Build a trace specification document per feature - defines the trace shape (root span + child spans + key attributes per OpenTelemetry semantic conventions) that production code MUST emit. The spec drives both implementation reviews AND trace-assertion tests, so a single declarative document is the source of truth for what observability "looks like" for a feature. Use before instrumenting a new feature, when existing spans have grown organically with no agreed shape, or after an incident where a debugging session stalled on missing span attributes.