_skin_set has no try/except around yaml.safe_load, so invalid YAML raises
and aborts the command. The {} fallback comes only from safe_load()
returning None on a zero-length file — which is exactly the state a torn,
unsynced write leaves behind, so the data-loss chain is unchanged.
`write_profile_meta` and `hermes skin set` are both read-modify-write
helpers that rewrite a user-visible YAML file with a bare truncating
write, bypassing `utils.atomic_yaml_write` — the shared helper whose
docstring states that "every destructive file rewrite in the codebase
shares one implementation".
Both read halves swallow a parse error and fall back to `{}`, so a
truncated file is not transient corruption. The next call reads `{}` and
silently, permanently drops every field the caller did not explicitly
pass:
* `write_profile_meta` promises "unspecified fields preserve existing
values". After an interrupted write, a follow-up call that only sets
`description_auto` erases the profile's `description` — it vanishes
from `hermes profile list` and never comes back.
* `_skin_set` exists so that "changing one token never disturbs the rest
of the look". `path.write_text(...)` neither fsyncs nor swaps
atomically, so a crash or power loss can leave `<skin>.yaml`
zero-length; the next tweak then rewrites from empty and the whole
palette is gone. The gateway's skin watcher repaints live surfaces
from this file within ~1s, so a half-written file is observable.
Routing both through `atomic_yaml_write` gives temp file + fsync +
`atomic_replace`, which also preserves a symlinked target (GitHub
#16743) and restores owner/mode, and emits emoji descriptions as real
UTF-8 instead of `\UXXXXXXXX` escapes (GitHub #51356).
Supersedes #51808, which fixed the unicode-escaping symptom alone by
adding `allow_unicode=True` to the same `yaml.safe_dump` call.
Changing a single color kept wrecking the rest because the agent hand-authored a
new skin (often from `default`, which has no `background`, resetting the terminal
to black). Add `hermes skin set <key> <hex>`: edits the ACTIVE skin's one key in
place (a built-in is forked into an editable copy carrying its full palette), so
everything else — background included — is preserved. Plus `skin use` / `skin
list`. The skill now points tweaks at this command instead of hand-authoring.
briandevans
Brooklyn Nicholson