diff --git a/.docker/consumer-app.yml b/.docker/consumer-app.yml
new file mode 100644
index 0000000..c1f0714
--- /dev/null
+++ b/.docker/consumer-app.yml
@@ -0,0 +1,15 @@
+# SPDX-FileCopyrightText: 2026 LibreCode coop and contributors
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+services:
+  nextcloud:
+    volumes:
+      - type: bind
+        source: ${APP_SOURCE:?APP_SOURCE must point to the downstream app checkout}
+        target: ${APP_CONTAINER_PATH:?APP_CONTAINER_PATH must be set by the consumer contract}
+  nginx:
+    volumes:
+      - type: bind
+        source: ${APP_SOURCE:?APP_SOURCE must point to the downstream app checkout}
+        target: ${APP_CONTAINER_PATH:?APP_CONTAINER_PATH must be set by the consumer contract}
+        read_only: true
diff --git a/.github/workflows/proxy-tests.yml b/.github/workflows/proxy-tests.yml
index 62a893a..ca9bc6c 100644
--- a/.github/workflows/proxy-tests.yml
+++ b/.github/workflows/proxy-tests.yml
@@ -155,3 +155,36 @@ jobs:
           if [ "$MARIADB_VERSION" = 10.11 ]; then
             DB_TYPE=mariadb sh ./dev-worker maria-peer destroy || true
           fi
+
+  consumer-worker:
+    name: Downstream app consumer integration
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+      - name: Build PHP 8.3 development image
+        run: docker build -f .docker/Dockerfile.php83 -t ghcr.io/librecodecoop/nextcloud-dev-php83:latest .docker
+      - name: Start two downstream consumers
+        run: |
+          APP_SOURCE="$GITHUB_WORKSPACE/tests/worker/fixtures/consumer-a" APP_ID=fixture APP_SETUP_HOOK=setup.sh DB_TYPE=sqlite sh ./dev-worker consumer-a up
+          APP_SOURCE="$GITHUB_WORKSPACE/tests/worker/fixtures/consumer-b" APP_ID=fixture APP_SETUP_HOOK=setup.sh DB_TYPE=sqlite sh ./dev-worker consumer-b up
+      - name: Verify source and hook isolation
+        run: |
+          test "$(APP_SOURCE="$GITHUB_WORKSPACE/tests/worker/fixtures/consumer-a" APP_ID=fixture DB_TYPE=sqlite sh ./dev-worker consumer-a exec cat /var/www/html/apps-extra/fixture/identity.txt)" = alpha
+          test "$(APP_SOURCE="$GITHUB_WORKSPACE/tests/worker/fixtures/consumer-b" APP_ID=fixture DB_TYPE=sqlite sh ./dev-worker consumer-b exec cat /var/www/html/apps-extra/fixture/identity.txt)" = beta
+          test "$(APP_SOURCE="$GITHUB_WORKSPACE/tests/worker/fixtures/consumer-a" APP_ID=fixture DB_TYPE=sqlite sh ./dev-worker consumer-a exec cat /var/www/html/data/consumer-hook)" = alpha
+          test "$(APP_SOURCE="$GITHUB_WORKSPACE/tests/worker/fixtures/consumer-b" APP_ID=fixture DB_TYPE=sqlite sh ./dev-worker consumer-b exec cat /var/www/html/data/consumer-hook)" = beta
+      - name: Verify teardown is worker-scoped
+        run: |
+          APP_SOURCE="$GITHUB_WORKSPACE/tests/worker/fixtures/consumer-a" APP_ID=fixture DB_TYPE=sqlite sh ./dev-worker consumer-a destroy
+          APP_SOURCE="$GITHUB_WORKSPACE/tests/worker/fixtures/consumer-b" APP_ID=fixture DB_TYPE=sqlite sh ./dev-worker consumer-b status | grep -q 'installed: true'
+      - name: Collect consumer logs
+        if: failure()
+        run: |
+          APP_SOURCE="$GITHUB_WORKSPACE/tests/worker/fixtures/consumer-a" APP_ID=fixture DB_TYPE=sqlite sh ./dev-worker consumer-a logs || true
+          APP_SOURCE="$GITHUB_WORKSPACE/tests/worker/fixtures/consumer-b" APP_ID=fixture DB_TYPE=sqlite sh ./dev-worker consumer-b logs || true
+      - name: Destroy remaining consumer
+        if: always()
+        run: |
+          APP_SOURCE="$GITHUB_WORKSPACE/tests/worker/fixtures/consumer-a" APP_ID=fixture DB_TYPE=sqlite sh ./dev-worker consumer-a destroy || true
+          APP_SOURCE="$GITHUB_WORKSPACE/tests/worker/fixtures/consumer-b" APP_ID=fixture DB_TYPE=sqlite sh ./dev-worker consumer-b destroy || true
diff --git a/README.md b/README.md
index 21d20d3..c46dc6a 100644
--- a/README.md
+++ b/README.md
@@ -21,4 +21,5 @@ and other advanced configuration, see the
 
