agentfootprint/dist/esm/memory/entry/decay.js

The explainable agent framework — backtrack a wrong answer to the exact context that caused it (evidence, not guesses). Built on footprintjs.

/**
 * Maximum compounding boost from `accessCount`. Caps the access term at
 * ~10×; tuned against the intuition that "a heavily used memory is important
 * but not more important than an exact-match recent memory."
 */
const MAX_BOOST_MULTIPLIER = 10;
/**
 * Compute the decay factor for an entry at a given moment.
 *
 * @param entry   The memory entry to score. Must have `lastAccessedAt` and
 *                `accessCount` set (storage adapters populate these).
 * @param now     The reference time (unix ms). Defaults to `Date.now()`.
 * @param policy  Optional override — when omitted, uses `entry.decayPolicy`.
 *                Stages can pass a stage-wide default so entries without a
 *                per-entry policy still decay consistently. If neither is
 *                set, returns 1.0 (no decay applied).
 *
 * @returns Scaling factor in `[0, MAX_BOOST_MULTIPLIER]` — stages multiply
 *          this against their existing relevance score.
 */
export function computeDecayFactor(entry, now = Date.now(), policy) {
    const effective = policy ?? entry.decayPolicy;
    if (!effective)
        return 1;
    const ageMs = Math.max(0, now - entry.lastAccessedAt);
    // Time factor: 2^(-age / halfLife).
    //   - halfLifeMs === 0 models "instant decay" — any age > 0 ⇒ 0.
    //     Without this guard, 0/0 → NaN poisons the result.
    //   - halfLifeMs > 0 uses the standard exponential.
    let timeFactor;
    if (effective.halfLifeMs === 0) {
        timeFactor = ageMs === 0 ? 1 : 0;
    }
    else {
        timeFactor = Math.pow(2, -ageMs / effective.halfLifeMs);
    }
    // Access factor: clamp `accessBoost` to a positive value before
    // exponentiating. A negative or zero boost would either produce NaN
    // (fractional powers of negatives) or collapse relevance to 0 for any
    // accessCount > 0 — neither is the intended semantic. The documented
    // contract is accessBoost > 0; this clamp hardens against misconfigs.
    const safeBoost = Math.max(Number.EPSILON, effective.accessBoost);
    const rawBoost = Math.pow(safeBoost, entry.accessCount);
    const accessFactor = Math.min(rawBoost, MAX_BOOST_MULTIPLIER);
    return timeFactor * accessFactor;
}
/**
 * Compute decay for multiple entries in one call. Order-preserving; returns
 * one factor per entry. Convenience for stages that rank whole batches.
 */
export function computeDecayFactors(entries, now = Date.now(), policy) {
    return entries.map((e) => computeDecayFactor(e, now, policy));
}
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