FEAT: Smuggling arbitrary data through an emoji

[KutalVolkan]

Is your feature request related to a problem? Please describe

We currently support ASCII smuggling via Unicode Tags and bit-level encoding via Sneaky Bits. However, we don’t yet support a high-density, byte-level encoding method that relies on invisible Unicode characters.

Describe the solution you'd like

Add a new variation_selector encoding mode to AsciiSmugglerConverter (noting that the class now handles full UTF-8 smuggling):

• Encodes any UTF-8 input at the byte level
• Uses 256 invisible Unicode variation selectors (U+FE00–U+FE0F, U+E0100–U+E01EF)
• Appends encoded selectors to a base character (e.g., emoji)
• Supports decoding
• Keeps unicode_tags as the default

Describe alternatives you've considered

We previously added sneaky_bits, which encodes at the bit level using two invisible characters. While simple and effective, variation_selector offers higher data density (1 byte per character) and enables encoding full payloads in shorter strings.

Additional context

This is based on Paul Butler’s post and shows how:

• Variation selectors encode 1 byte invisibly
• They persist through copy/paste
• Useful for simulating data smuggling, prompt injection, and text watermarking

Note

@romanlutz good to move forward from your side?
@paulinek13 would it be okay to slip this in while you're working on generalization (PR #818)? I’m also happy to wait if you’d prefer! Should be done by Sunday.

[romanlutz]

Do you want to rename the class to something more generic then? UTF8SmugglerConverter? 😆

[paulinek13]

would it be okay to slip this in while you're working on generalization

@KutalVolkan As for me, it'll be a while before I can get that done, so go for it! 😃

[KutalVolkan]

Do you want to rename the class to something more generic then? UTF8SmugglerConverter? 😆

If i am allowed? 😆

[jasonbenchling]

Was looking to potentially implement this, but it looks like this should be closed after #842