Search Blocks overlay: auto-open on initial page load when URL has ?s=keyword (SEARCH-232)

The existing handlePopState() already maps URL → overlay visibility for back/
forward navigation. Wire it to the initial-paint URL too so deep links and the
WordPress core search form's GET submission surface results in the blocks-
powered overlay the same way they do in the legacy instant-search overlay.

Author: kangzj

projects/packages/search/changelog/SEARCH-232-overlay-url-trigger

@@ -0,0 +1,4 @@
+Significance: patch
+Type: fixed
+
+Search Blocks overlay: auto-open on initial page load when the URL contains `?s=` or `?q=`, matching the legacy instant-search overlay's deep-link behavior.

projects/packages/search/src/search-blocks/overlay-bootstrap/index.js

@@ -298,3 +298,13 @@ const overlayEl = getOverlay();
 if ( overlayEl ) {
 	overlayEl.addEventListener( 'click', handleOverlayClick );
 }
+
+// Honor the URL on initial paint the same way `popstate` does on back/forward:
+// if the page loaded with `?s=` or `?q=`, open the overlay. This matches the
+// legacy instant-search behavior where deep links and core-search-form GET
+// submissions surface results in the overlay without a click.
+if ( document.readyState === 'loading' ) {
+	document.addEventListener( 'DOMContentLoaded', handlePopState, { once: true } );
+} else {
+	handlePopState();
+}