 - [Advanced setup](docs/advanced-setup.md)
 - [App development](docs/apps-development.md)
+- [Downstream app consumers](docs/downstream-consumers.md)
 - [FAQ](docs/faq.md)
\ No newline at end of file
diff --git a/dev-worker b/dev-worker
index 2813185..2786315 100644
--- a/dev-worker
+++ b/dev-worker
@@ -25,6 +25,9 @@ Environment:
   PHP_VERSION=<version>     Existing PHP image selector
   VERSION_NEXTCLOUD=<ref>   Existing Nextcloud ref selector
   WORKER_READY_TIMEOUT=180  Seconds to wait for a clean installation
+  APP_SOURCE=<path>         Optional downstream app checkout to mount
+  APP_ID=<id>              App directory name under apps-extra
+  APP_SETUP_HOOK=<path>    Optional POSIX shell hook relative to APP_SOURCE
 EOF
 }
 
@@ -65,6 +68,34 @@ esac
 
 worker_root="$repo_root/.workers/$worker_id"
 worker_volumes_dir="$worker_root/volumes"
+consumer_enabled=0
+
+if [ -n "${APP_SOURCE:-}" ] || [ -n "${APP_ID:-}" ] || [ -n "${APP_SETUP_HOOK:-}" ]; then
+	[ -n "${APP_SOURCE:-}" ] || { echo "APP_SOURCE is required when configuring a downstream app" >&2; exit 2; }
+	[ -n "${APP_ID:-}" ] || { echo "APP_ID is required when configuring a downstream app" >&2; exit 2; }
+	[ -d "$APP_SOURCE" ] || { echo "APP_SOURCE is not a directory: $APP_SOURCE" >&2; exit 2; }
+
+	case "$APP_ID" in
+		*[!a-z0-9_-]*|'') echo "Invalid APP_ID: $APP_ID" >&2; exit 2 ;;
+	esac
+	case "$APP_ID" in
+		[a-z0-9]*) ;;
+		*) echo "APP_ID must start with a lowercase letter or digit: $APP_ID" >&2; exit 2 ;;
+	esac
+
+	if [ -n "${APP_SETUP_HOOK:-}" ]; then
+		case "$APP_SETUP_HOOK" in
+			/*|../*|*/../*|*/..) echo "APP_SETUP_HOOK must be a relative path without '..': $APP_SETUP_HOOK" >&2; exit 2 ;;
+		esac
+		[ -f "$APP_SOURCE/$APP_SETUP_HOOK" ] || { echo "APP_SETUP_HOOK does not exist: $APP_SOURCE/$APP_SETUP_HOOK" >&2; exit 2; }
+	fi
+
+	APP_SOURCE="$(CDPATH= cd -- "$APP_SOURCE" && pwd)"
+	export APP_SOURCE
+	export APP_ID
+	export APP_CONTAINER_PATH="/var/www/html/apps-extra/$APP_ID"
+	consumer_enabled=1
+fi
 
 export COMPOSE_PROJECT_NAME="${COMPOSE_PROJECT_NAME:-ncdev-$worker_id}"
 export WORKER_VOLUMES_DIR="$worker_volumes_dir"
@@ -89,7 +120,13 @@ else
 fi
 
 compose() {
-	docker compose --project-directory "$repo_root" --file "$repo_root/docker-compose.yml" "$@"
+	if [ "$consumer_enabled" -eq 1 ]; then
+		docker compose --project-directory "$repo_root" \
+			--file "$repo_root/docker-compose.yml" \
+			--file "$repo_root/.docker/consumer-app.yml" "$@"
+	else
+		docker compose --project-directory "$repo_root" --file "$repo_root/docker-compose.yml" "$@"
+	fi
 }
 
