LangChain LangGraph Agents (Python)

Overview

Two failure modes hit every team writing their first LangGraph 1.0 ReAct agent:

Loop-to-cap on vague prompts (P10). create_react_agent defaults to recursion_limit=25. A prompt like "help me with my account" never converges — the model calls a retrieval tool, gets irrelevant results, calls another tool, and repeats until GraphRecursionError: Recursion limit of 25 reached without hitting a stop condition fires. Cost dashboards show the damage after the fact: $5-$15 per runaway loop on Sonnet with a 3-tool agent, assuming no tool is itself expensive.

Silent tool errors on legacy AgentExecutor (P09). The legacy executor defaults handle_parsing_errors=True and catches tool exceptions, feeding the error string back as the next observation. When the error serializes to empty (e.g., a ValueError("") or an HTTP 500 with no body), the loop continues with no signal. The agent says "I couldn't find the answer" — which was actually a silent crash three tool calls ago.