GeezerVison

Propagates a caller-supplied end_user_id onto trace spans automatically, so agents get end-user attribution without threading the value through their own code.

The identifier arrives as a new optional field on the four ACP routes (seen in companion agentex PR scaleapi/scale-agentex#386)

The framework then includes this field as a context var. Sync agent handling is simple, however temporal require a interceptor that harvests it from the workflow's start and signal args and rehydrates it per activity for async ones.

Trace.start_span then merges it into span.data, which has to happen at span construction rather than at export because export runs on a shared background task that no longer knows which request a given span came from.

Extensibility: Adding another request-scoped value (tenant id, correlation id, experiment variant) means widening one contextvar behind an allowlist rather than touching the tracing code.