INVALID_CHAT_HISTORY: resuming an agent with unanswered tool calls

INVALIDCHATHISTORY

How you get here

1. You invoke the graph with a hand-built message list containing an AIMessage with tool_calls and no ToolMessages.
2. The graph was interrupted before the tools node ran (you set interrupt_before=["tools"], or a tool raised an unhandled error), and you resumed with a plain HumanMessage or new input instead of the pending tool results.

Fix

Option A: supply the missing ToolMessages and invoke; they append to history and the graph runs from the START node:

graph.invoke({"messages": [ToolMessage(content="...", tool_call_id="...")]})

Option B: repair the state and resume from the interrupt:

1. graph.get_state(config) and look at the recent messages.
2. Remove the unanswered tool calls from the AIMessages, or add ToolMessages with matching toolcallids.
3. graph.update_state(config, {"messages": [...]}) with the fixed list.
4. Resume with graph.invoke(None, config).

Rule

On resume after an interrupt, the input must answer the pending tool calls. New user input goes in only after the tool results are in place.

Error catalog entry grounded in the official INVALIDCHATHISTORY error page, verified 2026-09-26. Error page: https://docs.langchain.com/oss/python/langgraph/errors/INVALIDCHATHISTORY