Launch site: resolve back_to on click, not once per memo

The launch URL was built inside a useMemo keyed on [ site, postLaunchUrl ],
but back_to now comes from redirectToDashboardLink(), which reads
window.location. Neither dep changes on a client-side navigation within the
same site, so back_to froze on the page the button first rendered on — and
the two omnibars that render it sit outside the router and can outlive
several navigations without re-rendering at all.

Drop the memo so the href is fresh per render, and re-resolve the URL on
click, following the fresh one when the rendered href has gone stale.
Unmodified primary clicks only, so cmd/ctrl-click still opens the href in a
new tab.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Su9dfy7uw3VtuXzxnC8wRo

Author: paulopmt1

client/dashboard/sites/site-launch-button/test/index.test.tsx

@@ -45,6 +45,10 @@ const mockLaunchApi = () =>
 		.reply( 200, {} );
 
 describe( '<SiteLaunchButton>', () => {
+	afterEach( () => {
+		window.history.pushState( {}, '', '/' );
+	} );
+
 	test( 'opens the pre-launch modal instead of launching immediately for a paid site with a custom domain', async () => {
 		const user = userEvent.setup();
 		mockDomainsApi( [
@@ -201,8 +205,62 @@ describe( '<SiteLaunchButton>', () => {
 		expect( query.get( 'redirect_to' ) ).toBe(
 			'https://my.wordpress.com/sites/kaonashi.wordpress.com'
 		);
+	} );
 
-		window.history.pushState( {}, '', '/' );
+	test( 'resolves the Back target again on click, in case the page changed after render', async () => {
+		const user = userEvent.setup();
+		mockDomainsApi( [ createMockDomain( 'kaonashi.wordpress.com', false ) ] );
+		window.history.pushState( {}, '', '/sites/kaonashi.wordpress.com/settings/site-visibility' );
+
+		render(
+			<SiteLaunchButton
+				site={ createMockSite( {
+					plan: {
+						product_slug: 'free_plan',
+						product_name: 'Free',
+						is_free: true,
+					},
+				} as Partial< Site > ) }
+				tracksContext="test"
+			/>
+		);
+
+		const launchLink = await screen.findByRole( 'link', { name: 'Launch your site' } );
+
+		// The omnibars rendering this button sit outside the router and can outlive a navigation
+		// without re-rendering, which leaves a stale `back_to` baked into the href.
+		window.history.pushState( {}, '', '/sites/kaonashi.wordpress.com/plugins' );
+
+		// `Location.assign` isn't writable, so read through to the real location and swap the
+		// object out only for the click.
+		const realLocation = window.location;
+		const assign = jest.fn();
+		Object.defineProperty( window, 'location', {
+			configurable: true,
+			value: {
+				get href() {
+					return realLocation.href;
+				},
+				get origin() {
+					return realLocation.origin;
+				},
+				get hostname() {
+					return realLocation.hostname;
+				},
+				assign,
+			},
+		} );
+
+		try {
+			await user.click( launchLink );
+		} finally {
+			Object.defineProperty( window, 'location', { configurable: true, value: realLocation } );
+		}
+
+		expect( assign ).toHaveBeenCalledTimes( 1 );
+		const query = new URL( assign.mock.calls[ 0 ][ 0 ] as string, window.location.origin )
+			.searchParams;
+		expect( query.get( 'back_to' ) ).toContain( '/sites/kaonashi.wordpress.com/plugins' );
 	} );
 
 	test( 'renders a link to the launch flow for a free site without an immediate launch', async () => {

client/dashboard/sites/site-launch-button/use-site-launch.tsx

@@ -3,7 +3,7 @@ import { domainsQuery, siteLaunchMutation } from '@automattic/api-queries';
 import { useQuery, useMutation } from '@tanstack/react-query';
 import { __ } from '@wordpress/i18n';
 import { addQueryArgs } from '@wordpress/url';
-import { useMemo, useState, type ComponentType, type ReactElement } from 'react';
+import { useState, type ComponentType, type MouseEvent, type ReactElement } from 'react';
 import { useSiteLaunchGatingVariant } from 'calypso/lib/use-site-launch-gating-variant';
 import { getCurrentDashboard } from '../../app/routing';
 import { withSnackbar } from '../../app/snackbars/with-snackbar';
@@ -41,7 +41,7 @@ export interface UseSiteLaunchResult {
 	isDisabled: boolean;
 	isBusy: boolean;
 	href?: string;
-	onClick: () => void;
+	onClick: ( event?: MouseEvent ) => void;
 	modal: ReactElement | null;
 }
 
@@ -78,7 +78,10 @@ export function useSiteLaunch(
 	const isDisabled = ! getIsSitePlanLaunchable( site );
 	const shouldImmediatelyLaunch = isSitePlanHostingTrial || site.is_wpcom_staging_site;
 
-	const launchUrl = useMemo( () => {
+	// Reads `window.location`, so it must not be memoized: the omnibars that render this button
+	// live outside the router and can outlast several navigations, which would freeze `back_to`
+	// on the page the button first rendered on.
+	const getLaunchUrl = () => {
 		if ( isSitePlanBigSkyTrial( site ) ) {
 			return addQueryArgs( wpcomLink( '/setup/ai-site-builder/domains' ), {
 				siteId: site.ID,
@@ -97,12 +100,34 @@ export function useSiteLaunch(
 			...( postLaunchUrl ? { redirect_to: postLaunchUrl } : {} ),
 			dashboard: getCurrentDashboard(),
 		} );
-	}, [ site, postLaunchUrl ] );
+	};
+
+	const launchUrl = getLaunchUrl();
 
 	const track = () => {
 		recordTracksEvent( 'calypso_dashboard_site_launch_button_click', { context: tracksContext } );
 	};
 
+	// Those same omnibars may not have re-rendered since the user navigated, so resolve `back_to`
+	// again on click and follow the fresh URL when the rendered `href` has gone stale.
+	const openLaunchUrl = ( event?: MouseEvent ) => {
+		track();
+
+		if ( ! event || event.defaultPrevented ) {
+			return;
+		}
+
+		if ( event.metaKey || event.ctrlKey || event.shiftKey || event.altKey ) {
+			return;
+		}
+
+		const currentLaunchUrl = getLaunchUrl();
+		if ( currentLaunchUrl !== launchUrl ) {
+			event.preventDefault();
+			window.location.assign( currentLaunchUrl );
+		}
+	};
+
 	const redirectAfterLaunch = ( options: { celebrate?: boolean } = {} ) => {
 		const targetUrl = addQueryArgs( postLaunchUrl ?? window.location.href, {
 			...( options.celebrate ? { celebrateLaunch: 'true' } : {} ),
@@ -212,7 +237,7 @@ export function useSiteLaunch(
 				...baseResult,
 				isHidden: false,
 				href: launchUrl,
-				onClick: track,
+				onClick: openLaunchUrl,
 			};
 	}
 }