Add parallel update checking and improve artifact update handling

src/StaticPHP/Artifact/ArtifactCache.php

@@ -282,6 +282,16 @@ class ArtifactCache
         logger()->debug("Removed binary cache entry for [{$artifact_name}] on platform [{$platform}]");
     }
 
+    /**
+     * Get the names of all artifacts that have at least one downloaded entry (source or binary).
+     *
+     * @return array<string> Artifact names
+     */
+    public function getCachedArtifactNames(): array
+    {
+        return array_keys($this->cache);
+    }
+
     /**
      * Save cache to file.
      */