Linux hosts have no documented way to keep moshi-hook alive

[tburny]

What changes for the user

Today the skill's host-setup guidance assumes macOS: §1 "Host Readiness" and §5 "Agent Hooks" tell the user to keep the moshi-hook daemon alive with brew services start moshi-hook, and pairing defaults to Keychain. There is no Homebrew-services equivalent on Linux, so a Linux user who follows the skill ends up paired but with no documented way to keep moshi-hook serve running across logout or reboot. After this change the skill would include a Linux path — a systemd user service plus linger — so Linux hosts are covered the same way macOS hosts are.

Why it matters

moshi-hook serve is a long-lived daemon (agent-hook Unix socket + remote-approval WebSocket). If it isn't supervised it dies on logout, and remote approvals / Live Activity / Watch stop working until the user manually restarts it. macOS users get brew services; Linux users currently have to improvise their own supervision. The skill already documents the Linux-friendly moshi-hook pair --store file flow, so Linux is clearly a supported target — it just stops short of the "keep it running" step.

Desired behaviour — acceptance criteria

• Following the skill on Linux, the user ends with moshi-hook serve running under systemctl --user and Active: running.
• The daemon survives logout and reboot (skill instructs loginctl enable-linger).
• The skill provides a copy-pasteable ~/.config/systemd/user/moshi-hook.service unit.
• Linux pairing points at moshi-hook pair --token <T> --store file (already in the skill) rather than Keychain.
• Verification steps are given: systemctl --user is-active moshi-hook and moshi-hook status showing paired.

Reference — a unit that works (verified on Linux, moshi-hook 0.2.34)

[Unit]
Description=Moshi hook daemon (agent-hook Unix socket + remote-approval WebSocket)
Documentation=https://getmoshi.app

[Service]
Type=simple
ExecStart=%h/.local/bin/moshi-hook serve
Restart=always
RestartSec=5

[Install]
WantedBy=default.target

systemctl --user enable --now moshi-hook.service
loginctl enable-linger "$USER"   # daemon survives logout / reboot

Verified end-to-end on Ubuntu (Linux 6.8), moshi-hook 0.2.34: service Active: running, Linger=yes, and after pair --store file the daemon logs paired=true and ws bridge connected (remote approvals live).

Out of scope

• Distro service packaging (deb/rpm) or a system-wide unit — this is user-level systemd only.
• Teaching moshi-hook to install the unit itself — this is a skill-documentation addition, not a CLI feature.
• The moshi DIR tmux launcher and tmux config (§2/§4) — unchanged.

Where the details live

• Current skill: skills/moshi-best-practices/SKILL.md — §1 "Host Readiness" and §5 "Agent Hooks" (the brew services start moshi-hook line and the --store file pairing block).