the-custodian/canon/architecture/adr-002-custodian-agent-runtime-design.md

---
id: ADR-002
type: architecture-decision-record
title: "Custodian Agent Runtime — v0.1 Bootstrap Design"
status: accepted
decided_by: Bernd Worsch
date: "2026-03-12"
tags: ["architecture", "agent-runtime", "llm", "ooda", "bounded-agency"]
---

# ADR-002: Custodian Agent Runtime — v0.1 Bootstrap Design

## Status

Accepted.

## Context

CUST-WP-0001 requires a first working skeleton of the Custodian as an acting
agent: a loop that observes project state, reasons about it, and executes
bounded write operations — without human interaction for each step.

The dependencies (llm-connect, operational Railiance infra) are now resolved.
This ADR captures the five key architectural decisions for the v0.1 bootstrap.

## Decisions

### D1 — Location: `runtime/` inside the-custodian (not a new repo)

**Decision:** The runtime lives under `the-custodian/runtime/` as a standalone
Python package (`pyproject.toml`, own venv) rather than a new repository.

**Rationale:** The runtime is tightly coupled to canon (reads constitution,
memory) and the state-hub (its primary coordination layer). A separate repo
adds friction with no v0.1 benefit. The existing `runtime/` scaffold confirms
the original intent. Extraction to its own repo is deferred to when the
runtime has stable boundaries and multiple consumers.

### D2 — OODA loop: single-pass synchronous CLI

**Decision:** One `run()` call = one complete Observe → Orient → Decide → Act
cycle. Entry point is a CLI (`agent.py`) invoked manually or by a cron job.

```
Observe  — HTTP GET to state-hub: state summary or domain summary
Orient   — Load constitution + build structured LLM context prompt
Decide   — Single LLM call (via llm-connect) returns a JSON action plan
Act      — Execute only sanctioned write operations from the plan
```

**Rationale:** Async event loops and daemons add operational complexity that
v0.1 doesn't need. A single-pass CLI is testable, debuggable, and can be
scheduled externally. The transition to an event-driven loop is Phase 2.

### D3 — LLM backend: ClaudeCodeAdapter by default

**Decision:** The runtime uses `llm_connect.ClaudeCodeAdapter` as its default
LLM backend (shells out to `claude --print`). Provider is configurable via
`--llm` flag to support `gemini`, `openrouter`, or `openai`.

**Rationale:** `ClaudeCodeAdapter` requires no API key and honours the
Local-First value (V2). All current deployments have Claude Code available.
The llm-connect abstraction means switching providers is a one-line change.

### D4 — Action constraint: three sanctioned write operations only

**Decision:** The agent may execute exactly three state-hub write operations
without human approval:
1. `add_progress_event` — append an observation to the event log
2. `update_task_status` — mark a task done/in_progress (reversible)
3. `flag_for_human` — raise an intervention flag (escalation, not action)

All other operations (create workstream, record decision, resolve decision,
write to canon) require human approval before execution.

**Rationale:** Constitution §3/§4 require bounded agency. The three operations
are either append-only (progress events), reversible (task status), or
explicitly escalating (flag). They cannot produce irreversible harm.

### D5 — LLM response format: JSON block in markdown

**Decision:** The LLM is prompted to return a Markdown response with a
fenced ```json block containing the structured action plan:

```json
{
  "observations": ["..."],
  "progress_events": [
    {"summary": "...", "workstream_id": "...", "event_type": "note"}
  ],
  "tasks_to_update": [
    {"task_id": "...", "status": "done"}
  ],
  "tasks_to_flag": [
    {"task_id": "...", "note": "..."}
  ]
}
```

The surrounding Markdown is preserved as a human-readable reasoning trace
and written to `memory/working/` as a session note.

**Rationale:** JSON blocks are robust to extraction (delimited), LLMs produce
them reliably with clear instructions, and the surrounding prose gives Bernd
an auditable reasoning trace without requiring a separate reasoning step.

## Consequences

- `runtime/` becomes a standalone Python package; `make agent-run DOMAIN=x`
  invokes it.
- The runtime has no DB schema changes and no new API endpoints — it is a
  pure client of the existing state-hub HTTP API.
- Autonomous actions are limited to append-only writes and escalations. Any
  expansion of the action surface requires a new ADR and human approval.
- The v0.1 loop is single-user (Bernd). Multi-agent expansion is Phase 2+.

## Deferred

- Async event loop / daemon mode (Phase 2)
- RAG over canon (Phase 1 roadmap item)
- Tool adapters beyond state-hub HTTP (planned in `runtime/tool_adapters/`)
- Deployment on Railiance k3s as a scheduled CronJob