diff --git a/.github/workflows/build-minio-mirror.yml b/.github/workflows/build-minio-mirror.yml
new file mode 100644
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--- /dev/null
+++ b/.github/workflows/build-minio-mirror.yml
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+name: Build MinIO Mirror
+
+# Publishes ghcr.io/thepalaceproject/palace-ci-minio, the MinIO image used by the test suites of
+# circulation, library-registry and virtual-library-card. MinIO withdrew anonymous public access
+# to its own image (Docker Hub, then quay.io), so we host a copy built from its official GitHub
+# release binaries. See docker/Dockerfile.minio.mirror for the full rationale.
+#
+# The image is pinned to a single upstream release and its content is fully determined by the
+# checksums in that Dockerfile, so there is no scheduled rebuild: running this again produces the
+# same image. It runs only when the Dockerfile or this workflow changes, or on demand.
+#
+# One-time manual step: GHCR packages are created private. After the first successful run, set the
+# package visibility to public (Org -> Packages -> palace-ci-minio -> Package settings), matching
+# the other Palace images. Without that, every developer and CI job would need a docker login.
+
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - .github/workflows/build-minio-mirror.yml
+      - docker/Dockerfile.minio.mirror
+  # Build (but do not push) on PRs that touch the mirror, so a broken Dockerfile or workflow is
+  # caught in review rather than on main, where the failure would leave the image unpublished.
+  pull_request:
+    paths:
+      - .github/workflows/build-minio-mirror.yml
+      - docker/Dockerfile.minio.mirror
+  workflow_dispatch:
+
+concurrency:
+  group: build-minio-mirror-${{ github.ref_name }}-${{ github.event_name }}
+  cancel-in-progress: true
+
+jobs:
+  build:
+    name: Build MinIO Mirror
+    runs-on: ubuntu-24.04
+    timeout-minutes: 30
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          persist-credentials: false
+
+      # See comment here: https://github.com/actions/runner-images/issues/1187#issuecomment-686735760
+      - name: Disable network offload
+        run: sudo ethtool -K eth0 tx off rx off
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v4
+
+      - name: Login to GitHub Container Registry
+        if: github.event_name != 'pull_request'
+        uses: docker/login-action@v4.6.0
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      # The Dockerfile is the single source of truth for which upstream release we mirror, so the
+      # tag is read back out of it rather than duplicated here where the two could drift apart.
+      - name: Determine image and tag
+        id: image
+        run: |
+          set -euo pipefail
+          image="ghcr.io/${GITHUB_REPOSITORY_OWNER,,}/palace-ci-minio"
+          tag=$(sed -n 's/^ARG MINIO_RELEASE=\(.*\)$/\1/p' docker/Dockerfile.minio.mirror | head -1)
+          if [[ -z "$tag" ]]; then
+            echo "::error::Could not read MINIO_RELEASE from docker/Dockerfile.minio.mirror"
+            exit 1
+          fi
+          echo "Publishing $image:$tag"
+          echo "image=$image" >> "$GITHUB_OUTPUT"
+          echo "tag=$tag" >> "$GITHUB_OUTPUT"
+
+      # The mirror contains no RUN instructions, so both architectures cross-build on this single
+      # amd64 runner with no QEMU emulation and no per-arch runner matrix.
+      - name: Build mirror image
+        uses: docker/build-push-action@v7
+        with:
+          context: .
+          file: ./docker/Dockerfile.minio.mirror
+          target: minio
+          platforms: linux/amd64,linux/arm64
+          # On a pull request this builds both architectures and verifies the pinned checksums,
+          # then throws the result away. Only main and manual runs publish.
+          push: ${{ github.event_name != 'pull_request' }}
+          # Deliberately no `latest` tag: consumers pin this exact release. Following a moving
+          # upstream tag is part of how we ended up needing this mirror.
+          tags: ${{ steps.image.outputs.image }}:${{ steps.image.outputs.tag }}
+
+      - name: Verify published image
+        if: github.event_name != 'pull_request'
+        run: |
+          set -euo pipefail
+          ref="${{ steps.image.outputs.image }}:${{ steps.image.outputs.tag }}"
+          docker buildx imagetools inspect "$ref"
+          # Confirm both architectures actually made it into the published manifest list.
+          platforms=$(docker buildx imagetools inspect "$ref" --raw \
+            | jq -r '.manifests[] | select(.platform.os != "unknown") | "\(.platform.os)/\(.platform.architecture)"')
+          echo "Published platforms: $platforms"
+          for platform in linux/amd64 linux/arm64; do
+            grep -qx "$platform" <<< "$platforms" \
+              || { echo "::error::$platform missing from $ref"; exit 1; }
+          done
+          # Smoke-test the runner's native architecture.
+          docker run --rm --entrypoint /usr/bin/minio "$ref" --version
diff --git a/docker/Dockerfile.minio.mirror b/docker/Dockerfile.minio.mirror
new file mode 100644
index 0000000000..d0ebdac570
--- /dev/null
+++ b/docker/Dockerfile.minio.mirror
@@ -0,0 +1,95 @@
+# syntax=docker/dockerfile:1.7
+#
+# Mirror of the upstream MinIO server image, published as
+# ghcr.io/thepalaceproject/palace-ci-minio.
