fix(deploy): reuse staging backend images by default

docs/V21-UI-ACCEPTANCE-CHECKLIST.md

@@ -154,3 +154,9 @@ V21 结构：三张套餐 feature 卡片，免费版/专业版/企业版，推
 - Host-shell 执行 deploy-staging.sh 时脚本默认 HOST_PREFIX=/host，导致找不到 /host/var/lib/xiaoxia-saas-staging/repo。
 - Workflow 已改为 HOST_PREFIX= WEB_PORT=3001 .../deploy-staging.sh，适配宿主机直接执行。
 
+
+## 2026-06-24 Staging 后端镜像复用记录
+
+- Staging 当前目标是验证 V21 Web UI，deploy 不应因未变更的 API/Worker 基础镜像拉取失败而阻塞。
+- deploy-staging.sh 已改为默认只构建 Web；如需后端重建/迁移，显式设置 REBUILD_BACKEND=1 / RUN_MIGRATIONS=1。
+

infra/docker/deploy-staging.sh

@@ -35,10 +35,13 @@ export WEB_PORT
 export DOCKER_BUILDKIT=0
 export COMPOSE_DOCKER_CLI_BUILD=0
 
-docker compose build --pull=false api
-docker compose build --pull=false worker
+if [ "${REBUILD_BACKEND:-0}" = "1" ]; then
+  docker compose build --pull=false api
+  docker compose build --pull=false worker
+fi
 docker compose build --pull=false web
-docker compose run --rm --no-deps api sh -c '
+if [ "${RUN_MIGRATIONS:-0}" = "1" ]; then
+  docker compose run --rm --no-deps api sh -c '
   cd /app
   set +e
   python - <<"PY"
@@ -72,5 +75,6 @@ PY
     exit "$status"
   fi
 '
+fi
 docker compose up -d api worker web
 docker compose ps