---
status: active
initiated: 2026-08-23
touches:
  - 02-DECISIONS/0017-modules-outside-the-core-are-grouped-by-domain.md
  - 03-DESIGN/00-as-is/10-module-catalogue.md
  - 03-DESIGN/00-as-is/02-modules-and-manifests.md
became: []
---

# 005 — Which domains the catalogue groups into

[ADR 0017](../../02-DECISIONS/0017-modules-outside-the-core-are-grouped-by-domain.md) settles
that modules outside the platform core are grouped by domain rather than by single function,
and deliberately does not settle the list. This effort settles the list — and, first, tests
whether the premise survives measurement.

## What is being investigated

Eighty-nine modules sit outside the platform core. The question is which of them belong
together, and the method is evidence rather than intuition: **which modules actually change
together**, measured across the full history of the code repository.

## Why

The argument in ADR 0017 is that the catalogue's shape records what was installed rather than
what anything is for — that four modules constituting "how a node is reachable" have no
relationship the mesh can see, so a change to connectivity is made four times.

That argument is testable. If those modules genuinely change together, the grouping is
justified by more than tidiness. If they do not, the premise needs revising before a list is
drawn from it.

## What it touches

The catalogue's shape, the manifest, and — for one candidate grouping — the provisioning
reference itself, since a requirement names a provider **module**. Grouping providers would
change what a consumer names.

## Status

Measurement is done and is in [`analysis.md`](analysis.md). It **partly contradicts the
premise**, in a way that narrows the effort usefully:

- Non-platform modules overwhelmingly change **alone** — 10% of commits touch more than one,
  and 50 of 89 never co-change with anything.
- Two clusters do exist. One of them, reachability, holds up as a domain.
- The other, the provisioned infrastructure providers, co-changes for a reason that argues
  **against** grouping rather than for it.

The remaining work is the list itself, for the modules where grouping is justified, plus the
open questions below.

## Open questions

| Question | Why it is open |
|---|---|
| Whether provider modules group at all, and if so what a consumer's requirement names instead of a module. | The provisioning reference is load-bearing; getting it wrong is expensive. Opinion and evidence in the analysis; not yet decided. |
| Whether applications group into domains now and leave the monorepo later as a unit, or leave first. | Decided in principle — group first, then split — but the migration order has real cost either way. |
| What to do with the ~50 modules that co-change with nothing. | The evidence gives no grouping signal for them at all. That may mean they are correctly sized already. |
| Whether "group or leave" is even the right pair of options. | [Research 006](../006-mesh-from-scratch/code-skeleton.md) finds a third fate — **absorbed into the node host**, ceasing to be a module at all — and argues it is the correct answer for the reachability cluster this effort measured. If so, the cluster this effort found is evidence for absorption rather than for grouping. |