LangChain LangGraph Basics (Python) Overview A conditional edge whose router returns a string that is not in halts the graph without reaching . No exception. No log line. The invocation just returns whatever state existed at the halt point — pain-catalog entry P56, and the single most common reason a newly wired "almost works." The sibling pain: wipes the prior message history because was declared as a plain instead of — the reducer is what turns into "append" instead of "replace" (P18). Two more gotchas this skill defuses: - P55 — fires on graphs that never loop, because counts supersteps (o…