Pydantic bytes fields silently fail JSON serialization for binary content

Pydantic v2 bytes fields serialize text-like content to JSON fine but raise PydanticSerializationError: invalid utf-8 sequence for actual binary data. This surfaces only when model_dump_json() is called with binary content, validation and dict operations work fine. Use pydantic.Base64Bytes instead, which base64-encodes on serialization and decodes on deserialization. Note that Base64Bytes requires base64-encoded string input even from Python, raw b"hello" raises a base64 decoding error.

Use pydantic.Base64Bytes instead of bytes for any Pydantic field that may contain binary data and needs to round-trip through JSON.