
+
+	/** @param {any} thing */
+	function replacer(thing) {
+		if (typeof thing?.then === 'function') {
+			const id = promise_id++;
+			count += 1;
+
+			thing
+				.then(/** @param {any} data */ (data) => ({ data }))
+				.catch(
+					/** @param {any} error */ async (error) => ({
+						error: await handle_error_and_jsonify(event, event_state, options, error)
+					})
+				)
+				.then(
+					/**
+					 * @param {{data: any; error: any}} result
+					 */
+					async ({ data, error }) => {
+						count -= 1;
+
+						let str;
+						try {
+							str = devalue.uneval(error ? [, error] : [data], replacer);
+						} catch {
+							error = await handle_error_and_jsonify(
+								event,
+								event_state,
+								options,
+								new Error(`Failed to serialize promise while rendering ${event.route.id}`)
+							);
+							data = undefined;
+							str = devalue.uneval([, error], replacer);
+						}
+
+						const { nonce, global } = await info;
+						push(
+							`<script${nonce}>${global}.resolve(${id}, ${str.includes('app.decode') ? `(app) => ${str}` : `() => ${str}`})</script>\n`
+						);
+						if (count === 0) done();
+					}
+				);
+
+			return `${global_placeholder}.defer(${id})`;
+		} else {
+			for (const key in options.hooks.transport) {
+				const encoded = options.hooks.transport[key].encode(thing);
+				if (encoded) {
+					return `app.decode('${key}', ${devalue.uneval(encoded, replacer)})`;
+				}
+			}
+		}
+	}
+
+	const strings = /** @type {string[]} */ ([]);
+
+	return {
+		serialize(i, node) {
+			try {
+				if (!node) {
+					strings[i] = 'null';
+					return;
+				}
+
+				/** @type {any} */
+				const payload = { type: 'data', data: node.data, uses: serialize_uses(node) };
+				if (node.slash) payload.slash = node.slash;
+
+				strings[i] = devalue.uneval(payload, replacer);
+			} catch (e) {
+				// @ts-expect-error
+				e.path = e.path.slice(1);
+				throw new Error(clarify_devalue_error(event, /** @type {any} */ (e)));
+			}
+		},
+
+		get_data(csp, global) {
+			set_info({ global, nonce: csp.script_needs_nonce ? ` nonce="${csp.nonce}"` : '' });
+			return {
+				data: `[${strings.join(',').replaceAll(global_placeholder, global)}]`,
+				chunks: count > 0 ? iterator : null
+			};
+		}
+	};
+}
+
+/**
+ * If the serialized data contains promises, `chunks` will be an
+ * async iterable containing their resolutions
+ * @param {import('@sveltejs/kit').RequestEvent} event
+ * @param {import('types').RequestState} event_state
+ * @param {import('types').SSROptions} options
+ * @returns {import('./types.js').ServerDataSerializerJson}
+ */
+export function server_data_serializer_json(event, event_state, options) {
+	let promise_id = 1;
+	let count = 0;
+
+	const { iterator, push, done } = create_async_iterator();
+
+	const reducers = {
+		...Object.fromEntries(
+			Object.entries(options.hooks.transport).map(([key, value]) => [key, value.encode])
+		),
+		/** @param {any} thing */
+		Promise: (thing) => {
+			if (typeof thing?.then === 'function') {
+				const id = promise_id++;
+				count += 1;
+
+				/** @type {'data' | 'error'} */
+				let key = 'data';
+
+				thing
+					.catch(
+						/** @param {any} e */ async (e) => {
+							key = 'error';
+							return handle_error_and_jsonify(event, event_state, options, /** @type {any} */ (e));
+						}
+					)
+					.then(
+						/** @param {any} value */
+						async (value) => {
+							let str;
+							try {
+								str = devalue.stringify(value, reducers);
+							} catch {
+								const error = await handle_error_and_jsonify(
+									event,
+									event_state,
+									options,
+									new Error(`Failed to serialize promise while rendering ${event.route.id}`)
+								);
+
+								key = 'error';
+								str = devalue.stringify(error, reducers);
+							}
+
+							count -= 1;
+
+							push(`{"type":"chunk","id":${id},"${key}":${str}}\n`);
+							if (count === 0) done();
+						}
+					);
+
+				return id;
+			}
+		}
+	};
+
+	const strings = /** @type {string[]} */ ([]);
+
+	return {
+		serialize(i, node) {
+			try {
+				if (!node) {
+					strings[i] = 'null';
+					return;
+				}
+
+				if (node.type === 'error' || node.type === 'skip') {
+					strings[i] = JSON.stringify(node);
+					return;
+				}
+
+				return `{"type":"data","data":${devalue.stringify(node.data, reducers)},"uses":${JSON.stringify(
+					serialize_uses(node)
+				)}${node.slash ? `,"slash":${JSON.stringify(node.slash)}` : ''}}`;
+			} catch (e) {
+				// @ts-expect-error
+				e.path = 'data' + e.path;
+				throw new Error(clarify_devalue_error(event, /** @type {any} */ (e)));
+			}
+		},
+
+		get_data() {
+			return {
+				data: `{"type":"data","nodes":[${strings.join(',')}]}\n`,
+				chunks: count > 0 ? iterator : null
+			};
+		}
+	};
+}
diff --git a/packages/kit/src/runtime/server/page/index.js b/packages/kit/src/runtime/server/page/index.js
index 7d24641f062d..202b94c808ea 100644
--- a/packages/kit/src/runtime/server/page/index.js
+++ b/packages/kit/src/runtime/server/page/index.js
@@ -1,22 +1,22 @@
 import { text } from '@sveltejs/kit';
 import { Redirect } from '@sveltejs/kit/internal';
+import { DEV } from 'esm-env';
 import { compact } from '../../../utils/array.js';
 import { get_status, normalize_error } from '../../../utils/error.js';
+import { PageNodes } from '../../../utils/page_nodes.js';
 import { add_data_suffix } from '../../pathname.js';
-import { redirect_response, static_error_page, handle_error_and_jsonify } from '../utils.js';
+import { get_remote_action, handle_remote_form_post } from '../remote.js';
+import { handle_error_and_jsonify, redirect_response, static_error_page } from '../utils.js';
 import {
 	handle_action_json_request,
 	handle_action_request,
 	is_action_json_request,
 	is_action_request
 } from './actions.js';
+import { server_data_serializer, server_data_serializer_json } from './data_serializer.js';
 import { load_data, load_server_data } from './load_data.js';
 import { render_response } from './render.js';
 import { respond_with_error } from './respond_with_error.js';
-import { get_data_json } from '../data/index.js';
-import { DEV } from 'esm-env';
-import { get_remote_action, handle_remote_form_post } from '../remote.js';
-import { PageNodes } from '../../../utils/page_nodes.js';
 
 /**
  * The maximum request depth permitted before assuming we're stuck in an infinite loop
@@ -147,7 +147,8 @@ export async function render_page(
 				options,
 				manifest,
 				state,
-				resolve_opts
+				resolve_opts,
+				data_serializer: server_data_serializer(event, event_state, options)
 			});
 		}
 
@@ -157,6 +158,12 @@ export async function render_page(
 		/** @type {Error | null} */
 		let load_error = null;
 
+		const data_serializer = server_data_serializer(event, event_state, options);
+		const data_serializer_json =
+			state.prerendering && should_prerender_data
+				? server_data_serializer_json(event, event_state, options)
+				: null;
+
 		/** @type {Array<Promise<import('types').ServerDataNode | null>>} */
 		const server_promises = nodes.data.map((node, i) => {
 			if (load_error) {
@@ -164,7 +171,7 @@ export async function render_page(
 				throw load_error;
 			}
 
-			return Promise.resolve().then(async () => {
+			const promise = Promise.resolve().then(async () => {
 				try {
 					if (node === leaf_node && action_result?.type === 'error') {
 						// we wait until here to throw the error so that we can use
@@ -192,6 +199,13 @@ export async function render_page(
 					throw load_error;
 				}
 			});
+
+			promise.then((server_data) => {
+				data_serializer.serialize(i, server_data);
+				data_serializer_json?.serialize(i, server_data);
+			});
+
+			return promise;
 		});
 
 		/** @type {Array<Promise<Record<string, any> | null>>} */
@@ -287,7 +301,8 @@ export async function render_page(
 									data: null,
 									server_data: null
 								}),
-								fetched
+								fetched,
+								data_serializer: server_data_serializer(event, event_state, options)
 							});
 						}
 					}
@@ -303,14 +318,9 @@ export async function render_page(
 			}
 		}
 
-		if (state.prerendering && should_prerender_data) {
+		if (state.prerendering && data_serializer_json) {
 			// ndjson format
-			let { data, chunks } = get_data_json(
-				event,
-				event_state,
-				options,
-				branch.map((node) => node?.server_data)
-			);
+			let { data, chunks } = data_serializer_json.get_data();
 
 			if (chunks) {
 				for await (const chunk of chunks) {
@@ -339,7 +349,8 @@ export async function render_page(
 			error: null,
 			branch: ssr === false ? [] : compact(branch),
 			action_result,
-			fetched
+			fetched,
+			data_serializer
 		});
 	} catch (e) {
 		// if we end up here, it means the data loaded successfully
diff --git a/packages/kit/src/runtime/server/page/render.js b/packages/kit/src/runtime/server/page/render.js
index 141fbac33570..5b7816697256 100644
--- a/packages/kit/src/runtime/server/page/render.js
+++ b/packages/kit/src/runtime/server/page/render.js
@@ -1,22 +1,20 @@
-import * as devalue from 'devalue';
-import { readable, writable } from 'svelte/store';
-import { DEV } from 'esm-env';
 import { text } from '@sveltejs/kit';
+import { with_request_store } from '@sveltejs/kit/internal/server';
 import * as paths from '__sveltekit/paths';
+import * as devalue from 'devalue';
+import { DEV } from 'esm-env';
+import { readable, writable } from 'svelte/store';
+import { SVELTE_KIT_ASSETS } from '../../../constants.js';
 import { hash } from '../../../utils/hash.js';
-import { serialize_data } from './serialize_data.js';
 import { s } from '../../../utils/misc.js';
-import { Csp } from './csp.js';
-import { uneval_action_response } from './actions.js';
-import { clarify_devalue_error, handle_error_and_jsonify, serialize_uses } from '../utils.js';
-import { public_env } from '../../shared-server.js';
-import { create_async_iterator } from '../../../utils/streaming.js';
-import { SVELTE_KIT_ASSETS } from '../../../constants.js';
 import { SCHEME } from '../../../utils/url.js';
-import { create_server_routing_response, generate_route_object } from './server_routing.js';
 import { add_resolution_suffix } from '../../pathname.js';
-import { with_request_store } from '@sveltejs/kit/internal/server';
+import { public_env } from '../../shared-server.js';
 import { text_encoder } from '../../utils.js';
+import { uneval_action_response } from './actions.js';
+import { Csp } from './csp.js';
+import { serialize_data } from './serialize_data.js';
+import { create_server_routing_response, generate_route_object } from './server_routing.js';
 
