diff --git a/scripts/smoke-test-update-version-logic.js b/scripts/smoke-test-update-version-logic.js
index 1848a16..127c660 100644
--- a/scripts/smoke-test-update-version-logic.js
+++ b/scripts/smoke-test-update-version-logic.js
@@ -4,7 +4,7 @@ const {
   normalizeUpdateVersion,
   compareUpdateVersions,
   isNewerUpdateVersion
-} = require(path.join(process.cwd(), 'dist', 'update-version-utils.js'));
+} = require(path.join(process.cwd(), 'dist', 'main', 'domain', 'update-version-utils.js'));
 
 function run() {
   const failures = [];
diff --git a/src/main.ts b/src/main.ts
index 925840c..eb496c9 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -5,7 +5,7 @@ import { spawn, ChildProcess, execSync, spawnSync } from 'child_process';
 import { connect as tlsConnect, TLSSocket } from 'node:tls';
 import axios from 'axios';
 import { autoUpdater } from 'electron-updater';
-import { compareUpdateVersions, isNewerUpdateVersion, normalizeUpdateVersion } from './update-version-utils';
+import { compareUpdateVersions, isNewerUpdateVersion, normalizeUpdateVersion } from './main/domain/update-version-utils';
 import { CustomClip, MergeGroupItem, MergeGroup, QueueItem, DownloadProgress, DownloadResult } from './types';
 import {
     setDebugLogFn, initToolDirs,
diff --git a/src/main/domain/update-version-utils.test.ts b/src/main/domain/update-version-utils.test.ts
new file mode 100644
index 0000000..d27f8fc
--- /dev/null
+++ b/src/main/domain/update-version-utils.test.ts
@@ -0,0 +1,66 @@
+import { test, expect, describe } from 'vitest';
+import {
+    normalizeUpdateVersion,
+    compareUpdateVersions,
+    isNewerUpdateVersion,
+} from './update-version-utils';
+
+describe('normalizeUpdateVersion', () => {
+    test('strips v-prefix lowercase', () => {
+        expect(normalizeUpdateVersion('v1.2.3')).toBe('1.2.3');
+    });
+    test('strips V-prefix uppercase', () => {
+        expect(normalizeUpdateVersion('V1.2.3')).toBe('1.2.3');
+    });
+    test('trims whitespace', () => {
+        expect(normalizeUpdateVersion(' 1.2.3 ')).toBe('1.2.3');
+    });
+    test('handles null and undefined as empty string', () => {
+        expect(normalizeUpdateVersion(null)).toBe('');
+        expect(normalizeUpdateVersion(undefined)).toBe('');
+    });
+    test('passes plain version unchanged', () => {
+        expect(normalizeUpdateVersion('4.6.155')).toBe('4.6.155');
+    });
+});
+
+describe('compareUpdateVersions', () => {
+    test('older < newer in same minor', () => {
+        expect(compareUpdateVersions('4.1.10', '4.1.18')).toBeLessThan(0);
+    });
+    test('newer > older in same minor', () => {
+        expect(compareUpdateVersions('4.1.18', '4.1.10')).toBeGreaterThan(0);
+    });
+    test('equal versions return 0', () => {
+        expect(compareUpdateVersions('4.6.155', '4.6.155')).toBe(0);
+    });
+    test('v-prefix is normalized away', () => {
+        expect(compareUpdateVersions('v4.1.12', '4.1.12')).toBe(0);
+    });
+    test('extra trailing part is newer', () => {
+        expect(compareUpdateVersions('4.1.12', '4.1.12.1')).toBeLessThan(0);
+    });
+    test('major bump wins', () => {
+        expect(compareUpdateVersions('5.0.0', '4.99.99')).toBeGreaterThan(0);
+    });
+    test('null versions sort lowest', () => {
+        expect(compareUpdateVersions(null, '1.0.0')).toBeLessThan(0);
+        expect(compareUpdateVersions('1.0.0', null)).toBeGreaterThan(0);
+    });
+    test('both null returns 0', () => {
+        expect(compareUpdateVersions(null, null)).toBe(0);
+        expect(compareUpdateVersions('', '')).toBe(0);
+    });
+});
+
+describe('isNewerUpdateVersion', () => {
+    test('strictly newer returns true', () => {
+        expect(isNewerUpdateVersion('4.1.18', '4.1.17')).toBe(true);
+    });
+    test('equal returns false', () => {
+        expect(isNewerUpdateVersion('4.1.18', '4.1.18')).toBe(false);
+    });
+    test('older returns false', () => {
+        expect(isNewerUpdateVersion('4.1.17', '4.1.18')).toBe(false);
+    });
+});
diff --git a/src/update-version-utils.ts b/src/main/domain/update-version-utils.ts
similarity index 100%
rename from src/update-version-utils.ts
rename to src/main/domain/update-version-utils.ts