quartermaster-engine 0.2.1

Execution engine for AI agent graphs — traversal, branching, merging, memory, message passing, and error handling

quartermaster-engine

Execution engine for AI agent graphs with pluggable storage, dispatching, and memory.

Features

• FlowRunner orchestrates graph execution: traversal, branching, merging, and error handling
• Pluggable dispatchers: SyncDispatcher, ThreadDispatcher, AsyncDispatcher
• Pluggable storage: InMemoryStore, SQLiteStore, or implement your own ExecutionStore
• Two memory layers: FlowMemory (per-execution) and PersistentMemory (cross-execution)
• Real-time event streaming: NodeStarted, TokenGenerated, NodeFinished, FlowError, UserInputRequired
• Per-node error strategies: Stop, Retry (with configurable max retries), Skip
• Flow pause/resume for user interaction nodes
• Sync and async execution modes with run() and run_async()

Installation

pip install quartermaster-engine

# With SQLite persistent store
pip install quartermaster-engine[sqlite]

Quick Start

High-level path — provider_registry

The simplest way to run a graph: hand FlowRunner a provider registry and let it build the default node registry (covering every node type the bundled DSL emits — including AgentExecutor for agent() nodes with the canonical Quartermaster tool loop):

from quartermaster_engine import FlowRunner
from quartermaster_graph import Graph
from quartermaster_providers import register_local

provider_registry = register_local(
    "ollama",
    base_url="http://localhost:11434",   # or set $OLLAMA_HOST
    default_model="gemma4:26b",
)

graph = Graph("chat").start().user().agent().end().build()
runner = FlowRunner(graph=graph, provider_registry=provider_registry)
result = runner.run("Pozdravljen!")
print(result.success, result.final_output)

If you have a quartermaster_tools.ToolRegistry, pass it as tool_registry= so AgentExecutor can actually execute the tools your graph's .agent(tools=[...]) nodes request.

Low-level path — bring your own node_registry

For full control over which executor handles each node type (custom executors, alternative storage, etc.) hand FlowRunner a SimpleNodeRegistry directly. Use the helper build_default_registry(provider_registry) if you only want to swap one executor; pass the result back into FlowRunner(node_registry=...).

from uuid import uuid4
from quartermaster_engine import FlowRunner, InMemoryStore
from quartermaster_engine.nodes import SimpleNodeRegistry, NodeResult
from quartermaster_graph import GraphSpec, GraphNode, GraphEdge, NodeType

# 1. Define the graph
start_id, process_id, end_id = uuid4(), uuid4(), uuid4()

graph = GraphSpec(
    id=uuid4(),
    agent_id=uuid4(),
    start_node_id=start_id,
    nodes=[
        GraphNode(id=start_id, type=NodeType.START, name="Start"),
        GraphNode(
            id=process_id,
            type=NodeType.INSTRUCTION,
            name="Process",
            metadata={"llm_system_instruction": "Summarize the input.", "llm_model": "gpt-4o"},
        ),
        GraphNode(id=end_id, type=NodeType.END, name="End"),
    ],
    edges=[
        GraphEdge(source_id=start_id, target_id=process_id),
        GraphEdge(source_id=process_id, target_id=end_id),
    ],
)

# 2. Register node executors
registry = SimpleNodeRegistry()
# registry.register("Instruction1", my_instruction_executor)

# 3. Run the flow
runner = FlowRunner(graph=graph, node_registry=registry)
result = runner.run("Please summarize this article about AI safety.")

print(result.success)          # True/False
print(result.final_output)     # The final text output
print(result.duration_seconds)

Using GraphBuilder from quartermaster-graph

from quartermaster_graph import GraphBuilder
from quartermaster_engine import FlowRunner
from quartermaster_engine.nodes import SimpleNodeRegistry

graph = (
    GraphBuilder("Support Agent")
    .start()
    .instruction("Classify", model="gpt-4o")
    .decision("Route", options=["billing", "technical"])
    .on("billing").instruction("Handle billing").end()
    .on("technical").instruction("Handle technical").end()
    .build()
)

registry = SimpleNodeRegistry()
runner = FlowRunner(graph=graph, node_registry=registry)
result = runner.run("I need help with my invoice")

Stream Events in Real Time

from quartermaster_engine import FlowRunner, FlowEvent, NodeStarted, NodeFinished, TokenGenerated, FlowError

def handle_event(event: FlowEvent):
    if isinstance(event, NodeStarted):
        print(f"[START] {event.node_name} ({event.node_type})")
    elif isinstance(event, TokenGenerated):
        print(event.token, end="", flush=True)
    elif isinstance(event, NodeFinished):
        print(f"\n[DONE] Node finished: {event.result[:50]}...")
    elif isinstance(event, FlowError):
        print(f"[ERROR] {event.error} (recoverable={event.recoverable})")

runner = FlowRunner(graph=graph, node_registry=registry, on_event=handle_event)
result = runner.run("Hello!")