 // TODO rename this function/module
 
@@ -40,6 +38,7 @@ const updated = {
  *   event_state: import('types').RequestState;
  *   resolve_opts: import('types').RequiredResolveOptions;
  *   action_result?: import('@sveltejs/kit').ActionResult;
+ *   data_serializer: import('./types.js').ServerDataSerializer
  * }} opts
  */
 export async function render_response({
@@ -54,7 +53,8 @@ export async function render_response({
 	event,
 	event_state,
 	resolve_opts,
-	action_result
+	action_result,
+	data_serializer
 }) {
 	if (state.prerendering) {
 		if (options.csp.mode === 'nonce') {
@@ -297,14 +297,7 @@ export async function render_response({
 
 	const global = __SVELTEKIT_DEV__ ? '__sveltekit_dev' : `__sveltekit_${options.version_hash}`;
 
-	const { data, chunks } = get_data(
-		event,
-		event_state,
-		options,
-		branch.map((b) => b.server_data),
-		csp,
-		global
-	);
+	const { data, chunks } = data_serializer.get_data(csp, global);
 
 	if (page_config.ssr && page_config.csr) {
 		body += `\n\t\t\t${fetched
@@ -644,95 +637,3 @@ export async function render_response({
 				}
 			);
 }
-
-/**
- * If the serialized data contains promises, `chunks` will be an
- * async iterable containing their resolutions
- * @param {import('@sveltejs/kit').RequestEvent} event
- * @param {import('types').RequestState} event_state
- * @param {import('types').SSROptions} options
- * @param {Array<import('types').ServerDataNode | null>} nodes
- * @param {import('./csp.js').Csp} csp
- * @param {string} global
- * @returns {{ data: string, chunks: AsyncIterable<string> | null }}
- */
-function get_data(event, event_state, options, nodes, csp, global) {
-	let promise_id = 1;
-	let count = 0;
-
-	const { iterator, push, done } = create_async_iterator();
-
-	/** @param {any} thing */
-	function replacer(thing) {
-		if (typeof thing?.then === 'function') {
-			const id = promise_id++;
-			count += 1;
-
-			thing
-				.then(/** @param {any} data */ (data) => ({ data }))
-				.catch(
-					/** @param {any} error */ async (error) => ({
-						error: await handle_error_and_jsonify(event, event_state, options, error)
-					})
-				)
-				.then(
-					/**
-					 * @param {{data: any; error: any}} result
-					 */
-					async ({ data, error }) => {
-						count -= 1;
-
-						let str;
-						try {
-							str = devalue.uneval(error ? [, error] : [data], replacer);
-						} catch {
-							error = await handle_error_and_jsonify(
-								event,
-								event_state,
-								options,
-								new Error(`Failed to serialize promise while rendering ${event.route.id}`)
-							);
-							data = undefined;
-							str = devalue.uneval([, error], replacer);
-						}
-
-						const nonce = csp.script_needs_nonce ? ` nonce="${csp.nonce}"` : '';
-						push(
-							`<script${nonce}>${global}.resolve(${id}, ${str.includes('app.decode') ? `(app) => ${str}` : `() => ${str}`})</script>\n`
-						);
-						if (count === 0) done();
-					}
-				);
-
-			return `${global}.defer(${id})`;
-		} else {
-			for (const key in options.hooks.transport) {
-				const encoded = options.hooks.transport[key].encode(thing);
-				if (encoded) {
-					return `app.decode('${key}', ${devalue.uneval(encoded, replacer)})`;
-				}
-			}
-		}
-	}
-
-	try {
-		const strings = nodes.map((node) => {
-			if (!node) return 'null';
-
-			/** @type {any} */
-			const payload = { type: 'data', data: node.data, uses: serialize_uses(node) };
-			if (node.slash) payload.slash = node.slash;
-
-			return devalue.uneval(payload, replacer);
-		});
-
-		return {
-			data: `[${strings.join(',')}]`,
-			chunks: count > 0 ? iterator : null
-		};
-	} catch (e) {
-		// @ts-expect-error
-		e.path = e.path.slice(1);
-		throw new Error(clarify_devalue_error(event, /** @type {any} */ (e)));
-	}
-}
diff --git a/packages/kit/src/runtime/server/page/respond_with_error.js b/packages/kit/src/runtime/server/page/respond_with_error.js
index b1a6ae9ae606..9c276f7eafc8 100644
--- a/packages/kit/src/runtime/server/page/respond_with_error.js
+++ b/packages/kit/src/runtime/server/page/respond_with_error.js
@@ -1,9 +1,10 @@
 import { Redirect } from '@sveltejs/kit/internal';
-import { render_response } from './render.js';
-import { load_data, load_server_data } from './load_data.js';
-import { handle_error_and_jsonify, static_error_page, redirect_response } from '../utils.js';
 import { get_status } from '../../../utils/error.js';
 import { PageNodes } from '../../../utils/page_nodes.js';
+import { handle_error_and_jsonify, redirect_response, static_error_page } from '../utils.js';
+import { server_data_serializer } from './data_serializer.js';
+import { load_data, load_server_data } from './load_data.js';
+import { render_response } from './render.js';
 
 /**
  * @typedef {import('./types.js').Loaded} Loaded
@@ -45,6 +46,7 @@ export async function respond_with_error({
 		const nodes = new PageNodes([default_layout]);
 		const ssr = nodes.ssr();
 		const csr = nodes.csr();
+		const data_serializer = server_data_serializer(event, event_state, options);
 
 		if (ssr) {
 			state.error = true;
@@ -59,6 +61,7 @@ export async function respond_with_error({
 			});
 
 			const server_data = await server_data_promise;
+			data_serializer.serialize(0, server_data);
 
 			const data = await load_data({
 				event,
@@ -101,7 +104,8 @@ export async function respond_with_error({
 			fetched,
 			event,
 			event_state,
-			resolve_opts
+			resolve_opts,
+			data_serializer
 		});
 	} catch (e) {
 		// Edge case: If route is a 404 and the user redirects to somewhere from the root layout,
diff --git a/packages/kit/src/runtime/server/page/types.d.ts b/packages/kit/src/runtime/server/page/types.d.ts
index 300e05fefbe9..032333479d1f 100644
--- a/packages/kit/src/runtime/server/page/types.d.ts
+++ b/packages/kit/src/runtime/server/page/types.d.ts
@@ -1,5 +1,12 @@
 import { CookieSerializeOptions } from 'cookie';
-import { SSRNode, CspDirectives, ServerDataNode } from 'types';
+import {
+	CspDirectives,
+	ServerDataNode,
+	SSRNode,
+	type ServerDataSkippedNode,
+	type ServerErrorNode
+} from 'types';
+import type { Csp } from './csp.js';
 
 export interface Fetched {
 	url: string;
@@ -34,3 +41,16 @@ export interface Cookie {
 	value: string;
 	options: CookieSerializeOptions & { path: string };
 }
+
+export type ServerDataSerializer = {
+	serialize(i: number, node: ServerDataNode | null): void;
+	get_data(csp: Csp, global: string): { data: string; chunks: AsyncIterable<string> | null };
+};
+
+export type ServerDataSerializerJson = {
+	serialize(
+		i: number,
+		node: ServerDataSkippedNode | ServerDataNode | ServerErrorNode | null | undefined
+	): void;
+	get_data(): { data: string; chunks: AsyncIterable<string> | null };
+};
diff --git a/packages/kit/src/runtime/server/respond.js b/packages/kit/src/runtime/server/respond.js
index fe2ed1c6f86a..7590de924acc 100644
--- a/packages/kit/src/runtime/server/respond.js
+++ b/packages/kit/src/runtime/server/respond.js
@@ -1,32 +1,14 @@
 /** @import { RequestState } from 'types' */
-import { DEV } from 'esm-env';
 import { json, text } from '@sveltejs/kit';
 import { Redirect, SvelteKitError } from '@sveltejs/kit/internal';
 import { merge_tracing, with_request_store } from '@sveltejs/kit/internal/server';
-import { base, app_dir } from '__sveltekit/paths';
-import { is_endpoint_request, render_endpoint } from './endpoint.js';
-import { render_page } from './page/index.js';
-import { render_response } from './page/render.js';
-import { respond_with_error } from './page/respond_with_error.js';
+import { app_dir, base } from '__sveltekit/paths';
+import { DEV } from 'esm-env';
+import { validate_server_exports } from '../../utils/exports.js';
 import { is_form_content_type } from '../../utils/http.js';
-import {
-	handle_fatal_error,
-	has_prerendered_path,
-	method_not_allowed,
-	redirect_response
-} from './utils.js';
-import { decode_pathname, decode_params, disable_search, normalize_path } from '../../utils/url.js';
-import { exec } from '../../utils/routing.js';
-import { redirect_json_response, render_data } from './data/index.js';
-import { add_cookies_to_headers, get_cookies } from './cookie.js';
-import { create_fetch } from './fetch.js';
 import { PageNodes } from '../../utils/page_nodes.js';
-import { validate_server_exports } from '../../utils/exports.js';
-import { action_json_redirect, is_action_json_request } from './page/actions.js';
-import { INVALIDATED_PARAM, TRAILING_SLASH_PARAM } from '../shared.js';
-import { get_public_env } from './env_module.js';
-import { resolve_route } from './page/server_routing.js';
-import { validateHeaders } from './validate-headers.js';
+import { exec } from '../../utils/routing.js';
+import { decode_params, decode_pathname, disable_search, normalize_path } from '../../utils/url.js';
 import {
 	add_data_suffix,
 	add_resolution_suffix,
@@ -35,9 +17,28 @@ import {
 	strip_data_suffix,
 	strip_resolution_suffix
 } from '../pathname.js';
-import { get_remote_id, handle_remote_call } from './remote.js';
-import { record_span } from '../telemetry/record_span.js';
+import { INVALIDATED_PARAM, TRAILING_SLASH_PARAM } from '../shared.js';
 import { otel } from '../telemetry/otel.js';
+import { record_span } from '../telemetry/record_span.js';
+import { add_cookies_to_headers, get_cookies } from './cookie.js';
+import { redirect_json_response, render_data } from './data/index.js';
+import { is_endpoint_request, render_endpoint } from './endpoint.js';
+import { get_public_env } from './env_module.js';
+import { create_fetch } from './fetch.js';
+import { action_json_redirect, is_action_json_request } from './page/actions.js';
+import { server_data_serializer } from './page/data_serializer.js';
+import { render_page } from './page/index.js';
+import { render_response } from './page/render.js';
+import { respond_with_error } from './page/respond_with_error.js';
+import { resolve_route } from './page/server_routing.js';
+import { get_remote_id, handle_remote_call } from './remote.js';
+import {
+	handle_fatal_error,
+	has_prerendered_path,
+	method_not_allowed,
+	redirect_response
+} from './utils.js';
+import { validateHeaders } from './validate-headers.js';
 
