Refactor scope (maintainer)

In scope

• internal module restructuring
• improved tracing and replay tooling
• configuration cleanup (without breaking the contract)
• tests that tighten invariants

Out of scope (without explicit design work)

• new product features unrelated to auditability
• stateful cross-run storage
• dynamic user-defined pipeline graphs

If you want to expand scope, start with a design note and update the spec.