fix(adk): set streaming meta for agentic tool chunks

[shentongmartin]

Agentic Tool Stream Metadata

Problem

Streamable tool results emitted through the ADK event sender were converted into AgenticMessage chunks without StreamingMeta.

Expected behavior:

• streamed chunks from the same tool result are grouped by stream index
• schema.ConcatAgenticMessages materializes them into one final function_tool_result block

Actual behavior:

• every chunk looked like an independent non-streaming function_tool_result
• materialization could not group chunks because the stream grouping signal was missing

Solution

Mark AgenticMessage chunks produced by typedToolStreamEvent and typedToolEnhancedStreamEvent with StreamingMeta{Index: 0}.

This matches the existing AgenticToolsNode.Stream behavior and gives schema.ConcatAgenticMessages the grouping signal it needs. The final materialized message still drops transient StreamingMeta; it only uses the metadata while concatenating stream chunks.

Key Insight

There are two Agentic tool streaming producers:

• AgenticToolsNode.Stream, which already attaches StreamingMeta
• ADK event-sender wrappers, which re-wrap tool stream chunks for user-visible events and also need to attach StreamingMeta

StreamingMeta is not persisted as final message state. It is a transient stream-concat hint used before materialization.

Summary

Problem	Solution
ADK streamable tool chunks lacked StreamingMeta	Set StreamingMeta{Index: 0} in typedToolStreamEvent
Enhanced streamable tool chunks had the same risk	Set StreamingMeta{Index: 0} in typedToolEnhancedStreamEvent

---

Agentic 工具流式元数据

问题

ADK event sender 发出的 Streamable tool result 会被转换成 AgenticMessage chunk，但这些 chunk 没有 StreamingMeta。

预期行为：

• 同一个 tool result 的流式 chunk 按 stream index 分组
• schema.ConcatAgenticMessages 将它们物化成一个最终的 function_tool_result block

实际行为：

• 每个 chunk 都像独立的非流式 function_tool_result
• 因缺少 stream 分组信号，物化过程无法将这些 chunk 归并到同一个 tool result

解决方案

在 typedToolStreamEvent 和 typedToolEnhancedStreamEvent 生成的 AgenticMessage chunk 上设置 StreamingMeta{Index: 0}。

这与现有 AgenticToolsNode.Stream 行为保持一致，并为 schema.ConcatAgenticMessages 提供正确的分组信号。最终物化后的 message 仍然不会保留临时的 StreamingMeta；它只在流式 chunk 拼接阶段使用。

关键洞察

Agentic tool streaming 有两个生产者：

• AgenticToolsNode.Stream，它已经会设置 StreamingMeta
• ADK event-sender wrappers，它会重新包装 tool stream chunk 作为用户可见事件，也需要设置 StreamingMeta

StreamingMeta 不是最终消息状态的一部分。它是物化前用于 stream concat 的临时分组信号。

总结

问题	解决方案
ADK streamable tool chunk 缺少 StreamingMeta	在 typedToolStreamEvent 中设置 StreamingMeta{Index: 0}
enhanced streamable tool chunk 有同样风险	在 typedToolEnhancedStreamEvent 中设置 StreamingMeta{Index: 0}

[codecov]

Codecov Report

❌ Patch coverage is 55.55556% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.99%. Comparing base (804b9d4) to head (c04fb33).

Files with missing lines	Patch %	Lines
adk/wrappers.go	55.55%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1045      +/-   ##
==========================================
- Coverage   83.05%   82.99%   -0.07%     
==========================================
  Files         162      162              
  Lines       23029    23038       +9     
==========================================
- Hits        19127    19120       -7     
- Misses       2647     2659      +12     
- Partials     1255     1259       +4     

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