Preserve existing batcher re-entry guard in flush

Co-Authored-By: gpt-5.3-codex-high <noreply@anthropic.com>

Author: cursoragent

sentry_sdk/_batcher.py

@@ -115,11 +115,12 @@ def kill(self) -> None:
         self._flusher = None
 
     def flush(self) -> None:
+        old_flag = getattr(self._active, "flag", False)
         self._active.flag = True
         try:
             self._flush()
         finally:
-            self._active.flag = False
+            self._active.flag = old_flag
 
     def _add_to_envelope(self, envelope: "Envelope") -> None:
         envelope.add_item(

tests/test_batcher.py

@@ -0,0 +1,28 @@
+from sentry_sdk._batcher import Batcher
+
+
+class DummyBatcher(Batcher[int]):
+    def __init__(self) -> None:
+        super().__init__(
+            capture_func=lambda envelope: None,
+            record_lost_func=lambda *args, **kwargs: None,
+        )
+        self.flush_calls = 0
+
+    def _flush(self):
+        self.flush_calls += 1
+        return None
+
+    @staticmethod
+    def _to_transport_format(item):
+        return item
+
+
+def test_flush_restores_existing_reentry_guard():
+    batcher = DummyBatcher()
+    batcher._active.flag = True
+
+    batcher.flush()
+
+    assert batcher._active.flag is True
+    assert batcher.flush_calls == 1