Human-in-the-loop approval graph

"""LangGraph HITL: interrupt() pauses a node, checkpointer persists, Command(resume=...) continues.
No LLM involved: the 'proposal' node is deterministic (stands in for a model). All LangGraph code is real."""
from typing import TypedDict
from langgraph.graph import StateGraph, START, END
from langgraph.checkpoint.memory import InMemorySaver
from langgraph.types import interrupt, Command

class S(TypedDict, total=False):
    request: str
    action: dict
    decision: str
    result: str

def propose(state: S):
    print("  [propose] runs")
    return {"action": {"tool": "delete_records", "table": state["request"], "rows": 1200}}

def approval(state: S):
    print("  [approval] node (re)starts")  # NOTE: node re-executes from the top on resume
    answer = interrupt({"question": "Approve this action?", "action": state["action"]})
    if answer.get("approved"):
        return Command(goto="execute", update={"decision": "approved"})
    return Command(goto=END, update={"decision": "rejected", "result": f"rejected: {answer.get('reason')}"})

def execute(state: S):
    a = state["action"]
    return {"result": f"executed {a['tool']} on {a['table']} ({a['rows']} rows)"}

b = StateGraph(S)
b.add_node("propose", propose)
b.add_node("approval", approval, destinations=("execute", END))
b.add_node("execute", execute)
b.add_edge(START, "propose"); b.add_edge("propose", "approval"); b.add_edge("execute", END)
graph = b.compile(checkpointer=InMemorySaver())

for tid, resume in [("t-approve", {"approved": True}), ("t-reject", {"approved": False, "reason": "too many rows"})]:
    cfg = {"configurable": {"thread_id": tid}}
    print(f"== thread {tid} ==")
    out = graph.invoke({"request": "customers"}, cfg)
    intr = out["__interrupt__"][0]
    print("  paused, interrupt payload:", intr.value)
    snap = graph.get_state(cfg)
    print("  checkpoint next node:", snap.next)
    print("  -> human resumes with", resume)
    out = graph.invoke(Command(resume=resume), cfg)
    print("  final:", {k: out[k] for k in ("decision", "result")})

langgraph==1.2.15
langgraph-checkpoint==4.3.0

== thread t-approve ==
  [propose] runs
  [approval] node (re)starts
  paused, interrupt payload: {'question': 'Approve this action?', 'action': {'tool': 'delete_records', 'table': 'customers', 'rows': 1200}}
  checkpoint next node: ('approval',)
  -> human resumes with {'approved': True}
  [approval] node (re)starts
  final: {'decision': 'approved', 'result': 'executed delete_records on customers (1200 rows)'}
== thread t-reject ==
  [propose] runs
  [approval] node (re)starts
  paused, interrupt payload: {'question': 'Approve this action?', 'action': {'tool': 'delete_records', 'table': 'customers', 'rows': 1200}}
  checkpoint next node: ('approval',)
  -> human resumes with {'approved': False, 'reason': 'too many rows'}
  [approval] node (re)starts
  final: {'decision': 'rejected', 'result': 'rejected: too many rows'}

MIT License

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