fix:多source的节点跳不到的问题，例如：agent p\u\e, p->u,p->e,u->e 在运行当中，p或u无法跳到e

[rxy007]

Why are these changes needed?

Related issue number

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[ekzhu]

Thanks for the PR. Could you please add a test case in the unit test to show your fix addresses the scenario? Can you also update the PR description to show the original issue with a working code block and output.

[Copilot]

Pull Request Overview

This PR addresses an issue where nodes from multiple sources are not triggering as expected in the message thread update logic. The key change involves modifying the condition for appending a target node to the ready queue.

• Changed the condition from "== 0" to ">= 0" in the update_message_thread function to handle node activation.

[Copilot]

The condition '>= 0' may allow the target node to be added to the ready queue before all required processing is complete. Consider revisiting this logic to verify if the intended condition should remain '== 0' to ensure that nodes are only activated when their remaining count is exactly zero.

Suggested change

	if self._remaining[target][activation_group] >= 0:
	if self._remaining[target][activation_group] == 0:

[majiayu000]

Added regression test for multi-source join with max_turns and updated PR description in a follow-up PR: #7187 (from my fork). I couldn't edit this PR directly due to permissions. Feel free to cherry-pick commit ba458ee.