diff --git a/class-opengraph-fallback-embed.php b/class-opengraph-fallback-embed.php
index 18a8fe5..d9db322 100644
--- a/class-opengraph-fallback-embed.php
+++ b/class-opengraph-fallback-embed.php
@@ -23,6 +23,9 @@ class OpenGraph_Fallback_Embed {
 	/** @var int Cache duration in seconds (default 7 days). */
 	const CACHE_TTL = 604800;
 
+	/** @var string Transient key prefix for cached OG data. */
+	const CACHE_KEY_PREFIX = 'opengraph_fallback_embed_';
+
 	/* ------------------------------------------------------------------
 	 * Bootstrap
 	 * ----------------------------------------------------------------*/
@@ -104,8 +107,10 @@ public static function intercept_oembed_proxy( $response, $handler, $request ) {
 
 		$site_name = ! empty( $og['site_name'] ) ? $og['site_name'] : wp_parse_url( $url, PHP_URL_HOST );
 
-		// The editor renders "rich" embeds inside a sandboxed iframe,
-		// so styles must be inlined.
+		// The block editor renders "rich" type oEmbed responses inside a sandboxed
+		// iframe (wp.components.SandBox). The Embed block does not forward styles
+		// to SandBox, so wp_enqueue_style() / wp_add_inline_style() cannot reach
+		// the iframe. Inline styles in the oEmbed HTML are the only option.
 		$css_file  = plugin_dir_path( __FILE__ ) . 'build/og-embed/style-index.css';
 		$css       = file_exists( $css_file ) ? file_get_contents( $css_file ) : ''; // phpcs:ignore WordPress.WP.AlternativeFunctions.file_get_contents_file_get_contents
 		$card_html = self::render_card( $og, $url );
@@ -252,7 +257,7 @@ public static function rest_preview( WP_REST_Request $request ): WP_REST_Respons
 	 * @return array<string, string> Associative array of OG properties.
 	 */
 	public static function get_og_data( string $url ): array {
-		$cache_key = 'og_embed_' . md5( $url );
+		$cache_key = self::CACHE_KEY_PREFIX . md5( $url );
 		$cached    = get_transient( $cache_key );
 
 		if ( is_array( $cached ) ) {
diff --git a/readme.txt b/readme.txt
index 545c829..cec32d5 100644
--- a/readme.txt
+++ b/readme.txt
@@ -36,8 +36,20 @@ No. This plugin only activates when WordPress has no other embed handler for the
 
 The card uses the `.og-fallback-embed` CSS class. You can override styles in your theme.
 
+== Development ==
+
+The source code for this plugin, including unminified JavaScript and CSS, is available on GitHub:
+
+https://github.com/pento/opengraph-fallback-embed
+
+The plugin uses [@wordpress/scripts](https://developer.wordpress.org/block-editor/reference-guides/packages/packages-scripts/) for building. Source files are in the `src/` directory. See the repository README for build instructions.
+
 == Changelog ==
 
+= 1.3.5 =
+* Add source code repository link to readme.
+* Use plugin-specific prefix for transient cache keys.
+
 = 1.3.4 =
 * Tweak the plugin header.
 
diff --git a/tests/EmbedBlockFallbackTest.php b/tests/EmbedBlockFallbackTest.php
index bc18c74..35afde7 100644
--- a/tests/EmbedBlockFallbackTest.php
+++ b/tests/EmbedBlockFallbackTest.php
@@ -27,8 +27,8 @@ class EmbedBlockFallbackTest extends WP_UnitTestCase {
 
 	public function tear_down(): void {
 		parent::tear_down();
-		delete_transient( 'og_embed_' . md5( self::TEST_URL ) );
-		delete_transient( 'og_embed_' . md5( self::YOUTUBE_URL ) );
+		delete_transient( OpenGraph_Fallback_Embed::CACHE_KEY_PREFIX . md5( self::TEST_URL ) );
+		delete_transient( OpenGraph_Fallback_Embed::CACHE_KEY_PREFIX . md5( self::YOUTUBE_URL ) );
 	}
 
 	/* ------------------------------------------------------------------
diff --git a/tests/MaybeEmbedTest.php b/tests/MaybeEmbedTest.php
index e421711..28273c6 100644
--- a/tests/MaybeEmbedTest.php
+++ b/tests/MaybeEmbedTest.php
@@ -7,7 +7,7 @@ class MaybeEmbedTest extends WP_UnitTestCase {
 
 	public function tear_down(): void {
 		parent::tear_down();
-		delete_transient( 'og_embed_' . md5( 'https://example.com/article' ) );
+		delete_transient( OpenGraph_Fallback_Embed::CACHE_KEY_PREFIX . md5( 'https://example.com/article' ) );
 	}
 
 	public function test_url_with_og_data_returns_card(): void {
diff --git a/tests/ParseOgTagsTest.php b/tests/ParseOgTagsTest.php
index 0f6313d..be0a727 100644
--- a/tests/ParseOgTagsTest.php
+++ b/tests/ParseOgTagsTest.php
@@ -7,7 +7,7 @@ class ParseOgTagsTest extends WP_UnitTestCase {
 
 	public function tear_down(): void {
 		parent::tear_down();
-		delete_transient( 'og_embed_' . md5( 'https://example.com/article' ) );
+		delete_transient( OpenGraph_Fallback_Embed::CACHE_KEY_PREFIX . md5( 'https://example.com/article' ) );
 	}
 
 	/**