fix: don't trigger content-type transition on finish-only stream events

_current_content_type now returns None for events with no message content
(e.g. {"finishReason": "COMPLETE"}). The transition branch in
_transform_v2_event is skipped when event_content_type is None, so a
finish-only event after a thinking block no longer opens a spurious empty
text block before emitting content-end.

Author: fede-kamel

src/cohere/oci_client.py

@@ -953,21 +953,21 @@ def _emit_v2_event(event: typing.Dict[str, typing.Any]) -> bytes:
     def _emit_v1_event(event: typing.Dict[str, typing.Any]) -> bytes:
         return json.dumps(event).encode("utf-8") + b"\n"
 
-    def _current_content_type(oci_event: typing.Dict[str, typing.Any]) -> str:
+    def _current_content_type(oci_event: typing.Dict[str, typing.Any]) -> typing.Optional[str]:
         message = oci_event.get("message")
         if isinstance(message, dict):
             content_list = message.get("content")
             if content_list and isinstance(content_list, list) and len(content_list) > 0:
                 oci_type = content_list[0].get("type", "TEXT").upper()
-                if oci_type == "THINKING":
-                    return "thinking"
-        return "text"
+                return "thinking" if oci_type == "THINKING" else "text"
+        return None  # finish-only or non-content event — don't trigger a type transition
 
     def _transform_v2_event(oci_event: typing.Dict[str, typing.Any]) -> typing.Iterator[bytes]:
         nonlocal emitted_start, emitted_content_end, current_content_type, current_content_index
         nonlocal final_finish_reason, final_usage
 
         event_content_type = _current_content_type(oci_event)
+        open_type = event_content_type or "text"
 
         if not emitted_start:
             yield _emit_v2_event(
@@ -981,12 +981,12 @@ def _transform_v2_event(oci_event: typing.Dict[str, typing.Any]) -> typing.Itera
                 {
                     "type": "content-start",
                     "index": current_content_index,
-                    "delta": {"message": {"content": {"type": event_content_type}}},
+                    "delta": {"message": {"content": {"type": open_type}}},
                 }
             )
             emitted_start = True
-            current_content_type = event_content_type
-        elif current_content_type != event_content_type:
+            current_content_type = open_type
+        elif event_content_type is not None and current_content_type != event_content_type:
             yield _emit_v2_event({"type": "content-end", "index": current_content_index})
             current_content_index += 1
             yield _emit_v2_event(

tests/test_oci_client.py

@@ -954,6 +954,32 @@ def test_stream_wrapper_emits_new_content_block_on_thinking_transition(self):
         self.assertEqual(events[5]["type"], "content-delta")
         self.assertEqual(events[5]["index"], 1)
 
+    def test_stream_wrapper_no_spurious_block_on_finish_only_event(self):
+        """Finish-only event after thinking block must not open a spurious empty text block."""
+        import json
+        from cohere.oci_client import transform_oci_stream_wrapper
+
+        chunks = [
+            b'data: {"message": {"content": [{"type": "THINKING", "thinking": "Reasoning..."}]}}\n',
+            b'data: {"finishReason": "COMPLETE"}\n',
+            b"data: [DONE]\n",
+        ]
+
+        events = []
+        for raw in transform_oci_stream_wrapper(iter(chunks), "chat", is_v2=True):
+            line = raw.decode("utf-8").strip()
+            if line.startswith("data: "):
+                events.append(json.loads(line[6:]))
+
+        types = [e["type"] for e in events]
+        # Must not contain two content-start events
+        self.assertEqual(types.count("content-start"), 1)
+        # The single content block must be thinking
+        cs = next(e for e in events if e["type"] == "content-start")
+        self.assertEqual(cs["delta"]["message"]["content"]["type"], "thinking")
+        # Must end cleanly
+        self.assertEqual(events[-1]["type"], "message-end")
+
     def test_stream_wrapper_skips_malformed_json_with_warning(self):
         """Test that malformed JSON in SSE stream is skipped."""
         from cohere.oci_client import transform_oci_stream_wrapper