# ADR 0012 — Hermes/Oikos interaction architecture

**Status:** Accepted
**Date:** 2026-07-08

## Context

Hermes (the AI agent) is the primary operator interface for the hubris
homelab. It communicates with Oikos via the MCP protocol. The MCP tools
map to the OODA loop phases (Observe, Orient, Decide, Act). A thin client
model distributes agent context via API deltas instead of git clones.

## Decision

Hermes interacts with Oikos through three surface layers: MCP tools
(agent-facing), REST API endpoints (operator-facing and agent-facing), and
the SSH actuator (internal). All read paths go through the Postgres DB as
the single source of truth. All writes go through the API with audit
logging and policy classification.

## Hermes → Oikos interaction flow

```mermaid
sequenceDiagram
    participant H as Hermes (AI Agent)
    participant MCP as MCP Server (:8090/mcp)
    participant API as REST API (:8090/api/v1)
    participant DB as Postgres (TimescaleDB)
    participant Act as Actuator
    participant PVE as Proxmox Hosts
    participant Matrix as Matrix Notifier

    Note over H,Matrix: ── OODA: Observe ──

    H->>MCP: get_entity("service:caddy")
    MCP->>DB: SELECT * FROM entities WHERE slug=$1
    DB-->>MCP: {slug, type, state, health, attrs}
    MCP-->>H: entity record

    H->>MCP: get_state_snapshot()
    MCP->>DB: SELECT e.slug, st.health, st.disk_usage_pct FROM entities e LEFT JOIN entity_status st
    DB-->>MCP: [{slug, health, disk_pct, drift_count}, ...]
    MCP-->>H: fleet health snapshot

    H->>MCP: search_knowledge("jellyfin hardware acceleration")
    MCP->>DB: SELECT ... WHERE search @@ to_tsquery('jellyfin & hardware & acceleration')
    DB-->>MCP: [documents, runbooks]
    MCP-->>H: ranked FTS results

    H->>MCP: get_blast_radius("service:caddy")
    MCP->>DB: SELECT blast_radius($1, 3) -- recursive CTE
    DB-->>MCP: [{entity, depth}, ...]
    MCP-->>H: what breaks if caddy goes down

    Note over H,Matrix: ── OODA: Orient ──

    H->>MCP: explain("lxc:jellyfin")
    MCP->>DB: SELECT e.*, st.health, st.last_check FROM entities e LEFT JOIN entity_status st
    MCP->>DB: SELECT r.type, se.slug, te.slug FROM relationships r WHERE ...
    DB-->>MCP: compact context card
    MCP-->>H: {type, state, health, relations, version, updated_at}

    H->>MCP: preflight("lxc:jellyfin", "restart")
    MCP->>DB: SELECT risk_class, approval FROM classification_for($1, $2)
    DB-->>MCP: {risk_class: "reversible_low", approval: "auto-act"}
    MCP-->>H: safe to auto-act

    H->>MCP: preflight("lxc:jellyfin", "deploy")
    MCP->>DB: ...
    DB-->>MCP: {risk_class: "config_mutation", approval: "operator-approval"}
    MCP-->>H: needs operator approval

    Note over H,Matrix: ── OODA: Decide ──

    alt reversible_low (auto-act)
        H->>MCP: request_execution("lxc:caddy", "restart")
        MCP->>API: POST /executions {action:"restart", target:"lxc:caddy"}
        API->>DB: INSERT executions (auto_approved)
        API->>Act: queue execution
        Act->>PVE: ssh systemctl restart caddy
        Act->>DB: UPDATE execution status→completed
        MCP-->>H: execution {status: completed}
    else config_mutation (escalate)
        H->>MCP: request_execution("lxc:jellyfin", "deploy")
        MCP->>API: POST /executions
        API->>DB: INSERT executions (proposed, needs approval)
        API->>Matrix: send approval request via notifier
        Matrix->>Operator: "Approve deploy lxc:jellyfin? ✅/❌"
        Operator->>Matrix: ✅
        Matrix->>API: POST /approvals/{id}/approve
        API->>DB: UPDATE execution status→approved
        API->>Act: queue execution
        Act->>PVE: run deploy procedure
        MCP-->>H: execution {status: completed}
    end

    Note over H,Matrix: ── OODA: Act (mutation gated) ──

    H->>MCP: tail_log("caddy", lines=200)
    MCP->>PVE: ssh journalctl -u caddy -n 200
    PVE-->>MCP: log lines
    MCP-->>H: caddy logs

    H->>MCP: get_service_status("caddy")
    MCP->>PVE: ssh systemctl show caddy
    PVE-->>MCP: {ActiveState, SubState, ...}
    MCP-->>H: service status

    H->>MCP: list_lxcs()
    MCP->>DB: SELECT * FROM entity_status WHERE type='lxc'
    DB-->>MCP: [lxc:caddy, lxc:jellyfin, ...]
    MCP-->>H: all LXCs with state

    H->>MCP: get_lxc_state("lxc:caddy")
    MCP->>PVE: ssh pct status {vmid} --verbose
    PVE-->>MCP: RAM, CPU, disk, uptime
    MCP-->>H: LXC resource state
```

