fix(rewards): register ModuleAccounting as a proper SDK invariant

x/rewards/keeper/invariants.go

@@ -9,6 +9,48 @@
 	"github.com/kiichain/kiichain/v7/x/rewards/types"
 )
 
+// RegisterInvariants registers all rewards module invariants with the invariant
+// registry. Without registration the accounting check is never executed during
+// simulation runs or crisis-module invocations.
+func RegisterInvariants(ir sdk.InvariantRegistry, k Keeper) {
+	ir.RegisterRoute(types.ModuleName, "module-accounting", ModuleAccountingInvariant(k))
+}
+
+// ModuleAccountingInvariant checks that the rewards module bank account holds at
+// least the coins tracked by the CommunityPool. A deficit means phantom funds
+// are recorded, which will cause BeginBlocker bank sends to fail and halt the chain.
+func ModuleAccountingInvariant(k Keeper) sdk.Invariant {
+	return func(ctx sdk.Context) (string, bool) {
+		rewardPool, err := k.RewardPool.Get(ctx)
+		if err != nil {
+			return sdk.FormatInvariant(
+				types.ModuleName, "module-accounting",
+				"failed to retrieve reward pool from state",
+			), true
+		}
+
+		moduleAddr := authtypes.NewModuleAddress(types.ModuleName)
+		for _, poolCoin := range rewardPool.CommunityPool {
+			required := poolCoin.Amount.TruncateInt()
+			balance := k.bankKeeper.GetBalance(ctx, moduleAddr, poolCoin.Denom).Amount
+			if balance.LT(required) {
+				return sdk.FormatInvariant(
+					types.ModuleName, "module-accounting",
+					fmt.Sprintf(
+						"rewards module bank balance is less than CommunityPool for denom %s: "+
+							"bank=%s community_pool=%s — phantom funds will cause a chain halt",
+						poolCoin.Denom, balance, required,
+					),
+				), true
+			}
+		}
+
+		return sdk.FormatInvariant(
+			types.ModuleName, "module-accounting", "rewards module accounting is consistent",
+		), false
+	}
+}
+
 // ValidateModuleAccounting checks that the rewards module account holds at least the coins tracked by the CommunityPool
 func (k Keeper) ValidateModuleAccounting(ctx sdk.Context) error {
 	rewardPool, err := k.RewardPool.Get(ctx)