fix(ci): build MinIO from pinned release assets

.github/ci/minio/Dockerfile

@@ -0,0 +1,13 @@
+# CI only: upstream container registries deny these releases, but the official
+# GitHub release binaries remain available. Keep versions aligned with Compose.
+# The integration runners use linux/amd64; this is not a deployment image.
+FROM alpine:3.22.6@sha256:5291449c3df73caf6ed85e649dec1b9e818b39a5d8c871e97afc13e9cd5e8fa8
+
+RUN apk add --no-cache ca-certificates curl
+
+ADD --checksum=sha256:7c5bd8512c6e966455b1d198209358b2d191c77a83ab377c4073281065fb855f --chmod=755 \
+    https://github.com/minio/minio/releases/download/RELEASE.2025-09-07T16-13-09Z/minio.linux-amd64.RELEASE.2025-09-07T16-13-09Z /usr/local/bin/minio
+ADD --checksum=sha256:01f866e9c5f9b87c2b09116fa5d7c06695b106242d829a8bb32990c00312e891 --chmod=755 \
+    https://github.com/minio/mc/releases/download/RELEASE.2025-08-13T08-35-41Z/mc.linux-amd64.RELEASE.2025-08-13T08-35-41Z /usr/local/bin/mc
+
+ENTRYPOINT ["minio"]

.github/workflows/_ci-relay.yml

@@ -207,6 +207,8 @@ jobs:
             --archive-file target/ci/postgres-tests.tar.zst
 
   desktop-e2e-integration-shard:
+    env:
+      COMPOSE_FILE: docker-compose.yml:docker-compose.ci.yml
     name: Desktop E2E Integration (${{ matrix.shard }}/2)
     runs-on: ubuntu-latest
     timeout-minutes: 20
@@ -220,6 +222,8 @@ jobs:
     steps:
       - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
       - uses: cashapp/activate-hermit@cea9af7913204a965fd488637a8d1811bba2e616 # v1
+      - name: Build CI MinIO image
+        run: docker compose build minio
       - name: Start integration services
         run: |
           for attempt in 1 2 3; do
@@ -400,6 +404,8 @@ jobs:
           echo "Desktop E2E Integration shards passed"
 
   backend-integration:
+    env:
+      COMPOSE_FILE: docker-compose.yml:docker-compose.ci.yml
     name: Backend Integration (relay e2e)
     runs-on: ubuntu-latest
     timeout-minutes: 20
@@ -413,6 +419,8 @@ jobs:
         uses: taiki-e/install-action@0fd46367812ee04360509b4169d9f659d6892bb2 # v2.79.15
         with:
           tool: cargo-nextest@0.9.136
+      - name: Build CI MinIO image
+        run: docker compose build minio
       - name: Start integration services
         run: |
           for attempt in 1 2 3; do
@@ -562,6 +570,8 @@ jobs:
           if-no-files-found: ignore
 
   relay-e2e:
+    env:
+      COMPOSE_FILE: docker-compose.yml:docker-compose.ci.yml
     name: Relay E2E
     runs-on: ubuntu-latest
     timeout-minutes: 20
@@ -581,6 +591,8 @@ jobs:
         with:
           name: desktop-e2e-relay
           path: target/ci
+      - name: Build CI MinIO image
+        run: docker compose build minio
       - name: Start relay
         run: |
           chmod +x ./target/ci/buzz-relay ./target/ci/git-credential-nostr

.github/workflows/ci.yml

@@ -55,6 +55,8 @@ jobs:
               - 'deny.toml'
               - '.github/workflows/ci.yml'
               - '.github/workflows/_ci-*.yml'
+              - '.github/ci/minio/**'
+              - 'docker-compose.ci.yml'
               - 'scripts/run-tests.sh'
               - 'scripts/model-capabilities.json'
               - 'scripts/normative-corpus.json'

docker-compose.ci.yml

@@ -0,0 +1,13 @@
+# Layer over docker-compose.yml for the disposable AMD64 integration runners.
+# Build once with `docker compose build minio`; both services use that local image.
+services:
+  minio:
+    image: buzz-ci-minio:local
+    platform: linux/amd64
+    pull_policy: never
+    build:
+      context: .github/ci/minio
+  minio-init:
+    image: buzz-ci-minio:local
+    platform: linux/amd64
+    pull_policy: never

scripts/ci-selection.test.mjs

@@ -113,6 +113,8 @@ const scenarios = [
   ["relay", ["crates/buzz-relay/src/main.rs"], ["rust"]],
   ["migration", ["migrations/123.sql"], ["rust"]],
   ["shared workflow", [".github/workflows/ci.yml"], ["rust", "mobile"]],
+  ["CI MinIO image", [".github/ci/minio/Dockerfile"], ["rust"]],
+  ["CI Compose override", ["docker-compose.ci.yml"], ["rust"]],
   [
     "mixed mobile and relay",
     ["mobile/lib/main.dart", "crates/buzz-core/src/lib.rs"],

scripts/test-ci-required-context-isolation.sh

@@ -83,4 +83,17 @@ if grep -Eq '^  desktop-build-macos:|desktop_macos_result:' "$desktop_workflow";
   fail "Desktop Domain must not own the isolated macOS required check"
 fi
 
+# Each job has an isolated Docker daemon: every Compose consumer must build
+# the local MinIO image before starting services, including the script caller.
+for job in desktop-e2e-integration-shard backend-integration relay-e2e; do
+  body=$(extract_job "$job" "$relay_workflow")
+  [[ "$body" == *'COMPOSE_FILE: docker-compose.yml:docker-compose.ci.yml'* ]] ||
+    fail "$job must select the CI Compose override"
+  [[ "$body" == *'docker compose build minio'* ]] ||
+    fail "$job must build its own CI MinIO image"
+  before_build=${body%%docker compose build minio*}
+  [[ "$before_build" != *'docker compose up'* && "$before_build" != *'./scripts/start-relay-for-tests.sh'* ]] ||
+    fail "$job must build MinIO before starting services"
+done
+
 echo "CI required-context isolation contract passed"