`hermes import` wrote every zip member with `open(target, "wb")` followed by
`dst.write(src.read())`, at both restore sites in `run_import`. Opening for
write truncates the user's existing file to zero *before* any replacement
bytes exist, so a Ctrl-C, an ENOSPC, a corrupt zip member, or a crash leaves
`config.yaml`, `.env`, or an external provider config (e.g.
`~/.honcho/config.json`) empty with nothing behind it — during the
disaster-recovery path the user is running precisely because they already
lost something. The `_external/` branch writes outside HERMES_HOME, into
third-party configs under the user's home, so the blast radius is not
confined to Hermes state.
Both sites now stage the member into the target's own directory, fsync it,
and publish with `utils.atomic_replace`, so the target only ever moves from
its old contents to the complete new contents.
`atomic_replace` rather than a bare `os.replace`: it resolves a symlinked
target first, so deployments that link `config.yaml` into a dotfiles repo
keep the link instead of having it silently swapped for a regular file
(#16743), and it falls back to copy/fsync/unlink on EXDEV/EBUSY for
cross-device and bind-mount installs. Members stream through
`shutil.copyfileobj` instead of being read whole into memory. The temp file
is removed on any failure so a partial import leaves no residue, and
permission bits are carried across the replace so mkstemp's 0600 does not
silently tighten restored files.
This extends the module's own established idiom — `backup.py` already
publishes atomically via `os.replace` in `_atomic_output_path` and in the
snapshot writer — into the one path that still overwrote user files in place.
briandevans
e88c9f0ef2