Blob.display_name not preserved when loading binary artifacts from FileArtifactService / GcsArtifactService #5833

Description

When you save an artifact whose Part.inline_data.display_name is set (e.g., a
user-facing filename), the value is lost on load_artifact for
FileArtifactService and GcsArtifactService. InMemoryArtifactService
preserves it. Same shape as #3157 (.text lost on load), fixed by #5155 for
the text path.

Downstream, the genai → A2A converter at
part_converter.py:218
reads name=part.inline_data.display_name, so FilePart.file.name becomes
None and clients fall back to a generic attachment.<ext> label.

To Reproduce

import asyncio
import tempfile

from google.adk.artifacts import FileArtifactService, InMemoryArtifactService
from google.genai import types


async def main() -> None:
    for label, svc in [
        ("in-memory", InMemoryArtifactService()),
        ("file", FileArtifactService(base_path=tempfile.mkdtemp())),
    ]:
        await svc.save_artifact(
            app_name="app", user_id="u", session_id="s", filename="report.png",
            artifact=types.Part(
                inline_data=types.Blob(
                    mime_type="image/png",
                    data=b"\x89PNG\r\n\x1a\n...",
                    display_name="report.png",
                )
            ),
        )
        loaded = await svc.load_artifact(
            app_name="app", user_id="u", session_id="s", filename="report.png"
        )
        print(f"{label:10s} display_name={loaded.inline_data.display_name!r}")


asyncio.run(main())

Output:

in-memory  display_name='report.png'
file       display_name=None

Expected

display_name round-trips through save → load for all artifact services.

Observed

• FileArtifactService._load_artifact
  (line 494)
  rebuilds the Part as
  types.Part(inline_data=types.Blob(mime_type=mime_type, data=data)).
  display_name is also not written to metadata.json on save, so it's
  genuinely lost on disk.
• GcsArtifactService._load_artifact
  (line 271)
  uses Part.from_bytes(...), which sets display_name=None.

Environment

• google-adk==2.1.0
• Python 3.12.13, macOS (also reproduces on linux)

Question

Is this expected behavior, or a bug?

Related

• Artifact stored as text is not retrieved as text #3157 — .text not preserved on load. Same shape.
• fix: restore .text attribute when loading text artifacts from GCS #5155 — fix for Artifact stored as text is not retrieved as text #3157 (open, approved). The display_name fix would live
  in the same place.