beacon source realm

ChainHash, PeriodSeconds and RoundsPerDay are re-exported from p/splash/bls254, which holds the ONE copy of drand evmnet's identity. They are re-exported rather than restated so that a realm needing the cadence does not have to import a crypto package to get it, and so that there is still exactly one place the numbers are written down.

MaxEstimateStaleBlocks is maxEstimateStaleBlocks, exported so that a consumer can state its own tolerance as a fraction of the backstop, assert a relation to it at COMPILE TIME (r/splash/arcade/raffle does), or tell a user how fresh the beacon has to be. A const, so no caller can move it.

AnchorHeight is the chain height of the last relay that raised the estimate's anchor. Panics if no round has ever been published. See anchorHeight and StaleBlocks.

EstimateIsUsable reports whether EstimatedLatestRound would return rather than panic. A read, so a caller can check before committing to a transaction that would revert.

EstimatedLatestRound is this realm's best estimate of the round drand is currently on. Panics if no round has ever been published.

IT IS AN ESTIMATE AND THE NAME SAYS SO. There is no way to know the true current round on-chain: proving "round r is not signed yet" needs an UPPER bound on elapsed real time, published rounds give only a LOWER bound, and chain height gives none at all because a halted chain advances no height while drand advances 28800 rounds a day. Every round-number pin in this system is therefore an assumption about this chain keeping pace with drand, and this function is where that assumption lives instead of being spread across three realms.

THE CONSTRUCTION: take anchorScaled — the highest round-versus-height intercept any relay has ever evidenced — and read this height off that line. It is exactly latestRound at the moment latestRound is relayed. READ anchorScaled BEFORE CHANGING THIS: extrapolating from the highest round's own publication height instead is the obvious simplification, and it is exploitable.

WHY IT IS STRICTLY BETTER THAN Latest() FOR A PIN. A consumer pinning Latest() + offset measures its offset from whenever somebody last happened to relay something, so the pin drifts backwards in real time as the beacon goes quiet — and the raffle's offset is exactly one day larger than a week, so a single day of staleness puts the pinned round's randomness on the public API BEFORE the week's ticket sales close, which is finding 10's last-buyer attack verbatim. The correction removes that failure entirely in the honest case.

THE ERROR IS BOUNDED BY REFUSAL, AND THAT IS NEW AS OF THE STALENESS BOUND. The conversion assumes A = 86400/blocksPerDay = 3.29998 s blocks, so its error is S*(A - B) seconds of drand time for S blocks since the anchor was last raised and a real average block time B — 2.4 hours at one day of S and a 10% drift in B, NOT the ~14 minutes this comment claimed until the figure was re-derived (that number divided by the period twice; see maxEstimateStaleBlocks and AUDIT-2026-09-28.md finding 13). Unbounded S makes it unbounded in BOTH directions, so this function now REFUSES above maxEstimateStaleBlocks rather than returning a number nobody can put a bound on. What the refusal costs, and why it is nevertheless right, is at maxEstimateStaleBlocks and in AUDIT-2026-09-28.md finding 12.

MONOTONE IN HEIGHT AND NEVER BELOW latestRound: ChainHeight() only rises and anchorHeight/anchorScaled never move except upward, so the correction term is never negative.

EstimatedLatestRoundWithin is EstimatedLatestRound with the caller's own staleness tolerance, in blocks, for a consumer whose real-time margin is finer than the backstop's. r/splash/arcade/duel uses it: its bound round is 300 SECONDS out, and the backstop admits 2.4 hours of error.

IT CAN ONLY EVER ASK FOR LESS. A tolerance above maxEstimateStaleBlocks is refused, so this is not a way around the backstop — a consumer can tighten the bound and cannot loosen it. Read maxEstimateStaleBlocks for why the two-level shape exists at all.

Panics if no round has ever been published, if the tolerance is not positive, if it exceeds the backstop, or if the beacon is staler than the tolerance allows.

Latest returns the highest published round and its randomness. Panics if no round has been published yet.

