simbiot-harness/venv/lib/python3.12/site-packages/strands/multiagent/swarm.py
Simbiot Harness b60439152b Simbiot Harness v0.1: тактовая лестница на Strands + CQRS/ES-спина
- harness/es.py: append-only event store + проекции (образец — кооп-портал)
- harness/levels.py: уровни 1с/1м/1ч/1д, контекст ∝ масштабу
- harness/scheduler.py: уровневые потоки, идемпотентные тики, absorbed-стабы
- harness/isolated_runner.py + _llm_worker.py: LLM-тик в сабпроцессе
  (глобальный asyncio-рантайм Strands не переживает 2+ create_harness)
- cli.py: init/task/tasks/status/events + requeue (написан самим минутным агентом)
- 9router: отдельный ключ sk-simbiot, модель auto (glm-5.3 первым)
2026-09-29 15:28:50 +00:00

1201 lines
53 KiB
Python

"""Swarm Multi-Agent Pattern Implementation.
This module provides a collaborative agent orchestration system where
agents work together as a team to solve complex tasks, with shared context
and autonomous coordination.
Key Features:
- Self-organizing agent teams with shared working memory
- Tool-based coordination
- Autonomous agent collaboration without central control
- Dynamic task distribution based on agent capabilities
- Collective intelligence through shared context
- Human input via user interrupts raised in BeforeNodeCallEvent hooks and agent nodes
"""
import asyncio
import copy
import json
import logging
import sys
import time
from collections.abc import AsyncIterator, Callable, Mapping
from dataclasses import dataclass, field
from typing import Any, Literal, Optional, cast
from opentelemetry import trace as trace_api
from .._async import run_async
from ..agent import Agent
from ..agent.state import AgentState
from ..hooks.events import (
AfterMultiAgentInvocationEvent,
AfterNodeCallEvent,
BeforeMultiAgentInvocationEvent,
BeforeNodeCallEvent,
MultiAgentInitializedEvent,
)
from ..hooks.registry import HookCallback, HookOrder, HookProvider, HookRegistry
from ..interrupt import Interrupt, _InterruptState
from ..plugins.multiagent_plugin import MultiAgentPlugin
from ..plugins.multiagent_registry import _MultiAgentPluginRegistry
from ..session import SessionManager
from ..telemetry import get_tracer
from ..tools.decorator import tool
from ..types._events import (
MultiAgentHandoffEvent,
MultiAgentNodeCancelEvent,
MultiAgentNodeInterruptEvent,
MultiAgentNodeStartEvent,
MultiAgentNodeStopEvent,
MultiAgentNodeStreamEvent,
MultiAgentResultEvent,
)
from ..types.content import ContentBlock, Messages
from ..types.event_loop import Metrics, Usage
from ..types.multiagent import MultiAgentInput
from ..types.session import decode_bytes_values, encode_bytes_values
from ..types.traces import AttributeValue
from .base import (
MultiAgentBase,
MultiAgentResult,
NodeResult,
Status,
_accumulate_cache_usage,
_parse_metrics,
_parse_usage,
)
logger = logging.getLogger(__name__)
_DEFAULT_SWARM_ID = "default_swarm"
@dataclass
class SwarmNode:
"""Represents a node (e.g. Agent) in the swarm."""
node_id: str
executor: Agent
swarm: Optional["Swarm"] = None
_initial_messages: Messages = field(default_factory=list, init=False)
_initial_state: AgentState = field(default_factory=AgentState, init=False)
_initial_model_state: dict[str, Any] = field(default_factory=dict, init=False)
def __post_init__(self) -> None:
"""Capture initial executor state after initialization."""
# Deep copy the initial messages and state to preserve them
self._initial_messages = copy.deepcopy(self.executor.messages)
self._initial_state = AgentState(self.executor.state.get())
self._initial_model_state = copy.deepcopy(self.executor._model_state)
def __hash__(self) -> int:
"""Return hash for SwarmNode based on node_id."""
return hash(self.node_id)
def __eq__(self, other: Any) -> bool:
"""Return equality for SwarmNode based on node_id."""
if not isinstance(other, SwarmNode):
return False
return self.node_id == other.node_id
def __str__(self) -> str:
"""Return string representation of SwarmNode."""
return self.node_id
def __repr__(self) -> str:
"""Return detailed representation of SwarmNode."""
return f"SwarmNode(node_id='{self.node_id}')"
def reset_executor_state(self) -> None:
"""Reset SwarmNode executor state to initial state when swarm was created.
If Swarm is resuming from an interrupt, we reset the executor state from the interrupt context.
"""
if self.swarm and self.swarm._interrupt_state.activated:
context = self.swarm._interrupt_state.context[self.node_id]
self.executor.messages = context["messages"]
self.executor.state = AgentState(context["state"])
self.executor._interrupt_state = _InterruptState.from_dict(context["interrupt_state"])
self.executor._model_state = context.get("model_state", {})
return
self.executor.messages = copy.deepcopy(self._initial_messages)
self.executor.state = AgentState(self._initial_state.get())
self.executor._model_state = copy.deepcopy(self._initial_model_state)
@dataclass
class SharedContext:
"""Shared context between swarm nodes."""
context: dict[str, dict[str, Any]] = field(default_factory=dict)
def add_context(self, node: SwarmNode, key: str, value: Any) -> None:
"""Add context."""
self._validate_key(key)
self._validate_json_serializable(value)
if node.node_id not in self.context:
self.context[node.node_id] = {}
self.context[node.node_id][key] = value
def _validate_key(self, key: str) -> None:
"""Validate that a key is valid.
