Bug: Langfuse "Unknown observation type: event" fallback warning

[Abernaughty]

Description

Langfuse logs Unknown observation type: event, falling back to span during orchestrator runs. This appears when the OTEL bridge encounters observation types it doesn't natively support, and silently downgrades them to spans.

Log Output

Unknown observation type: event, falling back to span

Appears 2–3 times per task run, likely corresponding to SSE events or custom trace entries emitted by the orchestrator.

Impact

• Cosmetic only — all observations still appear in the Langfuse trace UI
• The fallback to span is a reasonable degradation; no data is lost
• Adds noise to FastAPI logs

Possible Fixes

1. Map custom events to spans explicitly — emit them as spans with an event attribute tag instead of using the event observation type
2. Langfuse config — check if newer SDK versions support the event type natively
3. Log level filter — suppress at the logging config level if the message is expected

Related

See also #102 (OTEL context detach warning) — both are Langfuse/OTEL integration noise.