fix(worker): preserve micro-batches across DLQ records

tests/test_delivery_regressions.py

@@ -96,10 +96,30 @@ class DeliverySafetyTests(unittest.TestCase):
     def test_invalid_record_cannot_commit_past_buffered_valid_record(self):
         self.worker.process_single_message(Message(payload(), offset=0))
         self.worker.process_single_message(Message(b"{malformed", offset=1))
-        self.assertEqual(self.events[0], ("insert", 1))
+        # Micro-batching preserved: invalid record does not force premature storage flush
+        self.assertEqual([e for e in self.events if e[0] == "insert"], [])
+        self.assertEqual(self.consumer.commits, [])
+        self.assertEqual(len(self.worker.buffer), 1)
+        # Flush commits both valid and completed DLQ offsets
+        self.worker.flush_buffer()
+        self.assertEqual([e for e in self.events if e[0] == "insert"], [("insert", 1)])
         self.assertEqual(self.consumer.commits[-1], {("cdr.raw", 0): 2})
         self.assertEqual(len(self.worker.buffer), 0)
 
+    def test_alternating_valid_and_invalid_records_preserves_microbatching(self):
+        self.worker.process_single_message(Message(payload(raw_id="r1"), offset=0))
+        self.worker.process_single_message(Message(b"{bad1", offset=1))
+        self.worker.process_single_message(Message(payload(raw_id="r2"), offset=2))
+        self.worker.process_single_message(Message(b"{bad2", offset=3))
+        self.worker.process_single_message(Message(payload(raw_id="r3"), offset=4))
+        # Verify no inserts occurred yet:
+        self.assertEqual([e for e in self.events if e[0] == "insert"], [])
+        self.assertEqual(len(self.worker.buffer), 3)
+        # Explicit flush should insert all 3 valid records in a single batch
+        self.worker.flush_buffer()
+        self.assertEqual([e for e in self.events if e[0] == "insert"], [("insert", 3)])
+        self.assertEqual(self.consumer.commits[-1], {("cdr.raw", 0): 5})
+
     def test_batch_commits_only_its_explicit_partition_offsets(self):
         self.worker.process_single_message(Message(payload(), offset=4, partition=0))
         self.worker.process_single_message(Message(payload(raw_id="second"), offset=9, partition=1))