diff --git a/bloxserver/runtime/__init__.py b/bloxserver/runtime/__init__.py
new file mode 100644
index 0000000..a97cbf8
--- /dev/null
+++ b/bloxserver/runtime/__init__.py
@@ -0,0 +1,13 @@
+"""
+BloxServer Runtime — Flow execution engine.
+
+This module bridges BloxServer flows to xml-pipeline's StreamPump.
+"""
+
+from bloxserver.runtime.flow_runner import FlowRunner, FlowRunnerState, ExecutionEvent
+
+__all__ = [
+    "FlowRunner",
+    "FlowRunnerState",
+    "ExecutionEvent",
+]
diff --git a/bloxserver/runtime/flow_runner.py b/bloxserver/runtime/flow_runner.py
new file mode 100644
index 0000000..130e3dd
--- /dev/null
+++ b/bloxserver/runtime/flow_runner.py
@@ -0,0 +1,686 @@
+"""
+FlowRunner — Execution bridge between BloxServer flows and xml-pipeline.
+
+The FlowRunner:
+1. Takes a Flow domain object
+2. Converts it to xml-pipeline configuration
+3. Creates and manages a StreamPump instance
+4. Handles triggers (webhook, schedule, manual)
+5. Tracks execution state and events
+
+Usage:
+    flow = Flow.from_canvas_json(canvas_data)
+    runner = FlowRunner(flow)
+    await runner.start()
+
+    # Trigger execution
+    await runner.trigger("my_webhook", payload={"query": "hello"})
+
+    # Or inject directly to a node
+    await runner.inject("researcher", {"query": "hello"})
+
+    await runner.stop()
+"""
+
+from __future__ import annotations
+
+import asyncio
+import importlib
+import logging
+import tempfile
+from dataclasses import dataclass, field
+from datetime import datetime, timezone
+from enum import Enum
+from pathlib import Path
+from typing import Any, Callable
+from uuid import UUID, uuid4
+
+from bloxserver.domain import Flow, AgentNode, ToolNode, GatewayNode
+from bloxserver.domain.triggers import Trigger, TriggerType
+
+logger = logging.getLogger(__name__)
+
+
+# =============================================================================
+# State & Events
+# =============================================================================
+
+
+class FlowRunnerState(str, Enum):
+    """Lifecycle states for a FlowRunner."""
+
+    CREATED = "created"  # Initial state
+    STARTING = "starting"  # Registering listeners, preparing pump
+    RUNNING = "running"  # Pump is active, accepting messages
+    STOPPING = "stopping"  # Graceful shutdown in progress
+    STOPPED = "stopped"  # Fully stopped
+    ERROR = "error"  # Failed to start or crashed
+
+
+@dataclass
+class ExecutionEvent:
+    """An event during flow execution (for logging/monitoring)."""
+
+    timestamp: datetime
+    event_type: str  # started, message_received, handler_called, error, stopped
+    node_name: str | None = None
+    thread_id: str | None = None
+    payload_type: str | None = None
+    message: str = ""
+    error: str | None = None
+
+    def to_dict(self) -> dict[str, Any]:
+        return {
+            "timestamp": self.timestamp.isoformat(),
+            "eventType": self.event_type,
+            "nodeName": self.node_name,
+            "threadId": self.thread_id,
+            "payloadType": self.payload_type,
+            "message": self.message,
+            "error": self.error,
+        }
+
+
+# =============================================================================
+# FlowRunner
+# =============================================================================
+
+
+class FlowRunner:
+    """
+    Runs a BloxServer Flow using xml-pipeline's StreamPump.
+
+    This is the bridge between the Flow domain model and the actual
+    message pump execution. It handles:
+
+    - Converting Flow nodes to xml-pipeline ListenerConfigs
+    - Creating and managing the StreamPump lifecycle
+    - Handling triggers (webhook, schedule, manual)
+    - Tracking execution events for monitoring
+
+    Note: For production use, each Flow runs in its own FlowRunner instance.
+    Multiple FlowRunners can run concurrently (one per active flow).
+    """
+
+    def __init__(
+        self,
+        flow: Flow,
+        port: int = 0,
+        event_callback: Callable[[ExecutionEvent], None] | None = None,
+    ):
+        """
+        Initialize a FlowRunner.
+
+        Args:
+            flow: The Flow domain object to run.
+            port: Port for the organism (0 = auto-assign).
+            event_callback: Optional callback for execution events.
