formatting, remove unnec. state vars, and better natspec

contracts/src/v0.8/ccip/pools/USDC/BurnMintWithLockReleaseFlagTokenPool.sol

@@ -1,10 +1,16 @@
-pragma solidity ^0.8.0;
+// SPDX-License-Identifier: BUSL-1.1
+pragma solidity 0.8.24;
 
 import {IBurnMintERC20} from "../../../shared/token/ERC20/IBurnMintERC20.sol";
 
 import {Pool} from "../../libraries/Pool.sol";
 import {BurnMintTokenPool} from "../BurnMintTokenPool.sol";
 
+/// @notice A standard BurnMintTokenPool with modified destPoolData so that the remote pool knows to release tokens
+/// instead of minting. This enables interoperability with HybridLockReleaseUSDCTokenPool which uses
+// the destPoolData to determine whether to mint or release tokens.
+/// @dev The only difference between this contract and BurnMintTokenPool is the destPoolData returns the
+/// abi-encoded LOCK_RELEASE_FLAG instead of an empty string.
 contract BurnMintWithLockReleaseFlagTokenPool is BurnMintTokenPool {
   /// bytes4(keccak256("NO_CCTP_USE_LOCK_RELEASE"))
   bytes4 public constant LOCK_RELEASE_FLAG = 0xfa7c07de;
@@ -20,7 +26,7 @@ contract BurnMintWithLockReleaseFlagTokenPool is BurnMintTokenPool {
   /// @dev The _validateLockOrBurn check is an essential security check
   function lockOrBurn(
     Pool.LockOrBurnInV1 calldata lockOrBurnIn
-  ) external virtual override returns (Pool.LockOrBurnOutV1 memory) {
+  ) external override returns (Pool.LockOrBurnOutV1 memory) {
     _validateLockOrBurn(lockOrBurnIn);
 
     _burn(lockOrBurnIn.amount);

contracts/src/v0.8/ccip/pools/USDC/HybridLockReleaseUSDCTokenPool.sol

@@ -49,7 +49,7 @@ contract HybridLockReleaseUSDCTokenPool is USDCTokenPool, USDCBridgeMigrator {
     address[] memory allowlist,
     address rmnProxy,
     address router
-  ) USDCTokenPool(tokenMessenger, token, allowlist, rmnProxy, router) USDCBridgeMigrator(address(token), router) {}
+  ) USDCTokenPool(tokenMessenger, token, allowlist, rmnProxy, router) USDCBridgeMigrator(address(token)) {}
 
   // ================================================================
   // │                   Incoming/Outgoing Mechanisms               |
@@ -170,10 +170,12 @@ contract HybridLockReleaseUSDCTokenPool is USDCTokenPool, USDCBridgeMigrator {
   function provideLiquidity(uint64 remoteChainSelector, uint256 amount) external {
     if (s_liquidityProvider[remoteChainSelector] != msg.sender) revert TokenPool.Unauthorized(msg.sender);
 
+    // Prevent adding liquidity to a chain which has already been migrated
     if (s_migratedChains.contains(remoteChainSelector)) {
       revert TokenLockingNotAllowedAfterMigration(remoteChainSelector);
     }
 
+    // prevent adding liquidity to a chain which has been proposed for migration
     if (remoteChainSelector == s_proposedUSDCMigrationChain) {
       revert LanePausedForCCTPMigration(remoteChainSelector);
     }
@@ -192,7 +194,7 @@ contract HybridLockReleaseUSDCTokenPool is USDCTokenPool, USDCBridgeMigrator {
   /// withdrawn on this chain, otherwise a mismatch may occur between locked token balance and remote circulating supply
   /// which may block a potential future migration of the chain to CCTP.
   function withdrawLiquidity(uint64 remoteChainSelector, uint256 amount) external onlyOwner {
-    // Circle requires a supply-lock to prevent outgoing messages once the migration process begins.
+    // A supply-lock is required to prevent outgoing messages once the migration process begins.
     // This prevents new outgoing messages once the migration has begun to ensure any the procedure runs as expected
     if (remoteChainSelector == s_proposedUSDCMigrationChain) {
       revert LanePausedForCCTPMigration(remoteChainSelector);
@@ -220,7 +222,8 @@ contract HybridLockReleaseUSDCTokenPool is USDCTokenPool, USDCBridgeMigrator {
   function transferLiquidity(address from, uint64 remoteChainSelector) external onlyOwner {
     OwnerIsCreator(from).acceptOwnership();
 