 wait_for_mariadb() {
@@ -151,6 +188,9 @@ case "$command" in
 			compose up -d
 		fi
 		wait_until_ready
+		if [ "$consumer_enabled" -eq 1 ] && [ -n "${APP_SETUP_HOOK:-}" ]; then
+			compose exec -T -u www-data nextcloud sh "$APP_CONTAINER_PATH/$APP_SETUP_HOOK"
+		fi
 		;;
 	exec)
 		[ "$#" -gt 0 ] || {
diff --git a/docs/apps-development.md b/docs/apps-development.md
index e7ab966..09a6dda 100644
--- a/docs/apps-development.md
+++ b/docs/apps-development.md
@@ -1,29 +1,27 @@
-# Start development of apps
-
-You will need create (or clone) the folder of the app that you will work inside the folder `volumes/nextcloud/apps-extra`.
-
-It's not required install all dependencis like php or nodejs to develop apps, with this project is only use the bash in container to compile app.
-
-## Sample
-
-Using the [LibreSign](https://github.com/LibreSign/libresign):
-
-To install LibreSign in the structure of develop is required [up servicer](#up-services). After nextcloud config and install.
-  - open folder `volumes/nextcloud/app-extra`
-  - clone project with `git clone https://github.com/LibreSign/libresign.git`
-  - open bash in nextcloud container with `docker compose exec -u www-data nextcloud bash`
-  - go to folder `apps-extra/libresign`
-    ```bash
-    cd apps-extra/libresign
-    ```
-  - Now you can run all the necessaries commands to build the project, i.e:
-    ```bash
-    # download composer dependencies
-    composer install
-    # download JS dependencies
-    npm ci
-    # build and watch JS changes
-    npm run watch
-    ```
+# Develop a Nextcloud app
+
+For a one-off local checkout, an app can still be placed under
+`volumes/nextcloud/apps-extra` and used from the `nextcloud` container.
+
+For app repositories that need a reusable development/devcontainer contract,
+prefer the [downstream app consumer](downstream-consumers.md) workflow instead
+of cloning or copying the full Docker Compose topology.
+
+The consumer contract mounts the app checkout into `apps-extra` while this
+repository remains responsible for Nextcloud, database, proxy, mail and runtime
+services.
+
+Example:
+
+```bash
+APP_SOURCE=/work/my-app APP_ID=my_app DB_TYPE=sqlite \
+  sh ./dev-worker my-app up
+
+APP_SOURCE=/work/my-app APP_ID=my_app DB_TYPE=sqlite \
+  sh ./dev-worker my-app exec sh -lc 'cd /var/www/html/apps-extra/my_app && composer install'
+```
+
+See [Downstream app consumers](downstream-consumers.md) for setup hooks and the
+minimal Compose adapter used by devcontainers.
 
