Explicit Identity Across Boundaries

Never rely on “latest” or “current” when crossing process or async boundaries.

Pattern

Pass explicit identifiers through the entire pipeline. “Most recent” is a race condition.

DO

• Pass --session-id $ID when spawning processes
• Store IDs in state files for later correlation
• Use full UUIDs, not partial matches
• Keep different ID types separate (don’t collapse concepts)

DON’T

• Query for “most recent session” at execution time
• Assume the current context will still be current after await/spawn
• Collapse different ID types:
  • session_id = Claude Code session (human-facing)
  • root_span_id = Braintrust trace (query key)
  • turn_span_id = Braintrust turn within session

Example

// BAD: race condition at session boundaries
spawn('analyzer', ['--learn'])  // defaults to "most recent"

// GOOD: explicit identity
spawn('analyzer', ['--learn', '--session-id', input.session_id])

Source Sessions

• 1c21e6c8: Defined session_id vs root_span_id distinction
• 6a9f2d7a: Fixed wrong-session attribution via explicit passing
• a541f08a: Confirmed pattern prevents race at session boundaries