[Feat]: Support adding metadata to Part in 1.0.0.Alpha (regression from 0.3.x)

[flex-myeonghyeon]

Is your feature request related to a problem? Please describe.

Background

In version 0.3.x of the A2A Java SDK, Part included a metadata field that allowed clients to attach additional information to each part.

However, after the redesign in 1.0.0.Alpha1, the metadata field was removed from Part.

Problem

Previously, metadata in Part (such as TextPart, DataPart, and FilePart) was useful for passing additional contextual or domain-specific information to clients.

For example:

• Custom rendering hints
• Classification tags
• Correlation identifiers
• Client-specific processing flags

Describe the solution you'd like

Proposal

Could you please consider reintroducing support for metadata in Part (or an equivalent extensibility mechanism)?

Describe alternatives you've considered

No response

Additional context

No response

Code of Conduct

• I agree to follow this project's Code of Conduct

[kabir]

We follow the specification, so if you have suggestions for the specification please open an issue in https://github.com/a2aproject/A2A

[flex-myeonghyeon]

@kabir According to the v1.0.0 specification, the Part interface includes metadata.
https://a2a-protocol.org/v0.1.0/specification/#65-part-union-type

[ehsavoie]

Yes this is correct, I think it was removed at one point but it came back