Docker

Builds, debugs, hardens, and ships Docker containers, images, and Compose stacks. Use when writing or reviewing a Dockerfile, a compose file, or a CI build step; when a container exits instantly, restart-loops, is OOM-killed, hangs on stop, or exits 137/139/127; when a published port is unreachable, containers cannot resolve each other, or requests hang behind a VPN; when the disk fills and `/var/lib/docker` will not prune; when a build is slow, the cache never hits, or fails only in CI; when `exec format error` or a musl-versus-glibc break is the problem; when choosing a base image or a multi-stage layout; when a registry login or pull rate limit fails; when a secret must stay out of image history; and when volumes need backup, restore or a permission fix. Covers Compose traps and Desktop/colima/OrbStack/Podman differences. Not for Kubernetes manifests or cluster scheduling (`k8s`).