refactor floating_domain to structured object-only payload

tests/test_ws_unified.py

@@ -50,7 +50,7 @@ async def _mock_home_stream(user_id, message, context):
 
 
 async def _mock_floating_stream(user_id, message, context):
-    yield "floating_domain", "tasks"
+    yield "floating_domain", {"type": "task", "id": None, "section": None}
     yield "token", "Here is a summary"
 
 
@@ -102,7 +102,7 @@ def test_floating_request_produces_domain_frame(client):
     assert types.index(WsFrameType.floating_domain) < types.index(WsFrameType.stream_end)
 
     domain_frame = next(f for f in frames if f["type"] == WsFrameType.floating_domain)
-    assert domain_frame["domain"] == "tasks"
+    assert domain_frame["domain"]["type"] == "task"
     assert domain_frame["request_id"] == "p1"