Move validateFormatInput() out of Utils.convertToByteArray()/convertToByteString(),
which are shared by ~50 operations, and into Ciphers.mjs where it's only
reachable via parseFormatString() (used by RC4/RC4Drop). This keeps the fix
scoped to issue #2004 instead of changing accepted input globally, and avoids
the unrelated HMAC/Scrypt regressions the broader validation caused.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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