02-DECISIONS/0096-an-upstream-image-is-copied-between-registries.md

@@ -0,0 +1,63 @@
+---
+topic: building it
+status: accepted
+date: 2026-09-21
+deciders: jochen
+reconstructed: false
+extends: 02-DECISIONS/0006-the-substrate-and-the-control-plane.md
+---
+
+# 96. An upstream image is copied between registries, never through a machine's image store
+
+## Context
+
+A module may declare that an artifact is an image published elsewhere, to be copied into the
+mesh's own registry so machines fetch it by a digest this mesh assigned rather than by a name
+somebody else controls. The builder pulled it into the build machine's image store and pushed it
+under the mesh's name, and the push was refused: a published image is an index over several
+architectures, the runtime's store keeps the index, and pushing one platform out of it fails
+however the platform is asked for
+([issue 046](../04-ISSUES/046-an-upstream-image-cannot-be-mirrored-into-the-mesh/00-report.md)).
+Every variant of pull-then-push was tried and failed the same way.
+
+## Considered Options
+
+1. **Resolve the index to one platform and push that.** Tried, reverted: it did not make the
+   push work, and a workaround for a store's behaviour is a thing nobody removes later.
+2. **Tooling that copies between registries**, installed on the build machine. Rejected: one
+   more thing the builder's image carries, for a protocol the builder already speaks for blobs.
+3. **Copy over the registry API**, in the builder. Adopted.
+
+## Decision
+
+The builder copies an upstream image between registries and never through a machine's image
+store: it reads the index and every manifest it names, moves each blob by digest into the mesh's
+registry — skipping what is already there, since blobs are content-named — puts the manifests
+and then the index under the module's repository, and pins the index's digest. Public images are
+read with the anonymous bearer token the registry hands out on challenge, which is how the
+public hub and the others the catalogue names serve them. The mesh mirrors the whole index, so
+what a machine fetches is the image for its own architecture; that every machine on one mesh is
+the same architecture is an assumption this mesh makes and had not written down until now.
+
+Genesis has no registry to copy into and keeps the pull: the image stays in the first machine's
+store, named by its own id, as every artifact does before there is anywhere to publish.
+
+## Consequences
+
+An upstream artifact builds. What got harder: the builder now holds a registry client of its
+own, some two hundred lines, where a runtime command used to do; and a private upstream that
+demands a credential is refused, since the copy is anonymous by design.
+
+## How it is checked
+
+A test raises a fake upstream registry serving an index over two platforms behind a bearer
+challenge, and a fake mesh registry that records what arrives: every blob of both platforms
+arrives once, two manifests and the index are put under their digests, the reference returned
+pins the index under the module's repository, and a second copy uploads nothing. A reference
+test reads names the way a runtime does.
+
+## References
+
+- [issue 046](../04-ISSUES/046-an-upstream-image-cannot-be-mirrored-into-the-mesh/00-report.md)
+- [ADR 0006](0006-the-substrate-and-the-control-plane.md)
+- [`03-DESIGN/01-to-be/18-building-a-module.md`](../03-DESIGN/01-to-be/18-building-a-module.md)

02-DECISIONS/README.md

@@ -161,6 +161,7 @@ python3 00-META/checks/index.py            fail if stale
 - **0076** — [The SDK is a published package, and the toolchain resolves it by version](0076-the-sdk-is-a-published-package.md)
 - **0082** — [The registry is reached by name, and the overlay is its security](0082-the-registry-is-reached-by-name-and-trusted-by-the-overlay.md)
 - **0086** — [A secret reaches a process as a file, and an exception is declared](0086-a-secret-reaches-a-process-as-a-file.md)
+- **0096** — [An upstream image is copied between registries, never through a machine's image store](0096-an-upstream-image-is-copied-between-registries.md)
 
 ### How it is checked
 

03-DESIGN/01-to-be/18-building-a-module.md

@@ -7,6 +7,7 @@ code:
   - mesh-catalog modules/builder
 updated: 2026-09-21
 decisions:
+  - 02-DECISIONS/0096-an-upstream-image-is-copied-between-registries.md
   - 02-DECISIONS/0091-a-mount-is-declared-three-ways.md
   - 02-DECISIONS/0087-a-seeded-file-is-created-once.md
   - 02-DECISIONS/0040-what-a-module-is.md
@@ -202,6 +203,18 @@ remedies, and a test parses every manifest in the catalogue beside the checkout.
 | `image` | built from a Dockerfile — for software that needs a particular base |
 | `upstream` | somebody else's image, mirrored and pinned by a digest this mesh assigned |
 
+**An upstream image is copied between registries, never through a machine's image store**
+([ADR 0096](../../02-DECISIONS/0096-an-upstream-image-is-copied-between-registries.md)). A
+published image is an index over several architectures, and a runtime's store refuses to push
+one platform out of an index it pulled. The builder reads the index and every manifest it names
+over the registry API, moves each blob by digest into the mesh's registry, puts the manifests and
+then the index under the module's repository, and pins the index — the whole image, so what a
+machine fetches is the one for its own architecture. Public images are read with the anonymous
+token a registry hands out on challenge; a private upstream is refused. *How it is checked:* a
+test copies an index over two platforms from a fake registry behind a bearer challenge into a fake
+mesh registry and asserts every blob arrived once, the manifests and index under their digests,
+and nothing uploaded on a second copy.
+
 ### What it puts on a machine
 
 | resource | is | a module may |

04-ISSUES/046-an-upstream-image-cannot-be-mirrored-into-the-mesh/00-report.md

@@ -1,9 +1,9 @@
 ---
-status: located
+status: resolved
 opened: 2026-09-14
 located-in: [mesh-controller internal/builder (upstream artifacts)]
-fixed-by:
-amended-design:
+fixed-by: ADR 0096; mesh-controller multiple-fixes (the builder copies the index and its manifests between registries over the registry API); proven by a test against a fake upstream serving an index over two platforms
+amended-design: 03-DESIGN/01-to-be/18-building-a-module.md
 ---
 
 # 046 — An upstream image cannot be mirrored into the mesh's own registry

04-ISSUES/046-an-upstream-image-cannot-be-mirrored-into-the-mesh/01-diagnosis.md

@@ -12,6 +12,8 @@
    than a limitation; today every machine on one mesh is the same architecture, and that
    assumption is now written down here rather than nowhere.
 
-**Located in:** the builder's upstream-artifact step. Not fixed here: a registry-to-registry copy
-is a few hundred lines against the registry API and is proven only against a real registry
-serving a real index, which is a lab run of its own.
+**Located in:** the builder's upstream-artifact step. Fixed as
+[ADR 0096](../../02-DECISIONS/0096-an-upstream-image-is-copied-between-registries.md): a copy over
+the registry API, proven against a fake upstream serving an index over two platforms behind a
+bearer challenge. A run against the public hub from a mesh's builder is the remaining proof, and
+the first build of a module with an upstream artifact will be it.