feat(ctb): Remove redundant check in LivenessModule

test(ctb): Add test for get75PercentThreshold

packages/contracts-bedrock/.gas-snapshot

@@ -305,6 +305,11 @@ LegacyERC20ETH_Test:test_transferFrom_doesNotExist_reverts() (gas: 12957)
 LegacyERC20ETH_Test:test_transfer_doesNotExist_reverts() (gas: 10755)
 LegacyMessagePasser_Test:test_passMessageToL1_succeeds() (gas: 34524)
 LibPosition_Test:test_pos_correctness_succeeds() (gas: 38689)
+LivenessGuard_ShowLiveness_Test:test_showLiveness_succeeds() (gas: 51339)
+LivenessModule_Get75PercentThreshold_Test:test_get75PercentThreshold_Works() (gas: 26339)
+LivenessModule_RemoveOwner_Test:test_removeOwner_allOwners_succeeds() (gas: 159764)
+LivenessModule_RemoveOwner_Test:test_removeOwner_oneOwner_succeeds() (gas: 109028)
+LivnessGuard_CheckTx_Test:test_checkTransaction_succeeds() (gas: 160454)
 MIPS_Test:test_add_succeeds() (gas: 122932)
 MIPS_Test:test_addiSign_succeeds() (gas: 122923)
 MIPS_Test:test_addi_succeeds() (gas: 123120)

packages/contracts-bedrock/semver-lock.json

@@ -18,6 +18,8 @@
   "src/L2/L2StandardBridge.sol": "0x284ebf5569c75d98f2d1920a276d1116524399355708c4a60ea5892283c56719",
   "src/L2/L2ToL1MessagePasser.sol": "0xafc710b4d320ef450586d96a61cbd58cac814cb3b0c4fdc280eace3efdcdf321",
   "src/L2/SequencerFeeVault.sol": "0x883e434a69b4789997a4a9a32060dbbd2e12db6f1970927f1310820336119575",
+  "src/Safe/LivenessGuard.sol": "0x31b4ecc88c982490243ab42914c3de75e5acfa421ffc0ea0d0f0997dcc0341b5",
+  "src/Safe/LivenessModule.sol": "0xb8c8178c1f4f78eed4777846a40eda6a3a0c1710085822d92267339ae752799b",
   "src/dispute/BlockOracle.sol": "0x7e724b1ee0116dfd744f556e6237af449c2f40c6426d6f1462ae2a47589283bb",
   "src/dispute/DisputeGameFactory.sol": "0xfdfa141408d7f8de7e230ff4bef088e30d0e4d569ca743d60d292abdd21ff270",
   "src/dispute/FaultDisputeGame.sol": "0x0766707ab32338a6586c2340ddfbfd4e9023eeb9dfa3ef87e4b404fb0260479f",

packages/contracts-bedrock/src/Safe/LivenessModule.sol

 // SPDX-License-Identifier: MIT
 pragma solidity 0.8.15;
 
-import { Safe } from "safe-contracts/Safe.sol";
+import { Safe, OwnerManager } from "safe-contracts/Safe.sol";
 import { Enum } from "safe-contracts/common/Enum.sol";
 import { OwnerManager } from "safe-contracts/base/OwnerManager.sol";
 import { LivenessGuard } from "src/Safe/LivenessGuard.sol";
@@ -29,6 +29,9 @@ contract LivenessModule is ISemver {
     /// @notice The fallback owner of the Safe
     address public fallbackOwner;
 
+    /// @notice The address of the first owner in the linked list of owners
+    address internal constant SENTINEL_OWNERS = address(0x1);
+
     /// @notice Semantic version.
     /// @custom:semver 1.0.0
     string public constant version = "1.0.0";
@@ -120,15 +123,15 @@ contract LivenessModule is ISemver {
         address[] memory owners = safe.getOwners();
         uint256 numOwners = owners.length;
         require(
-            (numOwners == 1 && owners[0] == fallbackOwner) || (numOwners >= minOwners),
-            "LivenessModule: Safe must have at least 1 owner or minOwners"
+            (numOwners >= minOwners) || (numOwners == 1 && owners[0] == fallbackOwner),
+            "LivenessModule: Safe must have the minimum number of owners, or be owned solely by the fallback owner"
         );
 
         // Check that the threshold is correct
         uint256 threshold = safe.getThreshold();
         require(
-            threshold == get75PercentThreshold(numOwners) || (numOwners == 1 && threshold == 1),
-            "LivenessModule: threshold must be 75% of the number of owners, or 1 if there is only 1 owner"
+            threshold == get75PercentThreshold(numOwners),
+            "LivenessModule: threshold must be 75% of the number of owners"
         );
     }
 
@@ -137,7 +140,7 @@ contract LivenessModule is ISemver {
         for (uint256 i = 0; i < owners.length; i++) {
             if (owners[i] == owner) {
                 if (i == 0) {
-                    prevOwner_ = address(0x1); // OwnerManager.SENTINEL_OWNERS
+                    prevOwner_ = SENTINEL_OWNERS;
                     break;
                 }
                 prevOwner_ = owners[i - 1];
@@ -147,6 +150,7 @@ contract LivenessModule is ISemver {
     }
 
     /// @notice For a given number of owners, return the lowest threshold which is greater than 75.
+    ///         Note: this function returns 1 for numOwners == 1.
     function get75PercentThreshold(uint256 _numOwners) public pure returns (uint256 threshold_) {
         threshold_ = (_numOwners * 75 + 99) / 100;
     }

packages/contracts-bedrock/test/LivenessModule.t.sol

@@ -36,6 +36,33 @@ contract LivnessModule_TestInit is Test, SafeTestTools {
     }
 }
 
+contract LivenessModule_Get75PercentThreshold_Test is LivnessModule_TestInit {
+    /// @dev check the return values of the get75PercentThreshold function against manually
+    ///      calculated values.
+    function test_get75PercentThreshold_Works() external {
+        assertEq(livenessModule.get75PercentThreshold(20), 15);
+        assertEq(livenessModule.get75PercentThreshold(19), 15);
+        assertEq(livenessModule.get75PercentThreshold(18), 14);
+        assertEq(livenessModule.get75PercentThreshold(17), 13);
+        assertEq(livenessModule.get75PercentThreshold(16), 12);
+        assertEq(livenessModule.get75PercentThreshold(15), 12);
+        assertEq(livenessModule.get75PercentThreshold(14), 11);
+        assertEq(livenessModule.get75PercentThreshold(13), 10);
+        assertEq(livenessModule.get75PercentThreshold(12), 9);
+        assertEq(livenessModule.get75PercentThreshold(11), 9);
+        assertEq(livenessModule.get75PercentThreshold(10), 8);
+        assertEq(livenessModule.get75PercentThreshold(9), 7);
+        assertEq(livenessModule.get75PercentThreshold(8), 6);
+        assertEq(livenessModule.get75PercentThreshold(7), 6);
+        assertEq(livenessModule.get75PercentThreshold(6), 5);
+        assertEq(livenessModule.get75PercentThreshold(5), 4);
+        assertEq(livenessModule.get75PercentThreshold(4), 3);
+        assertEq(livenessModule.get75PercentThreshold(3), 3);
+        assertEq(livenessModule.get75PercentThreshold(2), 2);
+        assertEq(livenessModule.get75PercentThreshold(1), 1);
+    }
+}
+
 contract LivenessModule_RemoveOwner_Test is LivnessModule_TestInit {
     function test_removeOwner_oneOwner_succeeds() external {
         uint256 ownersBefore = safeInstance.owners.length;