feat: gate_bus payload channel + should_cancel

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

gates/gate_bus.py

@@ -9,12 +9,14 @@ class GateCancelled(Exception):
 class GateBus:
     messages = {}     # node_id(str) -> chosen int (1-based)
     masks = {}        # node_id(str) -> PNG bytes
+    payloads = {}     # node_id(str) -> arbitrary payload (e.g., edited text)
     cancelled = False
 
     @classmethod
     def arm(cls, node_id):
         cls.messages.pop(str(node_id), None)
         cls.masks.pop(str(node_id), None)
+        cls.payloads.pop(str(node_id), None)
         cls.cancelled = False
 
     @classmethod
@@ -41,3 +43,17 @@ class GateBus:
     @classmethod
     def pop_mask(cls, node_id):
         return cls.masks.pop(str(node_id), None)
+
+    @classmethod
+    def put_payload(cls, node_id, value):
+        cls.payloads[str(node_id)] = value
+
+    @classmethod
+    def wait_payload(cls, node_id, period=0.1, should_cancel=None):
+        sid = str(node_id)
+        while sid not in cls.payloads:
+            if cls.cancelled or (should_cancel is not None and should_cancel()):
+                cls.cancelled = False
+                raise GateCancelled()
+            time.sleep(period)
+        return cls.payloads.pop(sid)

tests/test_gate_bus.py

@@ -36,3 +36,26 @@ def test_arm_clears_mask():
     gb.GateBus.put_mask("9", b"x")
     gb.GateBus.arm("9")
     assert gb.GateBus.pop_mask("9") is None
+
+def test_payload_roundtrip():
+    gb.GateBus.arm("p")
+    gb.GateBus.put_payload("p", "hello edited")
+    assert gb.GateBus.wait_payload("p") == "hello edited"
+
+def test_payload_consumed():
+    gb.GateBus.arm("p")
+    gb.GateBus.put_payload("p", "x")
+    gb.GateBus.wait_payload("p")
+    assert "p" not in gb.GateBus.payloads
+
+def test_arm_clears_payload():
+    gb.GateBus.put_payload("p", "stale")
+    gb.GateBus.arm("p")
+    assert "p" not in gb.GateBus.payloads
+
+def test_wait_payload_cancel_flag_raises():
+    import pytest
+    gb.GateBus.arm("p")
+    gb.GateBus.cancelled = True
+    with pytest.raises(gb.GateCancelled):
+        gb.GateBus.wait_payload("p")