[Bug]: TaskManager.updateWithMessage does not clear status.message after history update

[flex-myeonghyeon]

What happened?

Description

The TaskManager.updateWithMessage method updates multi-turn input messages.
When a task already has a message in its status, that message is appended to the history.
However, after being added to the history, status.message should be cleared (null), but it remains set.

Expected behavior

status.message should be set to null once the message is moved to history.

Reference

In the a2a-python implementation
, the message is correctly cleared after being added to history.

Suggested fix

Update the Java implementation to match the Python behavior by nullifying status.message after it is appended to history.

Relevant log output

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