feat(agents): support AbortSignal in createReactAgent

[christian-bromann]

Description

This PR adds support for AbortSignal in the createReactAgent function, allowing users to cancel agent execution and tool invocations. This is particularly useful for long-running agent operations where users may want to cancel execution based on external events or user interaction.

Key Changes:

1. Added abortSignal parameter to CreateReactAgentParams - Users can now pass an AbortSignal when creating an agent
2. Signal propagation to tools - The abort signal is passed to the ToolNode and properly merged with any existing signals from LangGraph's Pregel class
3. Signal merging with AbortSignal.any() - When both agent-level and config-level signals are present, they are merged using AbortSignal.any() (with appropriate TypeScript declarations for this newer API)
4. Improved error propagation - Abort signal reasons are now properly propagated throughout the execution chain
5. Comprehensive test coverage - Added tests to verify abort functionality works correctly at both the agent and tool levels

Usage Example:

const abortController = new AbortController();

const agent = createReactAgent({
  llm: model,
  tools: [myTool],
  abortSignal: abortController.signal,
});

// Start agent execution
const executionPromise = agent.invoke({
  messages: [{ role: "user", content: "Do something long running" }],
});

// Cancel after some condition
setTimeout(() => {
  abortController.abort("User cancelled operation");
}, 5000);

Additional Improvements:

• Fixed build script to not clean in watch mode (prevents IDE issues with missing types)
• Updated signal utilities in langchain-core to properly extract and propagate abort reasons
• Added TypeScript declarations for AbortSignal.any() which is not yet in TypeScript's lib

Fixes #(issue)

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Project	Deployment	Preview	Comments	Updated (UTC)
langchainjs-docs	Ready	Preview	Comment	Aug 16, 2025 9:14pm

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[hntrl]

I'd make the argument that an AbortSignal is better served as a call option then it is a "constructor" option.

[christian-bromann]

I'd make the argument that an AbortSignal is better served as a call option then it is a "constructor" option.

We should support both, a global abort signal that acts as default and one as invoke option that allows to overwrite the global one.