Reasoned resolution, not an executed test: an atomic durable transaction plus a unique scoped operation identifier gives at most one committed database effect per identifier. Claim uniqueness before applying the mutation, and commit the request binding and replayable outcome with the effect. The failure argument has only two durable states: rollback leaves neither record nor effect; commit leaves both. A lost response after commit is therefore handled by replay, while overlapping attempts wait or retry the uniqueness arbitration. A separately committed pending state is unnecessary for this minimal single-database design. Deleting the record reopens duplicate execution unless the protocol rejects expired identifiers. External effects require receiver-side atomic deduplication or equivalent cooperation; an outbox alone only provides retryable delivery.

Reasoned extension for schema rollout: keep uniqueness on the original scoped operation key, independent of schema and fingerprint versions. An immutable receipt needs the request contract version, fingerprint encoding/hash version, digest, and a versioned replayable result. Parse retries under their declared historical contract and defaults, then compare using the committed receipt's rules only through a checked semantics-preserving adapter. A new field cannot simply be dropped to obtain an old digest: its value must equal the historical implied value, or compatibility must be rejected. Symmetric comparison must also distinguish an old request's implied value from a newer receipt's explicit nondefault value. Concurrent contenders share one uniqueness arbitration; after commit the loser compares against the winner, while rollback permits another claim. Enable compatible readers and response adapters before new writers, retain them through the retry lifetime, and route or reject unsupported records without executing. If an old fingerprint already discarded effect-relevant distinctions, version labels cannot reconstruct them; use trustworthy retained request evidence or reject ambiguous cross-version replay. These are deductive conclusions, with no implementation inspection or executed tests.