hivectl: add hive-wide start/stop verbs

`hivectl stop` brings the whole hive down in one operator action — all
sub-agents plus the ci/forge/gateway/matrix infra containers — and
`hivectl start` brings it back up. Scope flags (--agents, --agent <name>,
--ci, --forge, --gateway, --matrix) narrow the set; a bare invocation
targets everything. hive-c0re never stops itself.

- hive-sh4re: HostRequest::{Stop,Start} + LifecycleScope wire type;
  priv_proto InfraAction + ControlInfraContainer + the
  CONTROLLABLE_INFRA_CONTAINERS allowlist (adds hive-matrix, excludes
  hive-c0re).
- hive-priv: control_infra_container handler (systemctl <verb>
  container@<name>, allowlist-validated root-side).
- hive-c0re: handle_stop / handle_start fan out agents via lifecycle and
  infra via hive-priv; per-target failures are aggregated. Infra
  systemctl routes through hive-priv (the privsep boundary).
- The --graceful flag is threaded through Stop now; the per-agent quiesce
  itself lands with the graceful-agent-stop work.

hive-sh4re/src/priv_proto.rs

@@ -27,6 +27,37 @@ pub const SIBLING_CONTAINERS: &[&str] = &["hive-forge", "hive-matrix", "hive-gat
 /// it is the authoritative allowlist regardless of what the caller sends.
 pub const RESTARTABLE_INFRA_CONTAINERS: &[&str] = &["hive-ci", "hive-gateway", "hive-forge"];
 
+/// Infra containers hive-c0re may stop/start/restart hive-wide for the
+/// `hivectl stop` / `hivectl start` operator flow. Superset of
+/// [`RESTARTABLE_INFRA_CONTAINERS`]: it adds `hive-matrix`, because a full
+/// stop is a deliberate operator action (unlike the disruptive mid-sync
+/// *restart* the `infra_admin` MCP path forbids). `hive-c0re` is still
+/// excluded — it runs the daemon servicing the request and must never stop
+/// itself. hive-priv re-validates against this list root-side.
+pub const CONTROLLABLE_INFRA_CONTAINERS: &[&str] =
+    &["hive-ci", "hive-gateway", "hive-forge", "hive-matrix"];
+
+/// Lifecycle verb for [`PrivRequest::ControlInfraContainer`]. Maps directly
+/// to `systemctl <verb> container@<container>.service`.
+#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum InfraAction {
+    Start,
+    Stop,
+    Restart,
+}
+
+impl InfraAction {
+    /// The `systemctl` subcommand this action maps to.
+    pub fn systemctl_verb(self) -> &'static str {
+        match self {
+            InfraAction::Start => "start",
+            InfraAction::Stop => "stop",
+            InfraAction::Restart => "restart",
+        }
+    }
+}
+
 /// Host path of the meta flake. The flake ref for agent `<name>` is
 /// `{META_DIR}#{name}`, derived by `hive-priv` — never passed over the wire.
 pub const META_DIR: &str = "/var/lib/hyperhive/meta";
@@ -316,6 +347,16 @@ pub enum PrivRequest {
         /// [`RESTARTABLE_INFRA_CONTAINERS`].
         container: String,
     },
+
+    /// Start/stop/restart a hive infrastructure container on the host via
+    /// `systemctl <action> container@<container>.service`. hive-priv
+    /// validates `container` against [`CONTROLLABLE_INFRA_CONTAINERS`]
+    /// root-side. Generalises [`PrivRequest::RestartInfraContainer`] for the
+    /// hive-wide `hivectl stop` / `hivectl start` operator flow.
+    ControlInfraContainer {
+        container: String,
+        action: InfraAction,
+    },
 }
 
 /// Response from the privileged helper.