fix(acceptance): 清理中止验收的未提交任务

验收失败后，排队及尚未提交上游的任务会继续占用队列与 API 数据库连接池，导致下一轮容量测试被历史负载污染。

中止验收时仅取消确认未提交上游的任务，删除其未提交 attempt 与准入记录，释放租约并生成幂等退款事件；提交中或已收到上游响应的任务继续自然收敛。新建验收前也会清理历史失败 Run 的安全遗留任务，并等待其余任务终态。

验证：Go 全量测试通过；临时 PostgreSQL 集成测试覆盖排队、运行未提交、提交中与退款事件；gofmt、bash -n、ShellCheck、git diff --check 通过。

scripts/cluster/run-production-acceptance.sh

@@ -218,6 +218,26 @@ wait_for_existing_tasks_to_drain() {
   return 1
 }
 
+wait_for_terminal_acceptance_tasks_to_drain() {
+  local deadline=$((SECONDS + 300))
+  local active
+  while (( SECONDS < deadline )); do
+    active=$(database_query "
+SELECT count(*)
+FROM gateway_tasks task
+JOIN gateway_acceptance_runs run ON run.id=task.acceptance_run_id
+WHERE run.status IN ('failed', 'aborted')
+  AND task.status IN ('queued', 'running');")
+    if [[ $active == 0 ]]; then
+      return 0
+    fi
+    echo "waiting_for_terminal_acceptance_tasks=$active"
+    sleep 2
+  done
+  echo "terminal acceptance tasks did not drain within 5 minutes: active=$active" >&2
+  return 1
+}
+
 ensure_acceptance_user_group() {
   local groups_response=$temporary_root/user-groups.json
   local group_response=$temporary_root/acceptance-user-group.json
@@ -621,6 +641,7 @@ create_and_activate_run() {
       echo 'previous failed acceptance Run did not return traffic to live' >&2
       return 1
     }
+    wait_for_terminal_acceptance_tasks_to_drain
   elif [[ $traffic_mode != live ]]; then
     echo "unsupported production traffic mode before acceptance: $traffic_mode" >&2
     return 1