diff --git a/.github/actions/build-and-scan/action.yml b/.github/actions/build-and-scan/action.yml
index 8814794..f633326 100644
--- a/.github/actions/build-and-scan/action.yml
+++ b/.github/actions/build-and-scan/action.yml
@@ -1,5 +1,5 @@
-name: Build and scan runtime images
-description: Build both runtime images for amd64 and arm64, then scan each image
+name: Build, scan, and validate runtime images
+description: Build and scan both runtime images, then run app image acceptance tests
 inputs:
   nextcloud_version:
     description: Nextcloud version passed to the app image build
@@ -7,6 +7,14 @@ inputs:
 runs:
   using: composite
   steps:
+    - name: Setup Bats
+      uses: bats-core/bats-action@77d6fb60505b4d0d1d73e48bd035b55074bbfb43 # 4.0.0
+      with:
+        support-install: false
+        assert-install: false
+        detik-install: false
+        file-install: false
+
     - name: Set up QEMU
       uses: docker/setup-qemu-action@v3
       with:
@@ -73,3 +81,15 @@ runs:
           'app@linux/arm64=scan/app:arm64' \
           'web@linux/amd64=scan/web:amd64' \
           'web@linux/arm64=scan/web:arm64'
+
+    - name: Runtime acceptance app image (linux/amd64)
+      shell: bash
+      env:
+        APP_IMAGE: scan/app:amd64
+      run: bats tests/app-image.bats
+
+    - name: Runtime acceptance app image (linux/arm64)
+      shell: bash
+      env:
+        APP_IMAGE: scan/app:arm64
+      run: bats tests/app-image.bats
diff --git a/Makefile b/Makefile
index fa9655d..16e5fcc 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,8 @@
 COMPOSE ?= docker compose
 GARAGES3_COMPOSE_FILE ?= docker-compose-garages3.yml
+APP_TEST_IMAGE ?= nextcloud-app:acceptance
 
-.PHONY: up-garages3 down-garages3 bootstrap-garages3 garage-status-garages3 start-garages3 wait-nextcloud-garages3 setup-garages3 test-hooks test-scan-images test-ncdd scan-images
+.PHONY: up-garages3 down-garages3 bootstrap-garages3 garage-status-garages3 start-garages3 wait-nextcloud-garages3 setup-garages3 test-hooks test-scan-images test-ncdd test-app-image test-current-app-image scan-images
 
 up-garages3:
 	$(COMPOSE) -f $(GARAGES3_COMPOSE_FILE) up -d garage
@@ -35,6 +36,18 @@ test-scan-images:
 test-ncdd:
 	bats tests/ncdd.bats
 
+test-app-image:
+	@test -n "$(APP_IMAGE)" || { echo 'Usage: make test-app-image APP_IMAGE=<local-image>' >&2; exit 2; }
+	APP_IMAGE="$(APP_IMAGE)" bats tests/app-image.bats
+
+test-current-app-image:
+	@set -e; \
+	  version="$$(sed -n 's/^NEXTCLOUD_VERSION=//p' .env.example | head -n 1)"; \
+	  test -n "$$version" || { echo 'NEXTCLOUD_VERSION is missing from .env.example' >&2; exit 1; }; \
+	  docker buildx build --platform linux/amd64 --load --tag "$(APP_TEST_IMAGE)" \
+	    --build-arg "NEXTCLOUD_VERSION=$$version" --file .docker/app/Dockerfile .docker/app; \
+	  $(MAKE) test-app-image APP_IMAGE="$(APP_TEST_IMAGE)"
+
 scan-images:
 	@set -e; \
 	  version="$$(sed -n 's/^NEXTCLOUD_VERSION=//p' .env.example | head -n 1)"; \
diff --git a/docs/images.md b/docs/images.md
index af436fd..a04aa50 100644
--- a/docs/images.md
+++ b/docs/images.md
@@ -149,6 +149,26 @@ Immutable web image:
 ghcr.io/librecodecoop/nextcloud-docker-web@sha256:<web-image-digest>
 ```
 
+## Runtime acceptance
+
+The app image has a runtime acceptance test based on the same behavioral checks used by the official Nextcloud container projects.
+
+The test operates on an already-built local image. It does not rebuild the image and does not use the repository deployment Compose files:
+
+```bash
+make test-app-image APP_IMAGE=scan/app:amd64
+```
+
+For a local build of the current app image followed by the same acceptance test:
+
+```bash
+make test-current-app-image
+```
+
+The Bats acceptance test creates an isolated Docker network and PostgreSQL container, starts the image with Nextcloud autoinstall variables, waits for the installation, runs `occ status` and `occ check`, and sends a FastCGI request through the FPM runtime. Test-created resources are removed on success and failure.
