fix: keep current status messages out of task history

[1fanwang]

Description

A streaming client currently puts the active status message in both Task.status.message and Task.history. A client that receives the update reconstructs different state from a later subscriber reading the server snapshot.

The client now moves only the previous status message into history. This matches the Java server and the Python and Go SDKs. The v0.3 compatibility client uses the same rule.

End-to-end repro

I used the existing stream lifecycle example with this temporary instrumentation:

-emitter.startWork();
+emitter.startWork(emitter.newAgentMessage(java.util.List.of(new TextPart("working")), null));

-System.out.printf("[%s] StatusUpdate — %s%n", subscriber, tue.getTask().status().state());
+System.out.printf("[%s] StatusUpdate — %s statusMessage=%s history=%s%n", subscriber, tue.getTask().status().state(), tue.getTask().status().message().messageId(), tue.getTask().history().stream().map(Message::messageId).toList());

-System.out.printf("[%s] TaskEvent — state: %s, id: %s%n", subscriber, te.getTask().status().state(), te.getTask().id());
+System.out.printf("[%s] TaskEvent — state: %s, id: %s statusMessage=%s history=%s%n", subscriber, te.getTask().status().state(), te.getTask().id(), te.getTask().status().message().messageId(), te.getTask().history().stream().map(Message::messageId).toList());

cd examples/stream-lifecycle/server && mvn -q quarkus:dev
cd examples/stream-lifecycle/client && mvn -q compile exec:java

Before:

StatusUpdate ... statusMessage=2b86bb5b-921a-4775-b413-6e90b667b8db history=[2b86bb5b-921a-4775-b413-6e90b667b8db]
TaskEvent ... statusMessage=2b86bb5b-921a-4775-b413-6e90b667b8db history=[]

After:

StatusUpdate ... statusMessage=30b9d47f-5358-4c0c-9805-f790becec694 history=[]
TaskEvent ... statusMessage=30b9d47f-5358-4c0c-9805-f790becec694 history=[]

• Followed the CONTRIBUTING Guide.
• Used a Conventional Commits title.
• mvn -pl client/base,compat-0.3/client/base -am test

[ERROR] Tests run: 14, Failures: 2, Errors: 0, Skipped: 0
[ERROR] Tests run: 1, Failures: 1, Errors: 0, Skipped: 0
[INFO] Tests run: 14, Failures: 0, Errors: 0, Skipped: 0
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO] BUILD SUCCESS

• No README update is needed because the public API is unchanged.

[Copilot]

🟢 Approval recommended

The focused implementation matches server behavior and includes regression coverage for both supported client models.

Pull request overview

Updates client task reconstruction so only superseded status messages enter task history, aligning current and v0.3 clients with server behavior.

Changes:

• Archives the previous status message when processing an update.
• Keeps the current message exclusively in Task.status.
• Updates tests for both protocol versions.

File summaries

File	Description
client/base/.../ClientTaskManager.java	Corrects current task-history reconstruction.
client/base/.../ClientTaskManagerTest.java	Updates status-message lifecycle assertions.
compat-0.3/client/base/.../ClientTaskManager_v0_3.java	Applies equivalent v0.3 behavior.
compat-0.3/client/base/.../ClientTaskManager_v0_3_Test.java	Adds v0.3 regression coverage.

Review details

• Files reviewed: 4/4 changed files
• Comments generated: 0
• Review effort level: Balanced

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