fix: don't use fork of unrelated route (#14947)

We haven't been checking if the fork still matches the route we want to load at the end of the navigation. At that point it could've changed, or it could never have matched (as in the related issue). Fixes #14946

Author: dummdidumm

.changeset/dull-spies-hammer.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: don't use fork of unrelated route

packages/kit/src/runtime/client/client.js

@@ -1690,8 +1690,9 @@ async function navigate({
 		}
 	}
 
+	// also compare ids to avoid using wrong fork (e.g. a new one could've been added while navigating)
+	const load_cache_fork = intent && load_cache?.id === intent.id ? load_cache.fork : null;
 	// reset preload synchronously after the history state has been set to avoid race conditions
-	const load_cache_fork = load_cache?.fork;
 	load_cache = null;
 
 	navigation_result.props.page.state = state;

packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/offline/slow-navigation/+page.svelte

@@ -0,0 +1 @@
+<p>slow navigation</p>

packages/kit/test/apps/basics/src/routes/data-sveltekit/preload-data/offline/target/+page.svelte

@@ -0,0 +1 @@
+<p>target</p>

packages/kit/test/apps/basics/test/client.test.js

@@ -1047,6 +1047,21 @@ test.describe('data-sveltekit attributes', () => {
 		expect(page).toHaveURL('/data-sveltekit/preload-data/offline/slow-navigation');
 	});
 
+	test('data-sveltekit-preload does not abort ongoing navigation #2', async ({ page }) => {
+		await page.goto('/data-sveltekit/preload-data/offline');
+
+		await page.locator('#slow-navigation').dispatchEvent('click');
+		await page.waitForTimeout(100); // wait for navigation to start
+		await page.locator('#one').dispatchEvent('mousemove');
+		await Promise.all([
+			page.waitForTimeout(100), // wait for preloading to start
+			page.waitForLoadState('networkidle') // wait for preloading to finish
+		]);
+
+		expect(page).toHaveURL('/data-sveltekit/preload-data/offline/slow-navigation');
+		await expect(page.getByText('slow navigation', { exact: true })).toBeVisible();
+	});
+
 	test('data-sveltekit-preload-data tap works after data-sveltekit-preload-code hover', async ({
 		page
 	}) => {