 /* global __SVELTEKIT_ADAPTER_NAME__ */
 /* global __SVELTEKIT_DEV__ */
@@ -541,7 +542,8 @@ export async function internal_respond(request, options, manifest, state) {
 					error: null,
 					branch: [],
 					fetched: [],
-					resolve_opts
+					resolve_opts,
+					data_serializer: server_data_serializer(event, event_state, options)
 				});
 			}
 

From 49eb7b14cfc66ae288658fc717387b6dc8f5daa1 Mon Sep 17 00:00:00 2001
From: Patrick <Patrick@ShowYou.us>
Date: Sat, 23 Aug 2025 00:35:38 +0200
Subject: [PATCH 04/25] Satisfy linter

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

diff --git a/packages/kit/src/runtime/server/page/index.js b/packages/kit/src/runtime/server/page/index.js
index 202b94c808ea..2456636ccdb6 100644
--- a/packages/kit/src/runtime/server/page/index.js
+++ b/packages/kit/src/runtime/server/page/index.js
@@ -200,7 +200,7 @@ export async function render_page(
 				}
 			});
 
-			promise.then((server_data) => {
+			void promise.then((server_data) => {
 				data_serializer.serialize(i, server_data);
 				data_serializer_json?.serialize(i, server_data);
 			});

From 7ac181c565a2833b2c4892fa36502620a5ab6be1 Mon Sep 17 00:00:00 2001
From: Patrick <Patrick@ShowYou.us>
Date: Sat, 23 Aug 2025 15:26:41 +0200
Subject: [PATCH 05/25] rethrow serialization error after load promises are
 resolved

---
 packages/kit/src/runtime/server/page/index.js | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/packages/kit/src/runtime/server/page/index.js b/packages/kit/src/runtime/server/page/index.js
index 2456636ccdb6..76d41ff26ca3 100644
--- a/packages/kit/src/runtime/server/page/index.js
+++ b/packages/kit/src/runtime/server/page/index.js
@@ -164,6 +164,9 @@ export async function render_page(
 				? server_data_serializer_json(event, event_state, options)
 				: null;
 
+		/** @type {Error | null} */
+		let serialization_error;
+
 		/** @type {Array<Promise<import('types').ServerDataNode | null>>} */
 		const server_promises = nodes.data.map((node, i) => {
 			if (load_error) {
@@ -201,8 +204,13 @@ export async function render_page(
 			});
 
 			void promise.then((server_data) => {
-				data_serializer.serialize(i, server_data);
-				data_serializer_json?.serialize(i, server_data);
+				if (serialization_error) return;
+				try {
+					data_serializer.serialize(i, server_data);
+					data_serializer_json?.serialize(i, server_data);
+				} catch (e) {
+					serialization_error = /** @type {Error} */ (e);
+				}
 			});
 
 			return promise;
@@ -239,7 +247,7 @@ export async function render_page(
 
 		// if we don't do this, rejections will be unhandled
 		for (const p of server_promises) p.catch(() => {});
-		for (const p of load_promises) p.catch(() => {});
+		for (const p of load_promises) p.catch(() => { });
 
 		for (let i = 0; i < nodes.data.length; i += 1) {
 			const node = nodes.data[i];
@@ -249,6 +257,9 @@ export async function render_page(
 					const server_data = await server_promises[i];
 					const data = await load_promises[i];
 
+					// @ts-ignore ts(2454) it is not used before being assigned
+					if (serialization_error) throw serialization_error;
+
 					branch.push({ node, server_data, data });
 				} catch (e) {
 					const err = normalize_error(e);

From 7be9a61c190b208bba8162b6a9c75fe7739f53c4 Mon Sep 17 00:00:00 2001
From: Patrick <Patrick@ShowYou.us>
Date: Sat, 23 Aug 2025 15:30:30 +0200
Subject: [PATCH 06/25] format

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

diff --git a/packages/kit/src/runtime/server/page/index.js b/packages/kit/src/runtime/server/page/index.js
index 76d41ff26ca3..c89b1b910971 100644
--- a/packages/kit/src/runtime/server/page/index.js
+++ b/packages/kit/src/runtime/server/page/index.js
@@ -247,7 +247,7 @@ export async function render_page(
 
 		// if we don't do this, rejections will be unhandled
 		for (const p of server_promises) p.catch(() => {});
-		for (const p of load_promises) p.catch(() => { });
+		for (const p of load_promises) p.catch(() => {});
 
 		for (let i = 0; i < nodes.data.length; i += 1) {
 			const node = nodes.data[i];

From b3f227ccd275edc9906291a096c4d5436558436a Mon Sep 17 00:00:00 2001
From: Patrick <Patrick@ShowYou.us>
Date: Sat, 23 Aug 2025 15:51:24 +0200
Subject: [PATCH 07/25] add changeset

---
 .changeset/blue-deer-relax.md | 5 +++++
 1 file changed, 5 insertions(+)
 create mode 100644 .changeset/blue-deer-relax.md

diff --git a/.changeset/blue-deer-relax.md b/.changeset/blue-deer-relax.md
new file mode 100644
index 000000000000..9b7c9e6bcf6a
--- /dev/null
+++ b/.changeset/blue-deer-relax.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: serialize server `load` data before passing to universal `load`, to handle mutations and promises

From 4975e7a1cd310030cae94fbced2382ba5e253947 Mon Sep 17 00:00:00 2001
From: Patrick <Patrick@ShowYou.us>
Date: Sat, 23 Aug 2025 20:18:52 +0200
Subject: [PATCH 08/25] get rid of the global placeholder

---
 .../runtime/server/page/data_serializer.js    | 28 ++++++++++---------
 .../kit/src/runtime/server/page/render.js     |  6 ++--
 .../kit/src/runtime/server/page/types.d.ts    |  2 +-
 packages/kit/src/runtime/server/utils.js      |  7 +++++
 4 files changed, 26 insertions(+), 17 deletions(-)

diff --git a/packages/kit/src/runtime/server/page/data_serializer.js b/packages/kit/src/runtime/server/page/data_serializer.js
index 663726587402..703927d535ed 100644
--- a/packages/kit/src/runtime/server/page/data_serializer.js
+++ b/packages/kit/src/runtime/server/page/data_serializer.js
@@ -1,6 +1,11 @@
 import * as devalue from 'devalue';
 import { create_async_iterator } from '../../../utils/streaming.js';
-import { clarify_devalue_error, handle_error_and_jsonify, serialize_uses } from '../utils.js';
+import {
+	clarify_devalue_error,
+	get_global_name,
+	handle_error_and_jsonify,
+	serialize_uses
+} from '../utils.js';
 
 /**
  * If the serialized data contains promises, `chunks` will be an
@@ -15,13 +20,11 @@ export function server_data_serializer(event, event_state, options) {
 	let count = 0;
 
 	const { iterator, push, done } = create_async_iterator();
-	const global_placeholder = `__GLOBAL__${Math.random().toString(36).slice(2)}__`;
+	const global = get_global_name(options);
 
-	/** @type {(info: { global: string; nonce: string; }) => void} */
-	let set_info;
-	const info = /** @type {Promise<{ global: string; nonce: string }>} */ new Promise(
-		(r) => (set_info = r)
-	);
+	/** @type {(nonce: string) => void} */
+	let set_nonce;
+	const nonce = /** @type {Promise<string>} */ new Promise((r) => (set_nonce = r));
 
 	/** @param {any} thing */
 	function replacer(thing) {
@@ -57,15 +60,14 @@ export function server_data_serializer(event, event_state, options) {
 							str = devalue.uneval([, error], replacer);
 						}
 
-						const { nonce, global } = await info;
 						push(
-							`<script${nonce}>${global}.resolve(${id}, ${str.includes('app.decode') ? `(app) => ${str}` : `() => ${str}`})</script>\n`
+							`<script${await nonce}>${global}.resolve(${id}, ${str.includes('app.decode') ? `(app) => ${str}` : `() => ${str}`})</script>\n`
 						);
 						if (count === 0) done();
 					}
 				);
 