+        """
+        self.flow = flow
+        self.port = port
+        self.event_callback = event_callback
+
+        # State
+        self.state = FlowRunnerState.CREATED
+        self.started_at: datetime | None = None
+        self.stopped_at: datetime | None = None
+        self.error_message: str | None = None
+
+        # StreamPump instance (created on start)
+        self._pump = None
+        self._pump_task: asyncio.Task | None = None
+
+        # Execution tracking
+        self.execution_id = uuid4()
+        self.events: list[ExecutionEvent] = []
+        self.message_count = 0
+
+        # Thread tracking (root thread per execution)
+        self._root_thread_id: str | None = None
+
+        # Trigger handlers (for webhook callbacks)
+        self._trigger_handlers: dict[UUID, Callable] = {}
+
+    # =========================================================================
+    # Lifecycle
+    # =========================================================================
+
+    async def start(self) -> None:
+        """
+        Start the flow runner.
+
+        This creates the StreamPump, registers all listeners, and starts
+        the message processing loop.
+        """
+        if self.state not in (FlowRunnerState.CREATED, FlowRunnerState.STOPPED):
+            raise RuntimeError(f"Cannot start FlowRunner in state: {self.state}")
+
+        self.state = FlowRunnerState.STARTING
+        self.started_at = datetime.now(timezone.utc)
+        self._emit_event("starting", message=f"Starting flow: {self.flow.name}")
+
+        try:
+            # Validate flow before starting
+            errors = self.flow.validate()
+            blocking_errors = [e for e in errors if e.severity == "error"]
+            if blocking_errors:
+                error_msg = "; ".join(e.message for e in blocking_errors)
+                raise ValueError(f"Flow validation failed: {error_msg}")
+
+            # Create the pump
+            self._pump = await self._create_pump()
+
+            # Start the pump in a background task
+            self._pump_task = asyncio.create_task(self._run_pump())
+
+            self.state = FlowRunnerState.RUNNING
+            self._emit_event("started", message=f"Flow running: {len(self.flow.nodes)} nodes")
+
+        except Exception as e:
+            self.state = FlowRunnerState.ERROR
+            self.error_message = str(e)
+            self._emit_event("error", error=str(e))
+            logger.exception(f"Failed to start flow {self.flow.id}: {e}")
+            raise
+
+    async def stop(self, timeout: float = 30.0) -> None:
+        """
+        Stop the flow runner gracefully.
+
+        Args:
+            timeout: Maximum time to wait for graceful shutdown.
+        """
+        if self.state not in (FlowRunnerState.RUNNING, FlowRunnerState.ERROR):
+            return
+
+        self.state = FlowRunnerState.STOPPING
+        self._emit_event("stopping", message="Initiating graceful shutdown")
+
+        try:
+            if self._pump:
+                await self._pump.shutdown()
+
+            if self._pump_task:
+                self._pump_task.cancel()
+                try:
+                    await asyncio.wait_for(self._pump_task, timeout=timeout)
+                except (asyncio.CancelledError, asyncio.TimeoutError):
+                    pass
+
+            self.state = FlowRunnerState.STOPPED
+            self.stopped_at = datetime.now(timezone.utc)
+            self._emit_event("stopped", message=f"Flow stopped after {self.message_count} messages")
+
+        except Exception as e:
+            self.state = FlowRunnerState.ERROR
+            self.error_message = str(e)
+            self._emit_event("error", error=str(e))
+            raise
+
+    async def _run_pump(self) -> None:
+        """Run the pump's main loop."""
+        try:
+            await self._pump.run()
+        except asyncio.CancelledError:
+            pass
+        except Exception as e:
+            self.state = FlowRunnerState.ERROR
+            self.error_message = str(e)
+            self._emit_event("error", error=f"Pump crashed: {e}")
+            logger.exception(f"Pump crashed for flow {self.flow.id}: {e}")
+
+    # =========================================================================
+    # Pump Creation
+    # =========================================================================
+
+    async def _create_pump(self):
+        """Create and configure the StreamPump from the Flow."""
+        from xml_pipeline.message_bus.stream_pump import (
+            StreamPump,
+            OrganismConfig,
+            ListenerConfig,
+        )
+        from xml_pipeline.message_bus.thread_registry import get_registry
+
+        # Build OrganismConfig
+        org_config = self._build_organism_config()
+
+        # Create pump
+        pump = StreamPump(org_config)
+
+        # Register system listeners (boot, todo)
+        self._register_system_listeners(pump)
+
+        # Register flow listeners
+        for node in self.flow.nodes:
+            listener_config = self._node_to_listener_config(node)
+            if listener_config:
+                pump.register_listener(listener_config)
+
+        # Build usage instructions for agents
+        pump.register_all()
+
+        # Initialize root thread
+        registry = get_registry()
+        self._root_thread_id = registry.initialize_root(f"flow-{self.flow.id}")
+
+        # Inject boot message
+        await self._inject_boot_message(pump)
+
+        return pump
+
+    def _build_organism_config(self):
+        """Build OrganismConfig from Flow settings."""
