ci(deps): bump the published images' bases within their version only

.github/dependabot.yml

@@ -31,8 +31,10 @@ updates:
     groups:
       npm-minor-and-patch:
         update-types: ["minor", "patch"]
-  # The infra images the release publishes. Each base is pinned by digest, and a release rebuilds an image only when its
+  # The images the release publishes. Each base is pinned by digest, and a release rebuilds an image only when its
   # sources change, so a bump here is what picks up a base's fixes: the next release builds and publishes the image.
+  # Only its fixes: a new digest or patch release of the version it's on. A major or minor version (postgres 16 to 18,
+  # python 3.12 to 3.15) is an upgrade, made by hand with whatever the images run on it.
   - package-ecosystem: "docker"
     directories:
       - "/src/agent_env/env/gateway"
@@ -42,6 +44,9 @@ updates:
     schedule:
       interval: "weekly"
     open-pull-requests-limit: 5
+    ignore:
+      - dependency-name: "*"
+        update-types: ["version-update:semver-major", "version-update:semver-minor"]
     groups:
       infra-base-images:
         patterns: ["*"]

AGENTS.md

@@ -285,7 +285,8 @@ Its jobs that run agent-env (`.github/scripts/infra_images.py`) hold no token th
 images or publish to PyPI install nothing and check what they're handed (`.github/scripts/infra_build.py`,
 standard library and the docker CLI only).
 Actions are pinned to commit SHAs; Dependabot updates them, the pinned uv, `uv.lock`, the UI's npm packages and
-the infra images' base images, each pinned by digest so that a bump rebuilds and republishes the image.
+the infra images' base images, each pinned by digest so that a bump rebuilds and republishes the image; Dependabot
+proposes only a base's digest and patch updates, and a major or minor upgrade is made by hand.
 
 ## Conventions
 

CONTRIBUTING.md

@@ -94,7 +94,8 @@ included), at `ghcr.io/scaleapi/agentenv-<name>:src-<hex>` for linux/amd64
 and linux/arm64, where the tag is the build context's source digest, so an unchanged Dockerfile is not built again.
 The Claude Code image installs the `agentenv-framework-protocol` its release pins, which is one of its sources, so each
 release builds it again, once the protocol is on PyPI and before `agentenv-framework` is published.
-Each of them pins its base images by digest, and Dependabot bumps those pins, so a base's fixes reach the published
+Each of them pins its base images by digest, and Dependabot bumps those pins within each base's major and minor
+version (an upgrade, such as postgres 16 to 18, is made by hand), so a base's fixes reach the published
 image: a bump changes the sources, and the next release builds it again.
 Installs pull them instead of building the infra images: a run on local stores registers a kind's images when GHCR has
 every one for the sources installed, by the digest the wheel records or, with no record, the one GHCR serves, and

tst/unit/test_release_infra_images.py

@@ -208,3 +208,13 @@ def test_every_infra_image_pins_its_bases_by_digest_and_dependabot_bumps_them():
                  if ref not in stages]
         assert bases and all(re.search(r"@sha256:[0-9a-f]{64}$", ref) for ref in bases), (image.name, bases)
         assert f"/{image.dockerfile.parent.relative_to(REPO)}" in docker["directories"], image.name
+
+
+def test_dependabot_proposes_a_bases_fixes_and_never_an_upgrade():
+    """A base's digest and patch updates are its fixes; its next major or minor version (postgres 16 to 18) changes what
+    the images run on, and is made by hand."""
+    dependabot = yaml.safe_load((REPO / ".github" / "dependabot.yml").read_text())
+    (docker,) = [update for update in dependabot["updates"] if update["package-ecosystem"] == "docker"]
+
+    assert {"dependency-name": "*", "update-types": ["version-update:semver-major", "version-update:semver-minor"]} in (
+        docker["ignore"])