Setting Up Devbox Agent Skill

Setting up a PostHog devbox

A devbox is a Coder workspace running the full PostHog stack on an EC2 instance, managed through hogli devbox:* (the only supported interface — drive those commands, don't reimplement them). It ships ready to use: the repo cloned at ~/posthog, the stack pre-warmed, and Claude Code installed. This skill gets a dev connected and working; how they personalize beyond that is their choice, not something to push.

Prerequisite: tailnet access (the thing people miss)

The devbox control plane lives inside a private VPC reachable only over Tailscale. The ACL that grants the route is tailnet-policy.hujson in posthog-cloud-infra: your email must be in group:engineering. Without that grant, the Coder control plane (10.70.0.1:443) is simply unroutable and _every_ hogli devbox:* command dies at the reachability check — not an auth or install problem, and no amount of re-running devbox:setup fixes it.

If hogli devbox:doctor reports the control plane unreachable, the fix is a PR adding the user to group:engineering in tailnet-policy.hujson (then ask Team DevEx if still blocked). Diagnose this before touching anything else.

Control plane unreachable with a DNS cause? Check the exit node first

When doctor shows [ok] Tailscale connected but fails reachability with a DNS cause (DNS lookup for coder.dev.posthog.dev failed), that's usually not the grant: the client's split-DNS routes don't cover dev.posthog.dev, so the name never reaches the internal resolver.

The fix is selecting a Tailscale exit node — it routes DNS through infra that resolves *.dev.posthog.dev.

Check available exit nodes and select one via the Tailscale menu bar app (Exit Node) or CLI:

tailscale exit-node list                            # list available exit nodes
tailscale set --exit-node=<name>                    # enable one (use the Name from the list)
# on macOS when `tailscale` isn't on PATH:
/Applications/Tailscale.app/Contents/MacOS/Tailscale exit-node list
/Applications/Tailscale.app/Contents/MacOS/Tailscale set --exit-node=<name>

Do not suggest /etc/hosts or /etc/resolver workarounds — they hardcode internal ELB IPs that rotate, and the exit node is the supported path.

To confirm it's resolution rather than the grant: dig coder.dev.posthog.dev @10.90.0.2 answering while the system resolver fails proves the name exists and only the resolution path is missing.

Workflow

1. Check state — hogli devbox:doctor

hogli devbox:doctor          # read-only: tailnet access, reachability, auth, ssh config, saved setup

A safe probe — it never prompts or mutates host config (unlike devbox:setup). If it flags the control plane unreachable, resolve the tailnet grant before anything else. For more detail: hogli devbox:list (your boxes), hogli devbox:status (state, template freshness), hogli devbox:secret:list (secret names only).

2. One-time local setup — hogli devbox:setup

Interactive: checks Tailscale + Coder reachability, installs and authenticates the coder CLI (plus the pinned mutagen binary that backs devbox:sync), and writes the SSH host entries that devbox:ssh/devbox:exec rely on. It then _offers_ git identity, git signing, a dotfiles repo, and your Claude token — all optional; --skip-* anything you don't want. Re-run one step with its flag, e.g. hogli devbox:setup --configure-git-signing.

3. Start and connect — hogli devbox:start

hogli devbox:start           # create or resume your box
hogli devbox:ssh             # shell in
hogli devbox:open --vscode   # or --cursor / --web
hogli devbox:stop            # when done — preserves disk, stops billing

4. Auth, if you want it (optional)

To have gh or Claude Code authenticated on the box, store the token once as a Coder user secret. It's injected as an env var into every box you start, so you set it once rather than per box:

hogli devbox:secret:set GH_TOKEN --env GH_TOKEN
hogli devbox:secret:set CLAUDE_CODE_OAUTH_TOKEN --env CLAUDE_CODE_OAUTH_TOKEN
# also supported: ANTHROPIC_API_KEY, OPENAI_API_KEY, OP_SERVICE_ACCOUNT_TOKEN, AWS_CREDENTIALS (--file)

Authing gh / Claude on a devbox is fine — that's what these are for. Set the value from --file or the hidden prompt; never paste a token into a command line or into this conversation. Restart a running box to pick up a newly set secret.

5. Make it yours — your call

The box is usable as shipped; personalize it however suits you, or not at all. Two supported paths, neither required, don't push one over the other:

• Tweak the box directly — devbox:ssh in and install tools, add aliases, clone repos. Changes under /home survive stop/start and template updates, but a devbox:destroy (or a brand-new box) starts fresh.
• A dotfiles repo — if you'd rather keep portable, version-controlled config that re-applies to every box: hogli devbox:setup --configure-dotfiles points the box at your dotfiles_uri, and Coder clones it (running an executable ~/dotfiles/install.sh if present) on each start.