-			return `${global_placeholder}.defer(${id})`;
+			return `${global}.defer(${id})`;
 		} else {
 			for (const key in options.hooks.transport) {
 				const encoded = options.hooks.transport[key].encode(thing);
@@ -98,10 +100,10 @@ export function server_data_serializer(event, event_state, options) {
 			}
 		},
 
-		get_data(csp, global) {
-			set_info({ global, nonce: csp.script_needs_nonce ? ` nonce="${csp.nonce}"` : '' });
+		get_data(csp) {
+			set_nonce(csp.script_needs_nonce ? ` nonce="${csp.nonce}"` : '');
 			return {
-				data: `[${strings.join(',').replaceAll(global_placeholder, global)}]`,
+				data: `[${strings.join(',')}]`,
 				chunks: count > 0 ? iterator : null
 			};
 		}
diff --git a/packages/kit/src/runtime/server/page/render.js b/packages/kit/src/runtime/server/page/render.js
index 5b7816697256..6c36b7bd18e1 100644
--- a/packages/kit/src/runtime/server/page/render.js
+++ b/packages/kit/src/runtime/server/page/render.js
@@ -11,6 +11,7 @@ import { SCHEME } from '../../../utils/url.js';
 import { add_resolution_suffix } from '../../pathname.js';
 import { public_env } from '../../shared-server.js';
 import { text_encoder } from '../../utils.js';
+import { get_global_name } from '../utils.js';
 import { uneval_action_response } from './actions.js';
 import { Csp } from './csp.js';
 import { serialize_data } from './serialize_data.js';
@@ -295,9 +296,8 @@ export async function render_response({
 		}
 	}
 
-	const global = __SVELTEKIT_DEV__ ? '__sveltekit_dev' : `__sveltekit_${options.version_hash}`;
-
-	const { data, chunks } = data_serializer.get_data(csp, global);
+	const global = get_global_name(options);
+	const { data, chunks } = data_serializer.get_data(csp);
 
 	if (page_config.ssr && page_config.csr) {
 		body += `\n\t\t\t${fetched
diff --git a/packages/kit/src/runtime/server/page/types.d.ts b/packages/kit/src/runtime/server/page/types.d.ts
index 032333479d1f..25fedee052bd 100644
--- a/packages/kit/src/runtime/server/page/types.d.ts
+++ b/packages/kit/src/runtime/server/page/types.d.ts
@@ -44,7 +44,7 @@ export interface Cookie {
 
 export type ServerDataSerializer = {
 	serialize(i: number, node: ServerDataNode | null): void;
-	get_data(csp: Csp, global: string): { data: string; chunks: AsyncIterable<string> | null };
+	get_data(csp: Csp): { data: string; chunks: AsyncIterable<string> | null };
 };
 
 export type ServerDataSerializerJson = {
diff --git a/packages/kit/src/runtime/server/utils.js b/packages/kit/src/runtime/server/utils.js
index 46fe454c06d7..caf812c50789 100644
--- a/packages/kit/src/runtime/server/utils.js
+++ b/packages/kit/src/runtime/server/utils.js
@@ -44,6 +44,13 @@ export function allowed_methods(mod) {
 	return allowed;
 }
 
+/**
+ * @param {import('types').SSROptions} options
+ */
+export function get_global_name(options) {
+	return __SVELTEKIT_DEV__ ? '__sveltekit_dev' : `__sveltekit_${options.version_hash}`;
+}
+
 /**
  * Return as a response that renders the error.html
  *

From 2596c1995be524345651349ccb68790c55e28208 Mon Sep 17 00:00:00 2001
From: Patrick <Patrick@ShowYou.us>
Date: Sat, 23 Aug 2025 20:42:09 +0200
Subject: [PATCH 09/25] fix dumb mistake

---
 packages/kit/src/runtime/server/page/data_serializer.js | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/packages/kit/src/runtime/server/page/data_serializer.js b/packages/kit/src/runtime/server/page/data_serializer.js
index 703927d535ed..704eeca62ba0 100644
--- a/packages/kit/src/runtime/server/page/data_serializer.js
+++ b/packages/kit/src/runtime/server/page/data_serializer.js
@@ -189,9 +189,10 @@ export function server_data_serializer_json(event, event_state, options) {
 					return;
 				}
 
-				return `{"type":"data","data":${devalue.stringify(node.data, reducers)},"uses":${JSON.stringify(
-					serialize_uses(node)
-				)}${node.slash ? `,"slash":${JSON.stringify(node.slash)}` : ''}}`;
+				strings[i] =
+					`{"type":"data","data":${devalue.stringify(node.data, reducers)},"uses":${JSON.stringify(
+						serialize_uses(node)
+					)}${node.slash ? `,"slash":${JSON.stringify(node.slash)}` : ''}}`;
 			} catch (e) {
 				// @ts-expect-error
 				e.path = 'data' + e.path;

From bf84d665f99622e164b91a105acf8603dbca52be Mon Sep 17 00:00:00 2001
From: Patrick <Patrick@ShowYou.us>
Date: Sat, 23 Aug 2025 21:29:04 +0200
Subject: [PATCH 10/25] fix errors

---
 packages/kit/src/runtime/server/page/index.js | 21 +++++--------------
 1 file changed, 5 insertions(+), 16 deletions(-)

diff --git a/packages/kit/src/runtime/server/page/index.js b/packages/kit/src/runtime/server/page/index.js
index c89b1b910971..498588024eaf 100644
--- a/packages/kit/src/runtime/server/page/index.js
+++ b/packages/kit/src/runtime/server/page/index.js
@@ -164,9 +164,6 @@ export async function render_page(
 				? server_data_serializer_json(event, event_state, options)
 				: null;
 
-		/** @type {Error | null} */
-		let serialization_error;
-
 		/** @type {Array<Promise<import('types').ServerDataNode | null>>} */
 		const server_promises = nodes.data.map((node, i) => {
 			if (load_error) {
@@ -182,7 +179,7 @@ export async function render_page(
 						throw action_result.error;
 					}
 
-					return await load_server_data({
+					const server_data = await load_server_data({
 						event,
 						event_state,
 						state,
@@ -197,19 +194,14 @@ export async function render_page(
 							return data;
 						}
 					});
-				} catch (e) {
-					load_error = /** @type {Error} */ (e);
-					throw load_error;
-				}
-			});
 
-			void promise.then((server_data) => {
-				if (serialization_error) return;
-				try {
 					data_serializer.serialize(i, server_data);
 					data_serializer_json?.serialize(i, server_data);
+
+					return server_data;
 				} catch (e) {
-					serialization_error = /** @type {Error} */ (e);
+					load_error = /** @type {Error} */ (e);
+					throw load_error;
 				}
 			});
 
@@ -257,9 +249,6 @@ export async function render_page(
 					const server_data = await server_promises[i];
 					const data = await load_promises[i];
 
-					// @ts-ignore ts(2454) it is not used before being assigned
-					if (serialization_error) throw serialization_error;
-
 					branch.push({ node, server_data, data });
 				} catch (e) {
 					const err = normalize_error(e);

From 96b203e8fa8e5a254765541a6d3c846ef8b71076 Mon Sep 17 00:00:00 2001
From: Patrick <Patrick@ShowYou.us>
Date: Sat, 23 Aug 2025 21:33:29 +0200
Subject: [PATCH 11/25] return directly again

---
 packages/kit/src/runtime/server/page/index.js | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/packages/kit/src/runtime/server/page/index.js b/packages/kit/src/runtime/server/page/index.js
index 498588024eaf..dcbb8ff4004a 100644
--- a/packages/kit/src/runtime/server/page/index.js
+++ b/packages/kit/src/runtime/server/page/index.js
@@ -171,7 +171,7 @@ export async function render_page(
 				throw load_error;
 			}
 
-			const promise = Promise.resolve().then(async () => {
+			return Promise.resolve().then(async () => {
 				try {
 					if (node === leaf_node && action_result?.type === 'error') {
 						// we wait until here to throw the error so that we can use
@@ -204,8 +204,6 @@ export async function render_page(
 					throw load_error;
 				}
 			});
-
-			return promise;
 		});
 
 		/** @type {Array<Promise<Record<string, any> | null>>} */

From caa49044cb17478f0f81cfe205ac68b7555a0ad1 Mon Sep 17 00:00:00 2001
From: Patrick <Patrick@ShowYou.us>
Date: Sat, 23 Aug 2025 21:46:21 +0200
Subject: [PATCH 12/25] return iterator even if all promises are resolved
 already

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

diff --git a/packages/kit/src/runtime/server/page/data_serializer.js b/packages/kit/src/runtime/server/page/data_serializer.js
index 704eeca62ba0..2f9fe62ca0b7 100644
--- a/packages/kit/src/runtime/server/page/data_serializer.js
+++ b/packages/kit/src/runtime/server/page/data_serializer.js
@@ -104,7 +104,7 @@ export function server_data_serializer(event, event_state, options) {
 			set_nonce(csp.script_needs_nonce ? ` nonce="${csp.nonce}"` : '');
 			return {
 				data: `[${strings.join(',')}]`,
-				chunks: count > 0 ? iterator : null
+				chunks: promise_id > 1 ? iterator : null
 			};
 		}
 	};
@@ -203,7 +203,7 @@ export function server_data_serializer_json(event, event_state, options) {
 		get_data() {
 			return {
 				data: `{"type":"data","nodes":[${strings.join(',')}]}\n`,
-				chunks: count > 0 ? iterator : null
+				chunks: promise_id > 1 ? iterator : null
 			};
 		}
 	};

From f90dc427fdcd0df0547f4c0544490160b0558004 Mon Sep 17 00:00:00 2001
From: Patrick <Patrick@ShowYou.us>
Date: Sat, 23 Aug 2025 22:40:39 +0200
Subject: [PATCH 13/25] prevent memory leak

