Every framework treats a retrieved fact as timeless. This ledger stamps each fact with a signed provenance stamp and answers, before an agent acts: is it still in date for an action of this irreversibility?
Register a retrieved fact and get a signed FactStamp (value hash, source, decay class, born_at, provenance hops). Half-lives are fitted per (source, fact class) from the source's own observed change intervals instead of a hand-set TTL; below 3 observations a labeled prior applies and is surfaced as a prior, never as a fitted value. Freshness checks return FRESH / STALE / EXPIRED scaled by the declared action class (draft 2.0 / standard 1.0 / irreversible 0.5 half-lives) - the same fact can be FRESH for a draft and STALE for a payment. Age survives compaction, handoff, and hibernation: a copied fact arrives older, never newborn; a stripped stamp reads UNKNOWN-AGE and a forged or future-born stamp reads INVALID, neither is ever FRESH. A completed task's staleness receipt lists which load-bearing facts were past half-life when acted on, hash-chained per operator.Stated plainly: no gate that does not re-query at action time reaches zero stale actions - the residual is the measured within-allowance floor (7.9% standard / 4.7% irreversible), and refresh re-queries on an expired fact are the customer's own retrieval or a metered x402 pass-through, never bundled into a flat tier.
Prices: Per-check $0.005/check (x402) · Fleet ledger $9/mo per agent (up to 1,000 tracked facts: stamp issuance, ledger storage, scheduled force-refresh sweeps, checks against own tracked facts) · Staleness receipt $0.01/receipt. First 100 freshness checks free, one time per operator (account and payer wallet enforced); receipts drawn while trial credit remains are free. No perpetual free tier.
API: https://textforagents.com/products/belief-half-life-fact-expiry-ledger/ · Docs: https://textforagents.com/products/belief-half-life-fact-expiry-ledger/openapi.json · Support: support@textforagents.com