-    // Withdraw all available liquidity from the old pool.
+    // Withdraw all available liquidity from the old pool. No check is needed for pending migrations, as the old pool
+    // will revert if the migration has begun.
     uint256 withdrawAmount = HybridLockReleaseUSDCTokenPool(from).getLockedTokensForChain(remoteChainSelector);
     HybridLockReleaseUSDCTokenPool(from).withdrawLiquidity(remoteChainSelector, withdrawAmount);
 
@@ -235,7 +238,7 @@ contract HybridLockReleaseUSDCTokenPool is USDCTokenPool, USDCBridgeMigrator {
 
   /// @notice Return whether a lane should use the alternative L/R mechanism in the token pool.
   /// @param remoteChainSelector the remote chain the lane is interacting with
-  /// @return bool Return true if the alternative L/R mechanism should be used
+  /// @return bool Return true if the alternative L/R mechanism should be used, and is decided by the Owner
   function shouldUseLockRelease(uint64 remoteChainSelector) public view virtual returns (bool) {
     return s_shouldUseLockRelease[remoteChainSelector];
   }

contracts/src/v0.8/ccip/pools/USDC/USDCBridgeMigrator.sol

@@ -1,12 +1,11 @@
+// SPDX-License-Identifier: BUSL-1.1
 pragma solidity ^0.8.24;
 
 import {OwnerIsCreator} from "../../../shared/access/OwnerIsCreator.sol";
 import {IBurnMintERC20} from "../../../shared/token/ERC20/IBurnMintERC20.sol";
 
 import {EnumerableSet} from "../../../vendor/openzeppelin-solidity/v4.8.3/contracts/utils/structs/EnumerableSet.sol";
 
-import {Router} from "../../Router.sol";
-
 /// @notice Allows migration of a lane in a token pool from Lock/Release to CCTP supported Burn/Mint. Contract
 /// functionality is based on hard requirements defined by Circle to allow for future CCTP compatibility
 /// https://github.com/circlefin/stablecoin-evm/blob/master/doc/bridged_USDC_standard.md
@@ -26,8 +25,7 @@ abstract contract USDCBridgeMigrator is OwnerIsCreator {
   error NoMigrationProposalPending();
   error InvalidChainSelector();
 
-  IBurnMintERC20 internal immutable i_USDC;
-  Router internal immutable i_router;
+  IBurnMintERC20 private immutable i_USDC;
 
   address internal s_circleUSDCMigrator;
   uint64 internal s_proposedUSDCMigrationChain;
@@ -39,9 +37,8 @@ abstract contract USDCBridgeMigrator is OwnerIsCreator {
 
   EnumerableSet.UintSet internal s_migratedChains;
 
-  constructor(address token, address router) {
+  constructor(address token) {
     i_USDC = IBurnMintERC20(token);
-    i_router = Router(router);
   }
 
   /// @notice Burn USDC locked for a specific lane so that destination USDC can be converted from

contracts/src/v0.8/ccip/test/pools/BurnMintWithLockReleaseFlagTokenPool.t.sol

@@ -3,7 +3,6 @@ pragma solidity 0.8.24;
 
 import {Pool} from "../../libraries/Pool.sol";
 import {RateLimiter} from "../../libraries/RateLimiter.sol";
-
 import {TokenPool} from "../../pools/TokenPool.sol";
 import {BurnMintWithLockReleaseFlagTokenPool} from "../../pools/USDC/BurnMintWithLockReleaseFlagTokenPool.sol";
 import {BurnMintSetup} from "./BurnMintSetup.t.sol";