fix(langchain): respect version:"v1" in afterModel router's pending tool call path

[Christian Bromann (christian-bromann)]

createAgent accepts a version option ("v1" | "v2", defaulting to "v2") that controls how tool calls are dispatched. With version: "v1" all tool calls from a single AIMessage are executed concurrently inside one ToolNode invocation via Promise.all, which is important for agents whose tools invoke sub-graphs — the v2 Send-per-task approach can serialize those calls due to LangGraph's per-task checkpoint writes.

This PR fixes a bug where version: "v1" was not fully respected when afterModel middleware was present and an interrupted run was being resumed.

Bug

#createAfterModelRouter contains a pendingToolCalls branch that fires during interrupt resumption — when some tool calls from an AIMessage have already completed and only a subset remain. That branch unconditionally dispatched each pending call as a separate Send task regardless of #toolBehaviorVersion:

// Before — always Send, ignoring version
if (pendingToolCalls && pendingToolCalls.length > 0) {
  return pendingToolCalls.map(
    (toolCall) => new Send(TOOLS_NODE_NAME, { ...state, lg_tool_call: toolCall })
  );
}

With version: "v1" this silently switched back to v2-style dispatch for the resumed portion of the run, breaking the parallelism guarantee.

Fix

The pendingToolCalls path now branches on #toolBehaviorVersion:

• v1: returns TOOLS_NODE_NAME as a plain string. ToolNode.run() receives the full message state, filters out already-completed calls internally, and runs the remainder via Promise.all.
• v2: keeps the existing Send-per-call dispatch unchanged.

This matches the Python LangGraph implementation where the equivalent post_model_hook_router only dispatches via Send and is structurally unreachable from version: "v1".

[changeset-bot]

🦋 Changeset detected

Latest commit: 0ae443b

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

This PR includes changesets to release 1 package

Name	Type
langchain	Patch

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