---
title: A tool list is also a security surface
series: control-loop
type: lab-note
published: 2026-09-06
author: tim
confidence: medium
project: authority-compiler
tags:
  - agent-runtime
  - permissions
  - tool-design
exposure:
  basis: architecture-analysis
tested_with: []
domains:
  - agent-systems
  - trust-boundary
thesis: Dynamic tool discovery is not only a context-efficiency optimization; it is an authority decision about which classes of action are currently available.
---

Dynamic tool discovery is usually framed as a way to keep irrelevant schemas
out of context. It is also a policy decision. The available tool surface tells
the reasoning system which classes of action are currently possible.

That makes tool design simultaneously model UX, security architecture, policy
surface, and observability design. A narrow, named operation is easier to
authorize, constrain, audit, simulate, rate-limit, and verify than a general
shell-shaped escape hatch.

This note records a bounded architectural hypothesis, not a hands-on observation,
tested environment, or claim about a released ReactorJet runtime. See
[Authority Compiler](/work/authority-compiler) and [Giving an agent a shell is
not the same as giving it a tool](/notes/teardown/giving-agent-shell-is-not-tool).