OTel: parallel task dispatch emits successful chat spans without response identity or usage

Describe the bug

With metadata-only OpenTelemetry file export enabled, a prompt-mode run that dispatches two named subagents emits two chat spans that have successful status and a stop finish reason but omit all of:

• gen_ai.response.id
• gen_ai.response.model
• gen_ai.usage.input_tokens
• gen_ai.usage.output_tokens

This also occurs when the parent model is explicitly pinned, so it is not limited to --model auto.

The remaining parent and subagent chat spans in the same trace contain complete request/response model and usage fields.

Affected version

GitHub Copilot CLI 1.0.83 on macOS.

Steps to reproduce

1. Enable the file exporter and force content capture off.
2. Run prompt mode with streaming enabled and an explicitly pinned parent model.
3. In one synthetic prompt, use the task tool twice with two named agent types and explicit models.
4. Parse the resulting JSONL.

A representative trace contained one root invoke_agent, two execute_tool task spans, two nested named invoke_agent spans, and seven chat spans. Every completed-response chat had the expected provider, request model, response model, response ID, and usage. Two root-level chats had request model, streaming=true, status code 0, and finish reason stop, but no response identity or usage.

Expected behavior

Each logical completed inference should contain independently reported response identity and usage when available. An abandoned, cancelled, routing, or retry attempt should not look like a successful completed chat: it should carry an explicit attempt/outcome classification or a non-success terminal status. Consumers must not have to synthesize gen_ai.response.model from the requested model.

Privacy

The reproduction used synthetic prompts with OTEL_INSTRUMENTATION_GENAI_CAPTURE_MESSAGE_CONTENT=false. No prompt, response, repository, or credential content is included here.

まず、メタデータのみの OpenTelemetry export、streaming、明示的に固定した親モデル、および名前付きの2つの task agent を使用して prompt-mode の trace を再現します。結果の JSONL を解析し、root レベルの不完全な chat span 2つを完全な chat span と比較します。完了の条件は、完了したすべての inference が、利用可能な場合に response identity と usage を報告し、中断された試行や未完了の試行が成功としてマークされないことです。