jschoubben
3d693a8735
ADR 0039 settles what belongs in an SDK. It does not say what happens when there is more than one, and there already is: the contracts are expressed as Go types in the control plane and host and as TypeScript types in the SDK, and nobody has felt it because both live in one repository. They already disagree. The provision's field is "resource" in one and "Provision" in the other; "consumer" means the module in one and the node in the other; the envelope declares six headers on one side and emits four on both — the missing two being x-causation-id and x-schema, the second of which is exactly what a body needs in order to change shape without silent misreads. That class of failure does not announce itself. Two implementations disagreeing about an envelope do not fail to compile — they ignore each other's messages, and a mesh where a module stops reacting looks like a mesh where nothing happened. So the decision is to specify the wire rather than share the types, because the shapes are the easy half. What two implementations actually disagree about is behaviour: queue naming and durability, which headers are required and what an unknown one means, taking identity from the sealed credential rather than the environment, dedup on an id only the emitter can make, pinning a fingerprint rather than trusting an authority. And the suite is executable rather than prose, because a specification nobody can run is a document two implementations drift from while both believe they conform. The two existing implementations are the first made to pass it — a suite only new SDKs must satisfy would certify every future language against a disagreement that is already here. Claude-Session: https://claude.ai/code/session_01D6qtiYU3P9jk3pnAXyAFyx
165 lines
11 KiB
Markdown
165 lines
11 KiB
Markdown
# 02-DECISIONS
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Architecture decision records — the "why" trail behind the rules in
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[`00-META`](../00-META/) and the specifications in [`03-DESIGN`](../03-DESIGN/).
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**Numbered `02` because a decision precedes the design it authorises.** Research concludes,
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the decision is recorded here, and only then is the design written. Following the folder
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numbers walks the process in the order it happens.
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One file per decision, numbered, never deleted. A superseded record has its `status:` changed
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and gains a pointer to what replaced it — **its text is never edited**. The reasoning that was
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rejected is the expensive half to rediscover.
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The records run in the order the decisions were taken, oldest first.
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**Every decision is a record.** There is no ledger and no index file — if a decision is worth
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recording it is worth a record, and if it is not worth a record it is not recorded
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([ADR 0019](0019-how-this-repository-works.md)). A "decision" small enough to be one line is
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almost always a **rule**, and a rule belongs in
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[`00-META/how-we-build.md`](../00-META/how-we-build.md), where it is enforced and keeps the
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incident that earned it.
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## Frontmatter
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```yaml
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---
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status: proposed | accepted | superseded
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date: YYYY-MM-DD # when the decision was taken, not when it was written down
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deciders: name
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reconstructed: true|false # true when the record was written after the fact from evidence
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superseded-by: # 02-DECISIONS/NNNN-....md, when status is superseded
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extends: # 02-DECISIONS/NNNN-....md, when this record widens an earlier one
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---
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```
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## Body
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```
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# N. Title in plain language
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## Context what was true, with evidence
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## Considered Options numbered, each with why it was rejected
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## Decision what was decided
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## Consequences what follows, including what got harder
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## References commits, pull requests, knowledge-base entries, prior art
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```
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State evidence, not assertion. *"Zero of 124 modules declare `brain` as a dependency"*
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outranks *"the dependency rule is not followed"*.
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## Reconstructed records
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Records 0001–0014 were written on 2026-08-23, after the decisions they describe. Records 0015 onward were taken as records. Those
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decisions were taken in implementation rather than in a document; the records state what was
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decided and the evidence it was decided from, and each carries `reconstructed: true` and says
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so in its first lines.
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A reconstructed record is not a transcript. Where the deliberation is not recoverable, the
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options section states what the alternatives were and why the chosen one won on the evidence
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available — not a discussion that did not happen. Where a date is not establishable it says so
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rather than guessing.
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## Index
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**A number identifies a record and never changes.** Records are referenced from outside this
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repository — code comments, commit messages — so a number that moves invalidates them silently.
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Renumbering once cost 96 references across two code repositories, and that is why the numbers
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are now fixed.
