Storage-rent repairs (version-gated): 64-bit fee arithmetic + EIP-27 re-emission carve-out

[arkadianet]

Fixes #2251. Reference implementation for discussion — draft because the activation vehicle (which release bundles block version 5) is a maintainer decision; merged as-is this changes nothing on any network, since every new branch is gated on the activated block version and unreachable until a v5 vote passes.

Specification: EIP-0048 — ergoplatform/eips#105

Problem 1: storage fee wraps in Int (#2251)

storageFeeFactor * box.bytes.length wraps in 32-bit arithmetic. At the default factor: boxes ≥ ~1,718 bytes get a negative fee, making the recreate floor exceed the box's own value — effectively rent-immune; boxes ≥ ~3,436 bytes wrap back to a small wrong positive fee. Both regions are reachable within the 4,096-byte box cap, and the wrap points move with the voted factor.

#2375 (credit @a-shannon) has the same arithmetic fix — .toLong — but ungated. Ungated, the fix flips transaction verdicts between patched and unpatched nodes: the regression-test transaction in #2375 itself is invalid under 6.0.x rules (wrapped fee is negative, so the recreate floor is box.value + |fee|) and valid under the patch. The first large-box rent claim mined by a patched node would fork it from every unpatched node, and any historical wrapped-fee claim would break resync. This PR contributes the version gate that makes the same arithmetic deployable; #2375 could equally rebase onto the gate if that ordering is preferred.

Problem 2: EIP-27 re-emission tokens make boxes permanently rent-immune

checkExpiredBox's recreate branch requires the claimed output to preserve the box's tokens (R2); verifyReemissionSpending forbids any output from carrying the re-emission token. No transaction satisfies both, and the full-consume escape is unreachable (post-activation only emission-tx outputs can carry the token, and a reward box's value always far exceeds its storage fee). So every unclaimed post-777,217 reward box still holding re-emission tokens becomes permanently exempt from storage rent once aged past the storage period — defeating rent's purpose (recirculating lost coins) for exactly the class most likely to be lost.

This is live today, not theoretical. The first such box — fbf119cbeb73cadc5866f63931599c85e26ea603b9db6d4a97914b88f1f82cfb (63 ERG reward, created 777,693) — became rent-eligible at ~1,828,900, and a mainnet node rejects both possible claim shapes via POST /transactions/check:

• token-preserving recreation → Transaction should conform EIP-27 rules
• token dropped + 12 ERG paid to pay-to-reemission → input script verification fails (checkExpiredBox → false)

Measured at height ~1,831,846: 10,917 unspent sub-100K-ERG boxes carry the token (~192K ERG, mostly recent rewards pending routine sweeps); 17 boxes / ~1,026 ERG have sat unswept for 4+ years, and the eligibility window rolls forward every block until ~3,067,199.

The change (all in checkExpiredBox, gated on blockVersion >= 5)

1. Fee in 64-bit: storageFeeFactor.toLong * box.bytes.length; legacy Int-wrap preserved verbatim below the gate (the wrap is consensus-observable — historical blocks must keep validating).
2. Re-emission carve-out: when the box carries the chain's re-emission token, the recreated output must drop it (all other registers/tokens preserved as before), and the recreation floor drops by 1 nanoErg per token — exactly the EIP-27 burn obligation. verifyReemissionSpending is unchanged: it already requires that released value be paid to the pay-to-reemission contract, so the rent path now executes the burn instead of deadlocking against it. Worked example for the real box above: recreated 50.83125 ERG (same owner/script), 12 ERG to pay-to-reemission (and thence to future miner emissions), 0.16875 ERG rent fee.

ErgoInterpreter learns the token id via a new optional constructor argument, threaded from chainSettings.reemission at the three construction sites (candidate generation, block execution, mempool validation); networks without EIP-27 pass None and are byte-identical.

Related: EIP-0033 (eips#68) tightens the full-consume branch (burn seized tokens); orthogonal and composable — under this PR the re-emission token is dropped, not seized, in both branches, which is EIP-0033-consistent.

Test plan

• testOnly org.ergoplatform.modifiers.mempool.ExpirationSpecification — 16/16: all 11 existing properties untouched and green (legacy semantics preserved), plus 5 new: first-wrap box uncollectable→fully-consumable, second-wrap box charged its true fee, token-dropped claim invalid→valid, token-kept claim valid→invalid, and an end-to-end property through ErgoState.execTransactions (production context→interpreter wiring, checkReemissionRules = true) where the repaired claim validates against the real pay-to-reemission contract and the same tx fails under legacy parameters.
• ergoWallet/test — 57/57; ergoCore/testOnly org.ergoplatform.reemission.ReemissionRulesSpec — green.

An independent Rust-node implementation of the current rules' consequence (claim builders must skip re-emission-token boxes, with the live-node rejections captured as fixtures): arkadianet/ergo#225

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