Use when planning or replanning engineering missions that create, change, port, migrate, integrate, or preserve durable codebase behavior across UI, API, CLI, background jobs, data/migrations, libraries, or operator workflows. Defines investigation, scope inventory, coherent VAL-* contracts, evidence floors, multi-target task topology, engineering validation, root-cause patching, and durable guidance. For pure metric search, use optimization-mission-playbook instead.