Queue guest document extraction

src/main/kotlin/com/android/trisolarisserver/component/ExtractionQueue.kt

@@ -0,0 +1,27 @@
+package com.android.trisolarisserver.component
+
+import jakarta.annotation.PreDestroy
+import org.springframework.stereotype.Component
+import java.util.concurrent.Executors
+
+@Component
+class ExtractionQueue {
+    private val executor = Executors.newSingleThreadExecutor { runnable ->
+        Thread(runnable, "doc-extraction-queue").apply { isDaemon = true }
+    }
+
+    fun enqueue(task: () -> Unit) {
+        executor.submit {
+            try {
+                task()
+            } catch (_: Exception) {
+                // Best-effort processing; failures should not crash the worker.
+            }
+        }
+    }
+
+    @PreDestroy
+    fun shutdown() {
+        executor.shutdown()
+    }
+}