+        from xml_pipeline.message_bus.stream_pump import OrganismConfig
+
+        return OrganismConfig(
+            name=f"flow-{self.flow.id}",
+            port=self.port,
+            max_concurrent_pipelines=50,
+            max_concurrent_handlers=20,
+            max_concurrent_per_agent=5,
+            llm_config={
+                "strategy": self.flow.settings.llm.strategy,
+                "retries": self.flow.settings.llm.retries,
+                "retry_base_delay": self.flow.settings.llm.retry_base_delay,
+            },
+        )
+
+    def _register_system_listeners(self, pump) -> None:
+        """Register system listeners (boot, todo) on the pump."""
+        from xml_pipeline.message_bus.stream_pump import ListenerConfig
+        from xml_pipeline.primitives import (
+            Boot, handle_boot,
+            TodoUntil, TodoComplete,
+            handle_todo_until, handle_todo_complete,
+        )
+
+        # Boot handler
+        pump.register_listener(ListenerConfig(
+            name="system.boot",
+            payload_class_path="xml_pipeline.primitives.Boot",
+            handler_path="xml_pipeline.primitives.handle_boot",
+            description="System boot handler",
+            payload_class=Boot,
+            handler=handle_boot,
+        ))
+
+        # TodoUntil handler
+        pump.register_listener(ListenerConfig(
+            name="system.todo",
+            payload_class_path="xml_pipeline.primitives.TodoUntil",
+            handler_path="xml_pipeline.primitives.handle_todo_until",
+            description="System todo handler - registers watchers",
+            payload_class=TodoUntil,
+            handler=handle_todo_until,
+        ))
+
+        # TodoComplete handler
+        pump.register_listener(ListenerConfig(
+            name="system.todo-complete",
+            payload_class_path="xml_pipeline.primitives.TodoComplete",
+            handler_path="xml_pipeline.primitives.handle_todo_complete",
+            description="System todo handler - closes watchers",
+            payload_class=TodoComplete,
+            handler=handle_todo_complete,
+        ))
+
+    def _node_to_listener_config(self, node):
+        """Convert a domain Node to a ListenerConfig."""
+        from xml_pipeline.message_bus.stream_pump import ListenerConfig
+        from bloxserver.domain.edges import compute_peers
+
+        node_map = {n.id: n.name for n in self.flow.nodes}
+
+        if isinstance(node, AgentNode):
+            # Agent node - needs dynamic handler
+            peers = compute_peers(node.id, self.flow.edges, node_map)
+
+            # For agents, we use a generic LLM handler
+            # The prompt is passed via config
+            handler, payload_class = self._get_agent_handler(node)
+
+            return ListenerConfig(
+                name=node.name,
+                payload_class_path=f"bloxserver.runtime.handlers.{node.name}",
+                handler_path=f"bloxserver.runtime.handlers.{node.name}",
+                description=node.description,
+                is_agent=True,
+                peers=peers,
+                prompt=node.prompt,
+                payload_class=payload_class,
+                handler=handler,
+            )
+
+        elif isinstance(node, ToolNode):
+            # Tool node - use built-in or custom handler
+            handler_path, payload_class_path = self._get_tool_paths(node)
+
+            # Import the actual classes
+            handler, payload_class = self._import_handler(handler_path, payload_class_path)
+
+            return ListenerConfig(
+                name=node.name,
+                payload_class_path=payload_class_path,
+                handler_path=handler_path,
+                description=node.description,
+                payload_class=payload_class,
+                handler=handler,
+            )
+
+        elif isinstance(node, GatewayNode):
+            # Gateway node - federation or REST
+            # TODO: Implement gateway handlers
+            logger.warning(f"Gateway nodes not yet implemented: {node.name}")
+            return None
+
+        return None
+
+    def _get_agent_handler(self, node: AgentNode):
+        """
+        Get or create a handler for an agent node.
+
+        Agents use a generic LLM completion handler that:
+        1. Gets the prompt from PromptRegistry
+        2. Builds conversation from ContextBuffer
+        3. Calls LLM router
+        4. Parses response and routes to peers
+        """
+        from dataclasses import dataclass
+        from third_party.xmlable import xmlify
+
+        # Create a dynamic payload class for this agent
+        @xmlify
+        @dataclass
+        class AgentInput:
+            """Input message for agent."""
