fix: scale reserve amount based on decimals

packages/policy-management/src/policies/SecureMintPolicy.sol

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: BUSL-1.1
 pragma solidity 0.8.26;
 
-import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
+import {IERC20Metadata} from "@openzeppelin/contracts/token/ERC20/extensions/IERC20Metadata.sol";
 import {AggregatorV3Interface} from "@chainlink/contracts/src/v0.8/shared/interfaces/AggregatorV3Interface.sol";
 import {IPolicyEngine} from "@chainlink/policy-management/interfaces/IPolicyEngine.sol";
 import {Policy} from "@chainlink/policy-management/core/Policy.sol";
@@ -214,14 +214,14 @@ contract SecureMintPolicy is Policy {
     } else if ($.reserveMarginMode == ReserveMarginMode.PositivePercentage) {
       // WARNING: May round to zero for very small reserves with high margins
       // e.g., reserves=1, margin=9999 → 1 * 1 / BASIS_POINTS = 0
-      return reserves * (BASIS_POINTS - $.reserveMarginAmount) / BASIS_POINTS;
+      return (reserves * (BASIS_POINTS - $.reserveMarginAmount)) / BASIS_POINTS;
     } else if ($.reserveMarginMode == ReserveMarginMode.PositiveAbsolute) {
       if (reserves < $.reserveMarginAmount) {
         return 0;
       }
       return reserves - $.reserveMarginAmount;
     } else if ($.reserveMarginMode == ReserveMarginMode.NegativePercentage) {
-      return reserves * (BASIS_POINTS + $.reserveMarginAmount) / BASIS_POINTS;
+      return (reserves * (BASIS_POINTS + $.reserveMarginAmount)) / BASIS_POINTS;
     } else if ($.reserveMarginMode == ReserveMarginMode.NegativeAbsolute) {
       return reserves + $.reserveMarginAmount;
     }
@@ -261,11 +261,30 @@ contract SecureMintPolicy is Policy {
       revert IPolicyEngine.PolicyRejected("reserve data is stale");
     }
 
-    IERC20 token = IERC20(subject);
-    if (amount + token.totalSupply() > totalMintableSupply(uint256(reserve))) {
+    IERC20Metadata token = IERC20Metadata(subject);
+    uint8 tokenDecimals = _tokenDecimals(token);
+    uint8 feedDecimals = $.reservesFeed.decimals();
+    // Scale reserve to token decimals even when the token omits metadata
+    uint256 scaledReserve = uint256(reserve);
+    if (tokenDecimals > feedDecimals) {
+      uint256 factor = 10 ** (uint256(tokenDecimals) - uint256(feedDecimals));
+      scaledReserve *= factor;
+    } else if (tokenDecimals < feedDecimals) {
+      uint256 factor = 10 ** (uint256(feedDecimals) - uint256(tokenDecimals));
+      scaledReserve /= factor;
+    }
+    if (amount + token.totalSupply() > totalMintableSupply(scaledReserve)) {
       revert IPolicyEngine.PolicyRejected("mint would exceed available reserves");
     }
 
     return IPolicyEngine.PolicyResult.Continue;
   }
+
+  function _tokenDecimals(IERC20Metadata token) private view returns (uint8) {
+    try token.decimals() returns (uint8 value) {
+      return value;
+    } catch {
+      return 18;
+    }
+  }
 }