From e318d0105fba19fec6bf111bba441b9742a53b2b Mon Sep 17 00:00:00 2001
From: floriskn <48930050+floriskn@users.noreply.github.com>
Date: Thu, 30 Oct 2025 01:42:05 +0100
Subject: [PATCH 1/5] fix: clone page.params in Pyramid component

---
 .changeset/modern-clowns-bet.md          | 5 +++++
 packages/kit/src/core/sync/write_root.js | 6 +++---
 2 files changed, 8 insertions(+), 3 deletions(-)
 create mode 100644 .changeset/modern-clowns-bet.md

diff --git a/.changeset/modern-clowns-bet.md b/.changeset/modern-clowns-bet.md
new file mode 100644
index 000000000000..cb9a62d74042
--- /dev/null
+++ b/.changeset/modern-clowns-bet.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Cloned page.params in Pyramid component for Svelte 5+ to prevent async updates from clearing them.
diff --git a/packages/kit/src/core/sync/write_root.js b/packages/kit/src/core/sync/write_root.js
index eb9c61885c9c..90e90d08a8ab 100644
--- a/packages/kit/src/core/sync/write_root.js
+++ b/packages/kit/src/core/sync/write_root.js
@@ -25,7 +25,7 @@ export function write_root(manifest_data, output) {
 	${
 		isSvelte5Plus()
 			? `<!-- svelte-ignore binding_property_non_reactive -->
-		<Pyramid_${l} bind:this={components[${l}]} data={data_${l}} {form} params={page.params} />`
+		<Pyramid_${l} bind:this={components[${l}]} data={data_${l}} {form} params={{...page.params}} />`
 			: `<svelte:component this={constructors[${l}]} bind:this={components[${l}]} data={data_${l}} {form} params={page.params} />`
 	}`;
 
@@ -36,7 +36,7 @@ export function write_root(manifest_data, output) {
 					isSvelte5Plus()
 						? dedent`{@const Pyramid_${l} = constructors[${l}]}
 						<!-- svelte-ignore binding_property_non_reactive -->
-						<Pyramid_${l} bind:this={components[${l}]} data={data_${l}} {form} params={page.params}>
+						<Pyramid_${l} bind:this={components[${l}]} data={data_${l}} {form} params={{...page.params}}>
 							${pyramid}
 						</Pyramid_${l}>`
 						: dedent`<svelte:component this={constructors[${l}]} bind:this={components[${l}]} data={data_${l}} params={page.params}>
@@ -50,7 +50,7 @@ export function write_root(manifest_data, output) {
 						? dedent`
 					{@const Pyramid_${l} = constructors[${l}]}
 					<!-- svelte-ignore binding_property_non_reactive -->
-					<Pyramid_${l} bind:this={components[${l}]} data={data_${l}} {form} params={page.params} />
+					<Pyramid_${l} bind:this={components[${l}]} data={data_${l}} {form} params={{...page.params}} />
 					`
 						: dedent`<svelte:component this={constructors[${l}]} bind:this={components[${l}]} data={data_${l}} {form} params={page.params} />`
 				}

From 1482111456e7eaca87b46051be172cdab340ed50 Mon Sep 17 00:00:00 2001
From: floriskn <48930050+floriskn@users.noreply.github.com>
Date: Thu, 30 Oct 2025 02:19:52 +0100
Subject: [PATCH 2/5] feat: added test

---
 .../src/routes/params-prop-async/+layout.svelte      |  8 ++++++++
 .../basics/src/routes/params-prop-async/+page.svelte |  0
 .../src/routes/params-prop-async/[x]/+page.svelte    |  7 +++++++
 packages/kit/test/apps/basics/test/test.js           | 12 ++++++++++++
 4 files changed, 27 insertions(+)
 create mode 100644 packages/kit/test/apps/basics/src/routes/params-prop-async/+layout.svelte
 create mode 100644 packages/kit/test/apps/basics/src/routes/params-prop-async/+page.svelte
 create mode 100644 packages/kit/test/apps/basics/src/routes/params-prop-async/[x]/+page.svelte

diff --git a/packages/kit/test/apps/basics/src/routes/params-prop-async/+layout.svelte b/packages/kit/test/apps/basics/src/routes/params-prop-async/+layout.svelte
new file mode 100644
index 000000000000..5c10cb145399
--- /dev/null
+++ b/packages/kit/test/apps/basics/src/routes/params-prop-async/+layout.svelte
@@ -0,0 +1,8 @@
+<script>
+	let { children } = $props();
+</script>
+
+<a href="/params-prop/123">123</a>
+<a href="/params-prop/456">456</a>
+
+{@render children()}
diff --git a/packages/kit/test/apps/basics/src/routes/params-prop-async/+page.svelte b/packages/kit/test/apps/basics/src/routes/params-prop-async/+page.svelte
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/packages/kit/test/apps/basics/src/routes/params-prop-async/[x]/+page.svelte b/packages/kit/test/apps/basics/src/routes/params-prop-async/[x]/+page.svelte
new file mode 100644
index 000000000000..883648964a42
--- /dev/null
+++ b/packages/kit/test/apps/basics/src/routes/params-prop-async/[x]/+page.svelte
@@ -0,0 +1,7 @@
+<script>
+	let { params } = $props();
+
+	await Promise.resolve();
+</script>
+
+<p>x: {params.x}</p>
diff --git a/packages/kit/test/apps/basics/test/test.js b/packages/kit/test/apps/basics/test/test.js
index 2518529e27d5..28c74ec329ae 100644
--- a/packages/kit/test/apps/basics/test/test.js
+++ b/packages/kit/test/apps/basics/test/test.js
@@ -2039,6 +2039,18 @@ test.describe('params prop', () => {
 	});
 });
 
