jschoubben
e20a09ae80
The design, rather than an account of what exists. A module provides names and requires names, and that single relation absorbs three things this effort had listed separately: requiring another module is requiring a concrete name, requiring a resource is requiring an abstract one, and an interface is simply a name with more than one provider. Nothing has to declare that it is an interface — it either has one provider or several. The move that does the most work: a NODE provides names too. Its profile is a set of them — display-server, container-runtime, an architecture — so a module requiring a display server is satisfied by the node exactly as one requiring a database is satisfied by another module. One resolution instead of two, and a graphical application cannot land on a node without a display server for the same reason, through the same code, that it cannot land without its libraries. Which makes the host's capability detection an input to resolution rather than something a person reads. It was built to be read; it turns out to be a provides-list. `excludes` is the one genuinely new relation, because it is not derivable: two modules that both provide message-bus look interchangeable when installing both would break the machine. Constraints are not placement. They say what must be true of a node, never which node — which is the mistake the measurement found in the current catalogue, where a module pins its database to a named node so a second node cannot provide it without editing the consumer. What it deletes, for the design: the module/resource distinction, the interface as a kind of thing, capability checking as a separate mechanism, domain grouping — folders assert relationships where edges record them, so a domain becomes a query over the graph rather than a directory somebody keeps true — and possibly tiers, if a tier is just a computed level. What it does not delete, stated so it is not discovered later: a resolver still has to exist, with version constraints and conflicts, and the design owes an answer on what it delegates rather than reimplements.
145 lines
11 KiB
Markdown
145 lines
11 KiB
Markdown
---
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status: active
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initiated: 2026-08-25
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touches:
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- 02-DECISIONS/0002-everything-is-a-module.md
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- 02-DECISIONS/0017-modules-outside-the-core-are-grouped-by-domain.md
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- 02-DECISIONS/0036-a-node-is-a-managed-machine.md
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- 03-DESIGN/00-as-is/02-modules-and-manifests.md
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- 03-DESIGN/00-as-is/10-module-catalogue.md
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- 04-ISSUES/007-an-installed-package-is-not-a-capability/00-report.md
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---
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# 011 — The module graph
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## What is being investigated
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Whether the catalogue's missing structure is a **graph** — modules declaring what they need,
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what they offer, and what they exclude — and what that replaces.
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**The design is in [`proposal.md`](proposal.md): one kind of edge.** A module provides names
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and requires names, and that single relation absorbs requiring a module, requiring a resource,
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and the interface-and-adapter idea — an interface is simply a name with more than one provider.
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A **node provides names too**, which makes capability checking stop being a separate mechanism
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and makes the host's own capability report an input to resolution rather than something a
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person reads.
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[`analysis.md`](analysis.md) measured the current catalogue. Its value to the design is two
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lessons rather than its machinery — a field that means *depends on* should say so, and
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placement does not belong in a manifest — and the rest is recorded as as-is evidence.
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**Measured, and the premise was wrong for the existing system: the graph is not missing there.**
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[`analysis.md`](analysis.md) — 126 manifests, 103 edges, no cycles, nothing dangling, and a
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resolver that topologically sorts them, already called by the tool loader, the installer and
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the delivery coordinator. What the effort assumed would need building is a thing to call.
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What survives is narrower: three declarations that do not exist (`excludes`, a required node
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capability, an interface with adapters), and two defects worth fixing whatever else is
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concluded — `provider:` is a dependency edge that is not read as one, which makes the closure
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for a working mesh come out without a database; and the resolver continues past a cycle and
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past a missing dependency, contrary to ADR 0008.
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[ADR 0017](../../02-DECISIONS/0017-modules-outside-the-core-are-grouped-by-domain.md) proposes
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grouping modules by domain. [Research 005](../005-domain-grouping/analysis.md) measured that
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proposal and found its evidence holds in exactly one place — reachability — which
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[ADR 0037](../../02-DECISIONS/0037-the-host-applies-it-does-not-decide.md) has since absorbed
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into the host. The measured case for domain grouping has therefore been consumed by a decision
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taken for unrelated reasons, and what remains is fifty modules that co-change with nothing.
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That leaves the original complaint unanswered: the catalogue records **what was installed**
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rather than **what anything is for**, and nothing in the system can see a relationship between
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two modules. Grouping asserts relationships. A graph records them.
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## Why now
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A proposal to split modules into *provisioning services* and *applications* was worked through
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and abandoned in favour of one concept with facets, for a reason worth keeping:
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- The split cannot be filed consistently. A git forge is consumed as a service *and* operated
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through a web interface. An analytics service grants tracking identity *and* is a dashboard
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somebody reads. An identity provider grants authentication *and* has an admin console.
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- The operator's correction is the sharper form: **what runs on the machine is a supervised
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container, not something a user started.** That is a fact about *how a thing runs*, not about
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what kind of thing it is — so it is a facet, not a taxonomy.
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Filing decisions that follow from nothing are the disease research 005 measured. A second
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taxonomy would reproduce it.
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So [ADR 0002](../../02-DECISIONS/0002-everything-is-a-module.md) survives, and the question
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becomes what a module must be able to **declare**.
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## The shape being investigated
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Five declarations, of which two exist today.
