Where Does the Why Live?

Rationale (the 'why') is well-homed at authoring time — it's the recorded why-not-what conversation and the grilling session — but orphaned for future readers: AI-native methods delete the PRD, bury discussion in PRs, and the prototype shows what not why; code explicitly can't hold it, context files hold policy not product-rationale, and only the richer-artifact axis partly answers it