hyperhive/docs/boundary.md

# The operator/agent boundary

Design rationale for hyperhive's two-principal trust model. The
_implementation_ work — container network isolation, the unifying
gateway, core-daemon privsep — is tracked as `area:ops` issues on
the forge.

The operator/agent boundary is technically enforced, not just a
convention: containers run in private netns (network isolation is
always on), the gateway proxies all operator-facing traffic, and
`hive-c0re` runs as the unprivileged `hive-core` user.

## Two principals, two paths

- **Operator** — reaches every UI (the dashboard + every
  per-agent page) through the gateway, on one origin.
  Operator-authority actions (approve / deny, answer-as-operator,
  lifecycle POSTs) are served by the core daemon and only
  reachable via the gateway.
- **Agent** — speaks only for itself, only over its per-agent
  unix socket. The socket's identity _is_ the agent (see
  `docs/conventions.md`, "identity = socket"). An agent must not
  be able to reach the core daemon's HTTP surface, another
  agent's socket, or another agent's web UI.

## Design rule

**Operator-authority actions never get a per-agent-socket entry
point.** They live on the core backend.

Worked example — answering an operator-targeted question is a
`POST /answer-question/{id}` on the core dashboard, _never_ an
`AgentRequest` variant. If it were a per-agent-socket request, an
agent could `curl` its own socket and spoof an operator answer.
The per-agent web UI POSTs cross-origin to the core for these
(see the inline-answer feature — the loose-ends section on each
agent page).

## Why network isolation is the load-bearing step

Without network isolation, containers share the host network namespace
and can reach `localhost:<core-port>`, the dashboard, and every other
agent's web port — the operator/agent split is on the honour system and
every boundary claim above is aspirational. Network isolation is what
makes the boundary _real_; the gateway and privsep are ergonomics and
defence-in-depth layered on top.

Network isolation is complete and always on: every agent container
runs in a private netns behind the hive bridge, and there is no
shared-netns mode. See `docs/network.md`.

Concretely, the core daemon's dashboard `/api` carries **no
application-layer authentication** — operator-authority routes are served
unauthenticated at the HTTP layer. Their protection is entirely (a) the
gateway, which fronts all operator traffic and is where operator auth lives,
and (b) network isolation, which keeps agents — and `hive-ci`'s untrusted PR
builds — off host-loopback so nothing can reach `127.0.0.1:<dashboard_port>`
directly. This is deliberate given the load-bearing role of network isolation
above, but it is a standing invariant: the `/api` must never be bound to a
non-loopback address or exposed outside the gateway, and every new
operator-authority route inherits that assumption. `hive-ci` is treated like an
agent for this purpose — it runs untrusted PR code and is netns-isolated for
the same reason.

The boundary rests on three layers:

1. **Gateway** — fronts all surfaces (dashboard + every per-agent UI)
   on one origin. An nginx nixos-container proxies per-agent UIs under
   `/agent/<name>/`, which is what lets the inline-answer POST to
   `/answer-question/{id}` go same-origin instead of needing a
   cross-origin CORS shim. Pure ergonomics — no behavioural risk on
   its own.
2. **Network isolation** — the load-bearing layer: every agent
   container runs in a private netns behind the hive bridge, always
   on and unconditional. This is what turns the operator/agent split
   from an honour-system convention into an enforced boundary.
3. **Privsep** — defence in depth on the core process; `hive-c0re`
   runs as the unprivileged `hive-core` user and delegates root
   operations to `hive-priv`, a narrow socket-activated helper. See
   [`docs/security.md`](security.md) for the privilege boundary table.

### hive-priv socket activation

`hive-priv` is **always** socket-activated by the `hive-priv.socket`
systemd unit. The unit binds `/run/hive/priv.sock` with
`SocketGroup=hive-core` and mode `0660` and passes the ready listener
to the helper as fd 3 (`LISTEN_FDS`). The helper requires this and
bails if it isn't socket-activated.

⚠️ There is intentionally no self-bind fallback: if `hive-priv` bound
the socket itself, it would create the file owned by root's primary
group rather than `hive-core`, and a `hive-core` client couldn't
connect the way the socket unit's `SocketGroup` grant intends.
Requiring socket activation everywhere keeps dev and prod on the
exact same path, so the group grant always holds.

### the per-agent socket dir

`/run/hive-agent/<name>/` is shared by **three principals that share no
group**, which is why its mode is what it is:

| principal | reaches | needs |
|---|---|---|
| the agent's harness | binds + unlinks `agent.sock`, `web.sock` | owner, `rwx` |
| `hive-c0re` | dials `agent.sock` (todo wakes) | traverse |
| the gateway's nginx | dials `web.sock` | traverse |

The last two land in "other", so the dir is **`0751`, owned by the
agent's container uid/gid** — `o=--x` is traverse without listing, and
both sockets are `0666`, which is all a dialer needs.

**Ownership is declared, not repaired.** The tmpfiles.d entry written by
`SyncAgentTmpfiles` names the uid/gid directly. Do not add a chown
alongside it: `d` re-applies on every boot *and* every agent
spawn/destroy, so ownership set afterwards is reverted the next time any
agent changes — which is exactly how this dir spent a long time at
`0777 root root` while a privileged chown appeared to be fixing it.

The mode is load-bearing, not cosmetic. Write permission on a
*directory* is what confers the right to unlink its entries, whoever owns
them, and the sticky bit is the only thing that would restrain that (it
is not set here). A world-writable socket dir therefore lets anything
able to reach the path delete an agent's socket and bind its own — and
nginx reaches all of `/run/hive-agent` as a plain host path. Dropping
`o=w` removes that permission rather than qualifying it.

⚠️ **The gateway's nginx and dnsmasq are host services, next to
`hive-c0re`** (see `docs/gateway.md`) — there is no namespace between
them and the rest of the host. That costs no network isolation: nginx
binds the host's `:80`/`:443` and reaches `localhost` upstreams, which a
netns would have to be opened up for anyway.
🔑 It does mean nothing *implicitly* scopes the privileged reload verb —
see [`docs/security.md`](security.md#hive-c0re-privilege-separation) for
how `PrivRequest::ReloadGatewayNginx`'s containment works.

⚠️ Contrast `/shared`, which *is* sticky world-writable (`1777`): it has
many legitimate writers, so sticky is the best available answer there.
This dir has exactly one writer, so it needs no world write at all.

### host admin socket access (`hivectl`)

`hivectl` drives the whole hive — spawn / kill / destroy / rebuild /
deploy — over the **host admin socket** `/run/hyperhive/host.sock`,
socket-activated by the `hive-c0re.socket` unit. That socket *is* the
full-control surface, so who can connect to it is a real trust
boundary.

By default the socket is `0660` group-owned by **`hive-admin`**, an
empty group — so it is effectively **root-only** until an operator is
explicitly granted access. Grant sudoless `hivectl` by listing login
users in `services.hyperhive.c0re.adminUsers`; each is added to
`hive-admin`, and members connect without `sudo`. The runtime dir
`/run/hyperhive` is `0751` (traverse-only, no listing) so the group can
reach the socket path; the socket's own `0660 hive-admin` mode gates
the connection, and the per-agent subdirs under it keep their own
restrictive perms. Keep `adminUsers` to trusted operators — membership
is equivalent to root over the hive.