---
 packages/kit/src/runtime/server/page/data_serializer.js | 4 ++++
 packages/kit/src/runtime/server/page/index.js           | 3 +++
 packages/kit/src/runtime/server/page/types.d.ts         | 1 +
 3 files changed, 8 insertions(+)

diff --git a/packages/kit/src/runtime/server/page/data_serializer.js b/packages/kit/src/runtime/server/page/data_serializer.js
index 2f9fe62ca0b7..9b3a594e8d40 100644
--- a/packages/kit/src/runtime/server/page/data_serializer.js
+++ b/packages/kit/src/runtime/server/page/data_serializer.js
@@ -106,6 +106,10 @@ export function server_data_serializer(event, event_state, options) {
 				data: `[${strings.join(',')}]`,
 				chunks: promise_id > 1 ? iterator : null
 			};
+		},
+
+		discard() {
+			set_nonce('');
 		}
 	};
 }
diff --git a/packages/kit/src/runtime/server/page/index.js b/packages/kit/src/runtime/server/page/index.js
index dcbb8ff4004a..c74dd1770332 100644
--- a/packages/kit/src/runtime/server/page/index.js
+++ b/packages/kit/src/runtime/server/page/index.js
@@ -281,6 +281,9 @@ export async function render_page(
 							const layouts = compact(branch.slice(0, j + 1));
 							const nodes = new PageNodes(layouts.map((layout) => layout.node));
 
+							// prevent memory leak by resolving the `nonce` promise of the unused data_serializer
+							data_serializer.discard()
+
 							return await render_response({
 								event,
 								event_state,
diff --git a/packages/kit/src/runtime/server/page/types.d.ts b/packages/kit/src/runtime/server/page/types.d.ts
index 25fedee052bd..e75dfef3c21c 100644
--- a/packages/kit/src/runtime/server/page/types.d.ts
+++ b/packages/kit/src/runtime/server/page/types.d.ts
@@ -45,6 +45,7 @@ export interface Cookie {
 export type ServerDataSerializer = {
 	serialize(i: number, node: ServerDataNode | null): void;
 	get_data(csp: Csp): { data: string; chunks: AsyncIterable<string> | null };
+	discard(): void;
 };
 
 export type ServerDataSerializerJson = {

From f3d038474a6a8efd4811b4c9e7a603867c947208 Mon Sep 17 00:00:00 2001
From: Patrick <Patrick@ShowYou.us>
Date: Sat, 23 Aug 2025 23:25:05 +0200
Subject: [PATCH 14/25] format

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

diff --git a/packages/kit/src/runtime/server/page/index.js b/packages/kit/src/runtime/server/page/index.js
index c74dd1770332..27cd3823d002 100644
--- a/packages/kit/src/runtime/server/page/index.js
+++ b/packages/kit/src/runtime/server/page/index.js
@@ -282,7 +282,7 @@ export async function render_page(
 							const nodes = new PageNodes(layouts.map((layout) => layout.node));
 
 							// prevent memory leak by resolving the `nonce` promise of the unused data_serializer
-							data_serializer.discard()
+							data_serializer.discard();
 
 							return await render_response({
 								event,

From fe10ccb309ca42f98bb4e62f317aa58b225c21c7 Mon Sep 17 00:00:00 2001
From: Patrick <me@patrick.id>
Date: Tue, 26 Aug 2025 18:37:30 +0200
Subject: [PATCH 15/25] use `DEV` from `esm-env`

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

diff --git a/packages/kit/src/runtime/server/utils.js b/packages/kit/src/runtime/server/utils.js
index 30a17cea507b..f7c33124a57b 100644
--- a/packages/kit/src/runtime/server/utils.js
+++ b/packages/kit/src/runtime/server/utils.js
@@ -48,7 +48,7 @@ export function allowed_methods(mod) {
  * @param {import('types').SSROptions} options
  */
 export function get_global_name(options) {
-	return __SVELTEKIT_DEV__ ? '__sveltekit_dev' : `__sveltekit_${options.version_hash}`;
+	return DEV ? '__sveltekit_dev' : `__sveltekit_${options.version_hash}`;
 }
 
 /**

From 05402a5291b5da04fee40b9c718a8c66d1781b9c Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 28 Aug 2025 14:53:46 -0400
Subject: [PATCH 16/25] revert reordering

---
 packages/kit/src/runtime/server/page/index.js | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/packages/kit/src/runtime/server/page/index.js b/packages/kit/src/runtime/server/page/index.js
index 27cd3823d002..75c2f08e9e0e 100644
--- a/packages/kit/src/runtime/server/page/index.js
+++ b/packages/kit/src/runtime/server/page/index.js
@@ -1,12 +1,9 @@
 import { text } from '@sveltejs/kit';
 import { Redirect } from '@sveltejs/kit/internal';
-import { DEV } from 'esm-env';
 import { compact } from '../../../utils/array.js';
 import { get_status, normalize_error } from '../../../utils/error.js';
-import { PageNodes } from '../../../utils/page_nodes.js';
 import { add_data_suffix } from '../../pathname.js';
-import { get_remote_action, handle_remote_form_post } from '../remote.js';
-import { handle_error_and_jsonify, redirect_response, static_error_page } from '../utils.js';
+import { redirect_response, static_error_page, handle_error_and_jsonify } from '../utils.js';
 import {
 	handle_action_json_request,
 	handle_action_request,
@@ -17,6 +14,9 @@ import { server_data_serializer, server_data_serializer_json } from './data_seri
 import { load_data, load_server_data } from './load_data.js';
 import { render_response } from './render.js';
 import { respond_with_error } from './respond_with_error.js';
+import { DEV } from 'esm-env';
+import { get_remote_action, handle_remote_form_post } from '../remote.js';
+import { PageNodes } from '../../../utils/page_nodes.js';
 
 /**
  * The maximum request depth permitted before assuming we're stuck in an infinite loop

From 76282d414e66158d31001b85c874fe180e457bcb Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 28 Aug 2025 15:00:13 -0400
Subject: [PATCH 17/25] revert reordering

---
 .../kit/src/runtime/server/page/load_data.js  |  2 +-
 .../kit/src/runtime/server/page/render.js     | 20 +++++++++----------
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/packages/kit/src/runtime/server/page/load_data.js b/packages/kit/src/runtime/server/page/load_data.js
index 0079cbf44d2b..520d6ff5bb85 100644
--- a/packages/kit/src/runtime/server/page/load_data.js
+++ b/packages/kit/src/runtime/server/page/load_data.js
@@ -1,7 +1,7 @@
-import { merge_tracing, with_request_store } from '@sveltejs/kit/internal/server';
 import { DEV } from 'esm-env';
 import { disable_search, make_trackable } from '../../../utils/url.js';
 import { validate_depends, validate_load_response } from '../../shared.js';
+import { with_request_store, merge_tracing } from '@sveltejs/kit/internal/server';
 import { record_span } from '../../telemetry/record_span.js';
 import { base64_encode, text_decoder } from '../../utils.js';
 import { NULL_BODY_STATUS } from '../constants.js';
diff --git a/packages/kit/src/runtime/server/page/render.js b/packages/kit/src/runtime/server/page/render.js
index 2702be1ccd31..2ad4908508d0 100644
--- a/packages/kit/src/runtime/server/page/render.js
+++ b/packages/kit/src/runtime/server/page/render.js
@@ -1,21 +1,21 @@
-import { text } from '@sveltejs/kit';
-import { with_request_store } from '@sveltejs/kit/internal/server';
-import * as paths from '__sveltekit/paths';
 import * as devalue from 'devalue';
-import { DEV } from 'esm-env';
 import { readable, writable } from 'svelte/store';
-import { SVELTE_KIT_ASSETS } from '../../../constants.js';
+import { DEV } from 'esm-env';
+import { text } from '@sveltejs/kit';
+import * as paths from '__sveltekit/paths';
 import { hash } from '../../../utils/hash.js';
+import { serialize_data } from './serialize_data.js';
 import { s } from '../../../utils/misc.js';
+import { Csp } from './csp.js';
+import { uneval_action_response } from './actions.js';
+import { public_env } from '../../shared-server.js';
+import { SVELTE_KIT_ASSETS } from '../../../constants.js';
 import { SCHEME } from '../../../utils/url.js';
+import { create_server_routing_response, generate_route_object } from './server_routing.js';
 import { add_resolution_suffix } from '../../pathname.js';
-import { public_env } from '../../shared-server.js';
+import { with_request_store } from '@sveltejs/kit/internal/server';
 import { text_encoder } from '../../utils.js';
 import { get_global_name } from '../utils.js';
-import { uneval_action_response } from './actions.js';
-import { Csp } from './csp.js';
-import { serialize_data } from './serialize_data.js';
-import { create_server_routing_response, generate_route_object } from './server_routing.js';
 
 // TODO rename this function/module
 

From 4d3994c3285b9a24b1d9e5c84114f3ff2eeb5f6b Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 28 Aug 2025 15:01:48 -0400
Subject: [PATCH 18/25] revert reordering

---
 packages/kit/src/runtime/server/page/respond_with_error.js | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/kit/src/runtime/server/page/respond_with_error.js b/packages/kit/src/runtime/server/page/respond_with_error.js
index 9c276f7eafc8..b1f185745519 100644
--- a/packages/kit/src/runtime/server/page/respond_with_error.js
+++ b/packages/kit/src/runtime/server/page/respond_with_error.js
@@ -1,10 +1,10 @@
 import { Redirect } from '@sveltejs/kit/internal';
+import { render_response } from './render.js';
+import { load_data, load_server_data } from './load_data.js';
+import { handle_error_and_jsonify, redirect_response, static_error_page } from '../utils.js';
 import { get_status } from '../../../utils/error.js';
 import { PageNodes } from '../../../utils/page_nodes.js';
-import { handle_error_and_jsonify, redirect_response, static_error_page } from '../utils.js';
 import { server_data_serializer } from './data_serializer.js';
-import { load_data, load_server_data } from './load_data.js';
-import { render_response } from './render.js';
 
 /**
  * @typedef {import('./types.js').Loaded} Loaded

From 1ad3db4b3eb90fb84ddd738ac7847f04476fb03f Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 28 Aug 2025 15:16:30 -0400
Subject: [PATCH 19/25] revert reordering

