Cant be used with non-yarn package managers and when yarn is also installed

[marc2332]

Describe the bug
Cant be used in projects using other package managers other than yarn and when yarn is also installed

To Reproduce
Steps to reproduce the behavior:

• (optional): npm install yarn -g
• mkdir bug && cd bug
• pnpm init
• pnpm add postman-code-generators

Expected code snippet and corresponding request
work

Screenshots

Additional context
#792

[comatory]

This is really frustrating. Why does this need to depend on this specific package manager?

[sumomo015]

I've found a reliable way to reproduce this issue. Here are the steps:

1. Create a Dockerfile with the following content:

FROM node:24.12.0

RUN npm install -g pnpm@10.26.2
RUN npm install -g yarn || true

WORKDIR /app

RUN pnpm init
# For demonstration only—enables 'dangerously-allow-all-builds', which is unsafe in production.
RUN echo "dangerously-allow-all-builds=true" >> .npmrc

# This step is expected to fail
RUN pnpm add postman-code-generators

CMD [ "echo", "Setup Complete" ]

2. Run the following command to build:

docker build -t bug .

Result: The build fails when trying to install postman-code-generators with pnpm.

1.473 .../node_modules/postman-code-generators postinstall$ node npm/deepinstall.js
1.723 .../node_modules/postman-code-generators postinstall: Detected package manager: yarn
1.794 .../node_modules/postman-code-generators postinstall: Detected yarn version: 1.22.22
1.794 .../node_modules/postman-code-generators postinstall: Running pre-package script
1.822 .../node_modules/postman-code-generators postinstall: Run successful languages.js saved in lib/assets
1.823 .../node_modules/postman-code-generators postinstall: csharp-httpclient: yarn install --production --frozen-lockfile
1.912 .../node_modules/postman-code-generators postinstall: Failed to run yarn install on codegen csharp-httpclient, here is the error:
1.912 .../node_modules/postman-code-generators postinstall: error This project's package.json defines "packageManager": "yarn@pnpm@10.26.2". However the current global version of Yarn is 1.22.22.
1.913 .../node_modules/postman-code-generators postinstall: Presence of the "packageManager" field indicates that the project is meant to be used with Corepack, a tool included by default with all official Node.js distributions starting from 16.9 and 14.19.
1.913 .../node_modules/postman-code-generators postinstall: Corepack must currently be enabled by running corepack enable in your terminal. For more information, check out https://yarnpkg.com/corepack.
1.913 .../node_modules/postman-code-generators postinstall: csharp-restsharp: yarn install --production --frozen-lockfile
1.999 .../node_modules/postman-code-generators postinstall: Failed to run yarn install on codegen csharp-restsharp, here is the error:
1.999 .../node_modules/postman-code-generators postinstall: /node_modules/.pnpm/async@3.2.2/node_modules/async/dist/async.js:324
1.999 .../node_modules/postman-code-generators postinstall:             if (fn === null) throw new Error("Callback was already called.");
1.999 .../node_modules/postman-code-generators postinstall:                                    ^
1.999 .../node_modules/postman-code-generators postinstall: Error: Callback was already called.
1.999 .../node_modules/postman-code-generators postinstall:     at /node_modules/.pnpm/async@3.2.2/node_modules/async/dist/async.js:324:36
1.999 .../node_modules/postman-code-generators postinstall:     at /node_modules/.pnpm/async@3.2.2/node_modules/async/dist/async.js:3646:17
1.999 .../node_modules/postman-code-generators postinstall:     at /node_modules/.pnpm/postman-code-generators@2.1.0/node_modules/postman-code-generators/npm/deepinstall.js:82:16
2.000 .../node_modules/postman-code-generators postinstall:     at Array.forEach (<anonymous>)
2.000 .../node_modules/postman-code-generators postinstall:     at /node_modules/.pnpm/postman-code-generators@2.1.0/node_modules/postman-code-generators/npm/deepinstall.js:71:14
2.000 .../node_modules/postman-code-generators postinstall:     at /node_modules/.pnpm/async@3.2.2/node_modules/async/dist/async.js:3641:28
2.000 .../node_modules/postman-code-generators postinstall:     at replenish (/node_modules/.pnpm/async@3.2.2/node_modules/async/dist/async.js:446:21)
2.000 .../node_modules/postman-code-generators postinstall:     at iterateeCallback (/node_modules/.pnpm/async@3.2.2/node_modules/async/dist/async.js:430:21)
2.000 .../node_modules/postman-code-generators postinstall:     at /node_modules/.pnpm/async@3.2.2/node_modules/async/dist/async.js:327:20
2.000 .../node_modules/postman-code-generators postinstall:     at /node_modules/.pnpm/async@3.2.2/node_modules/async/dist/async.js:3646:17
2.000 .../node_modules/postman-code-generators postinstall: Node.js v24.12.0
2.002 .../node_modules/postman-code-generators postinstall: Failed
2.024  ELIFECYCLE  Command failed with exit code 1.