diff --git a/docker-compose.yml b/docker-compose.yml
index 5ad89e2..59b18c7 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -54,6 +54,9 @@ services:
       - CACHE_DIR=/data/cache
       # Set IPFS_PRIMARY=true to use IPFS-primary mode (everything on IPFS, no local cache)
       # - IPFS_PRIMARY=true
+      # Cluster key for trust domains - systems with same key can share work via IPFS
+      # Generate with: openssl rand -hex 32
+      - ARTDAG_CLUSTER_KEY=${ARTDAG_CLUSTER_KEY:-}
       # L2_SERVER, L2_DOMAIN, IPFS_GATEWAY_URL from .env file
     volumes:
       - l1_cache:/data/cache
@@ -78,6 +81,8 @@ services:
       - IPFS_API=/dns/ipfs/tcp/5001
       - CACHE_DIR=/data/cache
       - C_FORCE_ROOT=true
+      # Must match l1-server for consistent cache_ids
+      - ARTDAG_CLUSTER_KEY=${ARTDAG_CLUSTER_KEY:-}
     volumes:
       - l1_cache:/data/cache
     depends_on: