Correct the one-controller claim: the drone takes over, it does not refuse

Tested on the aircraft. A second ARSDK handshake is accepted and telemetry is
redirected to it; the first session's frames stop while it still reports
connected = True. So the claim inherited from pyparrot's error text, which had
reached our error messages, tool descriptions, simulator behaviour and a test
name, was wrong in the most misleading direction: a refusal would be loud, and
this is silent.

The simulator now models the takeover by default; refusal stays available
because a client must handle a non-zero status anyway.

tests/test_sim.py

@@ -74,6 +74,16 @@ def sim():
         yield fake
 
 
+@pytest.fixture
+def sim_factory():
+    """For tests that need the refusing simulator rather than the default.
+
+    The default models the aircraft: a second controller is accepted and the
+    first is starved. Refusal is the opt-in mode.
+    """
+    return FakeBebop
+
+
 @pytest.fixture
 def controller(sim):
     client = Controller(sim)
@@ -165,15 +175,34 @@ def test_handshake_is_accepted_and_names_a_c2d_port(sim, controller):
     assert sim.handshakes[0]["controller_name"] == "test"
 
 
-def test_a_second_controller_is_refused(sim, controller):
+def test_a_second_controller_is_accepted_by_default(sim, controller):
+    """Matching the aircraft, which accepts a newcomer and starves the first.
+
+    Tested on the real drone 2026-10-02. The refusal this test used to assert
+    was folklore inherited from pyparrot's error text.
+    """
     second = Controller(sim)
     try:
-        assert second.reply["status"] == 1
+        assert second.reply["status"] == 0
     finally:
         second.close()
 
 
+def test_a_second_controller_can_be_refused_when_asked(sim_factory):
+    """Kept because a client must still handle a non-zero status."""
+    with sim_factory(single_controller=True) as strict:
+        first = Controller(strict)
+        second = Controller(strict)
+        try:
+            assert first.reply["status"] == 0
+            assert second.reply["status"] == 1
+        finally:
+            second.close()
+            first.close()
+
+
 def test_the_slot_is_free_again_after_release(sim, controller):
+    """Only meaningful in the strict mode; the default never withholds a slot."""
     assert sim.occupied
     sim.release()
     third = Controller(sim)