RFE 002: type = "group" service for grouping/targeting

Summary

Add a type = "group" (or "target") service kind to zyginit. A
group service has no [exec] block; it exists only as a named
synchronization/enable point. Its [dependencies] list expands into
the set of services it represents.

This is the equivalent of systemd's .target units. It lets admins
enable/disable a feature set with one command without consolidating
unrelated daemons under a single supervisor.

Motivation

Hammerhead is converting the NFS, IPsec, and zones SMF service sets
to zyginit. NFS in particular spreads across multiple independent
daemons (nfsmapid, statd, lockd, nfs4cbd, plus the client
mount oneshot) — each with its own lifecycle, restart policy, and
log file.

The natural design is one zyginit service per daemon. But that loses
the SMF-era ergonomics of "enable nfs-client and the dependents come
along". Without a group abstraction we have two bad options:

1. Combine multiple daemons into one zyginit service. Cluttered:
   one contract becomes N contracts, restart semantics get fuzzy,
   log routing needs splitting, and the supervisor's child-death
   handling no longer maps 1:1 to a service.

2. Document the bundle and tell admins to enable each member.
   Error-prone and ugly:

   zygctl enable nfs-cbd nfs-mapid nfs-statd nfs-lockd nfs-client
   

A group service neatly avoids both:

[service]
name = "nfs-client"
description = "NFSv4 client services"
type = "group"
[dependencies]
requires = ["nfs-cbd", "nfs-mapid", "nfs-statd", "nfs-lockd",
            "nfs-client-mount"]

Then zygctl enable nfs-client is sufficient. zygctl status nfs-client
reports composite up/down derived from the members.

Suggested semantics

• type = "group" services have no [exec] block. The supervisor
  never forks anything for them.
• Status: running iff all requires members are running;
  stopped iff none are; partial (or degraded) if some.
• zygctl enable <group> symlinks the group's TOML in enabled.d/
  and recursively enables each member that is not already enabled
  (or, simpler: refuses unless all members are also enabled —
  consistent with how SMF dependencies block enable today).
• zygctl disable <group> is symmetric.
• zygctl start <group> / stop <group> operate on the member set.
• Cycle detection treats group-edges the same as service-edges.

Use cases

Hammerhead would land this in roughly 4–6 group definitions.

Reporter

Hammerhead build team (Chris Tusa, christusa@gmail.com)
Filed during SMF-to-zyginit migration policy work, 2026-05-08.