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

diff --git a/packages/kit/src/runtime/server/page/respond_with_error.js b/packages/kit/src/runtime/server/page/respond_with_error.js
index b1f185745519..58b881f32bf5 100644
--- a/packages/kit/src/runtime/server/page/respond_with_error.js
+++ b/packages/kit/src/runtime/server/page/respond_with_error.js
@@ -1,7 +1,7 @@
 import { Redirect } from '@sveltejs/kit/internal';
 import { render_response } from './render.js';
 import { load_data, load_server_data } from './load_data.js';
-import { handle_error_and_jsonify, redirect_response, static_error_page } from '../utils.js';
+import { handle_error_and_jsonify, static_error_page, redirect_response } from '../utils.js';
 import { get_status } from '../../../utils/error.js';
 import { PageNodes } from '../../../utils/page_nodes.js';
 import { server_data_serializer } from './data_serializer.js';

From a1e91ed635540652a3540755aa18c9c95382cff5 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 28 Aug 2025 15:18:03 -0400
Subject: [PATCH 20/25] remove type, everything is a type in a .d.ts file

---
 packages/kit/src/runtime/server/page/types.d.ts | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/kit/src/runtime/server/page/types.d.ts b/packages/kit/src/runtime/server/page/types.d.ts
index e75dfef3c21c..89de1d756922 100644
--- a/packages/kit/src/runtime/server/page/types.d.ts
+++ b/packages/kit/src/runtime/server/page/types.d.ts
@@ -3,10 +3,10 @@ import {
 	CspDirectives,
 	ServerDataNode,
 	SSRNode,
-	type ServerDataSkippedNode,
-	type ServerErrorNode
+	ServerDataSkippedNode,
+	ServerErrorNode
 } from 'types';
-import type { Csp } from './csp.js';
+import { Csp } from './csp.js';
 
 export interface Fetched {
 	url: string;

From b86768619c3a1529d0c609931707a467abbe17a4 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 28 Aug 2025 15:22:57 -0400
Subject: [PATCH 21/25] revert reordering

---
 packages/kit/src/runtime/server/data/index.js | 10 ++--
 packages/kit/src/runtime/server/respond.js    | 50 +++++++++----------
 2 files changed, 30 insertions(+), 30 deletions(-)

diff --git a/packages/kit/src/runtime/server/data/index.js b/packages/kit/src/runtime/server/data/index.js
index b5aa34e3f5da..a16d72134c1f 100644
--- a/packages/kit/src/runtime/server/data/index.js
+++ b/packages/kit/src/runtime/server/data/index.js
@@ -1,14 +1,14 @@
 import { text } from '@sveltejs/kit';
-import { HttpError, Redirect, SvelteKitError } from '@sveltejs/kit/internal';
-import * as devalue from 'devalue';
+import { HttpError, SvelteKitError, Redirect } from '@sveltejs/kit/internal';
 import { normalize_error } from '../../../utils/error.js';
 import { once } from '../../../utils/functions.js';
-import { create_async_iterator } from '../../../utils/streaming.js';
-import { normalize_path } from '../../../utils/url.js';
-import { text_encoder } from '../../utils.js';
 import { server_data_serializer_json } from '../page/data_serializer.js';
 import { load_server_data } from '../page/load_data.js';
 import { clarify_devalue_error, handle_error_and_jsonify, serialize_uses } from '../utils.js';
+import { normalize_path } from '../../../utils/url.js';
+import * as devalue from 'devalue';
+import { create_async_iterator } from '../../../utils/streaming.js';
+import { text_encoder } from '../../utils.js';
 
 /**
  * @param {import('@sveltejs/kit').RequestEvent} event
diff --git a/packages/kit/src/runtime/server/respond.js b/packages/kit/src/runtime/server/respond.js
index cf1512af5515..2e97adaaf441 100644
--- a/packages/kit/src/runtime/server/respond.js
+++ b/packages/kit/src/runtime/server/respond.js
@@ -1,14 +1,32 @@
 /** @import { RequestState } from 'types' */
+import { DEV } from 'esm-env';
 import { json, text } from '@sveltejs/kit';
 import { Redirect, SvelteKitError } from '@sveltejs/kit/internal';
 import { merge_tracing, with_request_store } from '@sveltejs/kit/internal/server';
-import { app_dir, base } from '__sveltekit/paths';
-import { DEV } from 'esm-env';
-import { validate_server_exports } from '../../utils/exports.js';
+import { base, app_dir } from '__sveltekit/paths';
+import { is_endpoint_request, render_endpoint } from './endpoint.js';
+import { render_page } from './page/index.js';
+import { render_response } from './page/render.js';
+import { respond_with_error } from './page/respond_with_error.js';
 import { is_form_content_type } from '../../utils/http.js';
-import { PageNodes } from '../../utils/page_nodes.js';
+import {
+	handle_fatal_error,
+	has_prerendered_path,
+	method_not_allowed,
+	redirect_response
+} from './utils.js';
+import { decode_pathname, decode_params, disable_search, normalize_path } from '../../utils/url.js';
 import { exec } from '../../utils/routing.js';
-import { decode_params, decode_pathname, disable_search, normalize_path } from '../../utils/url.js';
+import { redirect_json_response, render_data } from './data/index.js';
+import { add_cookies_to_headers, get_cookies } from './cookie.js';
+import { create_fetch } from './fetch.js';
+import { PageNodes } from '../../utils/page_nodes.js';
+import { validate_server_exports } from '../../utils/exports.js';
+import { action_json_redirect, is_action_json_request } from './page/actions.js';
+import { INVALIDATED_PARAM, TRAILING_SLASH_PARAM } from '../shared.js';
+import { get_public_env } from './env_module.js';
+import { resolve_route } from './page/server_routing.js';
+import { validateHeaders } from './validate-headers.js';
 import {
 	add_data_suffix,
 	add_resolution_suffix,
@@ -17,28 +35,10 @@ import {
 	strip_data_suffix,
 	strip_resolution_suffix
 } from '../pathname.js';
-import { INVALIDATED_PARAM, TRAILING_SLASH_PARAM } from '../shared.js';
-import { otel } from '../telemetry/otel.js';
-import { record_span } from '../telemetry/record_span.js';
-import { add_cookies_to_headers, get_cookies } from './cookie.js';
-import { redirect_json_response, render_data } from './data/index.js';
-import { is_endpoint_request, render_endpoint } from './endpoint.js';
-import { get_public_env } from './env_module.js';
-import { create_fetch } from './fetch.js';
-import { action_json_redirect, is_action_json_request } from './page/actions.js';
 import { server_data_serializer } from './page/data_serializer.js';
-import { render_page } from './page/index.js';
-import { render_response } from './page/render.js';
-import { respond_with_error } from './page/respond_with_error.js';
-import { resolve_route } from './page/server_routing.js';
 import { get_remote_id, handle_remote_call } from './remote.js';
-import {
-	handle_fatal_error,
-	has_prerendered_path,
-	method_not_allowed,
-	redirect_response
-} from './utils.js';
-import { validateHeaders } from './validate-headers.js';
+import { record_span } from '../telemetry/record_span.js';
+import { otel } from '../telemetry/otel.js';
 
 /* global __SVELTEKIT_ADAPTER_NAME__ */
 

From 03c9a4a688eaeb80ba9ec221f9f45f9f9daece63 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 28 Aug 2025 15:56:40 -0400
Subject: [PATCH 22/25] serialize -> add_node

---
 packages/kit/src/runtime/server/data/index.js              | 2 +-
 packages/kit/src/runtime/server/page/data_serializer.js    | 4 ++--
 packages/kit/src/runtime/server/page/index.js              | 4 ++--
 packages/kit/src/runtime/server/page/respond_with_error.js | 2 +-
 packages/kit/src/runtime/server/page/types.d.ts            | 4 ++--
 5 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/packages/kit/src/runtime/server/data/index.js b/packages/kit/src/runtime/server/data/index.js
index a16d72134c1f..a57eddb8bdae 100644
--- a/packages/kit/src/runtime/server/data/index.js
+++ b/packages/kit/src/runtime/server/data/index.js
@@ -122,7 +122,7 @@ export async function render_data(
 		);
 
 		const data_serializer = server_data_serializer_json(event, event_state, options);
-		for (let i = 0; i < nodes.length; i++) data_serializer.serialize(i, nodes[i]);
+		for (let i = 0; i < nodes.length; i++) data_serializer.add_node(i, nodes[i]);
 		const { data, chunks } = data_serializer.get_data();
 
 		if (!chunks) {
diff --git a/packages/kit/src/runtime/server/page/data_serializer.js b/packages/kit/src/runtime/server/page/data_serializer.js
index 9b3a594e8d40..3d376f377df7 100644
--- a/packages/kit/src/runtime/server/page/data_serializer.js
+++ b/packages/kit/src/runtime/server/page/data_serializer.js
@@ -81,7 +81,7 @@ export function server_data_serializer(event, event_state, options) {
 	const strings = /** @type {string[]} */ ([]);
 
 	return {
-		serialize(i, node) {
+		add_node(i, node) {
 			try {
 				if (!node) {
 					strings[i] = 'null';
@@ -181,7 +181,7 @@ export function server_data_serializer_json(event, event_state, options) {
 	const strings = /** @type {string[]} */ ([]);
 
 	return {
-		serialize(i, node) {
+		add_node(i, node) {
 			try {
 				if (!node) {
 					strings[i] = 'null';
diff --git a/packages/kit/src/runtime/server/page/index.js b/packages/kit/src/runtime/server/page/index.js
index 75c2f08e9e0e..8c33dd09c479 100644
--- a/packages/kit/src/runtime/server/page/index.js
+++ b/packages/kit/src/runtime/server/page/index.js
@@ -195,8 +195,8 @@ export async function render_page(
 						}
 					});
 