+
+CI must run this test against the exact locally loaded app images produced by the build step. Runtime acceptance is a publication gate alongside vulnerability scanning; a separate deployment-stack test is not required for this contract.
+
 ## Implementation boundary
 
 This document defines the target contract. It does not by itself migrate the current Dockerfiles, workflows, or historical tags.
diff --git a/tests/app-image.bats b/tests/app-image.bats
new file mode 100644
index 0000000..6ba75d2
--- /dev/null
+++ b/tests/app-image.bats
@@ -0,0 +1,204 @@
+#!/usr/bin/env bats
+
+setup() {
+  : "${APP_IMAGE:?APP_IMAGE must reference an already-built local image}"
+
+  command -v docker >/dev/null 2>&1 || {
+    echo "Docker is required to run the app image acceptance test." >&2
+    return 127
+  }
+
+  docker image inspect "$APP_IMAGE" >/dev/null 2>&1 || {
+    echo "Image not found locally: $APP_IMAGE" >&2
+    return 2
+  }
+
+  POSTGRES_IMAGE=${NEXTCLOUD_IMAGE_TEST_POSTGRES_IMAGE:-postgres:18-alpine}
+  TIMEOUT_SECONDS=${NEXTCLOUD_IMAGE_TEST_TIMEOUT:-300}
+  RUNTIME_USER=${NEXTCLOUD_IMAGE_TEST_RUNTIME_USER:-www-data}
+
+  IMAGE_ARCH=$(docker image inspect --format '{{.Architecture}}' "$APP_IMAGE")
+  case "$IMAGE_ARCH" in
+    amd64|arm64) IMAGE_PLATFORM="linux/$IMAGE_ARCH" ;;
+    *)
+      echo "Unsupported image architecture: $IMAGE_ARCH" >&2
+      return 2
+      ;;
+  esac
+
+  TEST_ID="nextcloud-app-test-$$-${BATS_TEST_NUMBER}-${RANDOM}"
+  NETWORK_NAME="$TEST_ID"
+  DB_CONTAINER="${TEST_ID}-db"
+  APP_CONTAINER="${TEST_ID}-app"
+  FCGI_CLIENT_IMAGE="nextcloud-app-test-fcgi-client"
+
+  DB_USER=nextcloud
+  DB_DATABASE=nextcloud
+  DB_PASSWORD="test-${RANDOM}-${RANDOM}-password"
+  ADMIN_USER=test_admin
+  ADMIN_PASSWORD="test-${RANDOM}-${RANDOM}-admin-password"
+
+  NETWORK_CREATED=false
+  DB_CREATED=false
+  APP_CREATED=false
+}
+
+teardown() {
+  if $APP_CREATED; then
+    docker rm -f "$APP_CONTAINER" >/dev/null 2>&1 || true
+  fi
+  if $DB_CREATED; then
+    docker rm -f "$DB_CONTAINER" >/dev/null 2>&1 || true
+  fi
+  if $NETWORK_CREATED; then
+    docker network rm "$NETWORK_NAME" >/dev/null 2>&1 || true
+  fi
+}
+
+diagnostics() {
+  echo
+  echo "=== app container logs ===" >&2
+  if $APP_CREATED; then
+    docker logs "$APP_CONTAINER" >&2 || true
+  else
+    echo "app container was not created" >&2
+  fi
+
+  echo
+  echo "=== postgres container logs ===" >&2
+  if $DB_CREATED; then
+    docker logs "$DB_CONTAINER" >&2 || true
+  else
+    echo "postgres container was not created" >&2
+  fi
+}
+
+fail_with_diagnostics() {
+  local message=$1
+  diagnostics
+  echo "$message" >&2
+  return 1
+}
+
+wait_until() {
+  local description=$1
+  shift
+
+  local started now
+  started=$(date +%s)
+
+  while ! "$@"; do
+    now=$(date +%s)
+    if [ $((now - started)) -ge "$TIMEOUT_SECONDS" ]; then
+      fail_with_diagnostics "Timed out after ${TIMEOUT_SECONDS}s waiting for $description."
