feat(e2e): add login flow test cases

- Add login-flow.spec.ts with 4 test cases:
  - First-time user login via GitHub OAuth
  - CLI responsiveness after login
  - /usage command after login
  - Logout and re-login flow

Author: brandonkachen

e2e/flows/login-flow.spec.ts

@@ -0,0 +1,190 @@
+/**
+ * End-to-End Login Flow Tests
+ * 
+ * Tests the complete login flow: CLI → Browser → GitHub OAuth → Callback → CLI
+ * 
+ * Prerequisites:
+ * - Docker must be running
+ * - SDK must be built: cd sdk && bun run build
+ * - Playwright browsers installed: bunx playwright install chromium
+ * - GitHub test credentials configured
+ * 
+ * Run with: cd e2e && bun run test
+ */
+
+import { test, expect } from '@playwright/test'
+import { hasRequiredCredentials, logSkipReason } from '../utils/env'
+
+// Check credentials at module load time
+const hasCredentials = hasRequiredCredentials()
+
+if (!hasCredentials) {
+  logSkipReason('GitHub test credentials not configured (GH_TEST_EMAIL, GH_TEST_PASSWORD)')
+}
+
+// Only define tests if credentials are available
+if (hasCredentials) {
+  test.describe('E2E Login Flow', () => {
+    test.describe.configure({ mode: 'serial' }) // Run tests serially
+
+    // Lazy-load the heavy fixtures only when tests actually run
+    let testContext: typeof import('../fixtures/test-context') | null = null
+    
+    test.beforeAll(async () => {
+      // Dynamically import the test context (which imports infrastructure)
+      testContext = await import('../fixtures/test-context')
+      
+      const prereqs = testContext.checkPrerequisites()
+      if (!prereqs.ready) {
+        logSkipReason(prereqs.reason!)
+        test.skip(true, prereqs.reason)
+      }
+    })
+
+    test('first-time user can login via GitHub OAuth', async ({ page }) => {
+      test.skip(!testContext, 'Test context not initialized')
+    
+      const ctx = await testContext!.createE2ETestContext('first-login')
+    
+      try {
+        const { createCLISession, completeOAuth } = ctx
+
+        // 1. Launch CLI without existing credentials
+        console.log('[Test] Launching CLI...')
+        const cli = await createCLISession()
+
+        // 2. Wait for login prompt - auto-login triggers automatically via CODEBUFF_E2E_NO_BROWSER
+        console.log('[Test] Waiting for login prompt (auto-login will trigger)...')
+        await cli.waitForText(/Press ENTER|login|sign in/i, { timeout: 30000 })
+
+        // 3. Wait for login URL (auto-triggered after 1 second delay)
+        console.log('[Test] Waiting for login URL...')
+        const loginUrl = await cli.waitForLoginUrl(30000)
+        console.log(`[Test] Got login URL: ${loginUrl}`)
+
+        expect(loginUrl).toContain('auth_code=')
+
+        // 5. Complete OAuth in browser
+        console.log('[Test] Starting OAuth flow in browser...')
+        await completeOAuth(page, loginUrl)
+
+        // 6. Verify CLI detected successful login
+        console.log('[Test] Waiting for CLI to detect login...')
+        await cli.waitForText(/directory|welcome|logged in/i, { timeout: 45000 })
+
+        const cliText = await cli.text()
+        // CLI should show main interface after successful login
+        expect(cliText.toLowerCase()).toMatch(/directory|welcome|logged in/)
+
+        console.log('[Test] Login flow completed successfully!')
+      } finally {
+        await ctx.infra.cleanup()
+      }
+    })
+
+    test('CLI remains responsive after login', async ({ page }) => {
+      test.skip(!testContext, 'Test context not initialized')
+    
+      const ctx = await testContext!.createE2ETestContext('responsive')
+    
+      try {
+        const { createCLISession, completeOAuth } = ctx
+
+        // Complete login first (auto-login via CODEBUFF_E2E_NO_BROWSER)
+        const cli = await createCLISession()
+        await cli.waitForText(/Press ENTER|login|sign in/i, { timeout: 30000 })
+        const loginUrl = await cli.waitForLoginUrl(30000)
+        await completeOAuth(page, loginUrl)
+        await cli.waitForText(/directory/i, { timeout: 45000 })
+
+        // Test that CLI is responsive
+        console.log('[Test] Verifying CLI is responsive...')
+        await cli.type('hello test')
+        await cli.waitForText('hello test', { timeout: 5000 })
+
+        const text = await cli.text()
+        expect(text).toContain('hello test')
+
+        console.log('[Test] CLI is responsive after login!')
+      } finally {
+        await ctx.infra.cleanup()
+      }
+    })
+
+    test('/usage command works after login', async ({ page }) => {
+      test.skip(!testContext, 'Test context not initialized')
+    
+      const ctx = await testContext!.createE2ETestContext('usage-cmd')
+    
+      try {
+        const { createCLISession, completeOAuth } = ctx
+
+        // Complete login first (auto-login via CODEBUFF_E2E_NO_BROWSER)
+        const cli = await createCLISession()
+        await cli.waitForText(/Press ENTER|login|sign in/i, { timeout: 30000 })
+        const loginUrl = await cli.waitForLoginUrl(30000)
+        await completeOAuth(page, loginUrl)
+        await cli.waitForText(/directory/i, { timeout: 45000 })
+
+        // Test /usage command
+        console.log('[Test] Testing /usage command...')
+        await cli.type('/usage')
+        await cli.press('enter')
+
+        await cli.waitForText(/credit|usage|balance/i, { timeout: 15000 })
+
+        const text = await cli.text()
+        expect(text.toLowerCase()).toMatch(/credit|usage|balance/)
+
+        console.log('[Test] /usage command works!')
+      } finally {
+        await ctx.infra.cleanup()
+      }
+    })
+
+    test('logout and re-login flow works', async ({ page }) => {
+      test.skip(!testContext, 'Test context not initialized')
+    
+      const ctx = await testContext!.createE2ETestContext('logout-relogin')
+    
+      try {
+        const { createCLISession, completeOAuth } = ctx
+
+        // Complete initial login (auto-login via CODEBUFF_E2E_NO_BROWSER)
+        const cli = await createCLISession()
+        await cli.waitForText(/Press ENTER|login|sign in/i, { timeout: 30000 })
+        let loginUrl = await cli.waitForLoginUrl(30000)
+        await completeOAuth(page, loginUrl)
+        await cli.waitForText(/directory/i, { timeout: 45000 })
+
+        // Logout
+        console.log('[Test] Testing logout...')
+        await cli.type('/logout')
+        await cli.press('enter')
+
+        // Wait for logout to complete and login prompt to reappear
+        await cli.waitForText(/login|sign in|logged out/i, { timeout: 15000 })
+
+        // Re-login
+        console.log('[Test] Re-logging in...')
+        await cli.press('enter')
+        loginUrl = await cli.waitForLoginUrl(30000)
+        await completeOAuth(page, loginUrl)
+        await cli.waitForText(/directory/i, { timeout: 45000 })
+
+        const text = await cli.text()
+        expect(text.toLowerCase()).toContain('directory')
+
+        console.log('[Test] Logout and re-login flow works!')
+      } finally {
+        await ctx.infra.cleanup()
+      }
+    })
+  })
+} else {
+  // No credentials - register a single skipped test to show in the report
+  test.describe('E2E Login Flow', () => {
+    test.skip(true, 'GitHub test credentials not configured (GH_TEST_EMAIL, GH_TEST_PASSWORD)')
+    test('skipped - credentials not configured', () => {})
+  })
+}