-					data_serializer.serialize(i, server_data);
-					data_serializer_json?.serialize(i, server_data);
+					data_serializer.add_node(i, server_data);
+					data_serializer_json?.add_node(i, server_data);
 
 					return server_data;
 				} catch (e) {
diff --git a/packages/kit/src/runtime/server/page/respond_with_error.js b/packages/kit/src/runtime/server/page/respond_with_error.js
index 58b881f32bf5..0767e177d124 100644
--- a/packages/kit/src/runtime/server/page/respond_with_error.js
+++ b/packages/kit/src/runtime/server/page/respond_with_error.js
@@ -61,7 +61,7 @@ export async function respond_with_error({
 			});
 
 			const server_data = await server_data_promise;
-			data_serializer.serialize(0, server_data);
+			data_serializer.add_node(0, server_data);
 
 			const data = await load_data({
 				event,
diff --git a/packages/kit/src/runtime/server/page/types.d.ts b/packages/kit/src/runtime/server/page/types.d.ts
index 89de1d756922..f9e08cd2c64c 100644
--- a/packages/kit/src/runtime/server/page/types.d.ts
+++ b/packages/kit/src/runtime/server/page/types.d.ts
@@ -43,13 +43,13 @@ export interface Cookie {
 }
 
 export type ServerDataSerializer = {
-	serialize(i: number, node: ServerDataNode | null): void;
+	add_node(i: number, node: ServerDataNode | null): void;
 	get_data(csp: Csp): { data: string; chunks: AsyncIterable<string> | null };
 	discard(): void;
 };
 
 export type ServerDataSerializerJson = {
-	serialize(
+	add_node(
 		i: number,
 		node: ServerDataSkippedNode | ServerDataNode | ServerErrorNode | null | undefined
 	): void;

From 019c5734250420ddfe6e827c393fb16ed8d63c86 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 28 Aug 2025 16:25:40 -0400
Subject: [PATCH 23/25] unused

---
 packages/kit/src/runtime/server/data/index.js | 93 +------------------
 1 file changed, 1 insertion(+), 92 deletions(-)

diff --git a/packages/kit/src/runtime/server/data/index.js b/packages/kit/src/runtime/server/data/index.js
index a57eddb8bdae..83e16c3a9d12 100644
--- a/packages/kit/src/runtime/server/data/index.js
+++ b/packages/kit/src/runtime/server/data/index.js
@@ -4,10 +4,8 @@ import { normalize_error } from '../../../utils/error.js';
 import { once } from '../../../utils/functions.js';
 import { server_data_serializer_json } from '../page/data_serializer.js';
 import { load_server_data } from '../page/load_data.js';
-import { clarify_devalue_error, handle_error_and_jsonify, serialize_uses } from '../utils.js';
+import { handle_error_and_jsonify } from '../utils.js';
 import { normalize_path } from '../../../utils/url.js';
-import * as devalue from 'devalue';
-import { create_async_iterator } from '../../../utils/streaming.js';
 import { text_encoder } from '../../utils.js';
 
 /**
@@ -188,92 +186,3 @@ export function redirect_json_response(redirect) {
 		})
 	);
 }
-
-/**
- * If the serialized data contains promises, `chunks` will be an
- * async iterable containing their resolutions
- * @param {import('@sveltejs/kit').RequestEvent} event
- * @param {import('types').RequestState} event_state
- * @param {import('types').SSROptions} options
- * @param {Array<import('types').ServerDataSkippedNode | import('types').ServerDataNode | import('types').ServerErrorNode | null | undefined>} nodes
- *  @returns {{ data: string, chunks: AsyncIterable<string> | null }}
- */
-export function get_data_json(event, event_state, options, nodes) {
-	let promise_id = 1;
-	let count = 0;
-
-	const { iterator, push, done } = create_async_iterator();
-
-	const reducers = {
-		...Object.fromEntries(
-			Object.entries(options.hooks.transport).map(([key, value]) => [key, value.encode])
-		),
-		/** @param {any} thing */
-		Promise: (thing) => {
-			if (typeof thing?.then === 'function') {
-				const id = promise_id++;
-				count += 1;
-
-				/** @type {'data' | 'error'} */
-				let key = 'data';
-
-				thing
-					.catch(
-						/** @param {any} e */ async (e) => {
-							key = 'error';
-							return handle_error_and_jsonify(event, event_state, options, /** @type {any} */ (e));
-						}
-					)
-					.then(
-						/** @param {any} value */
-						async (value) => {
-							let str;
-							try {
-								str = devalue.stringify(value, reducers);
-							} catch {
-								const error = await handle_error_and_jsonify(
-									event,
-									event_state,
-									options,
-									new Error(`Failed to serialize promise while rendering ${event.route.id}`)
-								);
-
-								key = 'error';
-								str = devalue.stringify(error, reducers);
-							}
-
-							count -= 1;
-
-							push(`{"type":"chunk","id":${id},"${key}":${str}}\n`);
-							if (count === 0) done();
-						}
-					);
-
-				return id;
-			}
-		}
-	};
-
-	try {
-		const strings = nodes.map((node) => {
-			if (!node) return 'null';
-
-			if (node.type === 'error' || node.type === 'skip') {
-				return JSON.stringify(node);
-			}
-
-			return `{"type":"data","data":${devalue.stringify(node.data, reducers)},"uses":${JSON.stringify(
-				serialize_uses(node)
-			)}${node.slash ? `,"slash":${JSON.stringify(node.slash)}` : ''}}`;
-		});
-
-		return {
-			data: `{"type":"data","nodes":[${strings.join(',')}]}\n`,
-			chunks: count > 0 ? iterator : null
-		};
-	} catch (e) {
-		// @ts-expect-error
-		e.path = 'data' + e.path;
-		throw new Error(clarify_devalue_error(event, /** @type {any} */ (e)));
-	}
-}

From f0601595fc0fd880a337e6170f79995359e74df6 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 28 Aug 2025 16:39:32 -0400
Subject: [PATCH 24/25] simplify create_async_iterator

---
 .../runtime/server/page/data_serializer.js    | 90 +++++++++----------
 packages/kit/src/utils/streaming.js           | 26 +++---
 packages/kit/src/utils/streaming.spec.js      |  9 +-
 3 files changed, 62 insertions(+), 63 deletions(-)

diff --git a/packages/kit/src/runtime/server/page/data_serializer.js b/packages/kit/src/runtime/server/page/data_serializer.js
index 3d376f377df7..fa863aef6850 100644
--- a/packages/kit/src/runtime/server/page/data_serializer.js
+++ b/packages/kit/src/runtime/server/page/data_serializer.js
@@ -17,9 +17,8 @@ import {
  */
 export function server_data_serializer(event, event_state, options) {
 	let promise_id = 1;
-	let count = 0;
 
-	const { iterator, push, done } = create_async_iterator();
+	const { iterator, add } = create_async_iterator();
 	const global = get_global_name(options);
 
 	/** @type {(nonce: string) => void} */
@@ -30,9 +29,8 @@ export function server_data_serializer(event, event_state, options) {
 	function replacer(thing) {
 		if (typeof thing?.then === 'function') {
 			const id = promise_id++;
-			count += 1;
 
-			thing
+			const promise = thing
 				.then(/** @param {any} data */ (data) => ({ data }))
 				.catch(
 					/** @param {any} error */ async (error) => ({
@@ -44,8 +42,6 @@ export function server_data_serializer(event, event_state, options) {
 					 * @param {{data: any; error: any}} result
 					 */
 					async ({ data, error }) => {
-						count -= 1;
-
 						let str;
 						try {
 							str = devalue.uneval(error ? [, error] : [data], replacer);
@@ -60,13 +56,12 @@ export function server_data_serializer(event, event_state, options) {
 							str = devalue.uneval([, error], replacer);
 						}
 
-						push(
-							`<script${await nonce}>${global}.resolve(${id}, ${str.includes('app.decode') ? `(app) => ${str}` : `() => ${str}`})</script>\n`
-						);
-						if (count === 0) done();
+						return `<script${await nonce}>${global}.resolve(${id}, ${str.includes('app.decode') ? `(app) => ${str}` : `() => ${str}`})</script>\n`;
 					}
 				);
 
+			add(promise);
+
 			return `${global}.defer(${id})`;
 		} else {
 			for (const key in options.hooks.transport) {
@@ -124,9 +119,8 @@ export function server_data_serializer(event, event_state, options) {
  */
 export function server_data_serializer_json(event, event_state, options) {
 	let promise_id = 1;
-	let count = 0;
 
-	const { iterator, push, done } = create_async_iterator();
+	const { iterator, add } = create_async_iterator();
 
 	const reducers = {
 		...Object.fromEntries(
@@ -134,47 +128,47 @@ export function server_data_serializer_json(event, event_state, options) {
 		),
 		/** @param {any} thing */
 		Promise: (thing) => {
-			if (typeof thing?.then === 'function') {
-				const id = promise_id++;
-				count += 1;
+			if (typeof thing?.then !== 'function') {
+				return;
+			}
+
+			const id = promise_id++;
+
+			/** @type {'data' | 'error'} */
+			let key = 'data';
 
-				/** @type {'data' | 'error'} */
-				let key = 'data';
+			const promise = thing
+				.catch(
+					/** @param {any} e */ async (e) => {
+						key = 'error';
+						return handle_error_and_jsonify(event, event_state, options, /** @type {any} */ (e));
+					}
+				)
+				.then(
+					/** @param {any} value */
+					async (value) => {
+						let str;
+						try {
+							str = devalue.stringify(value, reducers);
+						} catch {
+							const error = await handle_error_and_jsonify(
+								event,
+								event_state,
+								options,
+								new Error(`Failed to serialize promise while rendering ${event.route.id}`)
+							);
 
-				thing
-					.catch(
-						/** @param {any} e */ async (e) => {
 							key = 'error';
-							return handle_error_and_jsonify(event, event_state, options, /** @type {any} */ (e));
+							str = devalue.stringify(error, reducers);
 						}
-					)
-					.then(
-						/** @param {any} value */
-						async (value) => {
-							let str;
-							try {
-								str = devalue.stringify(value, reducers);
-							} catch {
-								const error = await handle_error_and_jsonify(
-									event,
-									event_state,
-									options,
-									new Error(`Failed to serialize promise while rendering ${event.route.id}`)
-								);
-
-								key = 'error';
-								str = devalue.stringify(error, reducers);
-							}
-
-							count -= 1;
-
-							push(`{"type":"chunk","id":${id},"${key}":${str}}\n`);
-							if (count === 0) done();
-						}
-					);
 