Args:
key: The key to validate
Raises:
ValueError: If key is invalid
"""
if key is None:
raise ValueError("Key cannot be None")
if not isinstance(key, str):
raise ValueError("Key must be a string")
if not key.strip():
raise ValueError("Key cannot be empty")
def _validate_json_serializable(self, value: Any) -> None:
"""Validate that a value is JSON serializable.
Args:
value: The value to validate
Raises:
ValueError: If value is not JSON serializable
"""
try:
json.dumps(value)
except (TypeError, ValueError) as e:
raise ValueError(
f"Value is not JSON serializable: {type(value).__name__}. "
f"Only JSON-compatible types (str, int, float, bool, list, dict, None) are allowed."
) from e
@dataclass
class SwarmState:
"""Current state of swarm execution."""
current_node: SwarmNode | None # The agent currently executing
task: MultiAgentInput # The original task from the user that is being executed
completion_status: Status = Status.PENDING # Current swarm execution status
shared_context: SharedContext = field(default_factory=SharedContext) # Context shared between agents
node_history: list[SwarmNode] = field(default_factory=list) # Complete history of agents that have executed
start_time: float = field(default_factory=time.time) # When swarm execution began
results: dict[str, NodeResult] = field(default_factory=dict) # Results from each agent execution
# Total token usage across all agents
accumulated_usage: Usage = field(default_factory=lambda: Usage(inputTokens=0, outputTokens=0, totalTokens=0))
# Total metrics across all agents
accumulated_metrics: Metrics = field(default_factory=lambda: Metrics(latencyMs=0))
execution_time: int = 0 # Total execution time in milliseconds
handoff_node: SwarmNode | None = None # The agent to execute next
handoff_message: str | None = None # Message passed during agent handoff
def should_continue(
self,
*,
max_handoffs: int,
max_iterations: int,
execution_timeout: float,
repetitive_handoff_detection_window: int,
repetitive_handoff_min_unique_agents: int,
) -> tuple[bool, str]:
"""Check if the swarm should continue.
Returns: (should_continue, reason)
"""
# Check handoff limit
if len(self.node_history) >= max_handoffs:
return False, f"Max handoffs reached: {max_handoffs}"
# Check iteration limit
if len(self.node_history) >= max_iterations:
return False, f"Max iterations reached: {max_iterations}"
# Check timeout
elapsed = self.execution_time / 1000 + time.time() - self.start_time
if elapsed > execution_timeout:
return False, f"Execution timed out: {execution_timeout}s"
# Check for repetitive handoffs (agents passing back and forth)
if repetitive_handoff_detection_window > 0 and len(self.node_history) >= repetitive_handoff_detection_window:
recent = self.node_history[-repetitive_handoff_detection_window:]
unique_nodes = len(set(recent))
if unique_nodes < repetitive_handoff_min_unique_agents:
return (
False,
(
f"Repetitive handoff: {unique_nodes} unique nodes "
f"out of {repetitive_handoff_detection_window} recent iterations"
),
)
return True, "Continuing"
@dataclass
class SwarmResult(MultiAgentResult):
"""Result from swarm execution - extends MultiAgentResult with swarm-specific details."""
node_history: list[SwarmNode] = field(default_factory=list)
@dataclass
class _InflightTurn:
"""A node turn in progress: the handoff state it inherited, and whether it committed.
A checkpoint fires before the execution loop applies a handoff transition, so EXECUTING with a pending
handoff is ambiguous on its own: the node may have committed that handoff or merely inherited it.
Attributes:
handoff_node: Handoff target as it stood before the node ran.
handoff_message: Handoff message as it stood before the node ran.
shared_context: Shared context as it stood before the node ran.
outcome: Set by the execution loop where the turn's fate is known. A rolled-back turn stays
recorded, so the next checkpoint still knows the node owes work.
"""
handoff_node: SwarmNode | None
handoff_message: str | None
shared_context: dict[str, dict[str, Any]]
outcome: Literal["open", "committed", "rolled_back"] = "open"
class Swarm(MultiAgentBase):
"""Self-organizing collaborative agent teams with shared working memory."""
def __init__(
self,
nodes: list[Agent],
*,
entry_point: Agent | None = None,
max_handoffs: int = 20,
max_iterations: int = 20,
execution_timeout: float = 900.0,
node_timeout: float = 300.0,
repetitive_handoff_detection_window: int = 0,
repetitive_handoff_min_unique_agents: int = 0,
session_manager: SessionManager | None = None,
hooks: list[HookProvider] | None = None,
id: str = _DEFAULT_SWARM_ID,
trace_attributes: Mapping[str, AttributeValue] | None = None,
plugins: list[MultiAgentPlugin] | None = None,
) -> None:
"""Initialize Swarm with agents and configuration.
