followerSince: save timestamp

src/stamps/FollowerSinceStamp.sol

@@ -16,6 +16,9 @@ contract FollowerSinceStamp is Stamp, IFollowerSinceStamp {
 	/// @inheritdoc IFollowerSinceStamp
 	string public override FOLLOWED;
 
+	/// @notice Mapping to store the "since" timestamp for each follower
+	mapping(address => uint256) public followerSince;
+
 	/// @notice Initializes the FollowerSinceStamp contract
 	/// @param _signer The address authorized to sign mint requests
 	/// @param _platform The platform where the following relationship exists
@@ -52,6 +55,9 @@ contract FollowerSinceStamp is Stamp, IFollowerSinceStamp {
 
 		uint256 tokenId = _mintStamp(msg.sender, encodedData, signature, deadline);
 
+		// Store the "since" timestamp for the follower
+		followerSince[msg.sender] = since;
+
 		emit FollowerSince(PLATFORM, FOLLOWED, follower, since, tokenId, msg.sender);
 
 		return tokenId;

src/stamps/interfaces/IFollowerSinceStamp.sol

@@ -20,19 +20,22 @@ interface IFollowerSinceStamp is IStamp {
 	/// @notice The identifier of the followed account on the platform
 	function FOLLOWED() external view returns (string memory);
 
+	/// @notice Mapping to store the "since" timestamp for each follower
+	function followerSince(address follower) external view returns (uint256);
+
 	/// @notice Mints a new follower since stamp
 	/// @dev This function should verify the signature and mint a new stamp
 	/// @param follower The identifier of the follower on the platform
 	/// @param since The timestamp since when the user has been following
 	/// @param deadline The timestamp after which the signature is no longer valid
-	/// @param signature The signature authorizing the minting, likely signed by a trusted authority
-	/// @return The ID of the newly minted stamp
+	/// @param signature The signature authorizing the minting, signed by a trusted authority
+	/// @return stampId The ID of the newly minted stamp
 	function mintStamp(
 		string calldata follower,
 		uint256 since,
 		uint256 deadline,
 		bytes calldata signature
-	) external returns (uint256);
+	) external returns (uint256 stampId);
 
 	/// @notice Emitted when a new follower since stamp is minted
 	/// @param platform The platform identifier