well, fixed some problems with path etc but works now

Dockerfile

@@ -1,15 +1,15 @@
 ARG ALPINE_VERSION=3.21
 FROM alpine:${ALPINE_VERSION}
 
+# Re-declare after FROM — build ARGs don't persist across FROM
 ARG SUPERCRONIC_VERSION=0.2.33
-# TARGETARCH is auto-set by buildx per platform: "amd64", "arm64", etc.
 ARG TARGETARCH
 
 RUN apk add --no-cache docker-cli
 
 ADD https://github.com/aptible/supercronic/releases/download/v${SUPERCRONIC_VERSION}/supercronic-linux-${TARGETARCH} \
     /usr/local/bin/supercronic
-RUN chmod +x /usr/local/bin/supercronic
+RUN chmod 755 /usr/local/bin/supercronic
 
 # Match GID to your host's docker group. Check with: stat -c '%g' /var/run/docker.sock
 ARG DOCKER_GID=999

build.sh

@@ -1,7 +1,7 @@
 #!/bin/sh
 set -e
 
-IMAGE="${IMAGE:-docker-pruner}"
+IMAGE="${IMAGE:-registry.domandoman.xyz/cannibal}"
 TAG="${TAG:-latest}"
 DOCKER_GID="${DOCKER_GID:-$(stat -c '%g' /var/run/docker.sock)}"
 SUPERCRONIC_VERSION="${SUPERCRONIC_VERSION:-0.2.33}"
@@ -25,4 +25,5 @@ docker buildx build \
     --build-arg SUPERCRONIC_VERSION="${SUPERCRONIC_VERSION}" \
     --build-arg DOCKER_GID="${DOCKER_GID}" \
     --tag "${IMAGE}:${TAG}" \
+    --push \
     .

docker-compose.yml

@@ -1,14 +1,8 @@
 services:
   cannibal:
-    image: cannibal:latest
-    build:
-      context: .
-      args:
-        DOCKER_GID: "${DOCKER_GID:-999}"
+    image: registry.domandoman.xyz/cannibal:latest
     restart: unless-stopped
     environment:
       PRUNE_SCHEDULE: "0 3 * * *"  # every day at 3am
     volumes:
       - /var/run/docker.sock:/var/run/docker.sock
-    group_add:
-      - "${DOCKER_GID:-999}"

entrypoint.sh

@@ -5,6 +5,6 @@ echo "Docker pruner starting as $(whoami). Schedule: ${PRUNE_SCHEDULE}"
 
 # Write crontab from env var at runtime
 CRONTAB_FILE=/tmp/crontab
-echo "${PRUNE_SCHEDULE} docker system prune -af >> /tmp/prune.log 2>&1" > "${CRONTAB_FILE}"
+echo "${PRUNE_SCHEDULE} /bin/sh -c '/usr/bin/docker system prune -af >> /tmp/prune.log 2>&1'" > "${CRONTAB_FILE}"
 
-exec supercronic "${CRONTAB_FILE}"
+exec /usr/local/bin/supercronic "${CRONTAB_FILE}"