Async Execution

import asyncio
from quartermaster_engine import FlowRunner, TokenGenerated

async def run_flow():
    runner = FlowRunner(graph=graph, node_registry=registry)
    async for event in runner.run_async("Hello!"):
        if isinstance(event, TokenGenerated):
            print(event.token, end="", flush=True)

asyncio.run(run_flow())

Quick Execution with run_graph()

For rapid prototyping, use the convenience function:

from quartermaster_engine import run_graph

# Non-interactive (provide input)
run_graph(agent, user_input="Explain quantum computing")

# Interactive (prompts stdin at User nodes)
run_graph(agent)

# Force provider
run_graph(agent, user_input="Hello", provider="openai")

run_graph() handles provider detection, node registration, streaming output, and the pause/resume cycle for interactive User nodes.

API Reference

FlowRunner

The core orchestration class. Accepts a GraphSpec from quartermaster-graph (AgentGraph still works as a deprecated alias).

from quartermaster_engine import FlowRunner
from quartermaster_engine.dispatchers.sync_dispatcher import SyncDispatcher
from quartermaster_engine.messaging.context_manager import ContextManager

runner = FlowRunner(
    graph=spec,                      # GraphSpec from quartermaster-graph
    node_registry=registry,          # Maps node types to executors
    store=InMemoryStore(),           # Execution state storage
    dispatcher=SyncDispatcher(),     # How branches are dispatched
    context_manager=ContextManager(),  # LLM context window management
    on_event=handle_event,           # Real-time event callback
)

Method	Description
run(input_message, flow_id=None) -> FlowResult	Execute synchronously
run_async(input_message, flow_id=None) -> AsyncIterator[FlowEvent]	Execute asynchronously, yielding events
resume(flow_id, user_input) -> FlowResult	Resume a paused flow with user input
stop(flow_id)	Stop a running flow

FlowResult

Field	Type	Description
flow_id	UUID	Unique execution identifier
success	bool	Whether all nodes completed successfully
final_output	str	Text output from the End node
output_data	dict	Structured output data
error	str | None	Error message if failed
node_results	dict[UUID, NodeResult]	Per-node results
duration_seconds	float	Total execution time

Dispatchers

Control how successor nodes are executed.

Dispatcher	Description
SyncDispatcher	Execute nodes sequentially in the calling thread. Simple and predictable.
ThreadDispatcher(max_workers=4)	Execute branches in parallel using a thread pool. Good for I/O-bound nodes.
AsyncDispatcher	Execute branches concurrently using asyncio tasks. For async web applications.

All dispatchers implement the TaskDispatcher protocol:

class TaskDispatcher(Protocol):
    def dispatch(self, flow_id, node_id, execute_fn) -> None: ...
    def wait_all(self) -> None: ...
    def shutdown(self) -> None: ...

Execution Stores

Pluggable storage for flow state, memory, and messages.

Store	Description
InMemoryStore	Dict-backed, no persistence. Great for testing.
SQLiteStore(db_path)	SQLite-backed with WAL mode. For local development.

Implement ExecutionStore for custom backends (Redis, PostgreSQL, etc.):

from quartermaster_engine import ExecutionStore

class RedisStore:
    def save_node_execution(self, flow_id, node_id, execution) -> None: ...
    def get_node_execution(self, flow_id, node_id) -> NodeExecution | None: ...
    def get_all_node_executions(self, flow_id) -> dict[UUID, NodeExecution]: ...
    def save_memory(self, flow_id, key, value) -> None: ...
    def get_memory(self, flow_id, key) -> Any: ...
    def get_all_memory(self, flow_id) -> dict[str, Any]: ...
    def delete_memory(self, flow_id, key) -> None: ...
    def save_messages(self, flow_id, node_id, messages) -> None: ...
    def get_messages(self, flow_id, node_id) -> list[Message]: ...
    def append_message(self, flow_id, node_id, message) -> None: ...
    def clear_flow(self, flow_id) -> None: ...