6. Run commands on the box — hogli devbox:exec

devbox:exec runs one command over SSH and propagates its exit code — handy for scripts, agents, and quick checks without opening a shell:

hogli devbox:exec -- bash -lc 'gh auth status'
hogli devbox:exec -- bash -lc 'cd ~/posthog && git status'
hogli devbox:exec -n api -- bash -lc 'uname -a'    # -n targets a labeled box

Wrap commands in bash -lc '...': a non-login shell doesn't reliably source ~/.bashrc/~/.zshrc, so a bare gh auth status can report "command not found" for anything on a login-shell PATH (e.g. ~/.local/bin) — a false negative. The login shell also keeps the exit code trustworthy, so && chaining and if checks work. Use -- to separate hogli's flags from the command's own.

devbox:exec is not side-effect-free: like every devbox:* command it runs the reachability check first, which on Linux may sudo tailscale set --accept-routes and prompt for a password. Run hogli devbox:setup once interactively so routes and SSH config are in place before an agent drives devbox:exec unattended.

Editing locally, running on the box — hogli devbox:sync

When you want your fast local checkout to stay the place you edit but the heavy stack (hogli up) to run on the box, hogli devbox:sync mirrors your repo onto the box over mutagen, one-way: local is the source of truth, nothing comes back. Reach for this in an agentic loop — edit with your normal local tools, let the mirror carry each change, and drive the remote stack with devbox:exec — instead of committing and pushing every iteration or editing over Remote-SSH.

hogli devbox:start                                   # the box must be running first
hogli devbox:sync                                    # create the mirror (idempotent: re-run just reports status)
# edit files locally — changes propagate within seconds
hogli devbox:exec -- bash -lc 'cd ~/posthog && pnpm --filter=@posthog/frontend typescript:check'
hogli devbox:sync --status                           # watching / paused / conflicts
hogli devbox:sync --terminate                        # tear the mirror down when done

The non-obvious parts:

• It runs on your machine and pushes to the box — not the reverse. Don't invoke it through devbox:exec. It mirrors whichever checkout you run it from (it walks up from the cwd for hogli.yaml + .git), so run it from the repo root you are editing — including a /wt worktree.
• one-way-safe preserves remote-only files. The AMI's prewarmed node_modules, venv, and target/ are never deleted — they aren't in your local checkout and the mode leaves remote-only content alone. Lockfiles _do_ sync, so the box reconciles deps on its next start.
• The first sync of a feature branch conflicts per diverged file. The AMI is always on master; every file your branch changed relative to the box's master surfaces as a conflict in --status. That is expected one-way-safe behavior, and it is per-path — non-conflicting files (including brand-new ones) still sync. Resolve a path, or check the matching branch out on the box, only if you specifically need that file mirrored.
• Don't also edit those files on the box. Editing over Remote-SSH while the mirror is live fights the local source of truth; devbox:open --vscode|--cursor warns when a sync is active for exactly this reason.

The packaged ignore defaults are seeded once to ~/.hogli/mutagen.yml and never overwritten — it is yours to tweak. If a newer hogli ships updated ignore defaults, rm ~/.hogli/mutagen.yml and re-run devbox:setup to pick them up.

Persistence & multiple boxes

• devbox:stop → devbox:start and template/AMI updates preserve /home (the instance is stopped, not terminated). A devbox:destroy wipes it — intentional, so don't keep anything irreplaceable only inside a box.
• You can run more than one box. Box-local changes don't carry between them; user secrets do (user-scoped), and a dotfiles repo does if you use one. That's the practical reason to reach for those if you find yourself re-doing setup — but it's a choice, not a requirement.

Gotchas

• Never echo secret values into the transcript, logs, a PR, or a command line. devbox:secret:set reads from a hidden prompt or --file; secret:list shows names only. Keep it that way.
• Secrets need a restart. A new or changed secret only reaches boxes started afterward — hogli devbox:restart to pick it up on a running box.
• devbox:exec/devbox:ssh need devbox:setup to have run (it writes the coder.* SSH host config). Without it they fail at connection; devbox:doctor shows whether SSH access is configured.
• code-server (browser IDE) has no SSH agent forwarding, so commit signing via a forwarded key won't work there — use VS Code Desktop / Cursor / JetBrains (SSH-based) when you need to sign.