Fold-close the task card before merge

Why: close the task card inside its own PR so landing it needs no post-merge backfill or separate close PR.
Evidence: .task/feature-conversation-handoff.md -> .task/archive/feature-conversation-handoff.md; status 已完成（合入前闭合）; PR #651 https://git-home.u1680832.nyat.app:30319/weichen/Agent-System-Dev/pulls/651.
Impact: task metadata only; the card is archived within PR #651 and lands with its merge commit.
Refs: task.sh close --self

.task/archive/feature-conversation-handoff.md

@@ -1,6 +1,6 @@
 # feature/conversation-handoff 任务卡
 
-任务主记录：PR #651 https://git-home.u1680832.nyat.app:30319/weichen/Agent-System-Dev/pulls/651；状态：进行中（恢复：CI 阻塞）；owner：weichen
+任务主记录：PR #651 https://git-home.u1680832.nyat.app:30319/weichen/Agent-System-Dev/pulls/651；状态：已完成（合入前闭合）；owner：weichen
 
 ## 基线与授权
 
@@ -405,3 +405,9 @@
   "receipt_path": "/home/weichen/.cache/agent-system-dev/evidence/f676ac17f42a3634b98cc3287cb7f891df70b5361970c14c4bd3dcd77a6290fa.json"
 }
 ```
+
+## 闭合记录（合入前折叠）
+
+- 本卡在 PR #651（https://git-home.u1680832.nyat.app:30319/weichen/Agent-System-Dev/pulls/651）合入前闭合并归档，随该 PR 一同合入。
+- 该 PR 的合并提交即本任务的落地记录。
+- 合入后无需回填，也无需单独的闭合 PR。