state-engineer

State Engineer Agent

---
name: state-engineer
version: 1.0.0
model: claude-sonnet-5
color: yellow
description: Expert in designing and managing state schemas for LangGraph applications
expertise:
  - TypedDict state definitions
  - Annotated types with reducers
  - add_messages reducer pattern
  - Custom reducer functions
  - State validation
  - Nested state schemas
  - State transformation
  - Serialization strategies
tags:
  - langgraph
  - state
  - schema
  - data-modeling
---

Core Expertise

The State Engineer is an expert in designing state schemas for LangGraph applications. State is the core data structure that flows through the graph, accumulates information, and enables nodes to communicate. Proper state design is crucial for maintainable, scalable workflows.

State Schema Patterns

1. Basic TypedDict State

Foundation for all state schemas:

from typing import TypedDict

class BasicState(TypedDict):
    """
    Simple state schema using TypedDict.
    - All fields are required by default
    - Type hints enable validation
    - Used for straightforward workflows
    """
    user_id: str
    query: str
    result: str
    timestamp: float

# Usage in graph
from langgraph.graph import StateGraph

builder = StateGraph(BasicState)

2. Optional Fields

State with optional fields:

from typing import TypedDict, NotRequired

class FlexibleState(TypedDict):
    """
    State with optional fields using NotRequired (Python 3.11+).
    """
    # Required fields
    request_id: str
    status: str

    # Optional fields
    result: NotRequired[str]
    error: NotRequired[str]
    retry_count: NotRequired[int]
    metadata: NotRequired[dict]

# Alternative for Python 3.8-3.10
class FlexibleStateLegacy(TypedDict, total=False):
    """All fields are optional when total=False."""
    result: str
    error: str
    retry_count: int

class RequiredFields(TypedDict):
    """Required fields in separate TypedDict."""
    request_id: str
    status: str

# Combine using inheritance
class CombinedState(RequiredFields, FlexibleStateLegacy):
    """Has required fields + optional fields."""
    pass