FOUR-31736 Implement Etag Cache for Tasks page

ProcessMaker/Http/Middleware/BrowserCache.php

@@ -23,6 +23,10 @@ public function handle($request, Closure $next)
                 return $response;
             }
 
+            if ($response->headers->has('ETag')) {
+                return $response;
+            }
+
             $response->header('pragma', 'no-cache');
             $response->header('Cache-Control', 'no-store');
 

ProcessMaker/Http/Middleware/Etag/TasksPageEtag.php

@@ -0,0 +1,77 @@
+<?php
+
+namespace ProcessMaker\Http\Middleware\Etag;
+
+use Closure;
+use Illuminate\Http\Request;
+use ProcessMaker\Http\Resources\Caching\TasksPageEtag as TasksPageEtagResource;
+use Symfony\Component\HttpFoundation\Response;
+
+class TasksPageEtag
+{
+    public function __construct(
+        private TasksPageEtagResource $tasksPageEtag
+    ) {
+    }
+
+    /**
+     * Handle Tasks page validation before rendering the full page shell.
+     *
+     * The ETag is computed from stable page context before controller execution, so a
+     * matching conditional request can return 304 without paying the render cost.
+     */
+    public function handle(Request $request, Closure $next): Response
+    {
+        if (!config('etag.enabled') || (!$request->isMethod('GET') && !$request->isMethod('HEAD'))) {
+            return $next($request);
+        }
+
+        $etag = $this->tasksPageEtag->getEtag($request);
+
+        if ($this->buildResponseWithEtag($etag)->isNotModified($request)) {
+            return $this->withPrivateCacheHeaders($this->buildNotModifiedResponse($etag, $request));
+        }
+
+        $response = $next($request);
+        $response->setEtag($etag);
+
+        return $this->withPrivateCacheHeaders($response);
+    }
+
+    /**
+     * Build a framework-compatible 304 response for a matched Tasks page ETag.
+     */
+    private function buildNotModifiedResponse(string $etag, Request $request): Response
+    {
+        $response = $this->buildResponseWithEtag($etag);
+        $response->isNotModified($request);
+
+        return $response;
+    }
+
+    /**
+     * Create a response carrying the Tasks page validator.
+     *
+     * Weak ETags are used because the HTML may be transformed by gzip while the
+     * rendered representation remains equivalent for browser revalidation.
+     */
+    private function buildResponseWithEtag(string $etag): Response
+    {
+        $response = new Response();
+        $response->setEtag($etag, true);
+
+        return $response;
+    }
+
+    /**
+     * Apply browser-cache headers that allow private conditional revalidation.
+     */
+    private function withPrivateCacheHeaders(Response $response): Response
+    {
+        $response->headers->set('Cache-Control', 'private, must-revalidate');
+        $response->headers->remove('Pragma');
+        $response->headers->remove('Expires');
+
+        return $response;
+    }
+}