 ⬅️ [Back to index](../README.md)
diff --git a/docs/downstream-consumers.md b/docs/downstream-consumers.md
new file mode 100644
index 0000000..6294cd5
--- /dev/null
+++ b/docs/downstream-consumers.md
@@ -0,0 +1,66 @@
+# Downstream app consumers
+
+`nextcloud-docker-development` can provide the canonical Nextcloud runtime for
+another app repository without copying the infrastructure topology into that
+repository.
+
+## Worker contract
+
+Point the worker at an app checkout with:
+
+- `APP_SOURCE`: host path to the app checkout;
+- `APP_ID`: directory name under `/var/www/html/apps-extra`;
+- `APP_SETUP_HOOK`: optional POSIX shell script relative to the app checkout,
+  executed as the mapped `www-data` user after Nextcloud is ready.
+
+Example:
+
+```bash
+APP_SOURCE=/work/my-app APP_ID=my_app APP_SETUP_HOOK=.devcontainer/setup.sh \
+  DB_TYPE=sqlite sh ./dev-worker my-app-worker up
+
+APP_SOURCE=/work/my-app APP_ID=my_app DB_TYPE=sqlite \
+  sh ./dev-worker my-app-worker exec occ app:enable my_app
+
+APP_SOURCE=/work/my-app APP_ID=my_app DB_TYPE=sqlite \
+  sh ./dev-worker my-app-worker destroy
+```
+
+The app is mounted into the Nextcloud and nginx services. The normal worker
+contract still owns Compose naming, mutable state, database selection, runtime
+logs and teardown.
+
+## Devcontainer adapter
+
+Docker Compose `include` can keep the infrastructure model owned by this
+repository while a downstream repository keeps only a small adapter.
+
+A consumer can keep a local Compose file similar to:
+
+```yaml
+include:
+  - path:
+      - ${NCDD_ROOT:?set NCDD_ROOT}/docker-compose.yml
+      - ${NCDD_ROOT:?set NCDD_ROOT}/.docker/consumer-app.yml
+    project_directory: ${NCDD_ROOT:?set NCDD_ROOT}
+```
+
+Set `APP_SOURCE` to an absolute path, `APP_ID` to the app directory name
+and `APP_CONTAINER_PATH=/var/www/html/apps-extra/$APP_ID` before running Compose.
+The downstream devcontainer can then use the included `nextcloud` service as its
+runtime service.
+
+This adapter does not redefine Nextcloud, database, proxy, mail or Redis
+services. Changes to that infrastructure remain owned by
+`nextcloud-docker-development`.
+
+Docker Compose 2.20+ is required for the top-level `include` feature.
+
+## Isolation
+
+Each worker still receives its own Compose project and mutable directory. Two
+consumers may therefore use the same `APP_ID` and container path while mounting
+different source checkouts without sharing Nextcloud state.
+
+The worker ID is an isolation namespace for development convenience, not a
+security boundary between untrusted workloads sharing the same Docker daemon.
diff --git a/tests/worker/contract.bats b/tests/worker/contract.bats
index 668074f..20adfec 100644
--- a/tests/worker/contract.bats
+++ b/tests/worker/contract.bats
@@ -74,3 +74,18 @@ setup() {
 		grep -q 'pdo_sqlite' "$dockerfile"
 	done
 }
+
+@test "downstream app contract mounts an app checkout without duplicating the base topology" {
+	run env APP_SOURCE="$REPO_ROOT/tests/worker/fixtures/consumer-a" APP_ID=fixture DB_TYPE=sqlite sh "$WORKER" consumer-a config
+	[ "$status" -eq 0 ]
+	[[ "$output" == *"$REPO_ROOT/tests/worker/fixtures/consumer-a"* ]]
+	[[ "$output" == *"/var/www/html/apps-extra/fixture"* ]]
+}
+
+@test "downstream app contract rejects unsafe identifiers and setup hook traversal" {
+	run env APP_SOURCE="$REPO_ROOT/tests/worker/fixtures/consumer-a" APP_ID='../fixture' DB_TYPE=sqlite sh "$WORKER" consumer-a config
+	[ "$status" -eq 2 ]
+
+	run env APP_SOURCE="$REPO_ROOT/tests/worker/fixtures/consumer-a" APP_ID=fixture APP_SETUP_HOOK='../setup.sh' DB_TYPE=sqlite sh "$WORKER" consumer-a config
+	[ "$status" -eq 2 ]
+}
diff --git a/tests/worker/fixtures/consumer-a/identity.txt b/tests/worker/fixtures/consumer-a/identity.txt
new file mode 100644
index 0000000..4a58007
--- /dev/null
+++ b/tests/worker/fixtures/consumer-a/identity.txt
@@ -0,0 +1 @@
+alpha
diff --git a/tests/worker/fixtures/consumer-a/setup.sh b/tests/worker/fixtures/consumer-a/setup.sh
new file mode 100644
index 0000000..8d8cf93
--- /dev/null
+++ b/tests/worker/fixtures/consumer-a/setup.sh
@@ -0,0 +1,6 @@
+#!/bin/sh
+# SPDX-FileCopyrightText: 2026 LibreCode coop and contributors
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+set -eu
+cat "$(dirname "$0")/identity.txt" > /var/www/html/data/consumer-hook
diff --git a/tests/worker/fixtures/consumer-b/identity.txt b/tests/worker/fixtures/consumer-b/identity.txt
new file mode 100644
index 0000000..65b2df8
--- /dev/null
+++ b/tests/worker/fixtures/consumer-b/identity.txt
@@ -0,0 +1 @@
+beta
diff --git a/tests/worker/fixtures/consumer-b/setup.sh b/tests/worker/fixtures/consumer-b/setup.sh
new file mode 100644
index 0000000..8d8cf93
--- /dev/null
+++ b/tests/worker/fixtures/consumer-b/setup.sh
@@ -0,0 +1,6 @@
+#!/bin/sh
+# SPDX-FileCopyrightText: 2026 LibreCode coop and contributors
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+set -eu
+cat "$(dirname "$0")/identity.txt" > /var/www/html/data/consumer-hook