fix(agui): use unique message IDs for discontinuous text segments

[ZHCHJ888]

AgentScope-Java Version

2.0.3-SNAPSHOT

Description

Fixes #2988.

When a single model call emits text, then a tool call, then more text, the core previously reused the same text block ID. The AG-UI adapter consequently reused an already-ended message ID and emitted the second TEXT_MESSAGE_CONTENT without a matching TEXT_MESSAGE_START.

This change:

• assigns a distinct block ID to each contiguous text segment within a model call (text, text-2, ...);
• derives a distinct AG-UI message ID for subsequent segments while preserving the original reply ID for the first segment;
• adds core and AG-UI regression tests for the text -> tool call -> text sequence.

Testing

• ReActAgentNewLoopReplyTest: 14 passed, 0 failed.
• AG-UI module test suite: 500 passed, 0 failed.
• Core module full suite: 2,319 tests; 0 failures, 2 environment errors, 8 skipped. The two errors are Windows symlink-creation tests that require privileges unavailable on this host.
• GracefulShutdownTest: 50 passed independently after an unrelated suite-order state leak was observed during an exclusion rerun.

Checklist

• Code passes Spotless checks.
• Relevant core and AG-UI tests pass.
• Javadoc is complete and clear.
• Documentation changes are not required for this internal lifecycle fix.
• The pull request is ready for review.

[jujn]

不只是 text，reasoning 也有同样的问题哈

[ZHCHJ888]

不只是 text，reasoning 也有同样的问题哈

收到老师，那我按相同思路为连续 reasoning 段生成独立的 blockId，并补充回归测试，预计改动量不大，感谢您审阅和提醒

[codecov]

Codecov Report

❌ Patch coverage is 89.06250% with 7 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../core/agui/adapter/strategy/AguiStreamContext.java	83.33%	0 Missing and 6 partials ⚠️
...e/src/main/java/io/agentscope/core/ReActAgent.java	94.73%	0 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!

[ZHCHJ888]

@jujn 老师，我补齐 reasoning 场景并增加了相关回归测试了，等您有空能麻烦再帮忙看一下吗