Architectural debt log

• Layer gap: Services vs orchestration remain split for public surface stability. Remove when CLI/tests can depend directly on _orchestrator.
• Policy flattening: Temporary removal of core/policy; revisit when compliance rules need isolation.
• Error-as-value: Only one path uses ExecutionOutcome; widen once callers migrate away from exceptions.
• Replay semantics: ND replay now re-executes and may diverge; formalize envelopes before widening backend set.