langchain-task-steering 0.1.1

Implicit state machine middleware for LangChain v1 agents. Ordered task pipelines with per-task tool scoping, prompt injection, and composable validation.

langchain-task-steering

Implicit state-machine middleware for LangChain v1 agents. Define ordered task pipelines with per-task tool scoping, dynamic prompt injection, and composable validation — all as a drop-in AgentMiddleware.

PENDING ──> IN_PROGRESS ──> COMPLETE

The model drives its own transitions by calling update_task_status. The middleware enforces ordering, scopes tools, injects the active task's instruction into the system prompt, and gates completion via pluggable validators.

When to use this

Scenario	task-steering	LangGraph explicit workflows
Linear task pipeline (A then B then C)	Best fit	Verbose — one node + edges per task
Per-task tool scoping	Built-in	Manual — separate tool lists per node
Dynamic tasks from config / DB	Easy — tasks are data	Hard — graph is compiled at build time
Branching / parallel execution	Not supported	Built-in — edges + Send()
Per-task human-in-the-loop interrupts	Not supported	Built-in — interrupt() per node
Complex orchestration with retries / cycles	Not supported	Built-in — conditional edges
Composition with other middleware	Native — it's an AgentMiddleware	N/A — different abstraction
Debuggability in LangGraph Studio	Opaque — single agent node	Clear — each node visible in traces

Rule of thumb: If your tasks are sequential and tool-scoped, use task-steering. If you need branching, parallelism, or per-task interrupts, use explicit LangGraph workflows.

Install

pip install langchain-task-steering

For development:

git clone https://github.com/edvinhallvaxhiu/langchain-task-steering
cd langchain-task-steering
pip install -e ".[dev]"

Requirements

• Python >= 3.10
• langchain >= 1.0.0
• langgraph >= 0.4.0

Quick start

from langchain.agents import create_agent
from langchain.tools import tool
from langchain_task_steering import TaskSteeringMiddleware, Task


@tool
def add_items(items: list[str]) -> str:
    """Add items to the inventory."""
    return f"Added {len(items)} items."


@tool
def categorize(categories: dict[str, list[str]]) -> str:
    """Assign items to categories."""
    return f"Categorized into {len(categories)} groups."


pipeline = TaskSteeringMiddleware(
    tasks=[
        Task(
            name="collect",
            instruction="Collect all relevant items from the user's input.",
            tools=[add_items],
        ),
        Task(
            name="categorize",
            instruction="Organize the collected items into categories.",
            tools=[categorize],
        ),
    ],
)

agent = create_agent(
    model="anthropic:claude-sonnet-4-6",
    middleware=[pipeline],
    system_prompt="You are an inventory assistant.",
)

result = agent.invoke(
    {"messages": [{"role": "user", "content": "I have apples, bolts, and milk."}]}
)

The agent automatically receives an update_task_status tool and sees a task pipeline block in its system prompt. It must complete collect before starting categorize.

How it works

What the model sees

Every model call, the middleware appends a status block to the system prompt:

<task_pipeline>
  [x] collect (complete)
  [>] categorize (in_progress)

  <current_task name="categorize">
    Organize the collected items into categories.
  </current_task>

  <rules>
    Required order: collect -> categorize
    Use update_task_status to advance. Do not skip tasks.
  </rules>
</task_pipeline>

Only the active task's tools (plus globals and update_task_status) are visible to the model.

Middleware hooks

Hook	Behavior
before_agent	Initializes task_statuses in state on first invocation.
wrap_model_call	Appends task status board + active task instruction to system prompt. Filters tools to only the active task's tools + globals + update_task_status. Delegates to task-scoped middleware if present.
wrap_tool_call	Intercepts update_task_status — runs validate_completion on the task's scoped middleware before allowing completion. Rejects out-of-scope tool calls. Delegates other tool calls to the active task's scoped middleware.
tools	Auto-registers all task tools + globals + update_task_status with the agent.

Task lifecycle

PENDING ──> IN_PROGRESS ──> COMPLETE

• The agent drives transitions by calling update_task_status(task, status).
• Transitions are enforced: pending -> in_progress -> complete only.
• When enforce_order=True, a task cannot start until all preceding tasks are complete.
• On complete, the task's middleware.validate_completion(state) runs first — rejection returns an error to the agent without completing the transition.