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So the folder is in creation order, and **the reading order lives here.** It is generated from
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each record's `topic:` and written, because a reader looking at the folder on a forge sees the
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folder rather than a command. The objection to a written index is that it drifts — which is
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answered by checking it rather than by refusing to write one:
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```
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python3 00-META/checks/index.py --write regenerate
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python3 00-META/checks/index.py fail if stale
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```
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<!-- index:start -->
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### What the mesh is
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- **0001** — [The mesh brokers capabilities; nodes host; agents think](0001-mesh-brokers-nodes-host-agents-think.md)
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- **0002** — [Nodes communicate over a message broker, not over HTTP](0002-nodes-communicate-over-a-broker.md)
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- **0003** — [An agent is a persistent employee, not an instance of a pool](0003-agents-are-persistent-employees.md)
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### Its tiers, from the bottom up
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- **0004** — [A node, and how it joins](0004-a-node-and-how-it-joins.md)
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- **0005** — [The node host](0005-the-node-host.md)
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- **0006** — [The substrate and the control plane](0006-the-substrate-and-the-control-plane.md)
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- **0007** — [Connectivity](0007-connectivity.md)
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- **0008** — [A context owns its store, exclusively](0008-a-context-owns-its-store.md)
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- **0028** — [The substrate supplies the control plane and nothing else](0028-the-substrate-supplies-the-control-plane-and-nothing-else.md)
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- **0029** — [A network is a shape, because an action cannot be undone](0029-a-network-is-a-shape-because-an-action-cannot-be-undone.md)
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- **0030** — [Data outlives the mesh that declared it](0030-data-outlives-the-mesh-that-declared-it.md)
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- **0031** — [The control plane authenticates nobody, so identity is a module](0031-the-control-plane-authenticates-nobody.md)
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- **0033** — [The substrate is a store and a broker](0033-the-substrate-is-a-store-and-a-broker.md)
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- **0036** — [Bootstrap ends at a usable mesh, and the first credential comes from a person](0036-bootstrap-ends-at-a-usable-mesh.md)
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- **0066** — [Public routing is name-agnostic, its names are resolved inside the mesh, and an internal authority can certify them](0066-public-routing-is-name-agnostic.md)
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- **0067** — [Genesis is a pivot: a temporary control plane installs the registry that makes it permanent](0067-genesis-is-a-pivot.md)
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- **0068** — [The lab takes requests, one at a time, and runs each from its own copy](0068-the-lab-takes-requests.md) *(proposed)*
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- **0069** — [A module is a repository and a path within it](0069-a-module-is-a-repository-and-a-path.md)
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- **0070** — [The catalogue owns the module graph, and genesis builds rather than carries](0070-the-catalogue-owns-the-module-graph.md)
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- **0071** — [Genesis clones from a mesh, and checks what it got](0071-where-genesis-gets-its-source.md)
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- **0072** — [Two graphs, and a build chain that orders itself](0072-two-graphs-and-the-build-chain.md)
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- **0073** — [The installer carries a builder, and the registry stays where it is](0073-the-installer-carries-a-builder.md)
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- **0074** — [The wire is specified; an SDK is whatever passes the conformance suite](0074-the-wire-is-specified-not-the-types.md) *(proposed)*
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### What runs on them, and how it gets there
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- **0009** — [Modules and the graph](0009-modules-and-the-graph.md)
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- **0010** — [Delivery](0010-delivery.md)
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- **0024** — [Model access is a provision, and a licence is a thing with a name](0024-model-access-is-a-provision.md)
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- **0026** — [The mesh has a session of its own, and it is the node session's mechanism](0026-the-mesh-has-a-session-of-its-own.md)
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- **0027** — [A provision names what the consumer is coupled to, not the role it plays](0027-a-provision-names-what-the-consumer-is-coupled-to.md)
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- **0035** — [One implementation, several surfaces, and what that costs](0035-one-implementation-several-surfaces.md)
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- **0038** — [The mesh assigns the port, and a module does not care](0038-the-mesh-assigns-the-port.md) *(proposed)*
