diff --git a/chv-guest/build.sh b/chv-guest/build.sh
index 7a00e81..6719d81 100755
--- a/chv-guest/build.sh
+++ b/chv-guest/build.sh
@@ -105,7 +105,7 @@ if [ "$DRY_RUN" = "0" ]; then
     echo "CHV_GUEST_BUILD needs a KVM host: /dev/kvm 不存在" >&2
     exit 1
   fi
-  for tool in curl qemu-img virt-customize virt-get-kernel python3 virt-cat; do
+  for tool in curl qemu-img virt-customize virt-get-kernel python3 virt-cat sgdisk guestfish; do
     if ! command -v "$tool" >/dev/null 2>&1; then
       echo "缺少构建工具：$tool，构建失败" >&2
       exit 1
@@ -148,6 +148,24 @@ else
   fi
 fi
 run qemu-img convert -f qcow2 -O raw "$IMG" "$OUT/disk.raw"
+# B-16：云镜像根分区只有 ~2.4G，apt 全量清单（texlive +
+# Playwright --with-deps + Chromium + CJK 字体）会写满根分区
+# （No space left on device，首轮真机构建实测）。先扩盘：
+# qemu-img resize 扩文件；sgdisk 把 1 号分区尾移到磁盘末尾
+# （只动 1 号分区，14/15/16 不动）；guestfish resize2fs 扩
+# 文件系统。注意不能用 virt-resize：它会重写分区表、把根分区
+# 从 1 号重编号为 4 号，而执行器默认 cmdline 是 root=/dev/vda1，
+# 重编号后无法启动。根分区起始扇区从 sgdisk -i 1 实测取，不写死。
+if [ "$DRY_RUN" = "0" ]; then
+  run qemu-img resize "$OUT/disk.raw" +12G
+  run sgdisk -e "$OUT/disk.raw"
+  ROOT_START="$(sgdisk -i 1 "$OUT/disk.raw" | awk '/^First sector:/ {print $3}')"
+  [ -n "$ROOT_START" ] || { echo "读不到根分区起始扇区" >&2; exit 1; }
+  run sgdisk -d 1 -n "1:${ROOT_START}:0" -t 1:8300 "$OUT/disk.raw"
+  run guestfish -a "$OUT/disk.raw" -m /dev/sda1 resize2fs /dev/sda1
+else
+  echo "DRY-RUN: qemu-img resize $OUT/disk.raw +12G; sgdisk 扩 1 号分区; guestfish resize2fs /dev/sda1"
+fi
 # 清单软件（照抄 cloud/docker/Dockerfile 的 apt/pip 清单，
 # 中文 LaTeX xelatex 故意不装，见 README；fonts-noto-cjk 只
 # 是浏览器渲染用的中文字体，不是 LaTeX。Playwright 默认开启