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OpenLast checked LangGraph#loop#state

interrupt() inside a while loop replays every earlier resume

A node that calls interrupt() inside while True reprints every earlier resume on the next Command(resume=...). The report's expected prints are I got -1 through I got -6 once each; the actual prints replay from -1 on every resume, ending with six copies of -1 through -6 before I got 30.

From GitHub

langchain-ai/langgraph

Issue

Difficulty
Easy
Time
~5 min
Steps
2
Fixed in
—
Last checked

Not fixed upstream yet: the issue is open. Source: issue open. Last checked 2026-10-20.

Symptom

A node that calls interrupt() inside while True reprints every earlier resume on the next Command(resume=...). The report's expected prints are I got -1 through I got -6 once each; the actual prints replay from -1 on every resume, ending with six copies of -1 through -6 before I got 30.

Evidence what you'll see

  • The reproduction is the docs' validating-human-input node: answer = interrupt(prompt) in a while True loop, then six invalid resumes (-1 through -6) and one valid 30.
  • A 13 May 2026 comment reproduces the same exponential output against HEAD and points at scratchpad.resume plus scratchpad.interrupt_counter() in langgraph/types.py.
  • A collaborator comment on 10 Jun 2026 says all code before an interrupt re-runs, and shows looping with a graph edge instead of while True so print(f"I got {answer}") runs once per resume.

Why it happens

interrupt() indexes a flat scratchpad.resume list by call order. Sequential interrupt sites each fire once, so that list matches. The same call site inside a loop fires N times, so each resume replays every earlier value from index 0. The linked issue does not give a merged change.

Affected versions

Darwin arm64, Python 3.13.11, langchain_core 1.4.0, langgraph_sdk 0.3.14. The original report does not name a langgraph version. A later comment reproduces against HEAD.

Fix steps

0 of 2 done

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How to check it worked

  • Six invalid resumes print I got -1 through I got -6 once each, and Command(resume=30) prints I got 30 once and sets age to 30.

If it still fails

  • The reporter's local workaround scratchpad.resume.clear() at the start of the loop is on the issue; a comment says it drops durability so a crash mid-loop replays from zero.
  • The linked issue does not name a release that consumes one resume per loop iteration at the same interrupt() site.

Sources and credit

Summarized in our own words from these public reports. Credit goes to their authors.

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