Port multi-task unit tests from pipecat-subagents

Brings over 215 tests across 15 files covering the new
multi-task framework: BaseTask / PipelineTask bus lifecycle,
job RPC and job groups, the bus message hierarchy and serializers,
TaskBus + AsyncQueueBus + RedisBus + PgmqBus (with direct and
isolated backends), TaskRegistry, the BusBridgeProcessor, the
WebSocket proxy tasks, the LLMTask deferral logic, and the
PipelineRunner spawn-and-attach flow.

tests/test_messages.py

@@ -0,0 +1,97 @@
+#
+# Copyright (c) 2026, Daily
+#
+# SPDX-License-Identifier: BSD 2-Clause License
+#
+
+import asyncio
+import unittest
+
+from pipecat.bus import (
+    AsyncQueueBus,
+    BusDataMessage,
+    BusFrameMessage,
+    BusSubscriber,
+)
+from pipecat.frames.frames import TextFrame
+from pipecat.processors.frame_processor import FrameDirection
+from pipecat.utils.asyncio.task_manager import TaskManager, TaskManagerParams
+
+
+class TestBusMessageRouting(unittest.IsolatedAsyncioTestCase):
+    async def test_broadcast_message_no_target(self):
+        """A BusMessage with no target is broadcast (target is None)."""
+        msg = BusDataMessage(source="task_a")
+        self.assertIsNone(msg.target)
+
+    async def test_targeted_message(self):
+        """A BusMessage with target set is only for that task."""
+        msg = BusDataMessage(source="task_a", target="task_b")
+        self.assertEqual(msg.target, "task_b")
+
+    async def test_broadcast_reaches_all_subscribers(self):
+        """Broadcast messages (no target) reach all subscribers."""
+        bus = AsyncQueueBus()
+        tm = TaskManager()
+        tm.setup(TaskManagerParams(loop=asyncio.get_running_loop()))
+        await bus.setup(tm)
+        received_a = []
+        received_b = []
+
+        class SubA(BusSubscriber):
+            @property
+            def name(self) -> str:
+                return "sub_a"
+
+            async def on_bus_message(self, message):
+                received_a.append(message)
+
+        class SubB(BusSubscriber):
+            @property
+            def name(self) -> str:
+                return "sub_b"
+
+            async def on_bus_message(self, message):
+                received_b.append(message)
+
+        await bus.subscribe(SubA())
+        await bus.subscribe(SubB())
+
+        await bus.start()
+        msg = BusDataMessage(source="task_x")  # no target
+        await bus.send(msg)
+        await asyncio.sleep(0.05)
+        await bus.stop()
+
+        # Both subscribers see the broadcast
+        self.assertEqual(len(received_a), 1)
+        self.assertEqual(len(received_b), 1)
+
+    async def test_bus_frame_message_wraps_frame(self):
+        """BusFrameMessage wraps a frame with source and direction."""
+        frame = TextFrame(text="hello")
+        msg = BusFrameMessage(
+            source="task_a",
+            frame=frame,
+            direction=FrameDirection.DOWNSTREAM,
+        )
+        self.assertIs(msg.frame, frame)
+        self.assertEqual(msg.direction, FrameDirection.DOWNSTREAM)
+        self.assertEqual(msg.source, "task_a")
+        self.assertIsNone(msg.target)
+
+    async def test_bus_frame_message_with_target(self):
+        """BusFrameMessage can carry a target for directed delivery."""
+        frame = TextFrame(text="hello")
+        msg = BusFrameMessage(
+            source="task_a",
+            target="task_b",
+            frame=frame,
+            direction=FrameDirection.DOWNSTREAM,
+        )
+        self.assertEqual(msg.target, "task_b")
+        self.assertIs(msg.frame, frame)
+
+
+if __name__ == "__main__":
+    unittest.main()