Install round-trip tests (systemd / launchd / Windows SCM)

[hyperpolymath]

Stacks on #81. Adds the round-trip tests that #81's README documented as "next step".

What's in this PR

Three platform-specific drivers that actually install → activate → stop → uninstall the service on the real service manager, complementing the lint-only checks in #81:

Driver	Platform	What it does
tests/install/roundtrip-linux.sh	Linux	systemctl --user enable --now round-trip. Also kills the unit's MainPID and asserts Restart=on-failure respawns it within RestartSec=5.
tests/install/roundtrip-macos.sh	macOS	launchctl bootstrap gui/$UID / bootout round-trip. Patches stub PATH= into the plist (launchd ignores user shell env).
tests/install/roundtrip-windows.ps1	Windows	Creates throwaway local user (burble-ci-test) with random password, installs Windows Service non-interactively, asserts SCM state, uninstalls, removes user in finally{}.

Supporting bits

• tests/install/stubs/{mix,deno} — sleep-forever stand-ins so spawned units satisfy systemd/launchd's "Active" check without needing the full Elixir/Deno toolchain in CI.

• scripts/wsl-bolt-udp-forward.ps1 — new -Credential [PSCredential] parameter on -Install that skips the Get-Credential prompt when supplied. Human-interactive behaviour unchanged when omitted. This is what makes the Windows round-trip testable in CI at all.

• .github/workflows/install-roundtrip.yml — three-OS matrix:

  • ubuntu-latest (with loginctl enable-linger $USER so user-systemd starts without a login session)
  • macos-14 (Apple Silicon)
  • windows-latest

  Path-filtered to install-machinery changes only, same as Add cross-platform background-service install (systemd/launchd/Windows) #81's install-tests.yml.

Safety

All drivers clean up after themselves on failure:

• shell: trap 'ec=$?; cleanup; exit $ec' EXIT (captures real exit code before cleanup runs)
• PowerShell: try { … } finally { Remove-LocalUser … }

Safe to run locally if you don't mind a brief service install on your box.

Things found while writing this

• set -u + unset $USER killed the script on a stripped container — falls back to id -un now
• The naïve trap 'cleanup' EXIT was swallowing the preflight's exit 2 — fixed with ec=$? capture
• Shellcheck SC2154 false-positive on the ec=$? pattern inside the trap (disabled inline with a comment)

Test plan

• CI green on all three jobs of install-roundtrip workflow
• CI green on install-tests workflow (the new round-trip ps1 + sh files are now in its shellcheck/PSScriptAnalyzer scope too)
• On your Windows + WSL setup: from inside WSL, tests/install/roundtrip-linux.sh should pass once you sudo loginctl enable-linger $USER && sleep 2. From elevated Windows PowerShell, tests\install\roundtrip-windows.ps1 should pass standalone (creates + removes its own user).
• macOS coverage will only land via CI unless you also test on a Mac.

Out of scope (still NOT tested)

• Whether UDP packets actually relay through the Windows forwarder (needs a real WSL distro on the runner — GH runners don't have one).
• Whether mix phx.server itself comes up clean under systemd/launchd (covered by elixir-ci.yml, not the install machinery).

https://claude.ai/code/session_016BNGnVKCbN5FBXcTXRpDXy

---

Generated by Claude Code