BUG: BinaryConverter rejects characters in words the selection strategy never converts

[UmerkhanGolandaz]

Describe the bug

BinaryConverter rejects a prompt because of a character in a word that the configured word selection strategy never converts.

WordLevelConverter.convert_async calls self.validate_input(prompt=prompt) on the whole prompt (pyrit/converter/word_level_converter.py:114) and only afterwards applies the selection strategy (:118). BinaryConverter.validate_input scans every character in the prompt, so an unselected word raises ValueError even though that word is passed through unencoded and cannot overflow bits_per_char.

Steps to reproduce

import asyncio

from pyrit.converter import BinaryConverter
from pyrit.converter.text_selection_strategy import WordIndexSelectionStrategy


async def main():
    # Only word 0 ("hello") is selected, so the emoji is never encoded.
    converter = BinaryConverter(
        bits_per_char=BinaryConverter.BitsPerChar.BITS_16,
        word_selection_strategy=WordIndexSelectionStrategy(indices=[0]),
    )
    print(await converter.convert_async(prompt="hello 👋", input_type="text"))


asyncio.run(main())

Expected behavior

hello is encoded at 16 bits per character and 👋 is passed through untouched, as it is for every other WordLevelConverter subclass.

Actual behavior

ValueError: bits_per_char=16 is too small for the characters in the prompt. Minimum required bits: 17.

Nothing is converted. The only way to encode hello is to raise bits_per_char to 32 for a character that is never encoded, which changes the encoding of every selected word.

Additional context

The default AllWordsSelectionStrategy path is unaffected: when every word is converted, whole-prompt and per-word validation agree. The mismatch only appears once a selection strategy is supplied.

Validating the words that are actually converted resolves this. I have a PR ready with that fix and regression tests. Happy to move the fix into WordLevelConverter.convert_async instead (validating after selection, which would cover any future subclass that overrides validate_input) if you prefer that shape.

Environment: PyRIT 1.2.0.dev0 (main at 623d57a), Python 3.14, Linux.