`interopZodTransformInputSchema` not stripping transform functions when wrapped around an optional def

[ro0sterjam]

Checked other resources

• This is a bug, not a usage question. For questions, please use the LangChain Forum (https://forum.langchain.com/).
• I added a very descriptive title to this issue.
• I searched the LangChain.js documentation with the integrated search.
• I used the GitHub search to find a similar question and didn't find it.
• I am sure that this is a bug in LangChain.js rather than my code.
• The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package).

Example Code

import { type InteropZodType, interopZodTransformInputSchema } from "@langchain/core/utils/types";
import { z } from "zod/v4";

const schemaWithOptional = z.object({
  messages: z.array(z.string().transform((x) => x.toUpperCase())).optional(),
});

const schemaWithoutOptional = z.object({
  messages: z.array(z.string().transform((x) => x.toUpperCase())),
});

interopZodTransformInputSchema(schemaWithOptional as unknown as InteropZodType, true);
interopZodTransformInputSchema(schemaWithoutOptional as unknown as InteropZodType, true);

const message = { messages: ["hello"] };

console.log(schemaWithOptional.parse(message)); // Logs { message: [ 'HELLO' ] }
console.log(schemaWithoutOptional.parse(message)); // Logs { message: [ 'hello' ] }

Error Message and Stack Trace (if applicable)

No response

Description

interopZodTransformInputSchema is suppose to strip the transform functions from a schema, but when an object or array is wrapped with an optional, the current logic seems to skip over this element and thus does not strip any nested transforms under it.

I believe it should be a relatively trivial fix by adding the addition check for optional here.

Something like:

// Handle nested optional schemas
else if (isZodOptionalV4(outputSchema)) {
  const innerType = interopZodTransformInputSchema(
    outputSchema._zod.def.innerType,
    recursive
  ) as z4.$ZodType;
  outputSchema = clone<z4.$ZodOptional>(outputSchema, {
    ...outputSchema._zod.def,
    innerType,
  });
}

System Info

Langchain 0.3.35
Node v24.5.0
OSX 15.6.1 (24G90)