Klever-Go is the Go implementation of the Klever blockchain protocol. Prior to 1.7.19, Klever-Go allows a mint-role holder to bypass a finite per-nonce MaxSupply on the semi-fungible token add-quantity path. In core/kapp/systemAccount/systemAcount.go, SFTAddCirculation performed meta.Circulation += amount before evaluating whether Circulation exceeded MaxSupply, without checking for signed int64 overflow. A large positive raw Amount supplied through processSemiFungibleAddQuantity in core/kapp/kda/mint.go can wrap Circulation negative, causing the signed maximum-supply comparison to pass and crediting approximately MaxInt64 units while corrupting the on-chain counter. The fungible path is not affected because its MintedValue <= 0 guard detects the overflow. The correction uses the consensus activation flag FixMarketBuyOverflow. This issue is fixed in version 1.7.19.

Affected: Go: github.com/klever-io/klever-go

## Summary On the SFT add-quantity path the only supply bound is `SFTAddCirculation`, which does `meta.Circulation += amount` with **no overflow guard**, then checks `if meta.Circulation > meta.MaxSupply && meta.MaxSupply != 0`. If `amount` overflows `int64` and wraps **negative**, `negative > MaxSupply` is false, the cap check passes, the function returns `nil`, and the balance credit stands. A nonce created with a finite `MaxSupply` (e.g. 1000) can thus be minted to ~`MaxInt64` tokens in one transaction. The fungible mint path is **not** vulnerable — it has a post-increment `MintedValue <= 0` guard that the SFT path lacks.

## Affected code - `core/kapp/systemAccount/systemAcount.go:132-138` (`SFTAddCirculation`, the unguarded `+=`). - Caller: `core/kapp/kda/mint.go:247-283` (`processSemiFungibleAddQuantity`); contrast guard `mint.go:289`.

## Impact A mint-role holder mints ~9.2e18 units of a nonce whose declared `MaxSupply` is small, with no authorized debit, and corrupts the on-chain `Circulation` counter to a negative value (misleading any market/indexer that reads it).

## Reachability Mint-role holder (asset owner or an address granted the role). The mint `Amount` is a raw `int64` from the contract with no upstream upper bound.

## Proof of concept

### Unit test `TestExploit_SFTCirculationOverflowBypassesCap` creates a nonce capped at `MaxSupply = 1000`, seeds `Circulation = 5`, then calls `SFTAddCirculation(MaxInt64)`. The call returns `nil` (cap bypassed) and `Cir…