Braintrust Tracing for Claude Code Comprehensive guide to tracing Claude Code sessions in Braintrust, including sub-agent correlation. Architecture Overview Hook Event Flow | Hook | Trigger | Creates | Key Fields | |------|---------|---------|------------| | SessionStart | Session begins | Root span | , | | UserPromptSubmit | User sends prompt | Turn span | , | | PreToolUse | Before tool runs | (modifies Task prompts) | | | PostToolUse | After tool runs | Tool span | , , | | Stop | Turn completes | LLM spans | , , | | SubagentStop | Sub-agent finishes | (no span) | of sub-agent | | SessionEnd…