ADR-0006 — Auto scope: one-shot strategies + auto --once + foreground loop; no systemd packaging

Context and Problem Statement

Unattended switching needs some scheduler. The question was how much process supervision to own in v1.

Decision Drivers

• Cover the three real usages: manual (switch), scripted (auto --once, meaningful exit codes), unattended (auto foreground loop).
• A correctly-supervised foreground loop is already systemd-runnable by the user; packaging our own unit adds a distribution concern without adding capability.

Considered Options

• auto foreground loop + --once tick
• Ship a systemd user unit
• cron/systemd-timer only

Decision Outcome

Chosen option: "auto foreground loop + --once tick", because it covers manual, scripted, and unattended use with no packaging surface.

v1 ships --strategy on switch, auto --once (exit 0 switched / 1 error / 2 no action / 3 blocked; a wrapper pages on blocked: wanted to switch but no viable target or the fleet is exhausted), and auto as a SIGTERM-clean foreground loop (default 60s interval, min 15s; threshold default 90%; cooldown 300s). systemd packaging is a non-goal.

Consequences

The loop must behave like a good foreground citizen, with clean SIGTERM and no orphan state, precisely because supervision is delegated. If packaged units are ever wanted, they wrap auto unchanged; nothing in the loop may assume it owns the terminal.

Pros and Cons of the Options

Option	Pro	Con
auto foreground loop + --once tick	Simplest thing that covers manual/scripted/unattended; SIGTERM-clean contract is ours to keep	User wires their own supervision
Ship a systemd user unit	Zero user wiring	Packaging surface, distro variance, install/upgrade machinery, for a loop a unit file wraps in 5 lines
cron/systemd-timer only	No daemon at all	Loses the loop's statefulness (cooldown, backoff) across runs without extra persistence work