fix: address Phase 1 code review findings

- Serve cache via template_redirect so feeds/404/REST are excluded and
  query conditionals work
- Bypass cache on query strings; key files by md5(host+path) to avoid
  collisions and support multisite
- Write wp-content/wp-recache-cache.php drop-in server and set WP_CACHE
  in wp-config.php so advanced-cache.php actually runs
- Only remove advanced-cache.php on deactivation when it is ours
- Respect DONOTCACHEPAGE, non-200 responses; bots read but never warm
  cache
- Fix comment purge (comment_post_ID) and heartbeat purge ($data arg)
- Fix exclude URLs textarea parsing; purge all when exclusions change
- Enqueue admin purge script on every admin-bar page, not just settings
- Sync tests, add TESTING.md manual test guide

includes/Common/Helpers.php

@@ -58,11 +58,12 @@ function wp_recache_should_exclude() {
         return true;
     }
 
-    if (wp_recache_is_robots()) {
+    // Dynamic query-string requests are never cached (story 11).
+    if (!empty($_SERVER['QUERY_STRING'])) {
         return true;
     }
 
-    if (is_preview()) {
+    if (is_preview() || is_feed() || is_404()) {
         return true;
     }
 
@@ -93,40 +94,22 @@ function wp_recache_is_robots() {
  * Check if request is a POST action.
  */
 function wp_recache_is_post_action() {
-    return $_SERVER['REQUEST_METHOD'] === 'POST';
+    return ($_SERVER['REQUEST_METHOD'] ?? 'GET') === 'POST';
 }
 
 /**
  * Get cache file path for URL.
  *
- * @param string $url URL to cache.
- */
-function wp_recache_get_cache_path($url) {
-    $path = wp_parse_url($url, PHP_URL_PATH);
-    $path = trim($path, '/');
-
-    if (empty($path)) {
-        $path = 'index';
-    }
-
-    $path = sanitize_file_name($path);
-
-    return WP_RECACHE_CACHE_PATH . $path . '.html';
-}
-
-/**
- * Get cache key for URL.
+ * Keyed by md5(host + path) so nested paths, hosts and multisite
+ * sub-directories never collide. Query strings are bypassed upstream.
  *
  * @param string $url URL to cache.
  */
-function wp_recache_get_cache_key($url) {
-    $key = wp_parse_url($url, PHP_URL_PATH);
+function wp_recache_get_cache_path($url) {
+    $host = (string) wp_parse_url($url, PHP_URL_HOST);
+    $path = (string) wp_parse_url($url, PHP_URL_PATH);
 
-    if (empty($key)) {
-        $key = '/';
-    }
-
-    return md5($key);
+    return WP_RECACHE_CACHE_PATH . md5($host . $path) . '.html';
 }
 
 /**
@@ -214,3 +197,18 @@ function wp_recache_get_cache_path_with_device($url) {
 
     return $path;
 }
+
+/**
+ * Enqueue the admin-bar purge script (admin and front-end admin bar).
+ */
+function wp_recache_enqueue_admin_bar_script() {
+    if (!is_admin_bar_showing() || !current_user_can('manage_options')) {
+        return;
+    }
+
+    wp_enqueue_script('wp-recache-admin', WP_RECACHE_URL . 'assets/admin.js', ['jquery'], WP_RECACHE_VERSION, true);
+    wp_localize_script('wp-recache-admin', 'wpRecache', [
+        'ajaxUrl' => admin_url('admin-ajax.php'),
+        'nonce' => wp_create_nonce('wp_recache_nonce'),
+    ]);
+}