Langgraph Persistence

Memory that actually works in LangGraph applications. This covers the checkpointer system that saves graph state at every step, thread management for isolated conversations, and the Store API for cross-thread data like user preferences. Shows you how to set up PostgreSQL persistence for production, navigate checkpoint history for debugging, and handle the tricky subgraph scoping decisions that determine whether child graphs inherit persistence or run isolated. The subgraph checkpointer table alone saves hours of trial and error when building complex multi-agent workflows that need human-in-the-loop interrupts or stateful conversations.