feat: reboot_host contract, guest agent declaration, port group targets

HostRebootMixin declares reboot_host(), mixed into DeviceTypeDriver so
any device may be restartable. netOrk restarted hosts by sending
/sbin/reboot through a driver's private _send_command; a driver talking
to an API had no such method and the reboot was silently skipped.

HypervisorDriver gains GUEST_AGENT_PACKAGES / GUEST_AGENT_RUNCMD, the
agent cloud-init installs so the hypervisor can read a new VM's IP.
The default stays qemu-guest-agent; VMware declares open-vm-tools.

NetworkTargetDict.kind may be "portgroup": a VMware port group fixes its
VLAN like an SDN vnet does, without being one.

tests/test_host_reboot.py

@@ -0,0 +1,29 @@
+"""reboot_host: the contract for restarting the device itself.
+
+netOrk used to restart a host by sending ``/sbin/reboot`` through a driver's
+private ``_send_command``. A driver that talks to an API instead has no such
+method, and the caller swallowed the resulting AttributeError, so the reboot
+"succeeded" without happening. A declared contract lets netOrk ask first.
+"""
+
+from __future__ import annotations
+
+import inspect
+
+from napalm_device_types import DeviceTypeDriver, HostRebootMixin
+
+
+def test_every_device_type_driver_carries_the_declaration():
+    assert issubclass(DeviceTypeDriver, HostRebootMixin)
+
+
+def test_declared_not_implemented():
+    """hasattr is netOrk's capability probe; only a driver that implements it
+    may answer True."""
+    assert not hasattr(DeviceTypeDriver, "reboot_host")
+
+
+def test_declaration_documents_the_contract():
+    source = inspect.getsource(HostRebootMixin)
+    assert "def reboot_host(self) -> None" in source
+    assert "RuntimeError" in source

tests/test_vm_identifiers.py

@@ -51,3 +51,20 @@ class TestVMConfigCarriesWhatAHardwareViewShows:
         from napalm_device_types.models import VMPassthroughDict
 
         assert get_type_hints(VMPassthroughDict) == {"slot": str, "kind": str, "config": str}
+
+
+class TestGuestAgentDeclaration:
+    """netOrk's cloud-init installed qemu-guest-agent on every new VM. A VMware
+    guest reports its IP through open-vm-tools instead; the hypervisor says
+    which, and netOrk stops hard-coding one of them."""
+
+    def test_default_is_qemu_guest_agent(self):
+        from napalm_device_types import HypervisorDriver
+
+        assert HypervisorDriver.GUEST_AGENT_PACKAGES == ("qemu-guest-agent",)
+        assert HypervisorDriver.GUEST_AGENT_RUNCMD == ("systemctl enable --now qemu-guest-agent",)
+
+    def test_attributes_are_not_methods(self):
+        from napalm_device_types import HypervisorDriver
+
+        assert not callable(vars(HypervisorDriver)["GUEST_AGENT_PACKAGES"])