Memory System

FlowMemory -- scoped to a single flow execution:

from quartermaster_engine import FlowMemory, InMemoryStore

store = InMemoryStore()
memory = FlowMemory(flow_id=my_flow_id, store=store)

memory.set("user_name", "Alice")
memory.set("preferences", {"language": "en"})

name = memory.get("user_name")            # "Alice"
all_data = memory.get_all()                # {"user_name": "Alice", ...}
keys = memory.list_keys()                  # ["user_name", "preferences"]
memory.delete("preferences")
memory.clear()

PersistentMemory -- cross-flow memory that survives between executions:

from quartermaster_engine import PersistentMemory, InMemoryPersistence

persistence = InMemoryPersistence()

persistence.write(agent_id, "user_pref", "dark_mode")
value = persistence.read(agent_id, "user_pref")     # "dark_mode"
persistence.update(agent_id, "user_pref", "light_mode")

results = persistence.search(agent_id, "pref")      # Substring search
keys = persistence.list_keys(agent_id)               # ["user_pref"]
persistence.delete(agent_id, "user_pref")

Error Handling

Per-node error strategies configured via GraphNode.error_handling:

Strategy	Behavior
ErrorStrategy.STOP	Halt entire flow on error (default)
ErrorStrategy.RETRY	Retry up to max_retries times with retry_delay backoff
ErrorStrategy.SKIP	Skip failed node, continue to successors

from quartermaster_engine.types import GraphNode, NodeType, ErrorStrategy

node = GraphNode(
    type=NodeType.INSTRUCTION,
    name="Unreliable API",
    error_handling=ErrorStrategy.RETRY,
    max_retries=3,
    retry_delay=2.0,
    timeout=30.0,
)

Events

Real-time events emitted during flow execution:

Event	Fields	Description
NodeStarted	flow_id, node_id, node_type, node_name	Node begins execution
TokenGenerated	flow_id, node_id, token	Streaming token from LLM
NodeFinished	flow_id, node_id, result, output_data	Node completed
FlowFinished	flow_id, final_output, output_data	Entire flow completed
UserInputRequired	flow_id, node_id, prompt, options	Flow paused for user input
FlowError	flow_id, node_id, error, recoverable	Node failed

run_graph() uses streaming by default -- TokenGenerated events are printed as they arrive, giving real-time output from LLM nodes without extra setup.

ExecutionContext

The runtime context passed to each node executor:

Field	Type	Description
flow_id	UUID	Flow execution identifier
node_id	UUID	Current node identifier
graph	GraphSpec	Full graph definition
current_node	GraphNode	Current node definition
messages	list[Message]	Conversation history
memory	dict[str, Any]	Flow-scoped memory snapshot
metadata	dict[str, Any]	Node metadata
on_token	Callable[[str], None] | None	Callback for streaming tokens

Helper methods:

Method	Description
get_meta(key, default=None)	Get value from node metadata, falling back to context metadata
set_meta(key, value)	Set a metadata value on this context
emit_token(token)	Emit a streaming token via callback
emit_message(content)	Emit a complete message via callback

Node Execution Protocol

Implement NodeExecutor to add custom node types:

from quartermaster_engine.nodes import NodeExecutor, NodeResult
from quartermaster_engine.context.execution_context import ExecutionContext

class MyInstructionExecutor:
    async def execute(self, context: ExecutionContext) -> NodeResult:
        system_instruction = context.get_meta("llm_system_instruction", "")
        # Call your LLM here...
        response_text = "Generated response"

        # Stream tokens in real time
        for token in response_text.split():
            context.emit_token(token + " ")

        return NodeResult(
            success=True,
            data={"model": "gpt-4o"},
            output_text=response_text,
        )

Register executors with SimpleNodeRegistry:

from quartermaster_engine.nodes import SimpleNodeRegistry

registry = SimpleNodeRegistry()
registry.register("Instruction1", MyInstructionExecutor())
registry.register("Decision1", MyDecisionExecutor())

# List registered types
registry.list_types()  # ["Instruction1", "Decision1"]

NodeResult

Returned by node executors after execution:

Field	Type	Description
success	bool	Whether execution succeeded
data	dict[str, Any]	Structured output data
error	str | None	Error message if failed
picked_node	str | None	For decision nodes: which successor to trigger
output_text	str | None	Main text output
wait_for_user	bool	If True, flow pauses for user input
user_prompt	str | None	Prompt to show the user
user_options	list[str] | None	Options for user selection

Configuration

SQLiteStore

from quartermaster_engine.stores.sqlite_store import SQLiteStore

store = SQLiteStore(db_path="my_agent.db")
runner = FlowRunner(graph=graph, node_registry=registry, store=store)

Tables are created automatically on first use. Uses WAL mode for concurrent read access.

ThreadDispatcher

from quartermaster_engine.dispatchers.thread_dispatcher import ThreadDispatcher

dispatcher = ThreadDispatcher(max_workers=8)
runner = FlowRunner(graph=graph, node_registry=registry, dispatcher=dispatcher)
result = runner.run("Process this in parallel")
dispatcher.shutdown()  # Clean up thread pool

Contributing

See CONTRIBUTING.md for guidelines.

License

Apache License 2.0 -- see LICENSE for details.