fix(telemetry): propagate span context in async generators and fix member agent input tracing

[Eliozhang]

问题

1. Span context 在 async generator 中丢失

start_as_current_span 返回的 context manager 在 async generator 被 cancel 时，__aexit__ 不保证执行（Python async generator 的已知行为）。这导致：

• context.detach() 未被调用，span context 丢失
• 子 span（agent_run、call_llm、execute_tool 等）无法正确解析父 span
• 链路追踪断裂，无法看到完整的调用链

复现路径： TeamAgent 调用 member agent 时，member agent 的执行是 async generator，cancel 时 span context 丢失。

2. Member agent 的 trace input 不准确

trace_agent 函数始终使用 user_content 记录 agent input，但当 member agent 被 TeamAgent 委派时，user_content 仍然是原始用户发给 leader agent 的内容，而不是 leader agent 转发给 member agent 的 override_messages。这导致 trace 中 member agent 的 input 和实际执行不匹配。

修复

Fix 1: runners.py + agents/_base_agent.py — span context 传播

用 start_span + context_api.attach/detach 替代 start_as_current_span：

• start_span 创建 span 但不自动设为 current
• context_api.attach(set_span_in_context(span, current_ctx)) 手动将 span 设为 current，返回 token
• 在 try/finally 的 finally 中调用 context_api.detach(token)
• 关键： try/finally 在 CancelledError 下也会执行（PEP 492），而 context manager 的 __aexit__ 不保证

Fix 2: telemetry/_trace.py — override_messages 优先

trace_agent 中优先检查 invocation_context.override_messages：

• 如果存在，从 override_messages 提取 text parts 作为 input
• 否则回退到原有的 user_content 逻辑

改动文件

文件	改动
trpc_agent_sdk/runners.py	start_span + attach/detach 传播 span context
trpc_agent_sdk/agents/_base_agent.py	同上
trpc_agent_sdk/telemetry/_trace.py	override_messages 优先于 user_content

测试

• 本地运行 TeamAgent + Member Agent 场景，确认 span 链路完整
• Cancel member agent 执行，确认 span 正确 close 且无 detach token error
• Member agent trace 中 input 为 leader 转发的内容而非原始用户输入
• 非 TeamAgent 场景（单 agent 直接运行）行为不变

[github-actions]

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[Eliozhang]

I have read the CLA Document and I hereby sign the CLA

[codecov]

Codecov Report

❌ Patch coverage is 63.15789% with 7 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@240e3c9). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
trpc_agent_sdk/telemetry/_trace.py	36.36364%	7 Missing ⚠️

Additional details and impacted files

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[Eliozhang]

I have read the CLA Document and I hereby sign the CLA