opencode-sandbox/README.md

OpenCode Sandbox

A rootless Podman container for running OpenCode with a pinned toolchain — Java, Node, pnpm, git — without touching your host machine's environment.

What this gives you

• A hash-pinned, integrity-verified build of OpenCode (not "latest" — an exact version, checked against a SHA256 captured at build time).
• JDK 25 (LTS), Node 24 (LTS), pnpm, git, curl, openssh-client.
• The current directory mounted read-write as /workspace.
• OpenCode's config, data, and session state shared across every workdir/container, so logging in once carries over everywhere.
• Every container joined to a shared Podman network so it can reach other dev containers by name.

Requirements

• Podman (rootless).
• On macOS: a running podman machine — make will start a stopped one automatically, but if you've never run Podman before you need to initialize one first:

  podman machine init
  

• GNU Make (macOS's bundled Make 3.81 works fine; the Makefile deliberately avoids features added in 3.82+).

Usage

make build      # build (or rebuild) the container image
make opencode   # launch the OpenCode TUI in the current directory
make shell      # open a bash shell in the container instead

Run make opencode or make shell from any project directory — the image is shared, so there's nothing per-project to set up.

How it's put together

Containerfile — multi-stage build on debian:trixie-slim:

• JDK and Node are copied in from their official upstream images (eclipse-temurin:25-jdk-noble, node:24-trixie-slim) rather than apt-installed, keeping the final image slim while staying on a mainstream glibc distro (Alpine/musl is avoided — it breaks JVM and native Node addon compatibility).
• pnpm is installed via its own standalone installer script, pinned to a specific version.
• OpenCode is downloaded directly from its canonical GitHub releases (github.com/anomalyco/opencode) for the container's architecture, and its SHA256 is checked against a hash pinned in the Containerfile before it's installed — there's no maintainer-published signature for OpenCode releases, so this hash is captured by hand and is the actual root of trust here. Bump OPENCODE_VERSION and re-run the sha256sum steps documented in the Containerfile's comments whenever you upgrade it.
• A few build-time smoke tests (ldd, java -version, node --version, etc.) fail the build immediately if anything is broken, rather than surfacing at first make opencode.

Makefile — three targets only, as designed:

• build builds the image.

• opencode and shell both run the container with the same flags: --userns=keep-id (so files created in the container are owned by your real host user, not root — verified: rootless Podman's user-namespace remapping means id shows root inside the container's own namespace view, but the file lands on the host owned by your actual UID/GID), the current directory bind-mounted to /workspace, and OpenCode's three XDG directories bind-mounted from your home directory:

  Host path	Container path	Contents
  ~/.config/opencode	/home/dev/.config/opencode	settings, plugins, themes
  ~/.local/share/opencode	/home/dev/.local/share/opencode	auth, database, snapshots
  ~/.local/state/opencode	/home/dev/.local/state/opencode	session/model history, locks

  Because these are real host paths shared by every container regardless of workdir, logging into OpenCode once carries over to every project you use the sandbox in.

• Both run targets join a shared, auto-created Podman network (opencode-sandbox-net) under a --network-alias derived from the current directory's name, so a container started from another dev-container setup on the same network can reach this one by that name (and vice versa).

macOS-specific notes

• Podman on macOS runs everything inside a Linux VM (podman machine, backend libkrun/applehv, virtiofs file sharing). The Makefile detects this and starts a stopped machine automatically before build, opencode, or shell.
• SELinux volume-relabeling suffixes (:Z/:z) are intentionally omitted — macOS's host filesystem has no SELinux concept, so they'd be a no-op.
• Known virtiofs limitation: inotify/file-watch events from the host don't propagate into the container. Not a blocker for normal use, just worth knowing if a tool inside the container tries to watch /workspace for live host-side changes.

Connecting to other dev containers

Any other container you attach to the opencode-sandbox-net network (podman network connect opencode-sandbox-net <container>, or by starting it with --network opencode-sandbox-net) can resolve and reach this sandbox by its workdir-derived alias, and vice versa.