Problem

hermes_cli/web_server.py → update_config() calls save_config(_denormalize_config_from_web(body.config)), and hermes_cli/config.py → save_config() replaces the entire ~/.hermes/config.yaml file with the provided dict.

If a caller (e.g. a dashboard UI) sends a PUT payload containing only the sections it manages (agent, display), the write silently deletes everything else — model, custom_providers, compression, auxiliary, fallback_model, etc.

Reproduction

1. Configure Hermes with: model, custom_providers, compression (etc.) in config.yaml.

2. From a UI client or curl:

   curl -X PUT http://127.0.0.1:9119/api/config \
   -H "Authorization: Bearer " \
   -H "Content-Type: application/json" \
   -d '{"config": {"agent": {"max_turns": 90}, "display": {"personality": "concise"}}}'

3. Inspect ~/.hermes/config.yaml → all other sections are gone.

Impact

• Third-party dashboards (e.g. outsourc-e/hermes-workspace Settings screen) silently destroy user-managed fields they don't know about.
• Users have to re-edit config.yaml from memory.
• Happens invisibly — no warning, no backup before the overwrite.

Expected behavior (proposals, any of the below)

(a) Deep-merge on server side. In update_config():

existing = load_config()
merged = _deep_merge(existing, _denormalize_config_from_web(body.config))
save_config(merged)

(b) Require the client to send the full config and reject PUTs that omit top-level keys present on disk (409 Conflict).

(c) Make save_config() take an explicit scope parameter listing which top-level keys to overwrite. Anything outside that scope is preserved.

I'd vote for (a) — it's the least surprising behavior and matches what every third-party client is already assuming.

Env

• Hermes v0.10.0
• Triggered by: outsourc-e/hermes-workspace Settings screen on x.joao.date
• Lost fields included: model, custom_providers, compression, auxiliary.vision

Happy to open a PR for option (a).