feat(fleet-identity): add version() function for upgrade verification

src/swarms/FleetIdentityUpgradeable.sol

@@ -732,6 +732,15 @@ contract FleetIdentityUpgradeable is
         return (uint32(countryCode) << uint32(ADMIN_SHIFT)) | uint32(adminCode);
     }
 
+    // ══════════════════════════════════════════════
+    // Version
+    // ══════════════════════════════════════════════
+
+    /// @notice Returns the contract version for upgrade verification.
+    function version() external pure virtual returns (string memory) {
+        return "1.0.0";
+    }
+
     // ══════════════════════════════════════════════
     // UUPS Authorization
     // ══════════════════════════════════════════════

test/upgrade-demo/TestUpgradeOnAnvil.s.sol

@@ -17,7 +17,7 @@ import {SwarmRegistryL1Upgradeable} from "../../src/swarms/SwarmRegistryL1Upgrad
 
 /// @dev Mock V2 that adds version() - inherits from V1 to preserve storage layout
 contract FleetIdentityUpgradeableV2 is FleetIdentityUpgradeable {
-    function version() external pure returns (string memory) {
+    function version() external pure override returns (string memory) {
         return "2.0.0";
     }
 }

test/upgradeable/UpgradeableContracts.t.sol

@@ -61,8 +61,8 @@ contract FleetIdentityUpgradeableV2Mock is FleetIdentityUpgradeable {
         fleetMetadata[tokenId] = metadata;
     }
 
-    function version() external pure returns (string memory) {
-        return "V2";
+    function version() external pure override returns (string memory) {
+        return "2.0.0";
     }
 }
 
@@ -259,6 +259,10 @@ contract UpgradeableContractsTest is Test {
         assertEq(fleetIdentity.symbol(), "SFID");
     }
 
+    function test_FleetIdentity_Version() public view {
+        assertEq(fleetIdentity.version(), "1.0.0");
+    }
+
     function test_FleetIdentity_CannotReinitialize() public {
         vm.expectRevert(Initializable.InvalidInitialization.selector);
         fleetIdentity.initialize(attacker, address(bondToken), BASE_BOND, 0);
@@ -289,7 +293,7 @@ contract UpgradeableContractsTest is Test {
 
         // Verify upgrade
         FleetIdentityUpgradeableV2Mock v2 = FleetIdentityUpgradeableV2Mock(fleetIdentityProxy);
-        assertEq(v2.version(), "V2");
+        assertEq(v2.version(), "2.0.0");
         assertGt(v2.v2InitializedAt(), 0);
 
         // Verify old state preserved
@@ -301,6 +305,16 @@ contract UpgradeableContractsTest is Test {
         assertEq(v2.fleetMetadata(tokenId), "metadata://test");
     }
 
+    function test_FleetIdentity_VersionChangesAfterUpgrade() public {
+        assertEq(fleetIdentity.version(), "1.0.0");
+
+        FleetIdentityUpgradeableV2Mock v2Impl = new FleetIdentityUpgradeableV2Mock();
+        vm.prank(owner);
+        fleetIdentity.upgradeToAndCall(address(v2Impl), "");
+
+        assertEq(FleetIdentityUpgradeableV2Mock(fleetIdentityProxy).version(), "2.0.0");
+    }
+
     function test_FleetIdentity_NonOwnerCannotUpgrade() public {
         FleetIdentityUpgradeableV2Mock v2Impl = new FleetIdentityUpgradeableV2Mock();