Args:
id: Unique swarm id (default: "default_swarm")
nodes: List of nodes (e.g. Agent) to include in the swarm
entry_point: Agent to start with. If None, uses the first agent (default: None)
max_handoffs: Maximum handoffs to agents and users (default: 20)
max_iterations: Maximum node executions within the swarm (default: 20)
execution_timeout: Total execution timeout in seconds (default: 900.0)
node_timeout: Individual node timeout in seconds (default: 300.0)
repetitive_handoff_detection_window: Number of recent nodes to check for repetitive handoffs
Disabled by default (default: 0)
repetitive_handoff_min_unique_agents: Minimum unique agents required in recent sequence
Disabled by default (default: 0)
session_manager: Session manager for persisting graph state and execution history (default: None)
hooks: List of hook providers for monitoring and extending graph execution behavior (default: None)
trace_attributes: Custom trace attributes to apply to the agent's trace span (default: None)
plugins: List of multi-agent plugins for extending swarm behavior (default: None)
"""
super().__init__()
self.id = id
self.entry_point = entry_point
self.max_handoffs = max_handoffs
self.max_iterations = max_iterations
self.execution_timeout = execution_timeout
self.node_timeout = node_timeout
self.repetitive_handoff_detection_window = repetitive_handoff_detection_window
self.repetitive_handoff_min_unique_agents = repetitive_handoff_min_unique_agents
self.shared_context = SharedContext()
self.nodes: dict[str, SwarmNode] = {}
self.state = SwarmState(
current_node=None, # Placeholder, will be set properly
task="",
completion_status=Status.PENDING,
)
self._interrupt_state = _InterruptState()
self.tracer = get_tracer()
self.trace_attributes: dict[str, AttributeValue] = self._parse_trace_attributes(trace_attributes)
self.session_manager = session_manager
self.hooks = HookRegistry()
if hooks:
for hook in hooks:
self.hooks.add_hook(hook)
if self.session_manager:
self.hooks.add_hook(self.session_manager)
self._plugin_registry = _MultiAgentPluginRegistry(self)
if plugins:
for plugin in plugins:
self._plugin_registry.add_and_init(plugin)
self._resume_from_session = False
self._turn: _InflightTurn | None = None
self._setup_swarm(nodes)
self._inject_swarm_tools()
run_async(lambda: self.hooks.invoke_callbacks_async(MultiAgentInitializedEvent(self)))
def add_hook(
self, callback: HookCallback, event_type: type | list[type] | None = None, *, order: float = HookOrder.DEFAULT
) -> None:
"""Register a hook callback with the swarm.
Args:
callback: The callback function to invoke when events of this type occur.
event_type: The class type(s) of events this callback should handle.
Can be a single type, a list of types, or None to infer from
the callback's first parameter type hint.
order: Execution priority. Lower values execute first.
"""
self.hooks.add_callback(event_type, callback, order=order)
def __call__(
self, task: MultiAgentInput, invocation_state: dict[str, Any] | None = None, **kwargs: Any
) -> SwarmResult:
"""Invoke the swarm synchronously.
Args:
task: The task to execute
invocation_state: Additional state/context passed to underlying agents.
Defaults to None to avoid mutable default argument issues.
**kwargs: Keyword arguments allowing backward compatible future changes.
"""
if invocation_state is None:
invocation_state = {}
return run_async(lambda: self.invoke_async(task, invocation_state))
async def invoke_async(
self, task: MultiAgentInput, invocation_state: dict[str, Any] | None = None, **kwargs: Any
) -> SwarmResult:
"""Invoke the swarm asynchronously.
This method uses stream_async internally and consumes all events until completion,
following the same pattern as the Agent class.
Args:
task: The task to execute
invocation_state: Additional state/context passed to underlying agents.
Defaults to None to avoid mutable default argument issues.
**kwargs: Keyword arguments allowing backward compatible future changes.
"""
events = self.stream_async(task, invocation_state, **kwargs)
final_event = None
async for event in events:
final_event = event
if final_event is None or "result" not in final_event:
raise ValueError("Swarm streaming completed without producing a result event")
return cast(SwarmResult, final_event["result"])
async def stream_async(
self, task: MultiAgentInput, invocation_state: dict[str, Any] | None = None, **kwargs: Any
) -> AsyncIterator[dict[str, Any]]:
"""Stream events during swarm execution.
Args:
task: The task to execute
invocation_state: Additional state/context passed to underlying agents.
Defaults to None to avoid mutable default argument issues.
**kwargs: Keyword arguments allowing backward compatible future changes.
Yields:
Dictionary events during swarm execution, such as:
- multi_agent_node_start: When a node begins execution
- multi_agent_node_stream: Forwarded agent events with node context
- multi_agent_handoff: When control is handed off between agents
- multi_agent_node_stop: When a node stops execution
- result: Final swarm result
"""
if invocation_state is None:
invocation_state = {}
await self.hooks.invoke_callbacks_async(BeforeMultiAgentInvocationEvent(self, invocation_state))
self._interrupt_state.resume(task)
logger.debug("starting swarm execution")
if self._resume_from_session or self._interrupt_state.activated:
self.state.completion_status = Status.EXECUTING
self.state.start_time = time.time()
else:
# Initialize swarm state with configuration
initial_node = self._initial_node()
self.state = SwarmState(
current_node=initial_node,
task=task,
completion_status=Status.EXECUTING,
shared_context=self.shared_context,
)
span = self.tracer.start_multiagent_span(task, "swarm", custom_trace_attributes=self.trace_attributes)
with trace_api.use_span(span, end_on_exit=True):
interrupts = []