+      return 1
+    fi
+    sleep 2
+  done
+}
+
+postgres_ready() {
+  docker exec "$DB_CONTAINER" pg_isready -U "$DB_USER" -d "$DB_DATABASE" >/dev/null 2>&1
+}
+
+nextcloud_installed() {
+  local status
+  status=$(docker exec -u "$RUNTIME_USER" "$APP_CONTAINER" php occ status --output=json 2>/dev/null) || return 1
+  grep -Eq '"installed"[[:space:]]*:[[:space:]]*true' <<<"$status"
+}
+
+ensure_fcgi_client() {
+  if docker image inspect "$FCGI_CLIENT_IMAGE" >/dev/null 2>&1; then
+    return
+  fi
+
+  docker build -q -t "$FCGI_CLIENT_IMAGE" - <<'EOF' >/dev/null
+FROM debian:trixie-slim
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends libfcgi-bin \
+    && rm -rf /var/lib/apt/lists/*
+ENTRYPOINT ["cgi-fcgi"]
+EOF
+}
+
+fcgi_status() {
+  docker run --rm -i \
+    --network "$NETWORK_NAME" \
+    -e REQUEST_METHOD=GET \
+    -e SCRIPT_NAME=/status.php \
+    -e SCRIPT_FILENAME=/var/www/html/status.php \
+    "$FCGI_CLIENT_IMAGE" \
+    -bind -connect app:9000 2>/dev/null
+}
+
+fpm_ready() {
+  local response
+  response=$(fcgi_status) || return 1
+  grep -Eq '"installed"[[:space:]]*:[[:space:]]*true' <<<"$response"
+}
+
+@test "app image installs Nextcloud and serves it through FPM" {
+  echo "Testing $APP_IMAGE ($IMAGE_PLATFORM)"
+
+  run docker network create "$NETWORK_NAME"
+  [ "$status" -eq 0 ]
+  NETWORK_CREATED=true
+
+  run docker run -d \
+    --name "$DB_CONTAINER" \
+    --network "$NETWORK_NAME" \
+    --network-alias db \
+    -e "POSTGRES_USER=$DB_USER" \
+    -e "POSTGRES_PASSWORD=$DB_PASSWORD" \
+    -e "POSTGRES_DB=$DB_DATABASE" \
+    "$POSTGRES_IMAGE"
+  [ "$status" -eq 0 ]
+  DB_CREATED=true
+
+  wait_until "PostgreSQL readiness" postgres_ready
+
+  run docker run -d \
+    --name "$APP_CONTAINER" \
+    --network "$NETWORK_NAME" \
+    --network-alias app \
+    --platform "$IMAGE_PLATFORM" \
+    -e POSTGRES_HOST=db \
+    -e "POSTGRES_USER=$DB_USER" \
+    -e "POSTGRES_PASSWORD=$DB_PASSWORD" \
+    -e "POSTGRES_DB=$DB_DATABASE" \
+    -e "NEXTCLOUD_ADMIN_USER=$ADMIN_USER" \
+    -e "NEXTCLOUD_ADMIN_PASSWORD=$ADMIN_PASSWORD" \
+    -e NEXTCLOUD_TRUSTED_DOMAINS=localhost \
+    "$APP_IMAGE"
+  [ "$status" -eq 0 ]
+  APP_CREATED=true
+
+  wait_until "Nextcloud installation" nextcloud_installed
+
+  run docker exec -u "$RUNTIME_USER" "$APP_CONTAINER" php occ status --output=json
+  if [ "$status" -ne 0 ]; then
+    fail_with_diagnostics "occ status failed."
+  fi
+  if ! grep -Eq '"installed"[[:space:]]*:[[:space:]]*true' <<<"$output"; then
+    printf '%s\n' "$output" >&2
+    fail_with_diagnostics "occ status did not report installed: true."
+  fi
+
+  run docker exec -u "$RUNTIME_USER" "$APP_CONTAINER" php occ check
+  if [ "$status" -ne 0 ]; then
+    fail_with_diagnostics "occ check failed."
+  fi
+
+  ensure_fcgi_client
+
+  wait_until "FPM readiness" fpm_ready
+
+  run fcgi_status
+  if [ "$status" -ne 0 ]; then
+    fail_with_diagnostics "FPM did not accept the FastCGI request after becoming ready."
+  fi
+  if ! grep -Eq '"installed"[[:space:]]*:[[:space:]]*true' <<<"$output"; then
+    printf '%s\n' "$output" >&2
+    fail_with_diagnostics "FPM response did not report installed: true."
+  fi
+}