diff --git a/src/platforms/slack/ensure-auth.ts b/src/platforms/slack/ensure-auth.ts
index f389f7e..1bc398d 100644
--- a/src/platforms/slack/ensure-auth.ts
+++ b/src/platforms/slack/ensure-auth.ts
@@ -27,7 +27,9 @@ export async function ensureSlackAuth(): Promise<void> {
       await credManager.setCurrentWorkspace(validWorkspaces[0].workspace_id)
     }
   } catch (error) {
-    if ((error as NodeJS.ErrnoException).code === 'EBUSY' || (error as Error).message.includes('locking the cookie')) {
+    const code = typeof error === 'object' && error !== null ? (error as NodeJS.ErrnoException).code : undefined
+    const message = error instanceof Error ? error.message : String(error)
+    if (code === 'EBUSY' || message.includes('locking the cookie')) {
       throw error
     }
     // Silently ignore other extraction errors (e.g. Slack not installed)
diff --git a/src/platforms/slack/token-extractor.test.ts b/src/platforms/slack/token-extractor.test.ts
index 190ba5b..24e5d70 100644
--- a/src/platforms/slack/token-extractor.test.ts
+++ b/src/platforms/slack/token-extractor.test.ts
@@ -153,10 +153,12 @@ describe('TokenExtractor Windows DPAPI', () => {
     })
 
     // when — then
-    const extractor = new TokenExtractor('darwin', slackDir)
-    await expect(extractor.extract()).rejects.toThrow('Quit the Slack app completely and try again')
-
-    copyFileSyncSpy.mockRestore()
+    try {
+      const extractor = new TokenExtractor('darwin', slackDir)
+      await expect(extractor.extract()).rejects.toThrow('Quit the Slack app completely and try again')
+    } finally {
+      copyFileSyncSpy.mockRestore()
+    }
   })
 
   test('extract decrypts Windows v10 cookies end-to-end with mocked DPAPI', async () => {