"HIGHEST PUBLISHED", WHICH IS NOT "CURRENT". Under an on-demand record nothing relays routinely, so this can be arbitrarily stale — a week old, a year old. A CONSUMER PINNING A FUTURE ROUND MUST NOT USE THIS AS "now": use EstimatedLatestRound, which corrects for the staleness using a clock no relayer controls. Reading this as the current round is exactly how the raffle's round pin would silently re-open AUDIT-2026-09-28.md finding 10.

LatestPublishedAtHeight returns the chain height at which the highest published round was relayed. Panics if no round has been published yet.

Publish verifies sig for round against drand evmnet's group key and stores it. PERMISSIONLESS: anyone may relay any round, because validity is what matters and not the sender. Panics if the round is already published or the signature does not verify — including if sigHex is not valid hex, which is just another shape of "not a valid signature".

THE ROUND NUMBER IS THE MESSAGE and the caller supplies nothing else: the signed digest is keccak256 of the round as a big-endian uint64 (bls254.DrandRoundMessage), so a relayer cannot choose what a round's randomness is, only whether to relay it. The chain is UNCHAINED, so no previous signature is needed and any round verifies on its own.

bls254.VerifyDrand, NOT bls254.Verify. The two implement different schemes and each rejects every signature of the other; Verify is the retired SPLASH try-and-increment scheme and is left untouched, still exercised by p/splash/bls254's own suite.

COST: 16,970,375 gas measured on this toolchain (zz_gas_test.gno), 0.57% of the 3e9 block limit — about 176 to a block. Of it, 13,396,451 is bls254.VerifyDrand and 12,004,207 of THAT is the RFC 9380 hash-to-curve rather than the pairing: 90% of the verification, 71% of the whole Publish. (CORRECTED 2026-09-30: this said "98%", which was the pre-optimisation ratio; DRAND-MIGRATION.md section 9.5.) It fits with a wide margin, and it is also the reason this realm cannot mirror drand.

A RELAYER CANNOT PUSH latestRound INTO THE FUTURE, and a great deal now rests on that. Under the SPLASH key one Publish of a far-future round moved latest arbitrarily far in a single transaction, which was the operator-triggered half of AUDIT-2026-09-28.md finding 7. drand cannot sign a round whose time has not come, so latestRound is bounded above by drand's real head, and that attack is dead.

Published reports whether a round has been published.

WHAT IT MEANS NOW: "somebody has relayed this round to this chain". NOT "this round's randomness exists" (it may exist on drand and simply not be here yet) and NOT "this round's randomness is obtainable" (it always is, from drand). Every caller that treats false as "lost" is wrong; see DRAND-MIGRATION.md section 3.

PublishedAtHeight returns the chain height at which a round was relayed. Panics if the round has not been published.

Randomness returns sha256(signature) for a published round, hex-encoded. Panics if the round has not been published.

This is drand's own derivation, not one of ours: the "randomness" field /public/<r> serves is exactly sha256 of the signature it serves beside it, which makes every real round an independent oracle for this function. testdata's fixtures were checked against it.

Render implements the realm's human-readable view.

StaleBlocks is how far the chain has moved since the last relay that RAISED the estimate's anchor: the one distance every error in this realm's extrapolation is proportional to. Panics if no round has ever been published.

IT IS NOT "BLOCKS SINCE THE LAST Publish", and the difference is the whole soundness argument — read anchorHeight. A relay that does not raise the anchor does not reduce the error, and "blocks since the last Publish" is resettable by anyone for the cost of relaying any one of drand's ~2.1e7 public past rounds.

EXPORTED SO A CONSUMER OR A FRONT END CAN SEE THE REFUSAL COMING rather than discover it as a panic in the middle of a settlement, and so a caller can decide to relay a round first. Clamped at zero: a negative distance is unreachable on chain (height only rises, anchorHeight only moves to a then-current height) and arises only under `gno test`, where ChainHeight() resets between test functions while realm state persists — DRAND-MIGRATION.md section 9.7.