[Python] How to implement subgraph memory/persistence in LangGraph when parent and subgraph...

I’m using LangGraph to orchestrate workflows with a parent graph and a subgraph. The subgraph has its own checkpointing mechanism for state persistence, but I need it to retain memory of its own state even when the parent graph modifies shared fields.

Current Behavior:

If the parent graph sets a shared field (e.g., A = None), the subgraph’s checkpoint loses its previous state.

I want the subgraph to ignore parent-overrides for specific fields and persist its own state across invocations.

Desired Behavior:

Subgraph maintains its own state (e.g., A = 5) even if the parent sets A = None.

Checkpoints should store subgraph-specific state independently.

Code Example:

from langgraph.graph import Graph

# Parent Graph
parent = Graph()
parent.add_node("parent_node", lambda state: {"A": None}) # Overrides A

# Subgraph with checkpointing
subgraph = Graph(checkpoint=True)
subgraph.add_node("sub_node", lambda state: {"B": state.get("A", "default")})

# Connect them
parent.add_edge("parent_node", subgraph)

# Initial state (subgraph should remember A=5)
initial_state = {"A": 5, "B": "unset"}

# Run
final_state = parent.run(initial_state)
print(final_state) # Expect: {"A": None, "B": 5} (but B becomes "default")


What I’ve Tried:

1. Explicit checkpointing:

subgraph.invoke(state, checkpoint={"A": state["A"]}) # Force subgraph memory (Fails: Parent’s A=None still overrides.)

1. 
   State separation: Used distinct field names (e.g., subgraph_A vs. parent_A), but this feels hacky.
   
   
2. 
   Global storage: Redis/database to store subgraph state, but adds external dependencies.
   

Question:

How can I configure LangGraph to let subgraphs preserve their own state (e.g., A=5) even when the parent graph modifies shared fields?

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