Interventional Memory: A Pre-Registered Randomised Crossover Measuring Whether Agent Memory Changes Agent Behaviour

THIS DEPOSIT IS A PRE-REGISTRATION: a study design, hypotheses and analysis plan fixed and published BEFORE the study runs. No outcome data exists at the time of deposit and no randomised epoch has been executed. Zenodo offers no dedicated resource type for pre-registrations, so this record is typed as a preprint and labelled here instead. Retrieval metrics score representation, not decision. This study measures whether the composition of an agent's memory changes what the agent does, using a fleet-wide randomised crossover on live production traffic rather than a curated benchmark. Epochs of 24 h are assigned to arms by a public randomness beacon whose round is declared before it exists; outcomes are adjudicated blind by a frozen multi-model panel; the primary outcome is repeated-failure density per session-hour. N = 174 epochs, powered for relative effects of 30% or more, sized on the upper confidence limit of the intra-cluster correlation (ICC 0.0985, 95% CI [0.0570; 0.1814]) rather than on its point estimate. The treatment writes one memory chunk per adjudicated-failure episode, in both arms, and differs only in a serving-time salience boost, so the contrast isolates weighting from creation. Measurement performed before registration establishes what the boost can reach. A chunk written from a failure episode enters a brief only through two coverage slots, and its reach depends on the severity it carries and on its age. Under the locked designation rule — the treatment boosts exactly one chunk per opportunity, the easiest to reach — the lowest dose in the band reaches 58% of opportunities and bounds the achievable effect at 60%, against a minimum detectable effect of 30%; the top dose reaches all of them, the modal S1 failure included. An earlier specification that boosted every match reached 19.8% and bounded the effect below the MDE, which would have made the primary hypothesis untestable; that is recorded in the deposit rather than removed. The three doses are pooled as one treatment arm for the primary contrast, so the dose-response comparison between them runs at 29 epochs per dose and is powered only for effects near 49% — a null there is reported as not detectable, never as evidence against the mechanism. These bounds are declared here rather than discovered later. VERIFIABILITY. The deposit carries the SHA-256 manifests of the frozen episode corpus, of the locked extractor and of the adjudication prompt; the three sampling seeds, each derived from a drand beacon round that was declared in a public commit before that round existed; and every analysis script, all deterministic and standard-library only. Anyone can recompute the sizing grid, the carry-over bound, the p95 winsorisation points and the intra-cluster correlation from the published inputs. WHAT IS DELIBERATELY ABSENT. No episode content is deposited. The adjudicated corpus contains real production work and stays out; this record points to it by hash. The only JSON Lines file included, positive-control.jsonl, holds six synthetic control episodes written by hand. All parameters were fixed on a historical corpus with no arm assignment, before any randomised epoch existed. Companion repository: https://github.com/totobusnello/memoria-nox (paper2-interventional/).