debug(phase2): join 前打印 th 指针/handle/started 定位 join 立即返回

ClassArrayTest join(0) 已正常等待 edd8（645e8e0 生效），但 join(1) 仍
立即返回 alive=0 且 e5fb Result=-1（worker 未写 Result）。新增
[LLC-DBG2] 插桩打印 th_j 指针/handle/started，区分句柄无效（存取错）
与 e5fb 线程已死两种可能。

App/lib/core/BuildPipeline.vp

@@ -638,10 +638,17 @@ def run_llc_parallel(tasks: bytes, task_count: int, max_threads: int) -> int:
         j = 0
         while j < batch_n:
             th_j: vthreading.Thread | t.CPtr = th_list.get(j)
+            #region debug-point LLC9
+            stdio.printf("[LLC-DBG2] j=%d ptr=%llx handle=%llx started=%d\n", j,
+                         t.CUInt64T(th_j), t.CUInt64T(th_j.handle), th_j.started)
+            #endregion
             #region debug-point LLC7
             stdio.printf("[LLC-DBG] join 前 %d\n", j)
             #endregion
             th_j.join(600000)
+            #region debug-point LLC10
+            stdio.printf("[LLC-DBG2] j=%d alive=%d\n", j, th_j.is_alive())
+            #endregion
             #region debug-point LLC8
             stdio.printf("[LLC-DBG] join 后 %d alive=%d\n", j, th_j.is_alive())
             #endregion