feat: gate_bus blocking choice waiter

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_gate_bus.py

@@ -0,0 +1,28 @@
+# tests/test_gate_bus.py
+import pytest
+from gates import gate_bus as gb
+
+def test_put_and_wait_returns_choice():
+    gb.GateBus.arm("7")
+    gb.GateBus.put("7", "3")
+    assert gb.GateBus.wait("7") == 3
+
+def test_wait_consumes_message():
+    gb.GateBus.arm("7")
+    gb.GateBus.put("7", "2")
+    gb.GateBus.wait("7")
+    assert "7" not in gb.GateBus.messages
+
+def test_cancel_raises_and_resets():
+    gb.GateBus.arm("7")
+    gb.GateBus.put("7", "__cancel__")
+    with pytest.raises(gb.GateCancelled):
+        gb.GateBus.wait("7")
+    assert gb.GateBus.cancelled is False      # reset after raising
+
+def test_arm_clears_stale_state():
+    gb.GateBus.put("1", "5")
+    gb.GateBus.cancelled = True
+    gb.GateBus.arm("1")
+    assert "1" not in gb.GateBus.messages
+    assert gb.GateBus.cancelled is False