feat: treat maxBidPrice == 0 as no effective cap

src/periphery/validationHooks/MaxBidPriceValidationHook.sol

@@ -8,7 +8,10 @@ import {IERC165} from '@openzeppelin/contracts/utils/introspection/IERC165.sol';
 /// @title IMaxBidPriceValidationHook
 interface IMaxBidPriceValidationHook is IValidationHookIntrospection {
     /// @notice The maximum bid price allowed for a continuous clearing auction
-    /// @return the max bid price allowed, in Q96 form
+    /// @dev A value of 0 means no effective cap: implementations MUST treat it as "unset" and accept
+    ///      every bid price. A literal cap of 0 is unreachable anyway, since a bid must price strictly
+    ///      above the clearing price, which starts at a floor of at least `ConstantsLib.MIN_FLOOR_PRICE`.
+    /// @return the max bid price allowed, in Q96 form, or 0 for no cap
     function maxBidPrice() external view returns (uint256);
 }
 
@@ -17,6 +20,7 @@ interface IMaxBidPriceValidationHook is IValidationHookIntrospection {
 /// @dev Since CCA requires all bids to be strictly above the current clearing price, using this hook
 ///      will prevent new bids from being placed once the maximum bid price is reached. All existing
 ///      bids will remain active and partially fill for the remaining supply of tokens.
+/// @dev Constructing with `_maxBidPrice = 0` disables the cap rather than rejecting every bid.
 contract MaxBidPriceValidationHook is IMaxBidPriceValidationHook, ValidationHookIntrospection {
     uint256 public immutable maxBidPrice;
 
@@ -29,7 +33,7 @@ contract MaxBidPriceValidationHook is IMaxBidPriceValidationHook, ValidationHook
 
     /// @inheritdoc IValidationHook
     function validate(uint256 maxPrice, uint128, address, address, bytes calldata) external view {
-        if (maxPrice > maxBidPrice) revert MaxBidPriceExceeded();
+        if (maxBidPrice != 0 && maxPrice > maxBidPrice) revert MaxBidPriceExceeded();
     }
 
     /// @inheritdoc IERC165

test/btt/periphery/validationHooks/maxBidPriceValidationHook.t.sol

@@ -17,17 +17,34 @@ contract MaxBidPriceValidationHookTest is BttBase {
         assertEq(hook.maxBidPrice(), _maxBidPrice);
     }
 
+    function test_WhenMaxBidPriceIsZero(
+        uint256 _maxPrice,
+        uint128 _amount,
+        address _owner,
+        address _sender,
+        bytes calldata _hookData
+    ) external {
+        // it does not revert
+
+        MaxBidPriceValidationHook hook = new MaxBidPriceValidationHook(0);
+        hook.validate(_maxPrice, _amount, _owner, _sender, _hookData);
+    }
+
+    modifier whenMaxBidPriceIsNotZero() {
+        _;
+    }
+
     function test_WhenMaxPriceGTMaxBidPrice(
         uint256 _maxBidPrice,
         uint256 _maxPrice,
         uint128 _amount,
         address _owner,
         address _sender,
         bytes calldata _hookData
-    ) external {
+    ) external whenMaxBidPriceIsNotZero {
         // it reverts with {MaxBidPriceExceeded}
 
-        _maxBidPrice = bound(_maxBidPrice, 0, type(uint256).max - 1);
+        _maxBidPrice = bound(_maxBidPrice, 1, type(uint256).max - 1);
         _maxPrice = bound(_maxPrice, _maxBidPrice + 1, type(uint256).max);
 
         MaxBidPriceValidationHook hook = new MaxBidPriceValidationHook(_maxBidPrice);
@@ -46,9 +63,11 @@ contract MaxBidPriceValidationHookTest is BttBase {
         address _owner,
         address _sender,
         bytes calldata _hookData
-    ) external whenMaxPriceLTEMaxBidPrice {
+    ) external whenMaxBidPriceIsNotZero whenMaxPriceLTEMaxBidPrice {
         // it does not revert
 
+        _maxBidPrice = bound(_maxBidPrice, 1, type(uint256).max);
+
         MaxBidPriceValidationHook hook = new MaxBidPriceValidationHook(_maxBidPrice);
         hook.validate(_maxBidPrice, _amount, _owner, _sender, _hookData);
     }
@@ -60,7 +79,7 @@ contract MaxBidPriceValidationHookTest is BttBase {
         address _owner,
         address _sender,
         bytes calldata _hookData
-    ) external whenMaxPriceLTEMaxBidPrice {
+    ) external whenMaxBidPriceIsNotZero whenMaxPriceLTEMaxBidPrice {
         // it does not revert
 
         _maxBidPrice = bound(_maxBidPrice, 1, type(uint256).max);

test/btt/periphery/validationHooks/maxBidPriceValidationHook.tree

@@ -2,13 +2,16 @@ MaxBidPriceValidationHookTest
 ├── constructor
 │   └── it sets maxBidPrice
 ├── validate
-│   ├── when maxPrice GT maxBidPrice
-│   │   └── it reverts with {MaxBidPriceExceeded}
-│   └── when maxPrice LTE maxBidPrice
-│       ├── when maxPrice EQ maxBidPrice
-│       │   └── it does not revert
-│       └── when maxPrice LT maxBidPrice
-│           └── it does not revert
+│   ├── when maxBidPrice is 0
+│   │   └── it does not revert
+│   └── when maxBidPrice is not 0
+│       ├── when maxPrice GT maxBidPrice
+│       │   └── it reverts with {MaxBidPriceExceeded}
+│       └── when maxPrice LTE maxBidPrice
+│           ├── when maxPrice EQ maxBidPrice
+│           │   └── it does not revert
+│           └── when maxPrice LT maxBidPrice
+│               └── it does not revert
 └── supportsInterface
     ├── when interface is supported
     │   └── it returns true