/**
 * Client-side msgId helper. Mirrors `@shade/inbox-server/msg-id` but lives
 * in this package so client code doesn't need to import the server bundle.
 *
 * `msgId = lowercase-hex( sha256(ciphertext) )`
 */
export async function computeMsgId(ciphertext: Uint8Array): Promise<string> {
  const buf = await globalThis.crypto.subtle.digest(
    'SHA-256',
    ciphertext as unknown as ArrayBuffer,
  );
  const arr = new Uint8Array(buf);
  return Array.from(arr, (b) => b.toString(16).padStart(2, '0')).join('');
}