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- **0040** — [What a module is](0040-what-a-module-is.md)
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- **0041** — [Events are a relationship, the lighter sibling of provisioning](0041-events-are-a-relationship.md)
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- **0042** — [The shape of an event on the wire](0042-the-shape-of-an-event-on-the-wire.md)
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- **0043** — [A module's broker account is scoped by what it emits and consumes](0043-a-module-broker-account-is-scoped-by-emits-and-consumes.md)
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- **0044** — [A public name is provisioned, not registered by hand](0044-a-public-name-is-provisioned-like-any-capability.md)
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- **0045** — [A machine's firewall is the sum of what its modules listen on](0045-a-machine-firewall-is-the-sum-of-what-it-listens-on.md)
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- **0046** — [A module's configuration is its assignment's, not its manifest's](0046-a-module-configuration-is-its-assignments-not-its-manifest.md)
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- **0047** — [A module runs its code as its own process, with its own account](0047-a-module-runs-its-code-as-its-own-process-with-its-own-account.md)
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- **0048** — [A provider creates the credential the mesh minted, and seals nothing](0048-a-provider-creates-the-credential-the-mesh-minted.md)
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- **0049** — [A consumer's identity is bounded by the tightest backend that must accept it](0049-a-consumers-identity-fits-the-tightest-backend.md)
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- **0050** — [Model access is vendor-agnostic, and a vendor is an adapter](0050-model-access-is-vendor-agnostic.md)
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- **0051** — [Shared data is the operator's, and a module is granted access to it](0051-shared-data-is-the-operators.md)
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- **0052** — [An init step is a container run once to completion, gating what follows](0052-a-step-that-runs-once-before-a-container.md)
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- **0053** — [A scheduled step is a container run on a recurring schedule](0053-a-step-that-runs-on-a-schedule.md)
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- **0054** — [Model usage is a vendor-neutral record, produced by the adapter, at two grains](0054-model-usage-is-recorded-at-two-grains.md)
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- **0055** — [Model access is answered by a licence, or by a node that hosts the model](0055-model-access-is-answered-by-a-licence-or-a-node.md)
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### How it is built
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- **0011** — [Managed files are generated onto nodes and never edited there](0011-managed-files-are-generated-never-edited.md)
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- **0012** — [The mesh creates no symlinks — a derived file is a copy](0012-the-mesh-creates-no-symlinks.md)
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- **0013** — [Schema and state changes are numbered migrations, in the same language as the code](0013-schema-changes-are-numbered-migrations.md)
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- **0014** — [No workspace — each module is a standalone package consuming published dependencies](0014-no-npm-workspace.md)
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- **0015** — [Applications live in their own repository; the monorepo is for the mesh](0015-applications-live-in-their-own-repository.md)
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- **0016** — [The lab](0016-the-lab.md)
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- **0037** — [Where a module lives](0037-where-a-module-lives.md) *(proposed)*
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- **0039** — [What the SDK holds, and what it refuses](0039-what-the-sdk-holds-and-refuses.md)
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### How it is checked
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- **0017** — [A test defends a decision](0017-a-test-defends-a-decision.md)
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- **0018** — [A picture of a system is read from the system, never from what asked for it](0018-a-picture-is-read-from-what-runs.md)
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### How we work
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- **0019** — [How this repository works](0019-how-this-repository-works.md)
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- **0020** — [The mesh is governed by a constitution, injected where work is decided](0020-the-mesh-is-governed-by-a-constitution.md)
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- **0021** — [HQ is the source of the mesh constitution](0021-hq-is-the-source-of-the-constitution.md)
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- **0022** — [The constitution absorbs what is already enforced](0022-the-constitution-absorbs-what-is-enforced.md)
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- **0023** — [The approval is the checkpoint, not the second pair of hands](0023-approval-is-the-checkpoint.md)
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- **0025** — [The design record is read where it is written, never copied to be found](0025-the-design-record-is-read-not-copied.md)
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- **0032** — [The local account owns the mesh; a surface delegates to a module](0032-the-local-account-owns-the-mesh.md) *(superseded)*
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- **0034** — [The local account owns the mesh, and a web application's login is not that](0034-the-local-account-owns-the-mesh.md)
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<!-- index:end -->
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