self._invocation_start_time = self.state.start_time
# A turn belongs to the invocation that ran it; carrying one over would let a finished
# invocation's outcome decide this one's frontier.
self._turn = None
try:
current_node = cast(SwarmNode, self.state.current_node)
logger.debug("current_node=<%s> | starting swarm execution with node", current_node.node_id)
logger.debug(
"max_handoffs=<%d>, max_iterations=<%d>, timeout=<%s>s | swarm execution config",
self.max_handoffs,
self.max_iterations,
self.execution_timeout,
)
async for event in self._execute_swarm(invocation_state):
if isinstance(event, MultiAgentNodeInterruptEvent):
interrupts = event.interrupts
yield event.as_dict()
except Exception:
logger.exception("swarm execution failed")
self.state.completion_status = Status.FAILED
raise
finally:
# On stream close this finally runs before _execute_swarm's teardown, so roll back here too.
self._rollback_uncommitted_turn()
self.state.execution_time = self._commit_active_interval(self.state.execution_time)
await self.hooks.invoke_callbacks_async(AfterMultiAgentInvocationEvent(self, invocation_state))
self._resume_from_session = False
# Yield final result after execution_time is set
result = self._build_result(interrupts)
yield MultiAgentResultEvent(result=result).as_dict()
async def _stream_with_timeout(
self, async_generator: AsyncIterator[Any], timeout: float | None, timeout_message: str
) -> AsyncIterator[Any]:
"""Wrap an async generator with timeout for total execution time.
Tracks elapsed time from start and enforces timeout across all events.
Each event wait uses remaining time from the total timeout budget.
Args:
async_generator: The generator to wrap
timeout: Total timeout in seconds for entire stream, or None for no timeout
timeout_message: Message to include in timeout exception
Yields:
Events from the wrapped generator as they arrive
Raises:
Exception: If total execution time exceeds timeout
"""
if timeout is None:
async for event in async_generator:
yield event
elif sys.version_info >= (3, 11):
try:
async with asyncio.timeout(timeout):
async for event in async_generator:
yield event
except asyncio.TimeoutError as err:
raise Exception(timeout_message) from err
else:
# Python 3.10 fallback: timeout is only checked between yielded events.
# A generator that hangs mid-await won't be interrupted until the next event.
# Remove once Python 3.10 support is dropped (Oct 2026).
start_time = asyncio.get_running_loop().time()
async for event in async_generator:
elapsed = asyncio.get_running_loop().time() - start_time
if elapsed > timeout:
raise Exception(timeout_message)
yield event
def _setup_swarm(self, nodes: list[Agent]) -> None:
"""Initialize swarm configuration."""
# Validate nodes before setup
self._validate_swarm(nodes)
# Validate agents have names and create SwarmNode objects
for i, node in enumerate(nodes):
if not node.name:
node_id = f"node_{i}"
node.name = node_id
logger.debug("node_id=<%s> | agent has no name, dynamically generating one", node_id)
node_id = str(node.name)
# Ensure node IDs are unique
if node_id in self.nodes:
raise ValueError(f"Node ID '{node_id}' is not unique. Each agent must have a unique name.")
self.nodes[node_id] = SwarmNode(node_id, node, swarm=self)
# Validate entry point if specified
if self.entry_point is not None:
entry_point_node_id = str(self.entry_point.name)
if (
entry_point_node_id not in self.nodes
or self.nodes[entry_point_node_id].executor is not self.entry_point
):
available_agents = [
f"{node_id} ({type(node.executor).__name__})" for node_id, node in self.nodes.items()
]
raise ValueError(f"Entry point agent not found in swarm nodes. Available agents: {available_agents}")
swarm_nodes = list(self.nodes.values())
logger.debug("nodes=<%s> | initialized swarm with nodes", [node.node_id for node in swarm_nodes])
if self.entry_point:
entry_point_name = getattr(self.entry_point, "name", "unnamed_agent")
logger.debug("entry_point=<%s> | configured entry point", entry_point_name)
else:
first_node = next(iter(self.nodes.keys()))
logger.debug("entry_point=<%s> | using first node as entry point", first_node)
def _validate_swarm(self, nodes: list[Agent]) -> None:
"""Validate swarm structure and nodes."""
# Check for duplicate object instances
seen_instances = set()
for node in nodes:
if id(node) in seen_instances:
raise ValueError("Duplicate node instance detected. Each node must have a unique object instance.")
seen_instances.add(id(node))
# Check for session persistence
if node._session_manager is not None:
raise ValueError("Session persistence is not supported for Swarm agents yet.")
def _inject_swarm_tools(self) -> None:
"""Add swarm coordination tools to each agent."""
# Create tool functions with proper closures
swarm_tools = [
self._create_handoff_tool(),
]
for node in self.nodes.values():
# Check for existing tools with conflicting names
existing_tools = node.executor.tool_registry.registry
conflicting_tools = []
if "handoff_to_agent" in existing_tools:
conflicting_tools.append("handoff_to_agent")
if conflicting_tools:
raise ValueError(
f"Agent '{node.node_id}' already has tools with names that conflict with swarm coordination tools: "
f"{', '.join(conflicting_tools)}. Please rename these tools to avoid conflicts."
)
# Use the agent's tool registry to process and register the tools
node.executor.tool_registry.process_tools(swarm_tools)
logger.debug(
"tool_count=<%d>, node_count=<%d> | injected coordination tools into agents",
len(swarm_tools),
len(self.nodes),
)
def _create_handoff_tool(self) -> Callable[..., Any]:
"""Create handoff tool for agent coordination."""
swarm_ref = self # Capture swarm reference
@tool
def handoff_to_agent(agent_name: str, message: str, context: dict[str, Any] | None = None) -> dict[str, Any]:
"""Transfer control to another agent in the swarm for specialized help.