+test.describe('params prop async', () => {
+	test('params prop is passed to the page', async ({ page, clicknav }) => {
+		await page.goto('/params-prop-async');
+
+		await clicknav('[href="/params-prop-async/123"]');
+		await expect(page.locator('p')).toHaveText('x: 123');
+
+		await clicknav('[href="/params-prop-async/456"]');
+		await expect(page.locator('p')).toHaveText('x: 456');
+	});
+});
+
 test.describe('service worker option', () => {
 	test('pass the options to the service worker', async ({ page }) => {
 		await page.goto('/');

From 9dfb03ebfa0f8fe79e748558f915dfdbe3b1b3bf Mon Sep 17 00:00:00 2001
From: floriskn <48930050+floriskn@users.noreply.github.com>
Date: Thu, 30 Oct 2025 02:47:32 +0100
Subject: [PATCH 3/5] fix: fixed test

---
 .../apps/basics/src/routes/params-prop-async/+layout.svelte   | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/kit/test/apps/basics/src/routes/params-prop-async/+layout.svelte b/packages/kit/test/apps/basics/src/routes/params-prop-async/+layout.svelte
index 5c10cb145399..3ea59f15a9b2 100644
--- a/packages/kit/test/apps/basics/src/routes/params-prop-async/+layout.svelte
+++ b/packages/kit/test/apps/basics/src/routes/params-prop-async/+layout.svelte
@@ -2,7 +2,7 @@
 	let { children } = $props();
 </script>
 
-<a href="/params-prop/123">123</a>
-<a href="/params-prop/456">456</a>
+<a href="/params-prop-async/123" data-sveltekit-preload-data="hover">123</a>
+<a href="/params-prop-async/456" data-sveltekit-preload-data="hover">456</a>
 
 {@render children()}

From 4780deed1ab50cebf701a1f0fb47026d1283b527 Mon Sep 17 00:00:00 2001
From: floriskn <48930050+floriskn@users.noreply.github.com>
Date: Thu, 30 Oct 2025 02:48:42 +0100
Subject: [PATCH 4/5] fix: fixed test

---
 packages/kit/test/apps/basics/test/test.js | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/packages/kit/test/apps/basics/test/test.js b/packages/kit/test/apps/basics/test/test.js
index 28c74ec329ae..a08fa3625b4d 100644
--- a/packages/kit/test/apps/basics/test/test.js
+++ b/packages/kit/test/apps/basics/test/test.js
@@ -2043,9 +2043,13 @@ test.describe('params prop async', () => {
 	test('params prop is passed to the page', async ({ page, clicknav }) => {
 		await page.goto('/params-prop-async');
 
+		await page.hover('[href="/params-prop-async/123"]');
+		await page.waitForTimeout(100);
 		await clicknav('[href="/params-prop-async/123"]');
 		await expect(page.locator('p')).toHaveText('x: 123');
 
+		await page.hover('[href="/params-prop-async/456"]');
+		await page.waitForTimeout(100);
 		await clicknav('[href="/params-prop-async/456"]');
 		await expect(page.locator('p')).toHaveText('x: 456');
 	});

From 7669fe4240e8c35ef86472e101a46c53eb9bc83e Mon Sep 17 00:00:00 2001
From: floriskn <48930050+floriskn@users.noreply.github.com>
Date: Thu, 30 Oct 2025 03:03:32 +0100
Subject: [PATCH 5/5] fix: fixed test

---
 packages/kit/test/apps/basics/test/test.js | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/packages/kit/test/apps/basics/test/test.js b/packages/kit/test/apps/basics/test/test.js
index a08fa3625b4d..dea657ca4865 100644
--- a/packages/kit/test/apps/basics/test/test.js
+++ b/packages/kit/test/apps/basics/test/test.js
@@ -2040,17 +2040,22 @@ test.describe('params prop', () => {
 });
 
 test.describe('params prop async', () => {
-	test('params prop is passed to the page', async ({ page, clicknav }) => {
+	test('params prop is passed to the page and persists after async updates', async ({
+		page,
+		clicknav
+	}) => {
 		await page.goto('/params-prop-async');
 
 		await page.hover('[href="/params-prop-async/123"]');
 		await page.waitForTimeout(100);
 		await clicknav('[href="/params-prop-async/123"]');
+		await page.waitForTimeout(100);
 		await expect(page.locator('p')).toHaveText('x: 123');
 
 		await page.hover('[href="/params-prop-async/456"]');
 		await page.waitForTimeout(100);
 		await clicknav('[href="/params-prop-async/456"]');
+		await page.waitForTimeout(100);
 		await expect(page.locator('p')).toHaveText('x: 456');
 	});
 });