02-DECISIONS/0097-a-vendor-image-is-a-declared-build-input.md

@@ -0,0 +1,59 @@
+---
+topic: building it
+status: accepted
+date: 2026-09-21
+deciders: jochen
+reconstructed: false
+extends: 02-DECISIONS/0096-an-upstream-image-is-copied-between-registries.md
+---
+
+# 97. A vendor image is a declared build input, and a recipe fetches nothing undeclared
+
+## Context
+
+Three modules could not be built by the mesh's builder because their recipes reached for what
+no manifest named: a public package, or a binary copied out of a public image
+([issue 064](../04-ISSUES/064-a-mesh-build-cannot-fetch-a-modules-external-dependencies/00-report.md)).
+A module already names the bases it stands on — another module's artifact, by name — and the
+builder answers with what the mesh holds; a vendor's image had no such declaration, so a recipe
+named it directly and the build worked when the public registry answered, which is sometimes.
+
+## Considered Options
+
+1. **Let the build environment reach public registries.** Rejected: a build that fetches from
+   somebody else's registry on its own is one the mesh cannot rebuild the same way twice.
+2. **A vendor image is a base like any other**, declared under `build.on` with the argument the
+   recipe reads it from, pinned by digest, copied into the mesh's registry before the build
+   ([ADR 0096](0096-an-upstream-image-is-copied-between-registries.md)). Adopted.
+
+## Decision
+
+A build's `on` entry is either a module's artifact or an image published elsewhere, pinned by
+digest, read from one build argument. Before the build the image is copied into the mesh's
+registry under the module's repository and the recipe is handed the copy; genesis, with no
+registry, pulls it into the first machine's store. A recipe whose `FROM` or `COPY --from` names a
+registry image the manifest did not declare is refused before the build, naming the image and
+the remedy; its own stages, declared arguments and `scratch` are not fetches. An unpinned vendor
+image is refused: a tag is what somebody else can move.
+
+The package half of the issue is not decided here: the mesh's package registry already proxies
+the public one, and the failure the report saw has to be run again to be placed.
+
+## Consequences
+
+A module's build inputs are all in its manifest, and every one of them is something the mesh
+holds a copy of. What got harder: a recipe that used to name a base image on its first line now
+names an argument, and the manifest names the image.
+
+## How it is checked
+
+A builder test declares a pinned vendor image, asserts it is copied under the module's
+repository and handed to the recipe as the argument, and asserts an unpinned one is refused. A
+recipe test asserts an undeclared `FROM`, an undeclared `COPY --from` and an undeclared argument
+are named, and that stages, declared arguments and `scratch` are not.
+
+## References
+
+- [issue 064](../04-ISSUES/064-a-mesh-build-cannot-fetch-a-modules-external-dependencies/00-report.md)
+- [ADR 0096](0096-an-upstream-image-is-copied-between-registries.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

@@ -162,6 +162,7 @@ python3 00-META/checks/index.py            fail if stale
 - **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)
+- **0097** — [A vendor image is a declared build input, and a recipe fetches nothing undeclared](0097-a-vendor-image-is-a-declared-build-input.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/0097-a-vendor-image-is-a-declared-build-input.md
   - 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
@@ -215,6 +216,14 @@ test copies an index over two platforms from a fake registry behind a bearer cha
 mesh registry and asserts every blob arrived once, the manifests and index under their digests,
 and nothing uploaded on a second copy.
 
+**A vendor image is a declared build input**
+([ADR 0097](../../02-DECISIONS/0097-a-vendor-image-is-a-declared-build-input.md)). A build's `on`
+entry is a module's artifact or an image published elsewhere, pinned by digest, read from one
+build argument; the image is copied into the mesh's registry before the build and the recipe is
+handed the copy. A recipe whose `FROM` or `COPY --from` names a registry image the manifest did not
+declare is refused before the build, naming it and the remedy. *How it is checked:* builder tests
+on a declared and an unpinned vendor image, and a recipe test on what counts as a fetch.
+
 ### What it puts on a machine
 
 | resource | is | a module may |

04-ISSUES/064-a-mesh-build-cannot-fetch-a-modules-external-dependencies/01-diagnosis.md

@@ -16,5 +16,8 @@
    repositories succeed in the same Dockerfiles.
 
 **Located in:** the builder (what it tells npm and the runtime) and the catalogue (three modules
-whose Dockerfiles fetch what no manifest names). Still open: a build must be re-run to place the
-404, and a decision is needed on whether a vendor image is declared as a build input.
+whose Dockerfiles fetch what no manifest names). The image half is decided and built:
+[ADR 0097](../../02-DECISIONS/0097-a-vendor-image-is-a-declared-build-input.md) — a vendor image
+is declared under `build.on`, copied in, and a recipe fetching what is undeclared is refused. Still
+open: the package half — a build must be re-run against the mesh's proxying registry to place the
+404 — and the three recipes themselves, which now declare their images or are refused.