feat: gate_bus blocking choice waiter

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

gates/gate_bus.py

@@ -0,0 +1,35 @@
+"""Blocking choice bus for the Image Gate node. Stdlib only — no comfy/torch."""
+import time
+
+
+class GateCancelled(Exception):
+    pass
+
+
+class GateBus:
+    messages = {}     # node_id(str) -> chosen int (1-based)
+    masks = {}        # node_id(str) -> PNG bytes
+    cancelled = False
+
+    @classmethod
+    def arm(cls, node_id):
+        cls.messages.pop(str(node_id), None)
+        cls.masks.pop(str(node_id), None)
+        cls.cancelled = False
+
+    @classmethod
+    def put(cls, node_id, message):
+        if message == "__cancel__":
+            cls.cancelled = True
+        else:
+            cls.messages[str(node_id)] = int(message)
+
+    @classmethod
+    def wait(cls, node_id, period=0.1):
+        sid = str(node_id)
+        while sid not in cls.messages:
+            if cls.cancelled:
+                cls.cancelled = False
+                raise GateCancelled()
+            time.sleep(period)
+        return cls.messages.pop(sid)