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## Summary This change adds first-class graph lifecycle callbacks to LangGraph so interrupt and resume transitions can be observed without overloading the existing LangChain custom event system. It introduces a dedicated graph callback manager and wires lifecycle emission through Pregel execution in both sync and async paths. ## Changes - **`libs/langgraph/langgraph/callbacks.py`**: Adds `GraphCallbackHandler` and `GraphCallbackManager` (built on LangChain base callback classes), plus config plumbing via `graph_callbacks` and `get_graph_callback_manager_for_config`. - **`libs/langgraph/langgraph/pregel/_loop.py`**: Introduces `GraphLifecycleEvent` and records lifecycle transitions (`resume`, `interrupt`) into an internal FIFO queue with `shift_graph_lifecycle_event()`. - **`libs/langgraph/langgraph/pregel/main.py`**: Resolves graph callback manager from config and drains lifecycle events while loop execution progresses, dispatching `on_resume` and `on_interrupt` consistently in sync and async runtimes. - **`libs/langgraph/tests/test_graph_callbacks.py`**: Adds sync and async coverage verifying lifecycle callbacks fire correctly and remain distinct from LangChain `on_custom_event` handlers. --------- Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>