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| Declaration | Today | Notes |
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|---|---|---|
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| **requires a resource** — a database, a bucket | yes | provisioning, [ADR 0005](../../02-DECISIONS/0005-capabilities-are-provisioned-on-declaration.md) |
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| **provides a resource** | yes | as above |
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| **requires another module** | **no** | the dependency edge — the graph's substance |
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| **excludes another module** | **no** | installing A makes B unavailable |
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| **requires a node capability** | **no** | a graphical session, a container runtime, an architecture |
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And one structural idea on top: **an interface module carries no implementation.** Adapters
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provide it. An assistant interface with several model-provider adapters; a terminal interface
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with several terminal adapters. A dependent names the interface and never an implementation.
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**Prior art to measure against, not invent past.** This is a package manager's model, and the
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platform's own package manager already has all of it: `depends` is the dependency edge,
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`conflicts` is exclusion, and `provides` is the interface — several packages provide one
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virtual name, and a dependent names the virtual one. That the design arrived at the same shape
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independently is evidence for it. It is also a warning: dependency resolution, version
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constraints, conflict handling and rollback are a long-solved and easily-botched problem, and
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the effort should establish what to **delegate** rather than reimplement.
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## Capabilities, and what may be installed
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The operator's formulation: *system specs are capabilities, and capabilities unlock installable
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modules — you cannot install a graphical application on a node with no display server.*
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The question that follows is whether the mesh may install a capability. The effort's working
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position, to be tested:
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- **Intrinsic capabilities** — hardware, architecture, network position — are facts about a
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machine. They are detected, never installed, and a module requiring one it does not have is
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not unresolved but **impossible** on that node.
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- **Provided capabilities** — a display server, a container runtime — are not a separate kind
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of thing at all. They are modules that provide a capability, and requiring one is an ordinary
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edge the graph resolves by installing it.
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If that holds, "may the mesh install a capability" is not a policy question. It is dependency
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resolution, and the only genuinely new thing is detection.
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Which is where [issue 007](../../04-ISSUES/007-an-installed-package-is-not-a-capability/00-report.md)
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bears directly: *an installed package is not a capability*. A provided capability is not real
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because a package is present — it is real when it is present, running and working, and the
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difference is exactly the class of fault this repository keeps recording.
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## What it touches beyond the catalogue
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The operator's assessment is that the machinery around a module is wanted and its integration
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is not: **scheduled tasks, hooks, migrations, configuration and environment settings are worth
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keeping; seeds are not; and the current integration is wrong enough to need a major refactor.**
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That is a claim to test rather than adopt. Research 005 already found supporting evidence from
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a different direction — that the densest apparent coupling in the catalogue is manifest
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boilerplate churn, cross-cutting changes to the machinery applied N times — which is what an
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integration being wrong looks like from the outside.
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## Open questions
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| Question | Why it is open |
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|---|---|
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| ~~What does the graph **delete**?~~ | **Answered for the design** in [`proposal.md`](proposal.md): the distinction between requiring a module and requiring a resource, the interface as a kind of thing, capability checking as a separate mechanism, domain grouping, and possibly tiers as a separate concept. *(For the existing system the answer was nothing, because it is already there — [`analysis.md`](analysis.md).)* |
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| When two modules provide one name, who chooses? | The substance of the interface idea, and the proposal does not settle it: a node setting, a mesh setting, or an explicit pin. |
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| Does an abstract name need a type? | A consumer of `database` needs credentials; a consumer of `terminal` needs a command to run. Whether that difference lives in the name, beside it, or in what the provider hands back is undecided. |
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| Would the missing declarations be used? | Zero manifests declare exclusions or capabilities, which is equally consistent with *nobody needs them* and *nobody can express them*. Nothing measured separates those. |
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| Should `provider:` become a real edge, or should the relationship be declared twice? | It names a module and means *depends on*. Reading it as an edge fixes the closure; the alternative is requiring the consumer to also list it under `dependencies:`, which is duplication a resolver already avoids elsewhere. |
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| Should placement leave the catalogue? | A provision pins itself to a named node, in the manifest. Which node runs what is an inventory decision — tier 2 by the skeleton's own test — and having it in tier 4 means a second node cannot provide the mesh's database without editing the module that consumes it. |
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| Where does resolution happen — mesh or platform package manager? | The mesh must model mesh-level edges. Whether it also resolves operating-system packages, or delegates, decides whether a solver has to be written. |
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| Is an interface a module, or a name? | Arch makes it a name that packages claim. Making it a module gives it a manifest, an owner and a place to document the contract — and a thing with no implementation to install. |
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| What does an exclusion mean for something already installed? | Refuse the install, or make the conflict visible and let it be decided. The second is a policy surface; the first is a package manager. |
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| Does node adoption scan for capabilities, applications, or both? | The operator proposes scanning an adopted node and enabling what it finds. Under the working position above, the scan is for capabilities — but a machine with a terminal already installed is also a module already satisfied, and whether that is adoption or drift is undecided. |
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| One installation image, or several? | Proposed: pre-built images carrying different capability sets, so a machine is adopted quickly. Several images bake capability sets at image time, which is the filing problem in a new form and reintroduces what detection exists to avoid. One image carrying the host and nothing else is [ADR 0038](../../02-DECISIONS/0038-a-node-joins-by-linking-first.md)'s *one binary installed by hand*, automated. The effort should settle which. |
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| What happens to domain grouping? | [ADR 0017](../../02-DECISIONS/0017-modules-outside-the-core-are-grouped-by-domain.md) is still `proposed`. If the graph is the answer, 0017 is superseded rather than narrowed — its text is never edited. |
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