Args:
agent_name: Name of the agent to hand off to
message: Message explaining what needs to be done and why you're handing off
context: Additional context to share with the next agent
Returns:
Confirmation of handoff initiation
"""
try:
context = context or {}
# Validate target agent exists
target_node = swarm_ref.nodes.get(agent_name)
if not target_node:
return {"status": "error", "content": [{"text": f"Error: Agent '{agent_name}' not found in swarm"}]}
# Execute handoff
swarm_ref._handle_handoff(target_node, message, context)
return {"status": "success", "content": [{"text": f"Handing off to {agent_name}: {message}"}]}
except Exception as e:
return {"status": "error", "content": [{"text": f"Error in handoff: {str(e)}"}]}
return handoff_to_agent
def _handle_handoff(self, target_node: SwarmNode, message: str, context: dict[str, Any]) -> None:
"""Handle handoff to another agent."""
# If task is already completed, don't allow further handoffs
if self.state.completion_status != Status.EXECUTING:
logger.debug(
"task_status=<%s> | ignoring handoff request - task already completed",
self.state.completion_status,
)
return
current_node = cast(SwarmNode, self.state.current_node)
self.state.handoff_node = target_node
self.state.handoff_message = message
# Store handoff context as shared context
if context:
for key, value in context.items():
self.shared_context.add_context(current_node, key, value)
logger.debug(
"from_node=<%s>, to_node=<%s> | handing off from agent to agent",
current_node.node_id,
target_node.node_id,
)
def _rollback_uncommitted_turn(self) -> None:
"""Undo the handoff state an uncommitted turn wrote, so a checkpoint cannot persist it.
Only an open turn rolls back, so this is safe to call from more than one teardown path.
"""
if self._turn is None or self._turn.outcome != "open":
return
self.state.handoff_node = self._turn.handoff_node
self.state.handoff_message = self._turn.handoff_message
self.shared_context.context = self._turn.shared_context
self._turn.outcome = "rolled_back"
def _build_node_input(self, target_node: SwarmNode) -> str:
"""Build input text for a node based on shared context and handoffs.
Example formatted output:
```
Handoff Message: The user needs help with Python debugging - I've identified the issue but need someone with more expertise to fix it.
User Request: My Python script is throwing a KeyError when processing JSON data from an API
Previous agents who worked on this: data_analyst → code_reviewer
Shared knowledge from previous agents:
• data_analyst: {"issue_location": "line 42", "error_type": "missing key validation", "suggested_fix": "add key existence check"}
• code_reviewer: {"code_quality": "good overall structure", "security_notes": "API key should be in environment variable"}
Other agents available for collaboration:
Agent name: data_analyst. Agent description: Analyzes data and provides deeper insights
Agent name: code_reviewer.
Agent name: security_specialist. Agent description: Focuses on secure coding practices and vulnerability assessment
You have access to swarm coordination tools if you need help from other agents. If you don't hand off to another agent, the swarm will consider the task complete.
```
""" # noqa: E501
context_info: dict[str, Any] = {
"task": self.state.task,
"node_history": [node.node_id for node in self.state.node_history],
"shared_context": {k: v for k, v in self.shared_context.context.items()},
}
context_text = ""
# Include handoff message prominently at the top if present
if self.state.handoff_message:
context_text += f"Handoff Message: {self.state.handoff_message}\n\n"
# Include task information if available
if "task" in context_info:
task = context_info.get("task")
if isinstance(task, str):
context_text += f"User Request: {task}\n\n"
elif isinstance(task, list):
context_text += "User Request: Multi-modal task\n\n"
# Include detailed node history
if context_info.get("node_history"):
context_text += f"Previous agents who worked on this: {' → '.join(context_info['node_history'])}\n\n"
# Include actual shared context, not just a mention
shared_context = context_info.get("shared_context", {})
if shared_context:
context_text += "Shared knowledge from previous agents:\n"
for node_name, context in shared_context.items():
if context: # Only include if node has contributed context
context_text += f"• {node_name}: {context}\n"
context_text += "\n"
# Include available nodes with descriptions if available
other_nodes = [node_id for node_id in self.nodes.keys() if node_id != target_node.node_id]
if other_nodes:
context_text += "Other agents available for collaboration:\n"
for node_id in other_nodes:
node = self.nodes.get(node_id)
context_text += f"Agent name: {node_id}."
if node and hasattr(node.executor, "description") and node.executor.description:
context_text += f" Agent description: {node.executor.description}"
context_text += "\n"
context_text += "\n"
context_text += (
"You have access to swarm coordination tools if you need help from other agents. "
"If you don't hand off to another agent, the swarm will consider the task complete."
)
return context_text
def _activate_interrupt(self, node: SwarmNode, interrupts: list[Interrupt]) -> MultiAgentNodeInterruptEvent:
"""Activate the interrupt state.
Note, a Swarm may be interrupted either from a BeforeNodeCallEvent hook or from within an agent node. In either
case, we must manage the interrupt state of both the Swarm and the individual agent nodes.
Args:
node: The interrupted node.
interrupts: The interrupts raised by the user.
