feat: added two new utils for mnemonic/english-word-indices conversion

[lwin-kyaw]

Summary

Mnemonic-to-index conversion currently lives in app-specific code (for example MetaMask Mobile) and is not available as a shared, browser-safe helper in @metamask/utils. Callers that store BIP-39 phrases as little-endian Uint16 wordlist indices have to duplicate that logic.

This PR adds two utilities in src/mnemonic.ts:

• uint8ArrayToMnemonic — reads little-endian Uint16 English BIP-39 word indices from a Uint8Array and returns the space-separated mnemonic string. Throws if the input is empty.
• convertMnemonicToWordlistIndices — splits a mnemonic string and encodes each word’s English BIP-39 wordlist index as little-endian Uint16 bytes in a Uint8Array.

Both use the English wordlist from @metamask/scure-bip39. No Node Buffer is used, so the helpers work in browsers.

---

Note

Medium Risk
New utilities operate on seed-phrase representations; invalid words are silently encoded as 65535 rather than rejected, which could surprise callers handling recovery phrases.

Overview
Adds shared browser-safe helpers for converting between English BIP-39 mnemonics and little-endian Uint16 wordlist indices stored in a Uint8Array, so callers no longer need app-local copies of this logic.

uint8ArrayToMnemonic decodes those bytes into a space-separated mnemonic (throws on empty input). convertMnemonicToWordlistIndices does the reverse via @metamask/scure-bip39’s English wordlist; words not in the list are encoded as index -1 (65535 as Uint16). Both are re-exported from the package entrypoints, with tests and changelog; @metamask/scure-bip39 is added as a dependency.

^{Reviewed by Cursor Bugbot for commit e6ce3df. Bugbot is set up for automated code reviews on this repo. Configure here.}

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	@​scure/​base@​1.1.3 ⏵ 1.1.9
	@​noble/​hashes@​1.3.3
	@​metamask/​scure-bip39@​2.1.1

View full report

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, have a team admin enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit ce170e3. Configure here.}