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fix(channel): coalesce queued stream deltas to reduce API calls
When LLM generates faster than channel can process, asyncio.Queue accumulates multiple _stream_delta messages. Each delta triggers a separate API call (~700ms each), causing visible delay after LLM finishes. Solution: In _dispatch_outbound, drain all queued deltas for the same (channel, chat_id) before sending, combining them into a single API call. Non-matching messages are preserved in a pending buffer for subsequent processing. This reduces N API calls to 1 when queue has N accumulated deltas.
This commit is contained in:
chengyongru
Xubin Ren
parent
1331084873
commit
5ff9146a24
@ -118,12 +118,20 @@ class ChannelManager:
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"""Dispatch outbound messages to the appropriate channel."""
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logger.info("Outbound dispatcher started")
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# Buffer for messages that couldn't be processed during delta coalescing
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# (since asyncio.Queue doesn't support push_front)
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pending: list[OutboundMessage] = []
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while True:
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try:
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msg = await asyncio.wait_for(
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self.bus.consume_outbound(),
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timeout=1.0
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)
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# First check pending buffer before waiting on queue
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if pending:
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msg = pending.pop(0)
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else:
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msg = await asyncio.wait_for(
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self.bus.consume_outbound(),
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timeout=1.0
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)
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if msg.metadata.get("_progress"):
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if msg.metadata.get("_tool_hint") and not self.config.channels.send_tool_hints:
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@ -131,6 +139,12 @@ class ChannelManager:
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if not msg.metadata.get("_tool_hint") and not self.config.channels.send_progress:
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continue
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# Coalesce consecutive _stream_delta messages for the same (channel, chat_id)
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# to reduce API calls and improve streaming latency
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if msg.metadata.get("_stream_delta") and not msg.metadata.get("_stream_end"):
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msg, extra_pending = self._coalesce_stream_deltas(msg)
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pending.extend(extra_pending)
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channel = self.channels.get(msg.channel)
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if channel:
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await self._send_with_retry(channel, msg)
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@ -150,6 +164,54 @@ class ChannelManager:
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elif not msg.metadata.get("_streamed"):
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await channel.send(msg)
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def _coalesce_stream_deltas(
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self, first_msg: OutboundMessage
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) -> tuple[OutboundMessage, list[OutboundMessage]]:
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"""Merge consecutive _stream_delta messages for the same (channel, chat_id).
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This reduces the number of API calls when the queue has accumulated multiple
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deltas, which happens when LLM generates faster than the channel can process.
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Returns:
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tuple of (merged_message, list_of_non_matching_messages)
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"""
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target_key = (first_msg.channel, first_msg.chat_id)
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combined_content = first_msg.content
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final_metadata = dict(first_msg.metadata or {})
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non_matching: list[OutboundMessage] = []
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# Drain all pending _stream_delta messages for the same (channel, chat_id)
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while True:
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try:
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next_msg = self.bus.outbound.get_nowait()
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except asyncio.QueueEmpty:
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break
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# Check if this message belongs to the same stream
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same_target = (next_msg.channel, next_msg.chat_id) == target_key
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is_delta = next_msg.metadata and next_msg.metadata.get("_stream_delta")
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is_end = next_msg.metadata and next_msg.metadata.get("_stream_end")
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if same_target and is_delta and not final_metadata.get("_stream_end"):
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# Accumulate content
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combined_content += next_msg.content
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# If we see _stream_end, remember it and stop coalescing this stream
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if is_end:
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final_metadata["_stream_end"] = True
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# Stream ended - stop coalescing this stream
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break
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else:
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# Keep for later processing
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non_matching.append(next_msg)
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merged = OutboundMessage(
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channel=first_msg.channel,
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chat_id=first_msg.chat_id,
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content=combined_content,
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metadata=final_metadata,
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)
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return merged, non_matching
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async def _send_with_retry(self, channel: BaseChannel, msg: OutboundMessage) -> None:
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"""Send a message with retry on failure using exponential backoff.
