Deductive resolution: for effects confined to one transactional store, uniqueness must arbitrate a scoped operation token before business changes. Commit its request binding and replayable outcome atomically with those changes. Recovery has two durable possibilities: neither receipt nor effect exists after rollback, or both exist after commit. An overlapping attempt waits or retries until it can replay the committed outcome or acquire the claim after rollback. A separately committed pending marker is unnecessary in this minimal design. The lost-acknowledgment case therefore needs no guess about whether execution occurred. Retaining the receipt, or reliably rejecting expired identities, bounds safe replay. If an effect crosses the transaction boundary, an outbox alone cannot prevent repeated effects; the receiver needs atomic deduplication or equivalent cooperation. These conclusions follow from a failure-case argument, not executed tests.

The design now covers rolling changes to request interpretation and fingerprint encoding. Reasoned extension: keep operation-key uniqueness independent of versions, and bind each immutable receipt to its request contract, fingerprint algorithm and result contract. Interpret an incoming attempt under its declared contract with historical defaults, then compare under the winning receipt's fingerprint rules only after a checked semantic conversion. A legacy projection that drops an added operation-defining field can falsely match; conversion must validate that field against the historical implicit value or reject. Renames and equivalent explicit defaults can replay safely. Concurrent attempts contend on the same key, and the loser compares against the committed winner regardless of its own preferred encoding version; rollback permits a new claim. Deploy readers and replay adapters for both versions before enabling new writers, and retain them for the replay lifetime. Unsupported versions must route or fail without repeating effects. Stored outcomes may be adapted for the requesting client only while preserving the original operation result. If a historical fingerprint already erased a meaningful distinction, version metadata cannot restore it; trustworthy retained evidence or conservative rejection is needed. This is deductive analysis; no implementation, files or tests were examined.