Returns:
MultiAgentNodeInterruptEvent
"""
logger.debug("node=<%s> | node interrupted", node.node_id)
self.state.completion_status = Status.INTERRUPTED
self._interrupt_state.context[node.node_id] = {
"activated": node.executor._interrupt_state.activated,
"interrupt_state": node.executor._interrupt_state.to_dict(),
"state": node.executor.state.get(),
"messages": node.executor.messages,
"model_state": node.executor._model_state,
}
self._interrupt_state.interrupts.update({interrupt.id: interrupt for interrupt in interrupts})
self._interrupt_state.activate()
return MultiAgentNodeInterruptEvent(node.node_id, interrupts)
async def _execute_swarm(self, invocation_state: dict[str, Any]) -> AsyncIterator[Any]:
"""Execute swarm and yield TypedEvent objects."""
try:
# Main execution loop
while True:
if self.state.completion_status != Status.EXECUTING:
reason = f"Completion status is: {self.state.completion_status}"
logger.debug("reason=<%s> | stopping streaming execution", reason)
break
should_continue, reason = self.state.should_continue(
max_handoffs=self.max_handoffs,
max_iterations=self.max_iterations,
execution_timeout=self.execution_timeout,
repetitive_handoff_detection_window=self.repetitive_handoff_detection_window,
repetitive_handoff_min_unique_agents=self.repetitive_handoff_min_unique_agents,
)
if not should_continue:
self.state.completion_status = Status.FAILED
logger.debug("reason=<%s> | stopping execution", reason)
break
current_node = self.state.current_node
if not current_node or current_node.node_id not in self.nodes:
logger.error("node=<%s> | node not found", current_node.node_id if current_node else "None")
self.state.completion_status = Status.FAILED
break
logger.debug(
"current_node=<%s>, iteration=<%d> | executing node",
current_node.node_id,
len(self.state.node_history) + 1,
)
before_event, interrupts = await self.hooks.invoke_callbacks_async(
BeforeNodeCallEvent(self, current_node.node_id, invocation_state)
)
# TODO: Implement cancellation token to stop _execute_node from continuing
try:
if interrupts:
yield self._activate_interrupt(current_node, interrupts)
break
if before_event.cancel_node:
cancel_message = (
before_event.cancel_node
if isinstance(before_event.cancel_node, str)
else "node cancelled by user"
)
logger.debug("reason=<%s> | cancelling execution", cancel_message)
yield MultiAgentNodeCancelEvent(current_node.node_id, cancel_message)
self.state.completion_status = Status.FAILED
break
self._turn = _InflightTurn(
self.state.handoff_node,
self.state.handoff_message,
copy.deepcopy(self.shared_context.context),
)
node_stream = self._stream_with_timeout(
self._execute_node(current_node, self.state.task, invocation_state),
self.node_timeout,
f"Node '{current_node.node_id}' execution timed out after {self.node_timeout}s",
)
node_result: NodeResult | None = None
async for event in node_stream:
# A completed turn commits before its terminal event is forwarded: the node's
# result, metrics, and shared-context writes are already recorded, so a teardown
# arriving at this yield must not roll it back. Only COMPLETED commits here — a
# failing node also emits a stop event, and its raise reaches the handler below.
if isinstance(event, MultiAgentNodeStopEvent):
node_result = event["node_result"]
if node_result.status == Status.COMPLETED:
self._interrupt_state.deactivate()
self.state.node_history.append(current_node)
self._turn.outcome = "committed"
yield event
node_result = cast(NodeResult, node_result)
if node_result.status == Status.INTERRUPTED:
# An interrupt commits the turn — resume continues past the node, so a handoff it
# requested stands — but a commit must never precede the state that makes it true,
# so it follows the activation that records the interrupt.
interrupt_event = self._activate_interrupt(current_node, node_result.interrupts)
self._turn.outcome = "committed"
yield interrupt_event
break
except (asyncio.CancelledError, GeneratorExit):
self._rollback_uncommitted_turn()
raise
except Exception:
logger.exception("node=<%s> | node execution failed", current_node.node_id)
self._rollback_uncommitted_turn()
self.state.completion_status = Status.FAILED
break
finally:
if self.state.completion_status != Status.INTERRUPTED:
await self.hooks.invoke_callbacks_async(
AfterNodeCallEvent(self, current_node.node_id, invocation_state)
)
logger.debug("node=<%s> | node execution completed", current_node.node_id)
# Check if handoff requested during execution
if self.state.handoff_node:
previous_node = current_node
current_node = self.state.handoff_node
self.state.handoff_node = None
self.state.current_node = current_node
# The handoff is applied, so the finished turn no longer speaks for the frontier: the node
# it promoted now owes a turn of its own, and no turn is in flight until that one starts.
self._turn = None
handoff_event = MultiAgentHandoffEvent(
from_node_ids=[previous_node.node_id],
to_node_ids=[current_node.node_id],
message=self.state.handoff_message or "Agent handoff occurred",
)
yield handoff_event
logger.debug(
"from_node=<%s>, to_node=<%s> | handoff detected",
previous_node.node_id,
current_node.node_id,
)
else:
logger.debug("node=<%s> | no handoff occurred, marking swarm as complete", current_node.node_id)
self.state.completion_status = Status.COMPLETED
break
except Exception:
logger.exception("swarm execution failed")
self.state.completion_status = Status.FAILED
finally:
elapsed_time = time.time() - self.state.start_time
logger.debug("status=<%s> | swarm execution completed", self.state.completion_status)
logger.debug(
"node_history_length=<%d>, time=<%s>s | metrics",
len(self.state.node_history),
f"{elapsed_time:.2f}",
)
async def _execute_node(
self, node: SwarmNode, task: MultiAgentInput, invocation_state: dict[str, Any]
) -> AsyncIterator[Any]:
"""Execute swarm node and yield TypedEvent objects."""
