---
title: Layers
description: The slices of a codebase, each with the one command that closes it and the boundary it owns.
---

A layer is a slice of the repository with three things attached: the tracker label that places an issue in it,
the globs it owns, and the one test that closes it.

```yaml
layers:
  - id: L2-runtime
    label: 'layer:L2'
    description: the execution runtime and its adapters
    paths: ['packages/runtime/**', 'packages/adapters/**']
    verify: pnpm test packages/runtime
    enforce: false
```

This block is the **source**. A layer's description in the tracker is a reflection of it, never the other way
round.

## What reads it

- **The decomposer** places a new issue in a layer when it breaks an approved design into issues.
- **The brief** tells the worker which layer its issue belongs to, what that layer owns, and the one command
  that closes it — cheaper than the whole suite, and more specific than "run the tests".
- **`deliver`** compares the pull request's changed files against the layer's globs and reports every crossing.

## Reporting first, blocking later

`enforce` is off by default, and that is the point. A boundary that blocks before a team has drawn it properly
costs more than it protects: every legitimate cross-cutting change becomes a fight with the loop, and people
learn to mislabel issues to get work through.

So the default is: the crossing is always reported, on the pull request and in the delivery actions, and the
merge continues. Turn `enforce: true` on for the layer once the reports stop surprising you — at that point the
boundary is real, and holding a PR that crosses it is enforcing something the team already believes.

Work outside the boundary has a name in the brief too: a bullet under **Follow-ups** in the pull request body,
not code in this pull request.

## Layers and the cheap verifier

`verifyCommandFor` answers "what closes this issue" with the layer's own command when the issue belongs to one,
and `delivery.verifyCommand` otherwise. That is [cost lever 1](/docs/concepts/cost): the cheap check runs before
the expensive review, and on a monorepo the difference between one package's tests and the whole suite is most
of the bill.