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262
tests/channels/test_channel_manager_delta_coalescing.py
Normal file
262
tests/channels/test_channel_manager_delta_coalescing.py
Normal file
@ -0,0 +1,262 @@
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"""Tests for ChannelManager delta coalescing to reduce streaming latency."""
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import asyncio
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from unittest.mock import AsyncMock, MagicMock
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import pytest
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from nanobot.bus.events import OutboundMessage
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from nanobot.bus.queue import MessageBus
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from nanobot.channels.base import BaseChannel
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from nanobot.channels.manager import ChannelManager
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from nanobot.config.schema import Config
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class MockChannel(BaseChannel):
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"""Mock channel for testing."""
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name = "mock"
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display_name = "Mock"
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def __init__(self, config, bus):
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super().__init__(config, bus)
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self._send_delta_mock = AsyncMock()
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self._send_mock = AsyncMock()
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async def start(self):
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pass
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async def stop(self):
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pass
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async def send(self, msg):
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"""Implement abstract method."""
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return await self._send_mock(msg)
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async def send_delta(self, chat_id, delta, metadata=None):
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"""Override send_delta for testing."""
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return await self._send_delta_mock(chat_id, delta, metadata)
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@pytest.fixture
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def config():
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"""Create a minimal config for testing."""
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return Config()
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@pytest.fixture
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def bus():
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"""Create a message bus for testing."""
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return MessageBus()
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@pytest.fixture
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def manager(config, bus):
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"""Create a channel manager with a mock channel."""
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manager = ChannelManager(config, bus)
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manager.channels["mock"] = MockChannel({}, bus)
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return manager
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class TestDeltaCoalescing:
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"""Tests for _stream_delta message coalescing."""
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@pytest.mark.asyncio
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async def test_single_delta_not_coalesced(self, manager, bus):
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"""A single delta should be sent as-is."""
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msg = OutboundMessage(
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channel="mock",
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chat_id="chat1",
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content="Hello",
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metadata={"_stream_delta": True},
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)
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await bus.publish_outbound(msg)
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# Process one message
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async def process_one():
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try:
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m = await asyncio.wait_for(bus.consume_outbound(), timeout=0.1)
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if m.metadata.get("_stream_delta"):
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m, pending = manager._coalesce_stream_deltas(m)
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# Put pending back (none expected)
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for p in pending:
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await bus.publish_outbound(p)
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channel = manager.channels.get(m.channel)
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if channel:
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await channel.send_delta(m.chat_id, m.content, m.metadata)
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except asyncio.TimeoutError:
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pass
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await process_one()
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manager.channels["mock"]._send_delta_mock.assert_called_once_with(
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"chat1", "Hello", {"_stream_delta": True}
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)
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@pytest.mark.asyncio
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async def test_multiple_deltas_coalesced(self, manager, bus):
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"""Multiple consecutive deltas for same chat should be merged."""
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# Put multiple deltas in queue
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for text in ["Hello", " ", "world", "!"]:
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await bus.publish_outbound(OutboundMessage(
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channel="mock",
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chat_id="chat1",
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content=text,
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metadata={"_stream_delta": True},
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))
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# Process using coalescing logic
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first_msg = await bus.consume_outbound()
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merged, pending = manager._coalesce_stream_deltas(first_msg)
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# Should have merged all deltas
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assert merged.content == "Hello world!"
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assert merged.metadata.get("_stream_delta") is True
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# No pending messages (all were coalesced)
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assert len(pending) == 0
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@pytest.mark.asyncio
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async def test_deltas_different_chats_not_coalesced(self, manager, bus):
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"""Deltas for different chats should not be merged."""
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# Put deltas for different chats
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await bus.publish_outbound(OutboundMessage(
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channel="mock",
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chat_id="chat1",
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content="Hello",
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metadata={"_stream_delta": True},
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))
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await bus.publish_outbound(OutboundMessage(
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channel="mock",
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chat_id="chat2",
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content="World",
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metadata={"_stream_delta": True},
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))
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first_msg = await bus.consume_outbound()
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merged, pending = manager._coalesce_stream_deltas(first_msg)
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# First chat should not include second chat's content
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assert merged.content == "Hello"
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assert merged.chat_id == "chat1"
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# Second chat should be in pending
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assert len(pending) == 1
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assert pending[0].chat_id == "chat2"
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assert pending[0].content == "World"
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@pytest.mark.asyncio
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async def test_stream_end_terminates_coalescing(self, manager, bus):
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"""_stream_end should stop coalescing and be included in final message."""