start_time = time.time()
node_name = node.node_id
# Emit node start event
start_event = MultiAgentNodeStartEvent(node_id=node_name, node_type="agent")
yield start_event
try:
if self._interrupt_state.activated and self._interrupt_state.context[node_name]["activated"]:
node_input = self._interrupt_state.context["responses"]
else:
# Prepare context for node
context_text = self._build_node_input(node)
node_input = [ContentBlock(text=f"Context:\n{context_text}\n\n")]
# Clear handoff message after it's been included in context
self.state.handoff_message = None
if not isinstance(task, str):
# Include additional ContentBlocks in node input
node_input = node_input + cast(list[ContentBlock], task)
# Execute node with streaming
node.reset_executor_state()
# Stream agent events with node context and capture final result
result = None
async for event in node.executor.stream_async(node_input, invocation_state=invocation_state):
# Forward agent events with node context
wrapped_event = MultiAgentNodeStreamEvent(node_name, event)
yield wrapped_event
# Capture the final result event
if "result" in event:
result = event["result"]
if result is None:
raise ValueError(f"Node '{node_name}' did not produce a result event")
execution_time = round((time.time() - start_time) * 1000)
status = Status.INTERRUPTED if result.stop_reason == "interrupt" else Status.COMPLETED
# Create NodeResult with extracted metrics
result_metrics = getattr(result, "metrics", None)
usage = getattr(result_metrics, "accumulated_usage", Usage(inputTokens=0, outputTokens=0, totalTokens=0))
metrics = getattr(result_metrics, "accumulated_metrics", Metrics(latencyMs=execution_time))
node_result = NodeResult(
result=result,
execution_time=execution_time,
status=status,
accumulated_usage=usage,
accumulated_metrics=metrics,
execution_count=1,
interrupts=result.interrupts or [],
)
# Store result in state
self.state.results[node_name] = node_result
# Accumulate metrics
self._accumulate_metrics(node_result)
# Emit node stop event with full NodeResult
complete_event = MultiAgentNodeStopEvent(
node_id=node_name,
node_result=node_result,
)
yield complete_event
except Exception as e:
execution_time = round((time.time() - start_time) * 1000)
logger.exception("node=<%s> | node execution failed", node_name)
# Create a NodeResult for the failed node
node_result = NodeResult(
result=e,
execution_time=execution_time,
status=Status.FAILED,
accumulated_usage=Usage(inputTokens=0, outputTokens=0, totalTokens=0),
accumulated_metrics=Metrics(latencyMs=execution_time),
execution_count=1,
)
# Store result in state
self.state.results[node_name] = node_result
# Emit node stop event even for failures
complete_event = MultiAgentNodeStopEvent(
node_id=node_name,
node_result=node_result,
)
yield complete_event
raise
def _accumulate_metrics(self, node_result: NodeResult) -> None:
"""Accumulate metrics from a node result."""
self.state.accumulated_usage["inputTokens"] += node_result.accumulated_usage.get("inputTokens", 0)
self.state.accumulated_usage["outputTokens"] += node_result.accumulated_usage.get("outputTokens", 0)
self.state.accumulated_usage["totalTokens"] += node_result.accumulated_usage.get("totalTokens", 0)
_accumulate_cache_usage(self.state.accumulated_usage, node_result.accumulated_usage)
self.state.accumulated_metrics["latencyMs"] += node_result.accumulated_metrics.get("latencyMs", 0)
def _build_result(self, interrupts: list[Interrupt]) -> SwarmResult:
"""Build swarm result from current state."""
return SwarmResult(
status=self.state.completion_status,
results=self.state.results,
accumulated_usage=self.state.accumulated_usage,
accumulated_metrics=self.state.accumulated_metrics,
execution_count=len(self.state.node_history),
execution_time=self.state.execution_time,
node_history=self.state.node_history,
interrupts=interrupts,
)
def serialize_state(self) -> dict[str, Any]:
"""Serialize the current swarm state to a dictionary."""
status_str = self.state.completion_status.value
# Only a committed turn earns its handoff target the frontier; a handoff standing mid-turn was
# inherited, and resuming its target would skip the node that never finished.
turn_committed = self._turn is not None and self._turn.outcome == "committed"
frontier_carries_handoff = False
if self.state.completion_status == Status.EXECUTING and turn_committed:
