Replay: re-running an execution with the same contract/ABI; deterministic checks equality, ND checks envelope. Replayable does not mean cached; it means re-execution is possible under the same contract.
Comparison: structured diff between executions (overlap, recall delta, rank instability), exact vs approximate.
Execution fidelity: mode expressing how close results adhere to exact semantics (deterministic exact vs ND approximate).
Stability: deterministic surfaces are frozen; ND/ANN is stable_bounded at the contract level but experimental in behavior (outcomes vary within declared envelopes).
Reproducibility: ability to recreate execution behavior under the same contract/plan/randomness (deterministic ⇒ equality, ND ⇒ bounded envelope).