[Bug]: RestHandler#sendMessage returns part with both "text" and "filename" fields

[yuyu123-yuyu]

What happened?

Hello!
I am currently using Alpha3 and ran into this problem:

I called RestHandler#sendMessage and expected to create a task with one TextPart.
But we get a part object like this:

{
  "tasks": [
  {
    "xxx": "xxx",
    "parts": [
      {
        "text": "abc",
        "metadata": {},
        "filename": "",
        "mediaType": ""
      }
    ]
  }
]
}

I believe the filename field is not supposed to be there.

I also found RestHandler use grpc models/functions internally, which might be the problem: when it performs proto deserialization, it added the filename to the part model.

Relevant log output

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[CokeLee777]

I’m experiencing the same issue on the JSON-RPC side.

When calling sendMessage, I expected a TextPart with only the text field, but the resulting part object also includes metadata, filename, and mediaType, even when they were not explicitly set.