From df6f5f367b3184b900bae88d738c97bbe747eb48 Mon Sep 17 00:00:00 2001
From: Ondrej Ulehla <ondrejulehla@gmail.com>
Date: Thu, 23 Jul 2026 17:36:09 +0200
Subject: [PATCH] fix: don't cache preloaded redirect results

The preload cache stored redirect results from load and replayed them on
navigation without re-running load. Since the cache is only cleared once
a navigation commits and a redirect never commits one, a preloaded
redirect into a mutually-redirecting pair looped until the 20-redirect
limit, even when a fresh evaluation would resolve.

Discard the cache when the preload resolves to a redirect, matching the
existing behavior for errors: both are transient results that must be
re-evaluated at navigation time.

Fixes #16484
---
 .changeset/preload-redirect-cache.md           |  5 +++++
 packages/kit/src/runtime/client/client.js      |  7 +++++--
 .../redirect-gate/dashboard/+page.server.js    |  9 +++++++++
 .../redirect-gate/dashboard/+page.svelte       |  1 +
 .../redirect-gate/select/+page.server.js       |  7 +++++++
 .../redirect-gate/start/+page.server.js        |  6 ++++++
 .../redirect-gate/start/+page.svelte           |  5 +++++
 .../preload-data/redirect-gate/state.js        |  1 +
 .../kit/test/apps/basics/test/client.test.js   | 18 ++++++++++++++++++
 9 files changed, 57 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/preload-redirect-cache.md
 create mode 100644 packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/dashboard/+page.server.js
 create mode 100644 packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/dashboard/+page.svelte
 create mode 100644 packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/select/+page.server.js
 create mode 100644 packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/start/+page.server.js
 create mode 100644 packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/start/+page.svelte
 create mode 100644 packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/state.js

diff --git a/.changeset/preload-redirect-cache.md b/.changeset/preload-redirect-cache.md
new file mode 100644
index 000000000000..fe08ba924b67
--- /dev/null
+++ b/.changeset/preload-redirect-cache.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: don't cache preloaded redirect results, so navigation re-runs `load` instead of replaying a stale redirect
diff --git a/packages/kit/src/runtime/client/client.js b/packages/kit/src/runtime/client/client.js
index a0b858ba0ddb..20685fe0c3a7 100644
--- a/packages/kit/src/runtime/client/client.js
+++ b/packages/kit/src/runtime/client/client.js
@@ -622,8 +622,11 @@ async function _preload_data(intent) {
 			token: preload,
 			promise: load_route({ ...intent, preload }).then((result) => {
 				preload_tokens.delete(preload);
-				if (result.type === 'loaded' && result.state.error) {
-					// Don't cache errors, because they might be transient
+				if (result.type === 'redirect' || (result.type === 'loaded' && result.state.error)) {
+					// Don't cache errors or redirects, because they might be transient.
+					// A cached redirect would be replayed without re-running `load`
+					// until a navigation commits, which can turn a resolvable
+					// redirect chain into a redirect loop
 					discard_load_cache();
 				}
 				return result;
diff --git a/packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/dashboard/+page.server.js b/packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/dashboard/+page.server.js
new file mode 100644
index 000000000000..20425a680b33
--- /dev/null
+++ b/packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/dashboard/+page.server.js
@@ -0,0 +1,9 @@
+import { redirect } from '@sveltejs/kit';
+import { state } from '../state.js';
+
+export function load() {
+	if (!state.selected) {
+		redirect(303, '/data-sveltekit/preload-data/redirect-gate/select');
+	}
+	return {};
+}
diff --git a/packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/dashboard/+page.svelte b/packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/dashboard/+page.svelte
new file mode 100644
index 000000000000..8b53980d76d2
--- /dev/null
+++ b/packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/dashboard/+page.svelte
@@ -0,0 +1 @@
+<h1>dashboard</h1>
diff --git a/packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/select/+page.server.js b/packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/select/+page.server.js
new file mode 100644
index 000000000000..e310689bf9d2
--- /dev/null
+++ b/packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/select/+page.server.js
@@ -0,0 +1,7 @@
+import { redirect } from '@sveltejs/kit';
+import { state } from '../state.js';
+
+export function load() {
+	state.selected = true;
+	redirect(303, '/data-sveltekit/preload-data/redirect-gate/dashboard');
+}
diff --git a/packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/start/+page.server.js b/packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/start/+page.server.js
new file mode 100644
index 000000000000..8c5dd3542d24
--- /dev/null
+++ b/packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/start/+page.server.js
@@ -0,0 +1,6 @@
+import { state } from '../state.js';
+
+export function load() {
+	// reset so the test can run repeatedly against the same server
+	state.selected = false;
+}
diff --git a/packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/start/+page.svelte b/packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/start/+page.svelte
new file mode 100644
index 000000000000..889614be7758
--- /dev/null
+++ b/packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/start/+page.svelte
@@ -0,0 +1,5 @@
+<a
+	id="gated"
+	href="/data-sveltekit/preload-data/redirect-gate/dashboard"
+	data-sveltekit-preload-data="hover">go to dashboard</a
+>
diff --git a/packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/state.js b/packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/state.js
new file mode 100644
index 000000000000..1cc97fae3184
--- /dev/null
+++ b/packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/redirect-gate/state.js
@@ -0,0 +1 @@
+export const state = { selected: false };
diff --git a/packages/kit/test/apps/basics/test/client.test.js b/packages/kit/test/apps/basics/test/client.test.js
index 8b5d6df581ee..46606fab0345 100644
--- a/packages/kit/test/apps/basics/test/client.test.js
+++ b/packages/kit/test/apps/basics/test/client.test.js
@@ -1071,6 +1071,24 @@ test.describe('data-sveltekit attributes', () => {
 		await expect(page).toHaveURL(offline_url);
 	});
 
+	test('preloaded redirect is not replayed on navigation', async ({ page }) => {
+		await page.goto('/data-sveltekit/preload-data/redirect-gate/start');
+
+		// preload /dashboard while its load redirects to /select
+		await page.locator('#gated').hover();
+		await page.locator('#gated').dispatchEvent('touchstart');
+		await Promise.all([
+			page.waitForTimeout(100), // wait for preloading to start
+			page.waitForLoadState('networkidle') // wait for preloading to finish
+		]);
+
+		// navigating must re-run load rather than replay the cached redirect,
+		// otherwise the mutual redirect never resolves and loops
+		await page.locator('#gated').click();
+		await expect(page.locator('h1')).toHaveText('dashboard');
+		await expect(page).toHaveURL(/redirect-gate\/dashboard/);
+	});
+
 	test('data-sveltekit-preload-data error does not block user navigation', async ({
 		page,
 		context,