Full design-best-practices manual with per-engineer evidence profiles (Hashimoto, Zechner, Ronacher, Dax Raad, Willison). Use when designing architecture, making structural decisions, writing BLUEPRINT.md, or when the user says "design canon", "check the manual", or mentions DRY / duplication / orthogonality / coupling / tracer bullets / prototype vs spike / a Pragmatic Programmer principle.
