fix(bootstrap): release 附件下载重试三次并检测卡死，回退本机构建前检查磁盘，所有 curl 下载带重试

docs/operations.md

@@ -136,7 +136,9 @@ the images are in the registry, when:
 - the release publishes no `SHA256SUMS` (one cut before release assets existed, or still
   uploading), or an asset is missing, fails its checksum or is malformed. Only that image is
   built (the registry and PostgreSQL images are pulled from Docker Hub instead), and a
-  warning names it; troubleshooting §15c lists the messages.
+  warning names it; troubleshooting §15c lists the messages. Each download is tried
+  three times first, and a host without the room for the build stops before installing
+  Docker (troubleshooting §15c).
 
 `FELIS_ARTIFACT_DIR=<absolute path>` installs from a directory instead of the release: a
 release's assets downloaded there (every `felis-*` file and `SHA256SUMS`), or the directory

docs/troubleshooting.md

@@ -1969,7 +1969,16 @@ A release install takes its images and the Velocity plugin from the release's as
 (operations §1, "Where the binary and the images come from"). When one cannot be used the
 installer names it and the reason, and builds that image with Docker instead (the registry
 and PostgreSQL images are pulled from Docker Hub). Nothing unchecked is used either way
-**[SH-TESTED]**.
+**[SH-TESTED]**. Each download is tried three times, five seconds apart, before it counts as
+failed, and a transfer that stalls under 1 KiB/s for a minute is cut off and tried again.
+
+Preflight counts no Docker builds for a release install, so the first build it falls back
+to checks the room first: Docker's images and build cache take about 8 GiB under
+`/var/lib/containerd` (2 GiB when Docker already has a cache there). Without it the install
+stops before Docker is installed, with `building here what the release did not supply takes
+about … MiB under /var/lib/containerd, and … has … MiB free; nothing has been built`. Rerun
+once the asset downloads (the messages above it say which one failed), free that space, or
+set `FELIS_PREFLIGHT=warn` to build anyway **[SH-TESTED]**.
 
 | Message | Meaning | What to do |
 |---|---|---|