Task-scoped middleware

Each task can have a TaskMiddleware that activates only when the task is IN_PROGRESS. This enables mid-task enforcement, not just completion gating.

from langchain.messages import ToolMessage
from langchain_task_steering import Task, TaskMiddleware, TaskSteeringMiddleware


class ThreatsMiddleware(TaskMiddleware):
    """Block gap_analysis until enough threats exist."""

    def __init__(self, min_threats: int = 25):
        super().__init__()
        self.min_threats = min_threats

    def validate_completion(self, state) -> str | None:
        threats = state.get("threats", [])
        if len(threats) < self.min_threats:
            return f"Only {len(threats)} threats — need at least {self.min_threats}."
        return None

    def wrap_tool_call(self, request, handler):
        if request.tool_call["name"] == "gap_analysis":
            threats = request.state.get("threats", [])
            if len(threats) < self.min_threats:
                return ToolMessage(
                    content=f"Cannot run gap_analysis: {len(threats)}/{self.min_threats} threats.",
                    tool_call_id=request.tool_call["id"],
                )
        return handler(request)


pipeline = TaskSteeringMiddleware(
    tasks=[
        Task(name="assets", instruction="...", tools=[create_assets]),
        Task(
            name="threats",
            instruction="Identify STRIDE threats for each asset.",
            tools=[create_threats, gap_analysis],
            middleware=ThreatsMiddleware(min_threats=25),
        ),
    ],
)

TaskMiddleware hooks

Method	When it runs	Purpose
validate_completion(state)	Before complete transition	Return error string to reject, None to allow
on_start(state)	After successful in_progress transition	Side effects (logging, state init)
on_complete(state)	After successful complete transition	Side effects (trail capture, cleanup)
wrap_tool_call(request, handler)	On every tool call during this task	Mid-task tool gating / modification
wrap_model_call(request, handler)	On every model call during this task	Extra prompt injection / request modification
state_schema	At middleware init	Merge custom state fields into the agent's state

Persistent state for task middleware

Task middleware can declare a state_schema to persist custom fields across interrupts:

from langchain.agents import AgentState
from typing_extensions import NotRequired


class ThreatsState(AgentState):
    gap_analysis_uses: NotRequired[int]


class ThreatsMiddleware(TaskMiddleware):
    state_schema = ThreatsState
    # ...

TaskSteeringMiddleware automatically merges all task middleware schemas into its own state_schema, so the fields survive checkpointing and interrupts.

Configuration

Parameter	Default	Description
tasks	(required)	Ordered list of Task definitions.
global_tools	[]	Tools available in every task.
enforce_order	True	Require tasks to be completed in definition order.

Task fields

Field	Required	Description
name	yes	Unique identifier (used in prompts and state).
instruction	yes	Injected into system prompt when this task is active.
tools	yes	Tools visible when this task is IN_PROGRESS.
middleware	no	Scoped TaskMiddleware — only active during this task.

Composability

TaskSteeringMiddleware is a standard AgentMiddleware. It composes with other LangChain v1 middleware:

from langchain.agents import create_agent
from langchain.agents.middleware import SummarizationMiddleware

agent = create_agent(
    model="anthropic:claude-sonnet-4-6",
    middleware=[
        SummarizationMiddleware(
            model="anthropic:claude-haiku-4-5-20251001",
            trigger={"tokens": 8000},
        ),
        pipeline,
    ],
)

Development

# Install with dev dependencies
pip install -e ".[dev]"

# Run tests
pytest

# Run tests with coverage
pytest --cov=langchain_task_steering

Project structure

langchain-task-steering/
  src/langchain_task_steering/
    __init__.py          # Public exports
    types.py             # Task, TaskMiddleware, TaskStatus, TaskSteeringState
    middleware.py         # TaskSteeringMiddleware implementation
  tests/
    conftest.py          # Fixtures and mock objects
    test_middleware.py    # Test suite
  examples/
    simple_agent.py      # End-to-end example with Bedrock
  pyproject.toml

License

MIT — see LICENSE.