Implement Apex Agent MVP scaffold

tests/test_device_manager.py

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+from __future__ import annotations
+
+import pytest
+
+from core.device_manager import DeviceManager
+from core.errors import DeviceOfflineError
+from tests.fakes import FakeDriver
+
+
+def test_device_manager_connect_disconnect_transitions() -> None:
+    driver = FakeDriver()
+    manager = DeviceManager()
+    manager.register_device("iphone-1", lambda: driver, connection_info={"wda_port": 8100})
+
+    assert manager.list_devices()[0].status == "idle"
+    assert manager.connect("iphone-1", max_retries=1) is driver
+    assert manager.status("iphone-1") == "busy"
+
+    manager.disconnect("iphone-1")
+    assert manager.status("iphone-1") == "idle"
+    assert driver.calls[0] == ("connect", ())
+    assert driver.calls[-1] == ("disconnect", ())
+
+
+def test_device_manager_marks_unreachable_device_offline() -> None:
+    manager = DeviceManager()
+    manager.register_device("iphone-1", lambda: FakeDriver(fail_connect=True))
+
+    with pytest.raises(DeviceOfflineError):
+        manager.connect("iphone-1", max_retries=2, retry_backoff_seconds=0)
+
+    assert manager.status("iphone-1") == "offline"
+