Close 1 merged task card(s) and archive them

Why: branches merged into main had left their task cards open; backfill status and archive to prevent bookkeeping debt.
Evidence: feature-agent-harness-p3.md(PR#140) — merges verified via git log --merges against origin/main.
Impact: .task/*.md moved to .task/archive/ with status backfilled; no code or submodule change.
Refs: task.sh close (card-autoclose-r1)

.task/archive/feature-agent-harness-p3.md

@@ -1,6 +1,6 @@
 # feature/agent-harness-p3 任务卡
 
-任务主记录：https://git-home.u1680832.nyat.app:30319/weichen/Agent-System-Dev/pulls/140 ；状态：进行中；owner：weichen
+任务主记录：https://git-home.u1680832.nyat.app:30319/weichen/Agent-System-Dev/pulls/140 ；状态：已完成（回填）；owner：weichen
 
 ## 基线与授权
 
@@ -76,3 +76,9 @@ cd deps/agent-command && go vet ./... && go test -count=1 ./...
 ok  	agent-command	0.002s
 ok  	agent-command/conformance	0.001s
 ```
+
+## 闭合记录（card-autoclose 回填）
+
+- 依据：merge 5096a052dcaef7ee08a3251ec50a47bf7f066618（PR #140）已包含于 origin/main，分支成果已落盘；本段为合入后回填。
+- 合并主题：Merge pull request 'Pin backend to the depth-one subagent loop' (#140) from feature/agent-harness-p3 into main
+- 归档：随闭合移入 .task/archive/；任务执行期的过程证据见原任务记录与 PR。