+#
+# Why this exists
+# ---------------
+# MinIO withdrew anonymous public access to its server image: first from Docker Hub
+# (~13 Sept 2026), then from quay.io (~24 Sept 2026). Both registries now answer 401 to
+# anonymous manifest requests for every tag, and the binary download host (dl.min.io) answers
+# 410. Every Palace repo that ran `FROM <registry>/minio/minio` in its test setup therefore
+# fails before its test suite starts. Pinning an older tag or relying on a local Docker cache
+# does not help: the whole repository is gated, and tox-docker passes `pull=True` on every
+# build, forcing a fresh pull each time.
+#
+# The one channel MinIO still serves anonymously is GitHub release assets, so this image is
+# assembled from the official release binaries rather than pulled and re-tagged. The binaries
+# below are byte-for-byte identical to the ones inside the last upstream image CI used
+# (quay.io/minio/minio:latest, labelled RELEASE.2025-09-07T16-13-09Z) — verified by comparing
+# their sha256 against /usr/bin/minio and /usr/bin/mc extracted from that image.
+#
+# Scope
+# -----
+# This is a bare passthrough. It contains no Palace configuration: no credentials, no buckets,
+# no entrypoint script. The repos that consume it (circulation, library-registry,
+# virtual-library-card) each configure MinIO differently and keep doing so in their own
+# Dockerfiles — they change only their `FROM` line. Baking configuration in here would fork
+# the image between repos immediately.
+#
+# This mirror is a bridge, not a destination; see the retirement ticket for replacing MinIO
+# outright. Do not add features to it.
+#
+# Updating
+# --------
+# The release strings and their checksums are a matched set. If you bump a version you MUST
+# also replace the matching `--checksum=` value, or the build will fail (by design).
+# Checksums come from the `.sha256sum` asset published alongside each binary.
+
+ARG BASE_IMAGE=registry.access.redhat.com/ubi9/ubi-minimal:9.6
+
+# MinIO publishes one binary per platform rather than a multi-arch artifact, and each has its
+# own checksum, so the download is split into a per-architecture stage that `fetch` selects
+# from using TARGETARCH. This keeps checksum verification native to BuildKit's ADD.
+FROM ${BASE_IMAGE} AS fetch-amd64
+ARG MINIO_RELEASE=RELEASE.2025-09-07T16-13-09Z
+ARG MC_RELEASE=RELEASE.2025-08-13T08-35-41Z
+ADD --chmod=755 --checksum=sha256:7c5bd8512c6e966455b1d198209358b2d191c77a83ab377c4073281065fb855f \
+    https://github.com/minio/minio/releases/download/${MINIO_RELEASE}/minio.linux-amd64.${MINIO_RELEASE} \
+    /staging/minio
+ADD --chmod=755 --checksum=sha256:01f866e9c5f9b87c2b09116fa5d7c06695b106242d829a8bb32990c00312e891 \
+    https://github.com/minio/mc/releases/download/${MC_RELEASE}/mc.linux-amd64.${MC_RELEASE} \
+    /staging/mc
+
+FROM ${BASE_IMAGE} AS fetch-arm64
+ARG MINIO_RELEASE=RELEASE.2025-09-07T16-13-09Z
+ARG MC_RELEASE=RELEASE.2025-08-13T08-35-41Z
+ADD --chmod=755 --checksum=sha256:5c83cd2cf151717ba0243f73e1c7802ff36e272b67144bdd7f1f7d684fd6f03d \
+    https://github.com/minio/minio/releases/download/${MINIO_RELEASE}/minio.linux-arm64.${MINIO_RELEASE} \
+    /staging/minio
+ADD --chmod=755 --checksum=sha256:14c8c9616cfce4636add161304353244e8de383b2e2752c0e9dad01d4c27c12c \
+    https://github.com/minio/mc/releases/download/${MC_RELEASE}/mc.linux-arm64.${MC_RELEASE} \
+    /staging/mc
+
+FROM fetch-${TARGETARCH} AS fetch
+
+FROM ${BASE_IMAGE} AS minio
+ARG MINIO_RELEASE=RELEASE.2025-09-07T16-13-09Z
+ARG MC_RELEASE=RELEASE.2025-08-13T08-35-41Z
+
+LABEL org.opencontainers.image.title="palace-ci-minio" \
+      org.opencontainers.image.description="Unmodified MinIO server build, mirrored for Palace CI because upstream withdrew anonymous registry access." \
+      org.opencontainers.image.version="${MINIO_RELEASE}" \
+      org.opencontainers.image.source="https://github.com/ThePalaceProject/circulation" \
+      org.opencontainers.image.vendor="The Palace Project" \
+      io.palace.minio.release="${MINIO_RELEASE}" \
+      io.palace.mc.release="${MC_RELEASE}"
+
+COPY --from=fetch /staging/minio /usr/bin/minio
+COPY --from=fetch /staging/mc /usr/bin/mc
+
+# Matches the upstream image: MinIO reads credentials from these files when the corresponding
+# environment variables are not set, and `mc` needs a writable config dir.
+ENV MINIO_ROOT_USER_FILE=access_key \
+    MINIO_ROOT_PASSWORD_FILE=secret_key \
+    MINIO_KMS_SECRET_KEY_FILE=kms_master_key \
+    MINIO_CONFIG_ENV_FILE=config.env \
+    MC_CONFIG_DIR=/tmp/.mc
+
+# Declaring the volume creates the mount point, so no RUN is needed here. Keeping this stage
+# free of RUN instructions means the image cross-builds for every architecture without QEMU.
+VOLUME ["/data"]
+EXPOSE 9000 9001
+
+# A plain, unconfigured server. Consumers override this with their own CMD/ENTRYPOINT.
+CMD ["minio", "server", "/data", "--address", ":9000", "--console-address", ":9001"]