fix(api): run.start on a cancelled thread must not fold input into a resume

[t3s7r]

Problem

createOrResumeRun decides input-vs-resume like this:

const isResume =
  params.input != null &&
  ((currentRun != null && currentStatus === "interrupted") ||
    hasPendingInterrupts);

A cancelled run also ends with status "interrupted" — the same status a genuine interrupt() pause has — but the thread has no pending interrupt to consume a resume value. LangGraph only delivers resume values to an interrupt() call, so when a client stops a run (stop() → runs.cancel) and then sends a follow-up message, that message is folded into Command(resume: input) that nothing reads: the message is silently dropped and the interrupted node re-runs with stale state.

Reproduction (SDK useStream against langgraphjs dev): start a run on a graph with a long-running node, stop() mid-node, then submit({ messages: [...] }). The created run has input: null and command.resume carrying the message; the thread's final state contains no trace of it.

Fix

Key the decision on hasPendingInterruptsForThread alone (already computed in the same scope; it reads thread-state tasks with subgraphs: true):

• thread paused at a real interrupt() → still resumes (unchanged),
• cancelled thread → plain input, i.e. a fresh run from the checkpoint that applies the message to state.

Applied to both copies of the condition: protocol/service.mts and experimental/embed/protocol.mts.

Test

tests/protocol-v2/run-start-cancelled.test.mts drives ProtocolService.handleCommand("run.start") with stub bindings: the cancel case (interrupted status, no pending interrupts) must submit input — red on current main; the pending-interrupt case must still produce Command(resume) — green before and after. pnpm typecheck clean; the rest of the suite unchanged (the three fetch failed files fail identically on clean main in my sandbox).

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: 271d965

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@langchain/langgraph-api	Patch
@langchain/langgraph-cli	Patch
@langchain/langgraph-ui	Patch

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commit: 271d965

[t3s7r]

The failing Unit Tests job is unrelated to this diff: 26.x on the runners moved from Node 26.7.0 to 26.8.1 on Aug 26/27, and tracing.test.ts > does not double stream tokens from a nested graph under tracing fails deterministically on 26.8.x on unmodified main (passes on 22.x and 26.7.0). Details and local bisection across Node versions in #2752. The earlier sdk-svelte failure was a one-off and passed on re-run; everything this diff touches is green.

[Christian Bromann (christian-bromann)]

LGTM 👍