# A committed turn owes only its handoff. Without one the swarm is done, so the frontier is
# empty rather than the node this turn just finished — re-listing it would make the checkpoint
# claim the node is both done and still owed, and each crash at this point would record it again.
if self.state.handoff_node:
next_nodes = [self.state.handoff_node.node_id]
frontier_carries_handoff = True
else:
next_nodes = []
elif self.state.completion_status in (Status.EXECUTING, Status.INTERRUPTED) and self.state.current_node:
next_nodes = [self.state.current_node.node_id]
else:
next_nodes = []
return {
"type": "swarm",
"id": self.id,
"status": status_str,
"node_history": [n.node_id for n in self.state.node_history],
"node_results": {k: v.to_dict() for k, v in self.state.results.items()},
"next_nodes_to_execute": next_nodes,
"current_task": encode_bytes_values(self.state.task),
"accumulated_usage": self.state.accumulated_usage,
"accumulated_metrics": self.state.accumulated_metrics,
"execution_time": self._execution_time_with_active_interval(self.state.execution_time),
"context": {
"shared_context": getattr(self.state.shared_context, "context", {}) or {},
# A persisted handoff always means its target still owes a turn, so a handoff the frontier
# already carries is not recorded. Settling that here, where the turn's outcome is known,
# is what spares restore the guess: a frontier equals its handoff target both when it
# carries that handoff and when a self-handoff is merely pending, and the two are
# indistinguishable afterwards.
"handoff_node": (
self.state.handoff_node.node_id
if self.state.handoff_node and not frontier_carries_handoff
else None
),
# The frontier node is the intended recipient either way.
"handoff_message": self.state.handoff_message,
},
"_internal_state": {
"interrupt_state": self._interrupt_state.to_dict(),
},
}
def deserialize_state(self, payload: dict[str, Any]) -> None:
"""Restore swarm state from a session dict and prepare for execution.
This method handles two scenarios:
1. If the swarm has no resume frontier (next_nodes_to_execute is empty — e.g. completed, or failed
at a dead end), resets all nodes and swarm state to allow re-execution from the beginning.
2. Otherwise, restores the persisted state and prepares to resume execution from the next node.
Note:
Resume is at-least-once: a crash between a node finishing and the next checkpoint replays that
node on restore (e.g. a terminal node whose completion checkpoint never landed), and a resume
frontier naming a node this swarm no longer defines re-runs the task from the beginning. Swarm
nodes should therefore be idempotent.
Args:
payload: Dictionary containing persisted state data including status,
node history, results, and next nodes to execute.
"""
if "_internal_state" in payload:
internal_state = payload["_internal_state"]
self._interrupt_state = _InterruptState.from_dict(internal_state["interrupt_state"])
# Restored state describes work no in-memory turn ran, so any turn from this process does not apply.
self._turn = None
next_node_ids = payload.get("next_nodes_to_execute") or []
# A frontier naming a node this swarm no longer defines is not resumable: the persisted history,
# results, and handoff all belong to a topology that no longer exists.
if not next_node_ids or next_node_ids[0] not in self.nodes:
self._reset_for_fresh_run()
return
self._resume_from_session = True
self._from_dict(payload)
def _reset_for_fresh_run(self) -> None:
"""Discard restored state so the next invocation runs the task from the initial node."""
# Clear interrupt state first, else reset_executor_state indexes its context by node_id and
# KeyErrors on a never-interrupted node.
self._interrupt_state = _InterruptState()
for node in self.nodes.values():
node.reset_executor_state()
# stream_async re-aliases the swarm-owned shared context onto the fresh state, so clear it here or
# a previous run's context survives the reset.
self.shared_context.context = {}
self.state = SwarmState(
current_node=SwarmNode("", Agent(), swarm=self),
task="",
completion_status=Status.PENDING,
)
self._resume_from_session = False
def _from_dict(self, payload: dict[str, Any]) -> None:
self.state.completion_status = Status(payload["status"])
# Point the state's shared context at the swarm-owned object, matching the identity a fresh run
# establishes in stream_async, so the serialize path (reads self.state.shared_context) and the
# node-input builder (reads self.shared_context) stay in sync after resume.
self.state.shared_context = self.shared_context
# Hydrate completed nodes & results
context = payload["context"] or {}
# Keyed by node id, so drop entries for nodes this swarm no longer defines rather than rendering a
# removed node's context into every prompt.
restored_context = context.get("shared_context") or {}
self.shared_context.context = {
node_id: entries for node_id, entries in restored_context.items() if node_id in self.nodes
}
handoff_node_id = context.get("handoff_node")
self.state.handoff_node = self.nodes.get(handoff_node_id) if handoff_node_id else None
# The message is written for the handoff target, so it only survives if that target still does.
target_vanished = handoff_node_id is not None and self.state.handoff_node is None
self.state.handoff_message = None if target_vanished else context.get("handoff_message")
self.state.accumulated_usage = _parse_usage(payload.get("accumulated_usage") or {})
self.state.accumulated_metrics = _parse_metrics(payload.get("accumulated_metrics") or {})
self.state.execution_time = int(payload.get("execution_time") or 0)
self.state.node_history = [self.nodes[nid] for nid in (payload.get("node_history") or []) if nid in self.nodes]
raw_results = payload.get("node_results") or {}
results: dict[str, NodeResult] = {}
for node_id, entry in raw_results.items():
if node_id not in self.nodes:
continue
try:
results[node_id] = NodeResult.from_dict(entry)
except Exception:
logger.exception("Failed to hydrate NodeResult for node_id=%s; skipping.", node_id)
raise
self.state.results = results
self.state.task = decode_bytes_values(payload.get("current_task", self.state.task))
# Only reached for a frontier that names a node this swarm defines.
self.state.current_node = self.nodes[payload["next_nodes_to_execute"][0]]
def _initial_node(self) -> SwarmNode:
if self.entry_point:
return self.nodes[str(self.entry_point.name)]
return next(iter(self.nodes.values())) # First SwarmNode