-				return id;
-			}
+						return `{"type":"chunk","id":${id},"${key}":${str}}\n`;
+					}
+				);
+
+			add(promise);
+
+			return id;
 		}
 	};
 
diff --git a/packages/kit/src/utils/streaming.js b/packages/kit/src/utils/streaming.js
index cfb0d6a04f93..209afb10aba5 100644
--- a/packages/kit/src/utils/streaming.js
+++ b/packages/kit/src/utils/streaming.js
@@ -18,11 +18,12 @@ function defer() {
  * Create an async iterator and a function to push values into it
  * @returns {{
  *   iterator: AsyncIterable<any>;
- *   push: (value: any) => void;
- *   done: () => void;
+ *   add: (promise: Promise<any>) => void;
  * }}
  */
 export function create_async_iterator() {
+	let count = 0;
+
 	const deferred = [defer()];
 
 	return {
@@ -37,15 +38,20 @@ export function create_async_iterator() {
 				};
 			}
 		},
-		push: (value) => {
-			deferred[deferred.length - 1].fulfil({
-				value,
-				done: false
+		add: (promise) => {
+			count += 1;
+
+			void promise.then((value) => {
+				deferred[deferred.length - 1].fulfil({
+					value,
+					done: false
+				});
+				deferred.push(defer());
+
+				if (--count === 0) {
+					deferred[deferred.length - 1].fulfil({ done: true });
+				}
 			});
-			deferred.push(defer());
-		},
-		done: () => {
-			deferred[deferred.length - 1].fulfil({ done: true });
 		}
 	};
 }
diff --git a/packages/kit/src/utils/streaming.spec.js b/packages/kit/src/utils/streaming.spec.js
index 320fbe3e2769..b9b999df4e95 100644
--- a/packages/kit/src/utils/streaming.spec.js
+++ b/packages/kit/src/utils/streaming.spec.js
@@ -2,14 +2,13 @@ import { expect, test } from 'vitest';
 import { create_async_iterator } from './streaming.js';
 
 test('works with fast consecutive promise resolutions', async () => {
-	const iterator = create_async_iterator();
+	const { iterator, add } = create_async_iterator();
 
-	void Promise.resolve(1).then((n) => iterator.push(n));
-	void Promise.resolve(2).then((n) => iterator.push(n));
-	void Promise.resolve().then(() => iterator.done());
+	add(Promise.resolve(1));
+	add(Promise.resolve(2));
 
 	const actual = [];
-	for await (const value of iterator.iterator) {
+	for await (const value of iterator) {
 		actual.push(value);
 	}
 

From 530de8820dba8c79afd0041d2ec47138e7e8cced Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 28 Aug 2025 17:02:00 -0400
Subject: [PATCH 25/25] avoid the need for set_nonce dance

---
 .../runtime/server/page/data_serializer.js    | 26 ++++++---------
 packages/kit/src/runtime/server/page/index.js |  3 --
 .../kit/src/runtime/server/page/types.d.ts    |  1 -
 packages/kit/src/utils/streaming.js           | 32 ++++++++++++-------
 packages/kit/src/utils/streaming.spec.js      |  6 ++--
 5 files changed, 33 insertions(+), 35 deletions(-)

diff --git a/packages/kit/src/runtime/server/page/data_serializer.js b/packages/kit/src/runtime/server/page/data_serializer.js
index fa863aef6850..2f0197ae648b 100644
--- a/packages/kit/src/runtime/server/page/data_serializer.js
+++ b/packages/kit/src/runtime/server/page/data_serializer.js
@@ -18,13 +18,9 @@ import {
 export function server_data_serializer(event, event_state, options) {
 	let promise_id = 1;
 
-	const { iterator, add } = create_async_iterator();
+	const iterator = create_async_iterator();
 	const global = get_global_name(options);
 
-	/** @type {(nonce: string) => void} */
-	let set_nonce;
-	const nonce = /** @type {Promise<string>} */ new Promise((r) => (set_nonce = r));
-
 	/** @param {any} thing */
 	function replacer(thing) {
 		if (typeof thing?.then === 'function') {
@@ -56,11 +52,11 @@ export function server_data_serializer(event, event_state, options) {
 							str = devalue.uneval([, error], replacer);
 						}
 
-						return `<script${await nonce}>${global}.resolve(${id}, ${str.includes('app.decode') ? `(app) => ${str}` : `() => ${str}`})</script>\n`;
+						return `${global}.resolve(${id}, ${str.includes('app.decode') ? `(app) => ${str}` : `() => ${str}`})`;
 					}
 				);
 
-			add(promise);
+			iterator.add(promise);
 
 			return `${global}.defer(${id})`;
 		} else {
@@ -96,15 +92,13 @@ export function server_data_serializer(event, event_state, options) {
 		},
 
 		get_data(csp) {
-			set_nonce(csp.script_needs_nonce ? ` nonce="${csp.nonce}"` : '');
+			const open = `<script${csp.script_needs_nonce ? ` nonce="${csp.nonce}"` : ''}>`;
+			const close = `</script>\n`;
+
 			return {
 				data: `[${strings.join(',')}]`,
-				chunks: promise_id > 1 ? iterator : null
+				chunks: promise_id > 1 ? iterator.iterate((str) => open + str + close) : null
 			};
-		},
-
-		discard() {
-			set_nonce('');
 		}
 	};
 }
@@ -120,7 +114,7 @@ export function server_data_serializer(event, event_state, options) {
 export function server_data_serializer_json(event, event_state, options) {
 	let promise_id = 1;
 
-	const { iterator, add } = create_async_iterator();
+	const iterator = create_async_iterator();
 
 	const reducers = {
 		...Object.fromEntries(
@@ -166,7 +160,7 @@ export function server_data_serializer_json(event, event_state, options) {
 					}
 				);
 
-			add(promise);
+			iterator.add(promise);
 
 			return id;
 		}
@@ -201,7 +195,7 @@ export function server_data_serializer_json(event, event_state, options) {
 		get_data() {
 			return {
 				data: `{"type":"data","nodes":[${strings.join(',')}]}\n`,
-				chunks: promise_id > 1 ? iterator : null
+				chunks: promise_id > 1 ? iterator.iterate() : null
 			};
 		}
 	};
diff --git a/packages/kit/src/runtime/server/page/index.js b/packages/kit/src/runtime/server/page/index.js
index 8c33dd09c479..9e05ab3a4334 100644
--- a/packages/kit/src/runtime/server/page/index.js
+++ b/packages/kit/src/runtime/server/page/index.js
@@ -281,9 +281,6 @@ export async function render_page(
 							const layouts = compact(branch.slice(0, j + 1));
 							const nodes = new PageNodes(layouts.map((layout) => layout.node));
 
-							// prevent memory leak by resolving the `nonce` promise of the unused data_serializer
-							data_serializer.discard();
-
 							return await render_response({
 								event,
 								event_state,
diff --git a/packages/kit/src/runtime/server/page/types.d.ts b/packages/kit/src/runtime/server/page/types.d.ts
index f9e08cd2c64c..bfe975fb37a9 100644
--- a/packages/kit/src/runtime/server/page/types.d.ts
+++ b/packages/kit/src/runtime/server/page/types.d.ts
@@ -45,7 +45,6 @@ export interface Cookie {
 export type ServerDataSerializer = {
 	add_node(i: number, node: ServerDataNode | null): void;
 	get_data(csp: Csp): { data: string; chunks: AsyncIterable<string> | null };
-	discard(): void;
 };
 
 export type ServerDataSerializerJson = {
diff --git a/packages/kit/src/utils/streaming.js b/packages/kit/src/utils/streaming.js
index 209afb10aba5..449507ac6695 100644
--- a/packages/kit/src/utils/streaming.js
+++ b/packages/kit/src/utils/streaming.js
@@ -16,9 +16,10 @@ function defer() {
 
 /**
  * Create an async iterator and a function to push values into it
+ * @template T
  * @returns {{
- *   iterator: AsyncIterable<any>;
- *   add: (promise: Promise<any>) => void;
+ *   iterate: (transform?: (input: T) => T) => AsyncIterable<T>;
+ *   add: (promise: Promise<T>) => void;
  * }}
  */
 export function create_async_iterator() {
@@ -27,16 +28,23 @@ export function create_async_iterator() {
 	const deferred = [defer()];
 
 	return {
-		iterator: {
-			[Symbol.asyncIterator]() {
-				return {
-					next: async () => {
-						const next = await deferred[0].promise;
-						if (!next.done) deferred.shift();
-						return next;
-					}
-				};
-			}
+		iterate: (transform = (x) => x) => {
+			return {
+				[Symbol.asyncIterator]() {
+					return {
+						next: async () => {
+							const next = await deferred[0].promise;
+
+							if (!next.done) {
+								deferred.shift();
+								return { value: transform(next.value), done: false };
+							}
+
+							return next;
+						}
+					};
+				}
+			};
 		},
 		add: (promise) => {
 			count += 1;
diff --git a/packages/kit/src/utils/streaming.spec.js b/packages/kit/src/utils/streaming.spec.js
index b9b999df4e95..2a94ad178bef 100644
--- a/packages/kit/src/utils/streaming.spec.js
+++ b/packages/kit/src/utils/streaming.spec.js
@@ -2,15 +2,15 @@ import { expect, test } from 'vitest';
 import { create_async_iterator } from './streaming.js';
 
 test('works with fast consecutive promise resolutions', async () => {
-	const { iterator, add } = create_async_iterator();
+	const { iterate, add } = create_async_iterator();
 
 	add(Promise.resolve(1));
 	add(Promise.resolve(2));
 
 	const actual = [];
-	for await (const value of iterator) {
+	for await (const value of iterate((n) => n * 10)) {
 		actual.push(value);
 	}
 
-	expect(actual).toEqual([1, 2]);
+	expect(actual).toEqual([10, 20]);
 });