feat(nh3-dev): zellij-fleet@.service — fleet zellij server in its own cgroup (for SVOS seat_up); installed, not enabled

2026-09-25 23:14:48 -07:00
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+# zellij-fleet@.service — fleet zellij session server in its own cgroup (nh3-dev)
+
+Asked for by svos-dev on 2026-09-25 for SVOS `seat_up`: Prime, through Miranda,
+assigned a way to bring agent seats up remotely. The rule it enforces is that
+**nothing forks the zellij server except this unit**.
+
+## Why
+
+`svos.service` runs with `KillMode=control-group`. If SVOS itself ran `zellij
+attach -b Claude` to create or resurrect the fleet session, the server and every
+agent pane would land in svos.service's cgroup. The next `systemctl --user
+restart svos` (a routine deploy, about 100 s of vault reads) would then SIGTERM
+the whole fleet. Started from this unit, the server gets a cgroup of its own
+(`app-zellij-fleet.slice/zellij-fleet@<session>.service`).
+
+## Behaviour (all measured on zellij 0.45.1, 2026-09-25, with a throwaway session)
+
+| case | result |
+|---|---|
+| session does not exist | created; server in the unit's cgroup |
+| session EXITED (serialized) | **resurrected with its layout; command panes HELD** (`start_suspended true`, no process running) |
+| session already running (e.g. Prime's ssh-started server) | `attach -b` is a no-op; that server stays in its own scope and stopping this unit does not touch it |
+| `systemctl --user stop` | `zellij kill-session`, then the cgroup; the session stays resurrectable (EXITED) |
+| environment | `zsh -lc` gives the login env (PATH plus the tokens from `.zshenv`/`.zprofile`, 23 vars). Bare systemd gives 13. The ssh server's extra vars are SSH_*, TERM, XDG_* and `.zshrc` interactive settings, which each pane's own interactive shell sets anyway |
+
+## Install
+
+```bash
+cp services/zellij-fleet/zellij-fleet@.service ~/.config/systemd/user/
+install -D -m 644 services/zellij-fleet/10-onfailure-althing.conf \
+  ~/.config/systemd/user/zellij-fleet@.service.d/10-onfailure-althing.conf
+systemctl --user daemon-reload
+```
+
+Installed on nh3-dev 2026-09-25. **`zellij-fleet@Claude` is NOT enabled.**
+Enabling it (`systemctl --user enable zellij-fleet@Claude`) makes the fleet
+session come back at boot with every pane held, instead of when Prime first logs
+in over ssh. That changes boot behaviour, so it waits until seat_up ships and
+Prime agrees. Do not `start` it while a Claude server is already running outside
+it: the start is a no-op, and a later `stop` would then not mean what it says.
+
+Contract use: seat_up checks `zellij list-sessions` for a RUNNING (not EXITED)
+session and calls `systemctl --user start zellij-fleet@<session>` only when
+there is none.