Supply hard-cap invariant: assert 21M DERO ceiling at coinbase verification (fixes #123) - #124
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Supply hard-cap invariant: assert 21M DERO ceiling at coinbase verification (fixes #123)#124liqdmetal wants to merge 1 commit into
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…at coinbase verification DERO's emission curve (CalcSupply) is a pure function of height that converges to ~20.89M DERO, but the 21M cap (the Bitcoin-parallel hard cap) is not enforced anywhere in consensus: Verify_Transaction_Coinbase was an IsCoinbase()-only no-op, and the coinbase mint (full_reward = base_reward + fees) had no overflow guard. Adds two layers: 1. config.MAX_SUPPLY = 21,000,000 DERO (2.1e12 atomic) — the hard cap. 2. Verify_Transaction_Coinbase asserts CalcSupply(height) <= MAX_SUPPLY, so any regression in CalcBlockReward / BaseReward / PREMINE that would inflate supply past the cap is rejected at verification — not a behavior change on the real curve, purely a defensive invariant. 3. Coinbase emission guards full_reward against uint64 wraparound and the cap (panic on overflow, which can only trip on a curve regression). Tests (blockchain/supply_cap_test.go): supply under cap across the full curve (genesis → 160 years, monotonic), reward converges to zero without underflow. Terminal supply 20.89M vs 21.00M cap = 0.51% margin — the assert is meaningful but never false-positives on the real curve. This is a consensus change (hard fork) — same category as K0 B1/B2.
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Summary
Adds a consensus supply hard-cap invariant asserting DERO's 21M-DERO ceiling at coinbase verification.
The finding
Verify_Transaction_Coinbasewas anIsCoinbase()-only no-op. The 21Mhard cap (the Bitcoin-parallel supply ceiling) was not enforced anywhere in
consensus — the
deroHardCapAtomicconstant inproof/proof_validation.goonly sanity-checks individual proof amounts, never chain supply. The coinbase
mint (
full_reward := base_reward + fees) had no overflow guard.DERO's emission curve is a pure function of height (
CalcSupply) thatconverges to ~20.89M DERO, so the real curve never approaches the cap —
but there is no invariant that would catch a regression in
CalcBlockReward/BaseReward/PREMINE(a bad>>shift, an accidentalreward inflation, uint64 wraparound) that would silently mint past the cap.
The change
config.MAX_SUPPLY = 21_000_000 * 100_000— the hard cap (2.1e12 atomic).Verify_Transaction_CoinbaseassertsCalcSupply(height) <= MAX_SUPPLY— every node recomputes the supply identically, so this is deterministic
and only trips on a curve regression. Purely a defensive invariant on the
real curve.
full_rewardagainst uint64 wraparound andthe cap (panic on overflow — can only fire on a curve regression).
Tests
TestCalcSupplyUnderHardCap— supply under the cap at every sampled height(genesis → 160 years), and monotonic.
TestCalcBlockRewardConvergence— reward non-increasing per epoch,converges to zero without underflow.
Terminal supply 20.89M vs cap 21.00M = 0.51% margin — the assert
is meaningful (it would catch an inflation bug) but never false-positives on
the real curve.
Consensus status
Hard-fork (consensus) change, same category as K0 Fix B1/B2. On the real
curve it changes nothing — it only adds rejection for a state that can only
arise from an emission bug.
Branch
fix/supply-hardcap, based oncommunity-dev.