diff --git a/docker/docker-compose.yml b/docker/docker-compose.yml
index 32c6ea42..3a5abc4b 100644
--- a/docker/docker-compose.yml
+++ b/docker/docker-compose.yml
@@ -108,6 +108,11 @@ services:
       retries: 3
       start_period: 10s
 
+    # Use tini as PID 1 to reap zombie child processes.
+    # Without this, grandchild processes (esbuild, cargo, etc.) spawned by
+    # npm/cargo during worktree setup and gate checks become zombies.
+    init: true
+
     # Restart policy – restart on crash but not on manual stop
     restart: unless-stopped