+            content: str
+
+        # Create handler that uses the agent's prompt
+        async def agent_handler(payload, metadata):
+            from xml_pipeline.message_bus.message_state import HandlerResponse
+            from xml_pipeline.platform import get_prompt_registry
+            from xml_pipeline.llm import complete
+
+            # Get the registered prompt
+            prompt_registry = get_prompt_registry()
+            prompt_data = prompt_registry.get(metadata.own_name)
+
+            system_prompt = ""
+            if prompt_data:
+                system_prompt = prompt_data.full_prompt
+
+            # Build messages for LLM
+            messages = [
+                {"role": "system", "content": system_prompt},
+                {"role": "user", "content": payload.content},
+            ]
+
+            # Call LLM
+            try:
+                response = await complete(
+                    model=node.model or "grok-4.1",
+                    messages=messages,
+                    agent_id=metadata.own_name,
+                    temperature=node.temperature,
+                    max_tokens=node.max_tokens,
+                )
+
+                # For now, just echo response
+                # TODO: Parse response for tool calls, routing
+                @xmlify
+                @dataclass
+                class AgentOutput:
+                    content: str
+
+                return HandlerResponse(
+                    payload=AgentOutput(content=response.content),
+                    to=metadata.from_id,  # Reply to caller
+                )
+
+            except Exception as e:
+                logger.error(f"Agent {metadata.own_name} LLM error: {e}")
+                return None
+
+        return agent_handler, AgentInput
+
+    def _get_tool_paths(self, node: ToolNode) -> tuple[str, str]:
+        """Get handler and payload class paths for a tool node."""
+        from bloxserver.domain.nodes import BUILTIN_TOOLS
+
+        if node.tool_type in BUILTIN_TOOLS:
+            info = BUILTIN_TOOLS[node.tool_type]
+            return info["handler"], info["payload_class"]
+
+        # Custom tool
+        if node.handler_path and node.payload_class_path:
+            return node.handler_path, node.payload_class_path
+
+        raise ValueError(f"Tool {node.name} has no handler configured")
+
+    def _import_handler(self, handler_path: str, payload_class_path: str):
+        """Import handler function and payload class."""
+        # Import payload class
+        mod_path, class_name = payload_class_path.rsplit(".", 1)
+        mod = importlib.import_module(mod_path)
+        payload_class = getattr(mod, class_name)
+
+        # Import handler
+        mod_path, fn_name = handler_path.rsplit(".", 1)
+        mod = importlib.import_module(mod_path)
+        handler = getattr(mod, fn_name)
+
+        return handler, payload_class
+
+    async def _inject_boot_message(self, pump) -> None:
+        """Inject the boot message to start the organism."""
+        from xml_pipeline.primitives import Boot
+
+        boot_payload = Boot(
+            organism_name=f"flow-{self.flow.id}",
+            timestamp=datetime.now(timezone.utc).isoformat().replace("+00:00", "Z"),
+            listener_count=len(pump.listeners),
+        )
+
+        boot_envelope = pump._wrap_in_envelope(
+            payload=boot_payload,
+            from_id="system",
+            to_id="system.boot",
+            thread_id=self._root_thread_id,
+        )
+
+        await pump.inject(boot_envelope, thread_id=self._root_thread_id, from_id="system")
+
+    # =========================================================================
+    # Message Injection
+    # =========================================================================
+
+    async def inject(
+        self,
+        target_node: str,
+        payload_data: dict[str, Any],
+        thread_id: str | None = None,
+    ) -> str:
+        """
+        Inject a message to a specific node.
+
+        Args:
+            target_node: Name of the target node.
+            payload_data: Payload data (will be wrapped in node's payload class).
+            thread_id: Optional thread ID (creates new thread if not provided).
+
+        Returns:
+            The thread ID used for this message.
+        """
+        if self.state != FlowRunnerState.RUNNING:
+            raise RuntimeError(f"Cannot inject: FlowRunner state is {self.state}")
+
+        if not self._pump:
+            raise RuntimeError("Pump not initialized")
+
+        # Get the listener
+        listener = self._pump.listeners.get(target_node)
+        if not listener:
+            raise ValueError(f"Unknown node: {target_node}")
+
+        # Create payload instance
+        payload = listener.payload_class(**payload_data)
+
+        # Get or create thread
+        from xml_pipeline.message_bus.thread_registry import get_registry
+        registry = get_registry()
+
+        if thread_id is None:
+            thread_id = registry.extend_chain(self._root_thread_id, target_node)
+
+        # Wrap in envelope
+        envelope = self._pump._wrap_in_envelope(
+            payload=payload,
+            from_id="external",
+            to_id=target_node,
+            thread_id=thread_id,
+        )
+
+        # Inject
+        await self._pump.inject(envelope, thread_id=thread_id, from_id="external")
+
+        self.message_count += 1
+        self._emit_event(
+            "message_injected",
+            node_name=target_node,
+            thread_id=thread_id,
+            payload_type=type(payload).__name__,
+        )
+
+        return thread_id
+
+    # =========================================================================
+    # Trigger Handling
+    # =========================================================================
+
+    async def trigger(
+        self,
+        trigger_id: UUID | str,
+        payload_data: dict[str, Any] | None = None,
+    ) -> str:
+        """
+        Fire a trigger to start flow execution.
