sdl-lab-hostops

Whitelisted host-operations MCP server for SDL2 lab machines. It answers "is the service up, what did it log, did the USB adapter come back, is the local device API answering" — the class of incident (boot USB-enumeration races, corrupt-venv locks, silent partial syncs) that a network client can see but not diagnose.

Deliberate non-goals: no shell tool, no arbitrary commands, and no path to any device /control/* endpoint. Hardware control belongs to the lab-skills SDK and its MCP server (ac-organic-lab — AGENT_RULES §1.1). The tool surface below is the complete surface; every target must be whitelisted in config.toml, so a service or port not listed cannot be touched at all.

Tools

Tool	Mutates?	Notes
host_info()	no	hostname, OS, uptime, disk free, loadavg, backend
service_status(service)	no	systemd unit / Windows service state
tail_service_log(service, lines)	no	journald (Linux) or NSSM .out/.err logs (Windows); 10–400 lines
restart_service(service)	yes	only services in the smaller restartable list; Windows path runs nssm restart + the mandatory sc continue quirk; audited (see below)
list_serial_ports()	no	pyserial ([serial] extra) or /dev glob fallback
probe_local_status(port)	no	GET http://127.0.0.1:<port>/status for whitelisted ports

Backends

Selected automatically by platform:

• systemd (Linux, Raspberry Pi): systemctl / journalctl. Restarts can be prefixed with sudo -n (use_sudo = true) — grant only the exact units, e.g. /etc/sudoers.d/sdl-lab-hostops:

  sdl2 ALL=(root) NOPASSWD: /usr/bin/systemctl restart plateloc.service
  

• nssm (Windows device PCs): sc query, nssm restart + sc continue (DEVICE_PC_SETUP §7 quirk), log tails from C:\SDL_Logs\<svc>.{out,err}.log.

Transports & auth

• stdio (default): the MCP client spawns the process per connection. No daemon, no token. This is also the daemonless "lite" mode — see the Pi section.
• http (streamable-http): long-lived service. A non-loopback bind refuses to start unless HOSTOPS_TOKEN is set; clients send Authorization: Bearer <token>. Network reachability is additionally gated by Tailscale ACLs, per the lab's v1 auth posture (STATUS_SPEC §11). Exception: GET /status is unauthenticated — it serves a read-only STATUS_SPEC v1.2 envelope (read-only conformance clause, §9) so the dashboard can register the instance in equipment.yaml and monitor the watchers. Primary operation: none (ops service) — activity is permanently idle; claims/allowed_actions are N/A because there is no control surface.

Environment

Var	Meaning
HOSTOPS_CONFIG	path to config.toml (or pass --config)
HOSTOPS_TOKEN	bearer token, required for non-loopback http binds
HOSTOPS_INGEST_URL	e.g. http://sdl2-server:8001 — enables audit rows

Audit: every restart_service posts a hostops_action event to the dashboard's POST /api/ingest/events (best-effort, never blocks the restart). Reads are not audited. Register the hostops_action event type in ac-organic-lab/docs/LAB_MONITORING.md §4 when the first instance ships.

Install — Windows device PC (NSSM)

Follow ac-organic-lab/docs/DEVICE_PC_SETUP.md §3 with:

cd C:\Users\sdl2\Projects
git clone <this-repo> sdl-lab-hostops
cd sdl-lab-hostops
Copy-Item config.example.toml config.toml   # edit whitelists for this PC
C:\SDL_Tools\uv.exe sync --extra serial
nssm install sdl-lab-hostops C:\SDL_Tools\uv.exe run --project C:\Users\sdl2\Projects\sdl-lab-hostops lab-hostops-serve --transport http
nssm set sdl-lab-hostops AppDirectory C:\Users\sdl2\Projects\sdl-lab-hostops
nssm set sdl-lab-hostops AppEnvironmentExtra HOSTOPS_TOKEN=<token> HOSTOPS_INGEST_URL=http://sdl2-server-gaia.tail6a1dd7.ts.net:8001
# ... stdout/stderr logs, auto-start, run-as user: exactly as DEVICE_PC_SETUP §3
nssm start sdl-lab-hostops
sc continue sdl-lab-hostops

Note the service account needs rights to restart the other services (sc sdset per service, or run sdl-lab-hostops under an account that has them). A permission failure is reported truthfully in the tool result.

Install — Linux / Raspberry Pi (systemd)

git clone <this-repo> /opt/sdl-lab-hostops && cd /opt/sdl-lab-hostops
cp config.example.toml config.toml   # edit
uv sync                              # base deps only — no extras needed
sudo cp deploy/sdl-lab-hostops.service /etc/systemd/system/
sudo systemctl enable --now sdl-lab-hostops

Pi Zero 2W "lite" mode

The base install is small (mcp + httpx/starlette/uvicorn, all pure-Python or armv8 wheels) and idles at a few tens of MB — the same footprint class as the sense-every-zone gateway already running on sdl2-pi0-environ-01. Two ways to run it lighter:

1. http, minimal: skip the [serial] extra, keep the whitelist tiny.

2. daemonless stdio-over-SSH — zero resident footprint; the central Hermes spawns it on demand and SSH is the auth (no token, no open port):

   # Hermes mcp_servers entry on the central server
   hostops-pi0-environ:
     command: ssh
     args: [sdl2@sdl2-pi0-environ-01, /opt/sdl-lab-hostops/.venv/bin/lab-hostops-serve, --transport, stdio, --config, /opt/sdl-lab-hostops/config.toml]

   Requires key-based SSH from the central server. Prefer this on the Pis; prefer the http service on the Windows PCs (no SSH daemon there).

Client registration

Register each instance in the lab's reviewed MCP registry (ac-organic-lab/mcp/servers.yaml) with the full 6-tool include list, and mirror that allowlist in the client config (e.g. the Hermes lab-ops profile's mcp_servers.<name>.tools.include). A new tool added here should only reach an agent after both lists are updated — that's the point.

Tests

uv run pytest -q