Python: [Bug]: Should `Content.__deepcopy__` preserve unsafe fields

[TaoChenOSU]

Description

In Python, Content.__deepcopy__ preserves shallow copies of a list of fields marked in Content._SHALLOW_COPY_FIELDS. Currently the list only contains raw_representation.

Question: Should deepcopy preserve shallow-copied fields?
What we are currently doing obscures the meaning of deepcopy by creating a partially deepcopied object.

Proposal: discard the unsafe object and log a warning.

Package Versions

agent-framework-core

Python Version

No response

Additional Context

No response

[Sweetteabittersugar]

Hi Tao Chen (@TaoChenOSU), I'd like to work on this issue.

I reviewed the current Content.__deepcopy__ implementation and the original non-copyable raw_representation fix in #4493. My understanding of the trade-off is that preserving the field by reference avoids failures for provider SDK objects, but leaves the deep-copied Content sharing potentially mutable state; discarding it restores isolation but removes provider-specific raw data from the copy.

Before implementing, could you confirm the intended contract?

1. Set each non-None field named in _SHALLOW_COPY_FIELDS (currently raw_representation) to None in the deep copy.
2. Emit a warning when such data is discarded.
3. Continue deep-copying all other fields normally.

I would add focused tests for ordinary-field isolation, discarded raw data, and warning behavior. If this matches the intended direction, could you assign the issue to me?