Fix dropped Inkling reasoning at stream end (#31787)

test/registered/unit/parser/test_reasoning_parser.py

@@ -249,6 +249,24 @@ class TestInklingDetector(CustomTestCase):
                 content += detector.parse_streaming_increment(chunk).normal_text
             self.assertEqual(content, " worldnext", msg=f"chunks={chunks!r}")
 
+    def test_finish_flushes_reasoning_truncated_before_end_token(self):
+        """Bug regression: with stream_reasoning=False the detector buffers the
+        thinking block and only flushes it on a control/end token. When
+        generation is cut mid-block (e.g. max_tokens) the stream ends with no
+        end token, so the buffered trace was dropped entirely; finish() must
+        emit it, matching the non-streaming detect_and_parse path."""
+        detector = InklingDetector(stream_reasoning=False)
+        source = "<|message_model|><|content_thinking|>truncated thinking"
+        streamed_reasoning = ""
+        for char in source:
+            streamed_reasoning += detector.parse_streaming_increment(
+                char
+            ).reasoning_text
+        # The block never closed, so nothing surfaces mid-stream.
+        self.assertEqual(streamed_reasoning, "")
+        # finish() flushes the buffered trace instead of dropping it.
+        self.assertEqual(detector.finish().reasoning_text, "truncated thinking")
+
 
 class TestKimiDetector(CustomTestCase):
     def setUp(self):