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# Put deltas with stream_end at the end
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await bus.publish_outbound(OutboundMessage(
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channel="mock",
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chat_id="chat1",
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content="Hello",
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metadata={"_stream_delta": True},
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))
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await bus.publish_outbound(OutboundMessage(
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channel="mock",
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chat_id="chat1",
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content=" world",
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metadata={"_stream_delta": True, "_stream_end": True},
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))
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first_msg = await bus.consume_outbound()
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merged, pending = manager._coalesce_stream_deltas(first_msg)
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# Should have merged content
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assert merged.content == "Hello world"
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# Should have stream_end flag
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assert merged.metadata.get("_stream_end") is True
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# No pending
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assert len(pending) == 0
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@pytest.mark.asyncio
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async def test_non_delta_message_preserved(self, manager, bus):
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"""Non-delta messages should be preserved in pending list."""
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await bus.publish_outbound(OutboundMessage(
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channel="mock",
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chat_id="chat1",
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content="Delta",
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metadata={"_stream_delta": True},
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))
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await bus.publish_outbound(OutboundMessage(
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channel="mock",
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chat_id="chat1",
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content="Final message",
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metadata={}, # Not a delta
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))
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first_msg = await bus.consume_outbound()
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merged, pending = manager._coalesce_stream_deltas(first_msg)
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assert merged.content == "Delta"
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assert len(pending) == 1
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assert pending[0].content == "Final message"
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assert pending[0].metadata.get("_stream_delta") is None
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@pytest.mark.asyncio
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async def test_empty_queue_stops_coalescing(self, manager, bus):
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"""Coalescing should stop when queue is empty."""
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await bus.publish_outbound(OutboundMessage(
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channel="mock",
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chat_id="chat1",
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content="Only message",
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metadata={"_stream_delta": True},
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))
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first_msg = await bus.consume_outbound()
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merged, pending = manager._coalesce_stream_deltas(first_msg)
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assert merged.content == "Only message"
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assert len(pending) == 0
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class TestDispatchOutboundWithCoalescing:
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"""Tests for the full _dispatch_outbound flow with coalescing."""
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@pytest.mark.asyncio
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async def test_dispatch_coalesces_and_processes_pending(self, manager, bus):
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"""_dispatch_outbound should coalesce deltas and process pending messages."""
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# Put multiple deltas followed by a regular message
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await bus.publish_outbound(OutboundMessage(
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channel="mock",
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chat_id="chat1",
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content="A",
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metadata={"_stream_delta": True},
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))
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await bus.publish_outbound(OutboundMessage(
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channel="mock",
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chat_id="chat1",
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content="B",
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metadata={"_stream_delta": True},
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))
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await bus.publish_outbound(OutboundMessage(
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channel="mock",
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chat_id="chat1",
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content="Final",
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metadata={}, # Regular message
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))
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# Run one iteration of dispatch logic manually
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pending = []
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processed = []
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# First iteration: should coalesce A+B
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if pending:
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msg = pending.pop(0)
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else:
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msg = await bus.consume_outbound()
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if msg.metadata.get("_stream_delta") and not msg.metadata.get("_stream_end"):
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msg, extra_pending = manager._coalesce_stream_deltas(msg)
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pending.extend(extra_pending)
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channel = manager.channels.get(msg.channel)
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if channel:
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await channel.send_delta(msg.chat_id, msg.content, msg.metadata)
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processed.append(("delta", msg.content))
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# Should have sent coalesced delta
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assert processed == [("delta", "AB")]
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# Should have pending regular message
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assert len(pending) == 1
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assert pending[0].content == "Final"
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