fix(community): IBM WatsonX ChatWatsonx does not cancel requests on AbortSignal

[noobgramming]

Description

Fixes IBM WatsonX ChatWatsonx integration to properly handle AbortSignal by passing the signal parameter through to the underlying IBM SDK methods, enabling true server-side request cancellation.

Issue

Fixes a bug where abort signals were accepted but not actually passed to the IBM SDK, causing:

• Requests to continue executing on WatsonX servers after abort
• Users being charged for tokens generated after abort call
• Delayed cancellation (waiting for completion instead of immediate termination)

This is the same bug pattern as:

• #7257 - Qianfan chat models not handling abort signal (labeled auto:bug)
• #5001 - OpenAI abort controller not working (labeled auto:bug)

Both issues involved signals being passed to AsyncCaller but not to the underlying provider SDK.

Changes

Added signal: options?.signal to 4 SDK method calls:

Non-streaming methods (_generate):

// textChat() - line 680
this.service.textChat({
  ...params,
  ...scopeId,
  messages: watsonxMessages,
  signal: options?.signal,  // Added
}, watsonxCallbacks)

// deploymentsTextChat() - line 671
this.service.deploymentsTextChat({
  ...scopeId,
  messages: watsonxMessages,
  signal: options?.signal,  // Added
}, watsonxCallbacks)

Streaming methods (_streamResponseChunks):

this.service.textChatStream({
  ...params,
  ...scopeId,
  messages: watsonxMessages,
  returnObject: true,
  signal: options?.signal,  // Added
}, watsonxCallbacks)

this.service.deploymentsTextChatStream({
  ...scopeId,
  messages: watsonxMessages,
  returnObject: true,
  signal: options?.signal,  // Added
}, watsonxCallbacks)

Also removed ineffective manual abort checks that happened after requests completed.

Technical Details

The IBM WatsonX SDK already supports AbortSignal via the DefaultParams interface:

// From @ibm-cloud/watsonx-ai
interface DefaultParams {
  signal?: AbortSignal;
  headers?: OutgoingHttpHeaders;
}

export interface TextChatParams extends DefaultParams {
  modelId: string;
  messages: TextChatMessages[];
  // signal inherited from DefaultParams ✅
}

Signal flow:

1. LangChain accepts signal in options.signal
2. Now passed to IBM SDK methods (this PR)
3. IBM SDK passes to axios config
4. Axios aborts HTTP request on signal

Testing

Added 4 unit tests to verify signal is passed to all SDK methods:

1. textChat() with projectId
2. deploymentsTextChat() with idOrName
3. textChatStream() with projectId
4. deploymentsTextChatStream() with idOrName

Documentation Reference

Per https://js.langchain.com/docs/how_to/cancel_execution/:

"Individual integrations like chat models or retrievers may have missing or differing implementations for aborting execution."

This PR fixes the "missing implementation" for IBM WatsonX by using the SDK's signal support.

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[FilipZmijewski]

This is a valid PR for our implementation, we have previously added the abort on langchain side since we did not have aborting in our SDK, now it is supported and the above approach is correct. Thank you @noobgramming
Probably once langchain is finished with the big v1 release they will have a look at it.