## Thin client bootstrap flow

```mermaid
sequenceDiagram
    participant New as New Client (bare machine)
    participant Gitea as Gitea (raw URL)
    participant API as Oikos API
    participant DB as Postgres

    New->>Gitea: curl bootstrap.sh
    Gitea-->>New: bootstrap.sh

    New->>Gitea: fetch CLIENTS.md, AGENTS.md, OIKOS.md, tools/
    Gitea-->>New: agent orientation files

    New->>API: POST /clients/enroll {slug, hostname, mesh_ip}
    API->>DB: validate state, mesh IP
    API->>API: generate age keypair
    API->>DB: store pubkey, transition→provisioning
    API-->>New: {age_private_key, age_public_key, infisical_identity}

    New->>New: write /etc/age/key.txt, /etc/infisical/identity
    New->>New: install context-poller (launchd/systemd, every 5min)

    loop Every 5 minutes
        New->>API: GET /clients/ws:{hostname}/context?since={timestamp}
        API->>DB: SELECT files changed since {timestamp}
        API-->>New: {agent_files_changed, sops_config_changed, tools_changed}
        New->>Gitea: fetch only changed files
    end
```

## Internal Oikos component interactions

```mermaid
sequenceDiagram
    participant Sched as Scheduler
    participant API as API Server
    participant Notif as Notifier
    participant Act as Actuator
    participant DB as Postgres

    Note over Sched,DB: The OODA loop (internal)

    Sched->>DB: probe endpoints (HTTP, TCP, disk, cert-expiry)
    DB-->>Sched: results
    Sched->>DB: INSERT signals (dedup, flap suppression)
    Sched->>DB: UPDATE entity_status (health, disk, drift_count)

    Act->>DB: poll executions with status=auto_approved
    DB-->>Act: pending executions
    Act->>Act: circuit breaker check
    Act->>SSH: execute procedure
    Act->>DB: UPDATE execution status+result

    Notif->>DB: poll pending approvals
    DB-->>Notif: [approval requests]
    Notif->>Matrix: send approval messages

    API->>DB: INSERT audit_log (every mutation)
    API->>DB: NOTIFY oikos_events (SSE streaming)
```

## Tool ownership matrix

| Tool | Interface | Package | DB query | SSH |
|------|-----------|---------|----------|-----|
| `get_entity` | MCP | `internal/mcp/server.go` | DIRECT | — |
| `list_entities` | MCP | `internal/mcp/server.go` | DIRECT | — |
| `get_relations` | MCP | `internal/mcp/server.go` | DIRECT | — |
| `get_blast_radius` | MCP + REST | both | CTE function | — |
| `search_knowledge` | MCP | `internal/mcp/server.go` | FTS query | — |
| `get_health_summary` | MCP | `internal/mcp/server.go` | DIRECT | — |
| `whoami` | MCP | `internal/mcp/server.go` | DIRECT | — |
| `explain` | MCP | `internal/mcp/server.go` | DIRECT + JOIN | — |
| `preflight` | MCP | `internal/mcp/server.go` | CASE expression | — |
| `get_change_history` | MCP | `internal/mcp/server.go` | audit_log query | — |
| `get_state_snapshot` | MCP | `internal/mcp/server.go` | DIRECT + JOIN | — |
| `list_my_secrets` | MCP | `internal/mcp/server.go` | attributes query | — |
| `tail_log` | MCP | `internal/mcp/server.go` | — | journalctl |
| `get_service_status` | MCP | `internal/mcp/server.go` | — | systemctl show |
| `list_lxcs` | MCP | `internal/mcp/server.go` | entity_status query | — |
| `get_lxc_state` | MCP | `internal/mcp/server.go` | relationship query | pct status |
| `ping_service` | MCP | `internal/mcp/server.go` | — | probe |
| `request_execution` | MCP | `internal/mcp/server.go` | executions INSERT | SSH via actuator |
| `get_agent_activity` | MCP | `internal/mcp/server.go` | agent_activity query | — |
| `get_signal_history` | MCP | `internal/mcp/server.go` | signals query | — |
| `get_patterns` | MCP | `internal/mcp/server.go` | patterns query | — |
| `get_skills` | MCP | `internal/mcp/server.go` | skills query | — |
| `get_audit_trail` | MCP | `internal/mcp/server.go` | audit_log query | — |
| `get_trend` | MCP | `internal/mcp/server.go` | metrics query | — |
| `get_event_timeline` | MCP | `internal/mcp/server.go` | events query | — |
| `query_metrics` | MCP | `internal/mcp/server.go` | metric_samples query | — |
| `enroll` | REST | `internal/httpapi/impl.go` | entities+audit+events | — |
| `context` | REST | `internal/httpapi/impl.go` | context_files query | — |
| `secrets` | REST | `internal/httpapi/impl.go` | secrets.Manager.List | — |
| `provision` | REST | `internal/httpapi/impl.go` | entities+steps+relations | SSH via actuator |

## Consequences

- **Hermes is the primary operator interface.** All operator actions flow
  through Hermes → MCP → Oikos. The old `bin/homelab` CLI is dead.
- **MCP tools are read-only by design.** Mutations go through
  `request_execution`, which is policy-gated and requires operator
  approval for `config_mutation` and `destructive` actions.
- **The actuator holds the SSH key.** Hermes has no direct SSH access.
  The security boundary is Hermes → MCP → API → execution queue →
  actuator → SSH.
- **Thin clients poll for context deltas.** No git clones on workstations.
  The 5-minute poll replaces `git pull` with HTTP queries to
  `GET /clients/{slug}/context`.
- **The DB is the single source of truth.** All state transitions,
  audit entries, and event emissions go through Postgres. The scheduler,
  actuator, notifier, and API all read/write the same tables.

---

**2026-07-08 — renamed to Nomos.** The Hermes agent gateway was renamed to
Nomos (from *oikonomos*, the steward of the oikos) under the
[Nomos resident agent plan](../../plans/2026-07-08-nomos-resident-agent.md),
N0 milestone. The gateway binary (`cmd/nomos`), Docker service, DB slug
(`agent:nomos`), and all referencing docs were updated. All architectural
principles in this ADR remain unchanged.