---
layer: to-be
status: designed
code: []
updated: 2026-09-01
decisions:
  - 02-DECISIONS/0009-modules-and-the-graph.md
  - 02-DECISIONS/0005-the-node-host.md
  - 02-DECISIONS/0027-a-provision-names-what-the-consumer-is-coupled-to.md
---

# What a module must be able to say

**Measured, not guessed.** 127 manifests in the system being replaced were read and every key
counted, then set against what the new manifest can express. This document is the coverage
checklist: what is already sayable, what is deliberately not, and what is missing.

*Surveyed 2026-09-01. Counts are modules, not occurrences, unless stated.*

## Already sayable

| what it says | used by | how it is said here |
|---|---|---|
| **depends on another module** | 65 | `requires` naming a module. A requirement naming a module means *that module*, not anything providing the name |
| **system packages** | 28 | the `package` shape |
| **a container** | 48 | the `container` shape, pinned by digest |
| **systemd units** | 17 | a `file` for the unit, a `service` for the state it should be in |
| **how to reach it** | 17 | `serves`, with the mesh adding which machine and where |
| **a public name** | 11 | requiring `route` and contributing the name |
| **ports it opens** | 11 | `listens`, from which filtering is computed |
| **data directories, and who owns them** | 38 | `directory` with `owner`; never removed while holding anything ([ADR 0030](../../02-DECISIONS/0030-data-outlives-the-mesh-that-declared-it.md)) |
| **what it provides and requires** | 15 + 2 | `provides` / `requires`, named for what the consumer is coupled to |
| **restart when something changes** | 11 | `restart-on` |
| **a generated credential** | 20 | `own-secrets`, sealed to the machine |
| **a value that differs per node** | 43 | settings, and `computed` for what only the mesh knows |
| **images built from source** | 2 | `build.artifacts` |

## Deliberately not sayable

**Stage hooks — 36 modules.** Arbitrary code at install, configure and start. **The link may not
carry an action** ([ADR 0005](../../02-DECISIONS/0005-the-node-host.md)): what may be pushed is
bounded by form, and a command to run is not a form. A module needing setup logic ships a program
that reads what the mesh delivered and reconciles — which is what the provisioners are, and they
are ~350 lines each including the reasoning.

**Flavours — 6 modules.** Variants of one module. Retired in favour of claims
([ADR 0009](../../02-DECISIONS/0009-modules-and-the-graph.md)): two display servers are two
modules that both claim the seat, and adding a third changes nothing anywhere else. What is lost
is `extends` chains, which were doing inheritance and are better as separate modules.

## Missing, and what each would take

Ordered by how many modules need it. The largest entry turned out not to be a gap at all, which
is left in place rather than deleted: the first framing of it was wrong in an instructive way, and
a checklist that quietly loses its biggest item reads as though nobody looked.

### Tool servers — 56 modules — *not a gap*

Over half the modules ship a `tools/` directory that becomes tools an agent can call on that node.
This was written up as the largest single gap. **It is expressible with what exists**, and the
first framing of it was wrong in a way worth keeping: *a module provides `tools`, the session
requires them* does not work, because a requirement has exactly one answer and 56 modules offering
tools would be 56 answers to one question.

Turn it around and it fits exactly. The session **provides** `tool-host`; every module offering
tools **requires** it and **contributes** where its tools are. Many-to-one is what `contributes`
has always been, and the session receives all of them in one file:

```
given:  { from: gitea,  values: { at: … } }
        { from: minio,  values: { at: … } }
        { from: umami,  values: { at: … } }
```

Verified by resolving it, not by reading the code. It also only became possible today: until
[`022`](../../04-ISSUES/022-one-credential-per-node-per-provision-not-per-module/00-report.md) was
fixed, several modules on one node requiring the same thing was refused outright.

What remains is not vocabulary but a decision about **what a tool server is** — a container the
module already runs, and what the session does with the list. That is work, not a missing shape.

### Schema migrations — 14 modules

A module with a database needs its schema brought up to date before it runs. The mesh does this
for its own contexts and has no way for a *module* to declare it. The provisioner pattern covers
it — a program that runs migrations and exits — but nothing expresses *this must happen before
that starts*, which is the actual requirement.

