diff --git a/infra/docker/worker.Dockerfile b/infra/docker/worker.Dockerfile
index d7549fb28..9b0c0ca5c 100755
--- a/infra/docker/worker.Dockerfile
+++ b/infra/docker/worker.Dockerfile
@@ -26,18 +26,17 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     && rm -rf /var/lib/apt/lists/*
 
 # ---- 下载静态编译 ffmpeg（带缓存+完整性校验+多源重试）----
-# 问题背景：johnvansickle.com 偶尔返回损坏文件，缓存命中坏包后反复失败
+# 注意：必须用纯sh语法（dash兼容），不能用bash数组、[[ ]]等特性
 # 修复策略：1.三源下载 2.tar完整性校验 3.损坏删缓存重试 4.二进制可执行校验
 RUN --mount=type=cache,target=/tmp/ffmpeg-cache,sharing=locked \
     cd /tmp \
     && FFMPEG_FILE="/tmp/ffmpeg-cache/ffmpeg-release-amd64-static.tar.xz" \
-    && FFMPEG_SOURCES=( \
+    && download_ok=0 \
+    && for src in \
          "https://johnvansickle.com/ffmpeg/releases/ffmpeg-release-amd64-static.tar.xz" \
          "https://mirrors.tuna.tsinghua.edu.cn/ffmpeg/releases/ffmpeg-release-amd64-static.tar.xz" \
-         "https://mirrors.ustc.edu.cn/ffmpeg/releases/ffmpeg-release-amd64-static.tar.xz" \
-       ) \
-    && download_ok=0 \
-    && for src in "${FFMPEG_SOURCES[@]}"; do \
+         "https://mirrors.ustc.edu.cn/ffmpeg/releases/ffmpeg-release-amd64-static.tar.xz"; \
+       do \
          if [ $download_ok -eq 0 ] && [ -f "$FFMPEG_FILE" ] && tar -tf "$FFMPEG_FILE" >/dev/null 2>&1; then \
            echo "[ffmpeg] cache valid, skip download"; \
            download_ok=1; \