createAgent examples fail to save graph PNGs on Windows

[dvd233]

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 present on the latest main branch.

Example Code

The createAgent examples derive their graph PNG output path with new URL(import.meta.url).pathname. This self-contained reproduction exercises the same URL-to-path conversion without calling an LLM:

import fs from "node:fs/promises";
import os from "node:os";
import path from "node:path";
import { pathToFileURL } from "node:url";

const target = path.join(os.tmpdir(), "langchain-example-path-repro.png");
const currentFilePath = new URL(pathToFileURL(target)).pathname;

console.log({ currentFilePath, resolved: path.resolve(currentFilePath) });
await fs.writeFile(currentFilePath, "png data");

On Windows this prints a URL pathname and then resolves it as a different filesystem path:

{
  currentFilePath: '/C:/Users/<user>/AppData/Local/Temp/langchain-example-path-repro.png',
  resolved: 'C:\\C:\\Users\\<user>\\AppData\\Local\\Temp\\langchain-example-path-repro.png'
}

Error: ENOENT: no such file or directory, open 'C:\C:\Users\<user>\AppData\Local\Temp\langchain-example-path-repro.png'

Error Message and Stack Trace (if applicable)

ENOENT: no such file or directory, open 'C:\C:\Users\<user>\...\langchain-example-path-repro.png'

Description

Fifteen examples under examples/src/createAgent/ currently use this pattern before calling fs.writeFile:

const currentFilePath = new URL(import.meta.url).pathname;
const outputPath = currentFilePath.replace(/\.ts$/, ".png");
await fs.writeFile(outputPath, await agent.drawMermaidPng());

On POSIX, a file URL's pathname is usually a usable absolute path. On Windows, it starts with /C:/; Node resolves that as C:\C:\..., so the examples fail after the agent run instead of saving their visualization beside the source file. Percent-encoded characters in paths (for example spaces) are also left encoded by .pathname.

Expected: each example saves its graph PNG next to its TypeScript source on every supported Node platform.

Actual: all 15 affected examples fail with ENOENT on Windows when they attempt to write the PNG.

Node already provides the cross-platform conversion used elsewhere in this repository:

import { fileURLToPath } from "node:url";

const currentFilePath = fileURLToPath(import.meta.url);

I found no existing issue or PR for this specific example-path bug. If maintainers agree with the fix direction, I am happy to update the affected examples and run the examples workspace build and formatting checks.

System Info

langchainjs main: 53dbfc2fa033250fe7b711d7c3c8f6e7bfea9216
OS: Microsoft Windows 11 64-bit, build 26200
Node: v24.15.0
pnpm: 11.19.0 (the reproduction itself only uses Node built-ins)