+
+        Args:
+            trigger_id: The trigger ID (UUID or string).
+            payload_data: Optional payload data for the trigger.
+
+        Returns:
+            The thread ID for this execution.
+        """
+        if isinstance(trigger_id, str):
+            trigger_id = UUID(trigger_id)
+
+        # Find the trigger
+        trigger = next((t for t in self.flow.triggers if t.id == trigger_id), None)
+        if not trigger:
+            raise ValueError(f"Unknown trigger: {trigger_id}")
+
+        if not trigger.enabled:
+            raise ValueError(f"Trigger {trigger.name} is disabled")
+
+        # Get target nodes
+        if not trigger.target_node_ids:
+            raise ValueError(f"Trigger {trigger.name} has no target nodes")
+
+        # Find target node names
+        node_map = {n.id: n.name for n in self.flow.nodes}
+        target_names = [node_map.get(nid) for nid in trigger.target_node_ids]
+        target_names = [n for n in target_names if n]
+
+        if not target_names:
+            raise ValueError(f"Trigger {trigger.name} targets unknown nodes")
+
+        # Create thread for this execution
+        from xml_pipeline.message_bus.thread_registry import get_registry
+        registry = get_registry()
+        thread_id = registry.extend_chain(self._root_thread_id, target_names[0])
+
+        # Inject to each target
+        for target_name in target_names:
+            await self.inject(target_name, payload_data or {}, thread_id=thread_id)
+
+        self._emit_event(
+            "trigger_fired",
+            message=f"Trigger {trigger.name} fired to {target_names}",
+            thread_id=thread_id,
+        )
+
+        return thread_id
+
+    def get_webhook_handler(self, trigger_id: UUID) -> Callable | None:
+        """
+        Get a webhook handler for a trigger.
+
+        Used by the API layer to create webhook endpoints.
+        """
+        trigger = next((t for t in self.flow.triggers if t.id == trigger_id), None)
+        if not trigger or trigger.trigger_type != TriggerType.WEBHOOK:
+            return None
+
+        async def webhook_handler(payload: dict[str, Any]) -> str:
+            return await self.trigger(trigger_id, payload)
+
+        return webhook_handler
+
+    # =========================================================================
+    # Status & Events
+    # =========================================================================
+
+    def get_status(self) -> dict[str, Any]:
+        """Get current runner status."""
+        return {
+            "executionId": str(self.execution_id),
+            "flowId": str(self.flow.id),
+            "flowName": self.flow.name,
+            "state": self.state.value,
+            "startedAt": self.started_at.isoformat() if self.started_at else None,
+            "stoppedAt": self.stopped_at.isoformat() if self.stopped_at else None,
+            "messageCount": self.message_count,
+            "errorMessage": self.error_message,
+            "nodeCount": len(self.flow.nodes),
+            "triggerCount": len(self.flow.triggers),
+        }
+
+    def get_events(self, limit: int = 100) -> list[dict[str, Any]]:
+        """Get recent execution events."""
+        return [e.to_dict() for e in self.events[-limit:]]
+
+    def _emit_event(
+        self,
+        event_type: str,
+        node_name: str | None = None,
+        thread_id: str | None = None,
+        payload_type: str | None = None,
+        message: str = "",
+        error: str | None = None,
+    ) -> None:
+        """Emit an execution event."""
+        event = ExecutionEvent(
+            timestamp=datetime.now(timezone.utc),
+            event_type=event_type,
+            node_name=node_name,
+            thread_id=thread_id,
+            payload_type=payload_type,
+            message=message,
+            error=error,
+        )
+        self.events.append(event)
+
+        # Call external callback if provided
+        if self.event_callback:
+            try:
+                self.event_callback(event)
+            except Exception as e:
+                logger.warning(f"Event callback error: {e}")
+
+        # Log
+        if error:
+            logger.error(f"[{self.flow.name}] {event_type}: {error}")
+        else:
+            logger.info(f"[{self.flow.name}] {event_type}: {message or node_name or ''}")