test: yarn duplicate workspace error

examples/node-yarn-workspaces-nested/.gitignore

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+node_modules
+.pnp.cjs
+.pnp.loader.mjs
+.yarn/install-state.gz

examples/node-yarn-workspaces-nested/.yarnrc.yml

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+nodeLinker: pnp

examples/node-yarn-workspaces-nested/README.md

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+# node-yarn-workspaces-nested
+
+Reproduces [#463](https://github.com/railwayapp/railpack/issues/463): a Yarn
+Berry monorepo with a deeply-nested workspace package causes a phantom duplicate
+directory inside the container, making `yarn install` fail.
+
+## Structure
+
+The workspace glob is `packages/**/*` (recursive), with a package at
+`packages/prisma/timescaledb/`. The intermediate directory `packages/prisma/`
+happens to be named `prisma`, which matches the `prisma` entry in
+`SupportingInstallFiles`.
+
+## The bug
+
+`SupportingInstallFiles` returns both:
+
+- `packages/prisma/timescaledb/package.json` (matched as a file)
+- `packages/prisma` (matched as a directory named `prisma`)
+
+This produces two copy commands in the build plan:
+
+1. `copy packages/prisma/timescaledb/package.json` → creates
+   `/app/packages/prisma/timescaledb/`
+2. `copy packages/prisma → packages/prisma` → because BuildKit uses
+   `CopyDirContentsOnly: false`, the directory `prisma/` is placed *inside*
+   `/app/packages/prisma/`, creating the phantom
+   `/app/packages/prisma/prisma/timescaledb/`
+
+Yarn then sees two workspaces with the same name and fails:
+
+```
+Internal Error: Duplicate workspace name @wildmetrics/prisma-timescale:
+  /app/packages/prisma/timescaledb conflicts with
+  /app/packages/prisma/prisma/timescaledb
+```

examples/node-yarn-workspaces-nested/index.js

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+import { message } from "@wildmetrics/prisma-timescale";
+console.log(message);

examples/node-yarn-workspaces-nested/package.json

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+{
+  "name": "node-yarn-workspaces-nested",
+  "version": "1.0.0",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "start": "node index.js"
+  },
+  "workspaces": [
+    "packages/**/*"
+  ],
+  "dependencies": {
+    "@wildmetrics/prisma-timescale": "workspace:*"
+  },
+  "packageManager": "yarn@4.5.3"
+}

examples/node-yarn-workspaces-nested/packages/prisma/timescaledb/index.js

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+export const message = "hello from timescaledb package";

examples/node-yarn-workspaces-nested/packages/prisma/timescaledb/package.json

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+{
+  "name": "@wildmetrics/prisma-timescale",
+  "version": "1.0.0",
+  "type": "module",
+  "main": "index.js"
+}

examples/node-yarn-workspaces-nested/test.json

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+[
+  {
+    "expectedOutput": "hello from timescaledb package"
+  }
+]

examples/node-yarn-workspaces-nested/yarn.lock

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+# This file is generated by running "yarn install" inside your project.
+# Manual changes might be lost - proceed with caution!
+
+__metadata:
+  version: 8
+  cacheKey: 10c0
+
+"@wildmetrics/prisma-timescale@workspace:*, @wildmetrics/prisma-timescale@workspace:packages/prisma/timescaledb":
+  version: 0.0.0-use.local
+  resolution: "@wildmetrics/prisma-timescale@workspace:packages/prisma/timescaledb"
+  languageName: unknown
+  linkType: soft
+
+"node-yarn-workspaces-nested@workspace:.":
+  version: 0.0.0-use.local
+  resolution: "node-yarn-workspaces-nested@workspace:."
+  dependencies:
+    "@wildmetrics/prisma-timescale": "workspace:*"
+  languageName: unknown
+  linkType: soft