### Configuration merging — 18 modules, 134 files

Files assembled from a module's default plus per-node overrides, with a strategy (`replace`,
`merge`) and a format (`toml`, `yaml`, `json`). Settings already merge into a file's content; what
is missing is format-aware merging.

**And it should stay missing.** A mechanism that understands TOML will be asked for YAML, then
INI — which is how the arrangement being replaced became something nobody could hold in their
head. The module knows its own format because it wrote the rest of the file.

### Health checks — 7 modules

`{type: port|url, expect: …}`. The mesh knows whether a container is running, which is not the
same as whether it answers — a distinction this project has paid for twice already.

An `action` carries a `verify` and is exactly this shape. **It is not available to a module**: the
link may not carry a command to run ([ADR 0005](../../02-DECISIONS/0005-the-node-host.md)), and a
module's resources reach a machine over the link. So a health check needs a way to say *ask this
and expect that* without saying *run this* — closer to a `listens` entry than to an action.

**This is the gap most worth closing**, because *running* and *answering* being conflated is a
class of fault, not an inconvenience.

### Theme knobs — 3 modules, 101 values

`{theme: {kind: color|font|string, label}}` — declared so a ricing tool can offer them. Settings
already carry the value; what is missing is the **metadata** saying a value is presentable and
what kind it is. Small, self-contained, and only interesting once something presents them.

### Event routing — 2 modules

`{routing-key: tool}`, generating a consumer. Two modules; wait for a third before deciding.

### Publishing a package — 6 modules

Modules published to a registry and consumed as libraries. This is a *build* output the mesh does
not deliver to a node, so it may not belong here at all.

## What checking the coverage found

Two faults, both surfaced by asking what a *real* node looks like rather than what a test does.
Neither is about the vocabulary; both are about the machinery under it.

**A credential belonged to a machine, not to a module**
([`022`](../../04-ISSUES/022-one-credential-per-node-per-provision-not-per-module/00-report.md),
fixed). A node running three services against one database could not be planned at all — and on
the consumer's side did not refuse, it just gave two of the three no credential. Every scenario
written to date had one consumer per node, which is the natural shape of a small test and not the
shape of a machine.

**A consumer could not build a connection string**
([`023`](../../04-ISSUES/023-a-consumer-cannot-build-a-connection-string/00-report.md), fixed). It
had its password in the right shape and the host, port and user name were out of reach: the user
name was invented by the provisioner and recorded nowhere, and the bound values sat in a JSON
document that an application reading `KEY=value` cannot use.

The asymmetry was backwards, which is what made it worth stating. **The secret is the hard case** —
the mesh must not be able to read it — and the secret was the part that already arrived. The host
and port are ordinary facts held in the clear, and they were the ones stuck. Both halves came from
the same thing: the mesh knew something and did not say it.

## What the survey found that is not about coverage

**Declaration and reality had drifted in the system being replaced.** Several live provisions are
brokered by modules whose manifests declare nothing — a speech-to-text engine served to a consumer
on another node, an object-store bucket held by a module whose manifest mentions only its
database. **A manifest that does not have to be true stops being true**, which is the argument for
resolution refusing rather than warning.

**Two derivations of the same fact.** A module's kind was computed in two places from different
evidence — one from the manifest, one from what is on disk — producing different labels for the
same module. There is one derivation here, and there should stay one.

**A live listing returned credentials in plaintext.** Not a coverage question, but the reason
sealing is worth its inconvenience.

**An image store is a module, and was written up here as something the mesh does.** It was
considered for the substrate and removed, because the test is not *can it grant itself one* —
nearly anything passes that — but whether the control plane needs it before it can give its first
instruction. It does not. So a registry somebody runs for their own images is the same module as
the one the mesh runs for its own: it offers a place to push, and claims that role once per
machine.

**A rule was enforced only at the far end.** A module may not declare an action, and the host
refused one correctly — but the control plane accepted it into the catalogue, resolved it and
pushed it, so the refusal arrived on a machine with nothing tying it back to the manifest. The
rule held; it was just unusable, which is the same shape as the network shape that cost five
failing tests before anyone read the host's log. It is now refused where it is written.