Boost: Add edge-cache header on WP Cloud (#40557)

* Add edge-cache header on atomic

* changelog

* Update atomic check

* Add edge-cache header when uncached as well

Committed via a GitHub action: https://github.com/Automattic/jetpack/actions/runs/12439187804

Upstream-Ref: Automattic/jetpack@acacbbe

CHANGELOG.md

@@ -13,6 +13,7 @@ This is an alpha version! The changes listed here are not final.
 - Concatenate JS/CSS: Add a button that allows loading default excludes.
 - General: Added tracks events to clickable elements on the settings page.
 - General: Add WordPress filters to allow Cornerstone Pages list and Image Size Analyzer source data to be updated.
+- Minify: Added HTTP header to take advantage of WordPress.com edge caching
 - UI: Add notifications when interacting with dashboard settings.
 
 ### Changed

app/lib/minify/functions-service.php

@@ -60,6 +60,10 @@ function jetpack_boost_page_optimize_service_request() {
 			// phpcs:ignore WordPress.WP.AlternativeFunctions.file_get_contents_file_get_contents
 			$etag = '"' . md5( file_get_contents( $cache_file ) ) . '"';
 
+			// Check if we're on Atomic and take advantage of the Atomic Edge Cache.
+			if ( defined( 'ATOMIC_CLIENT_ID' ) ) {
+				header( 'A8c-Edge-Cache: cache' );
+			}
 			header( 'X-Page-Optimize: cached' );
 			header( 'Cache-Control: max-age=' . 31536000 );
 			header( 'ETag: ' . $etag );
@@ -77,6 +81,10 @@ function jetpack_boost_page_optimize_service_request() {
 	foreach ( $headers as $header ) {
 		header( $header );
 	}
+	// Check if we're on Atomic and take advantage of the Atomic Edge Cache.
+	if ( defined( 'ATOMIC_CLIENT_ID' ) ) {
+		header( 'A8c-Edge-Cache: cache' );
+	}
 	header( 'X-Page-Optimize: uncached' );
 	header( 'Cache-Control: max-age=' . 31536000 );
 	header( 'ETag: "' . md5( $content ) . '"' );