replace usage of Node's Buffer with browser-friendly code

[gabspeck]

📝 Description

This PR makes the delegation-toolkit package compatible with environments where Node.js's Buffer global is not available.

🔄 What Changed?

List the specific changes made:

• packages/delegation-toolkit/src/webAuthn.ts: parseAuthenticatorFlags changed to use Viem's hexToBytes in combination with Uint8Array

🚀 Why?

Explain the motivation behind these changes:

• I'm developing a vanilla JS browser-side application that calls toMetaMaskSmartAccount and ran into an error because Buffer is not defined on the browser.

🧪 How to Test?

Describe how to test these changes:

• Manual testing steps:

1. Create a vanilla JS script that creates a MetaMask smart account instance with toMetamaskSmartAccount, using the hybrid implementation
2. Use viem's "sendUserOperation" with that account
3. After signing the operation with your passkey, you'll get an error similar to:

Uncaught (in promise) ReferenceError: Buffer is not defined
    parseAuthenticatorFlags webAuthn.ts:150
    encodeDeleGatorSignature webAuthn.ts:108
    encodeSignature signatory.ts:78
    promise callback*signTypedData signatory.ts:92
    signUserOperation2 toMetaMaskSmartAccount.ts:159
    sendUserOperation sendUserOperation.ts:138
    sendUserOperation bundler.ts:292
    createAccount index.js:57
    async* index.html:10

• Automated tests added/updated
• All existing tests pass

⚠️ Breaking Changes

List any breaking changes:

• No breaking changes
• Breaking changes (describe below):

📋 Checklist

Check off completed items:

• Code follows the project's coding standards
• Self-review completed
• Documentation updated (if needed)
• Tests added/updated
• Changelog updated (if needed)
• All CI checks pass

🔗 Related Issues

Link to related issues:
Closes #
Related to #

📚 Additional Notes

Any additional information, concerns, or context:

---

Note

Switches parseAuthenticatorFlags to viem hexToBytes/Uint8Array with a bounds check, and adds a unit test for missing flags.

• Delegation Toolkit:
  • webAuthn.ts: Replace Node Buffer usage in parseAuthenticatorFlags with hexToBytes + Uint8Array; add error when flags byte is missing.
• Tests:
  • webAuthn.test.ts: Add test asserting an error when authenticator flags are not found at the expected offset.

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[jeffsmale90]

Thanks @gabspeck for this, and sorry for taking so long to get to it. We've been heads down on some other things. If I'm not mistaken, this is our first external contribution to the Delegation Toolkit 🎉

This all looks good - can you please just add a test for the "Authenticator flags not found in authenticator data"?

[gabspeck]

Thanks @gabspeck for this, and sorry for taking so long to get to it. We've been heads down on some other things. If I'm not mistaken, this is our first external contribution to the Delegation Toolkit 🎉

This all looks good - can you please just add a test for the "Authenticator flags not found in authenticator data"?

Thanks for the review, test added

[jeffsmale90]

Thanks @gabspeck! We will get this out in an update shortly.