braintrust-tracing

Comprehensive guide to tracing Claude Code sessions in Braintrust, including sub-agent correlation. SessionStart doesn't receive the Task prompt. We tried injecting trace context into Task prompts via PreToolUse: But SessionStart only receives session metadata, not the modified prompt. The injected context is lost. Task spans in parent session contain everything: SubagentStop hook receives the sub-agent's session_id : Current state: Sub-agents create orphaned traces (new root_span_id ). Correlation method: Future solution (not yet implemented): This would link: Task.agentId + Task.child_session_id -> orphaned trace root_span_id Each session file contains: No traces appearing: Sub-agents not linking: Missing spans: State corruption: Attempted: Inject trace context via PreToolUse into Task prompts. Result: Failed - SessionStart only receives session metadata, not the prompt. Discovery: Task spans already contain rich sub-agent data: Current correlation path: Future work: Write child_session_id to Task span metadata from PostToolUse after SubagentStop.