Use the native node:wasi module when available

[devin-ai-integration]

Adds support for using the native node:wasi module from workerd when available, following the pattern established in previous module conversion PRs.

This is part of a series to convert 9 remaining Node.js modules from unenv polyfills to native workerd implementations.

Changes

• Added getWasiOverrides() function to enable/disable the native wasi module based on compatibility flags
• Integrated wasi overrides into the preset system (both nativeModules and hybridModules)
• Added E2E tests for enable/disable flag behavior
• Requires experimental flag and enable_nodejs_wasi_module flag to enable
• Can be disabled with disable_nodejs_wasi_module flag

Key Differences: workerd vs unenv

The workerd implementation has complete constructor validation for all WASI options (version, args, env, preopens, stdin, stdout, stderr, returnOnExit), while unenv just throws immediately without validation. Both are non-functional stubs.

Review Focus

• Verify flag naming follows convention: enable_nodejs_wasi_module / disable_nodejs_wasi_module
• Confirm implementation matches the pattern from cluster/punycode modules
• Check test coverage is consistent with existing module tests

---

Link to Devin run: https://app.devin.ai/sessions/f2a8f635e47b47e8baa9bc1b68af0635
Requested by: @petebacondarwin (pbacondarwin@cloudflare.com)

---

• Tests
  • Tests included
• Public documentation
  • Documentation not necessary because: this is an experimental feature requiring the experimental flag
• Wrangler V3 Backport
  • Not necessary because: unenv-preset changes are never backported to v3

[devin-ai-integration]

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[changeset-bot]

🦋 Changeset detected

Latest commit: 8829564

The changes in this PR will be included in the next version bump.

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[github-actions]

Failed to automatically backport this PR's changes to Wrangler v3. Please manually create a PR targeting the v3-maintenance branch with your changes. Thank you for helping us keep Wrangler v3 supported!

Depending on your changes, running git rebase --onto v3-maintenance main devin/1760951437-node-wasi might be a good starting point.

Notes:

• your PR branch should be named v3-backport-11025
• add the skip-v3-pr label to the current PR to stop this workflow from failing

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commit: 8829564

[petebacondarwin]

Here is the unenv polyfill: https://github.com/unjs/unenv/blob/6493c25f2fb94b9f2c7dec528a26ac11f7f9b8b0/src/runtime/node/wasi.ts#L2

[petebacondarwin]

Here is the workerd implementation: https://github.com/cloudflare/workerd/blob/6daa2ba8e02a3ea25cc7afd60d70f70bd9a38c7e/src/node/wasi.ts#L22

[petebacondarwin]

Here is the Node.js implementation https://github.com/nodejs/node/blob/0b6ae6df14ac7b6dbec4ad5c0473b63072d98cff/lib/wasi.js#L37

[vicb]

Thanks Pete!

[devin-ai-integration]

❌ Cannot revive Devin session - the session is too old. Please start a new session instead.

[vicb]

force push is rebase + format

[vicb]

rebased (with conflicts resolution)