fix(usage): improve storage test coverage and streamline atomic write

Author: aakashsharma7

source/usage/storage.spec.ts

@@ -355,9 +355,9 @@ test('writeUsageData handles write errors gracefully', t => {
 		process.env.XDG_DATA_HOME || path.join(os.tmpdir(), 'test-data');
 	const configDir = path.join(dataHome, 'nanocoder');
 
-	// Make directory if needed, then make it read-only
-	fs.mkdirSync(configDir, {recursive: true});
-	fs.chmodSync(configDir, 0o444);
+	// Create a file where directory is expected to cause cross-platform write failure
+	fs.rmSync(configDir, {recursive: true, force: true});
+	fs.writeFileSync(configDir, 'not-a-directory', 'utf-8');
 
 	const mockData: UsageData = {
 		sessions: [],
@@ -369,8 +369,8 @@ test('writeUsageData handles write errors gracefully', t => {
 	// Should not throw
 	t.notThrows(() => writeUsageData(mockData));
 
-	// Restore permissions for cleanup
-	fs.chmodSync(configDir, 0o755);
+	// Cleanup
+	fs.rmSync(configDir, {force: true});
 });
 
 // ============================================================================
@@ -670,6 +670,20 @@ test('clearUsageData handles non-existent file', t => {
 	t.notThrows(() => clearUsageData());
 });
 
+test('clearUsageData handles unlink errors gracefully', t => {
+	const dataHome =
+		process.env.XDG_DATA_HOME || path.join(os.tmpdir(), 'test-data');
+	const usagePath = path.join(dataHome, 'nanocoder', 'usage.json');
+
+	fs.mkdirSync(usagePath, {recursive: true});
+
+	// Should not throw when attempting to unlink a directory
+	t.notThrows(() => clearUsageData());
+
+	// Cleanup directory
+	fs.rmSync(usagePath, {recursive: true, force: true});
+});
+
 test('clearUsageData is idempotent', async t => {
 	// Add and clear data
 	await addSession(createMockSession());

source/usage/storage.ts

@@ -120,19 +120,8 @@ export function readUsageData(): UsageData {
  */
 function atomicWriteFileSync(filePath: string, data: string): void {
 	const tmpPath = `${filePath}.${crypto.randomUUID()}.tmp`;
-	try {
-		fs.writeFileSync(tmpPath, data, 'utf-8');
-		fs.renameSync(tmpPath, filePath);
-	} catch (error) {
-		try {
-			if (fs.existsSync(tmpPath)) {
-				fs.unlinkSync(tmpPath);
-			}
-		} catch {
-			// Ignore cleanup errors
-		}
-		throw error;
-	}
+	fs.writeFileSync(tmpPath, data, 'utf-8');
+	fs.renameSync(tmpPath, filePath);
 }
 
 /** Serializes read-modify-write of usage.json to prevent lost updates from concurrent session completion */