diff --git a/docker-compose.host-mount.yml b/docker-compose.host-mount.yml
new file mode 100644
index 0000000..4ab2820
--- /dev/null
+++ b/docker-compose.host-mount.yml
@@ -0,0 +1,21 @@
+# Bind-mount overlay — replaces the `data` named volume with a bind mount
+# to /data on the host.
+#
+# Use this when /data is a persistent disk mounted by the VM startup script,
+# so Agnes data lives on the PD (not on the boot disk's Docker volume).
+#
+# Usage (combined with docker-compose.prod.yml):
+#   docker compose \
+#     -f docker-compose.yml \
+#     -f docker-compose.prod.yml \
+#     -f docker-compose.host-mount.yml \
+#     up -d
+#
+# Do NOT use this overlay in CI — /data does not exist on GitHub runners.
+volumes:
+  data:
+    driver: local
+    driver_opts:
+      type: none
+      o: bind
+      device: /data
diff --git a/docker-compose.prod.yml b/docker-compose.prod.yml
index 614acb5..3fab1da 100644
--- a/docker-compose.prod.yml
+++ b/docker-compose.prod.yml
@@ -1,9 +1,9 @@
-# Production override — uses pre-built GHCR image instead of local build,
-# and binds the `data` volume to /data on the host (so persistent-disk mounts
-# at /data are used by all services).
-#
+# Production override — uses pre-built GHCR image instead of local build.
 # Usage: docker compose -f docker-compose.yml -f docker-compose.prod.yml up -d
 # Override tag: AGNES_TAG=stable-2026.04.3 docker compose -f ... up -d
+#
+# For persistent-disk-backed /data on GCE, compose this overlay with
+# docker-compose.host-mount.yml — which binds the `data` named volume to /data.
 services:
   app:
     image: ghcr.io/keboola/agnes-the-ai-analyst:${AGNES_TAG:-stable}
@@ -19,15 +19,3 @@ services:
     image: ghcr.io/keboola/agnes-the-ai-analyst:${AGNES_TAG:-stable}
   session-collector:
     image: ghcr.io/keboola/agnes-the-ai-analyst:${AGNES_TAG:-stable}
-
-# Override the `data` named volume to bind-mount /data from the host.
-# This ensures a persistent disk mounted at /data (by Terraform startup
-# script) is the actual backing store, not a Docker-managed volume on the
-# boot disk.
-volumes:
-  data:
-    driver: local
-    driver_opts:
-      type: none
-      o: bind
-      device: /data
diff --git a/infra/modules/customer-instance/startup-script.sh.tpl b/infra/modules/customer-instance/startup-script.sh.tpl
index 39247eb..3ffd2fb 100644
--- a/infra/modules/customer-instance/startup-script.sh.tpl
+++ b/infra/modules/customer-instance/startup-script.sh.tpl
@@ -46,6 +46,8 @@ cd "$APP_DIR"
 # Fetch minimal docker-compose from public repo (main branch — stable)
 curl -fsSL "https://raw.githubusercontent.com/keboola/agnes-the-ai-analyst/main/docker-compose.yml" -o docker-compose.yml
 curl -fsSL "https://raw.githubusercontent.com/keboola/agnes-the-ai-analyst/main/docker-compose.prod.yml" -o docker-compose.prod.yml
+# Overlay which binds `data` volume to host /data (persistent disk mounted above)
+curl -fsSL "https://raw.githubusercontent.com/keboola/agnes-the-ai-analyst/main/docker-compose.host-mount.yml" -o docker-compose.host-mount.yml
 
 # TLS overlay (Caddy + Let's Encrypt) — jen pokud potřeba
 if [ "$TLS_MODE" = "caddy" ] && [ -n "$DOMAIN" ]; then
@@ -79,8 +81,10 @@ if [ "$TLS_MODE" = "caddy" ] && [ -n "$DOMAIN" ]; then
     COMPOSE_PROFILES_ARG="--profile tls"
 fi
 
-docker compose -f docker-compose.yml -f docker-compose.prod.yml $COMPOSE_PROFILES_ARG pull
-docker compose -f docker-compose.yml -f docker-compose.prod.yml $COMPOSE_PROFILES_ARG up -d
+COMPOSE_FILES="-f docker-compose.yml -f docker-compose.prod.yml -f docker-compose.host-mount.yml"
+
+docker compose $COMPOSE_FILES $COMPOSE_PROFILES_ARG pull
+docker compose $COMPOSE_FILES $COMPOSE_PROFILES_ARG up -d
 
 # --- 6. Auto-upgrade via cron (pullne nový tag každých 5 min) ---
 if [ "$UPGRADE_MODE" = "auto" ]; then
@@ -89,12 +93,13 @@ if [ "$UPGRADE_MODE" = "auto" ]; then
 # Spouští se z cronu — pullne nový image, pokud je, a restartne containers.
 set -euo pipefail
 cd /opt/agnes
+COMPOSE_FILES="-f docker-compose.yml -f docker-compose.prod.yml -f docker-compose.host-mount.yml"
 BEFORE=$(docker images --no-trunc --format '{{.Digest}}' ghcr.io/keboola/agnes-the-ai-analyst:$${AGNES_TAG:-stable} | head -1)
-docker compose -f docker-compose.yml -f docker-compose.prod.yml pull >/dev/null 2>&1
+docker compose $COMPOSE_FILES pull >/dev/null 2>&1
 AFTER=$(docker images --no-trunc --format '{{.Digest}}' ghcr.io/keboola/agnes-the-ai-analyst:$${AGNES_TAG:-stable} | head -1)
 if [ "$BEFORE" != "$AFTER" ]; then
     echo "$(date): new image digest — recreating containers"
-    docker compose -f docker-compose.yml -f docker-compose.prod.yml up -d
+    docker compose $COMPOSE_FILES up -d
     docker image prune -f >/dev/null 2>&1
 fi
 SCRIPTEOF