Omit X-Retry-Count header on first attempt, send only on retries

First request (retry_count=0) no longer includes the header. Retries
with retry_count > 0 continue to send X-Retry-Count: 1, 2, 3, etc.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: MichaelGHSeg

segment/analytics/request.py

@@ -54,8 +54,9 @@ def post(write_key, host=None, gzip=False, timeout=15, proxies=None, oauth_manag
     headers = {
         'Content-Type': 'application/json',
         'User-Agent': 'analytics-python/' + VERSION,
-        'X-Retry-Count': str(retry_count)
     }
+    if retry_count > 0:
+        headers['X-Retry-Count'] = str(retry_count)
 
     # Add Authorization header - prefer OAuth Bearer token, fallback to Basic auth
     if auth:

segment/analytics/test/test_request.py

@@ -120,14 +120,14 @@ def mock_post_fn(*args, **kwargs):
             self.assertEqual(headers['Authorization'], 'Bearer test_token_123')
 
     def test_x_retry_count_header(self):
-        """Test that X-Retry-Count header is included"""
+        """Test that X-Retry-Count header is omitted on first attempt and included on retries"""
         def mock_post_fn(*args, **kwargs):
             res = mock.Mock()
             res.status_code = 200
             return res
 
         with mock.patch('segment.analytics.request._session.post', side_effect=mock_post_fn) as mock_post:
-            # Test with retry_count=0 (first attempt)
+            # Test with retry_count=0 (first attempt) — header should be absent
             post('testsecret', retry_count=0, batch=[{
                 'userId': 'userId',
                 'event': 'python event',
@@ -136,8 +136,7 @@ def mock_post_fn(*args, **kwargs):
 
             args, kwargs = mock_post.call_args
             headers = kwargs['headers']
-            self.assertIn('X-Retry-Count', headers)
-            self.assertEqual(headers['X-Retry-Count'], '0')
+            self.assertNotIn('X-Retry-Count', headers)
 
         with mock.patch('segment.analytics.request._session.post', side_effect=mock_post_fn) as mock_post:
             # Test with retry_count=5