fix: only add signature to reasoning blocks if signature is provided (#806)

* fix: only add signature to reasoning blocks if signature is provided

---------

Co-authored-by: Mackenzie Zastrow <[email protected]>
Co-authored-by: Dean Schmigelski <[email protected]>

Author: zastrowm

src/strands/event_loop/streaming.py

@@ -289,7 +289,6 @@ async def process_stream(chunks: AsyncIterable[StreamEvent]) -> AsyncGenerator[T
         "text": "",
         "current_tool_use": {},
         "reasoningText": "",
-        "signature": "",
         "citationsContent": [],
     }
     state["content"] = state["message"]["content"]

tests/strands/event_loop/test_streaming.py

@@ -1,10 +1,12 @@
 import unittest.mock
+from typing import cast
 
 import pytest
 
 import strands
 import strands.event_loop
-from strands.types._events import TypedEvent
+from strands.types._events import ModelStopReason, TypedEvent
+from strands.types.content import Message
 from strands.types.streaming import (
     ContentBlockDeltaEvent,
     ContentBlockStartEvent,
@@ -565,6 +567,88 @@ async def test_process_stream(response, exp_events, agenerator, alist):
     assert non_typed_events == []
 
 
+def _get_message_from_event(event: ModelStopReason) -> Message:
+    return cast(Message, event["stop"][1])
+
+
+@pytest.mark.asyncio
+async def test_process_stream_with_no_signature(agenerator, alist):
+    response = [
+        {"messageStart": {"role": "assistant"}},
+        {
+            "contentBlockDelta": {
+                "delta": {"reasoningContent": {"text": 'User asks: "Reason about 2+2" so I will do that'}},
+                "contentBlockIndex": 0,
+            }
+        },
+        {"contentBlockDelta": {"delta": {"reasoningContent": {"text": "."}}, "contentBlockIndex": 0}},
+        {"contentBlockStop": {"contentBlockIndex": 0}},
+        {
+            "contentBlockDelta": {
+                "delta": {"text": "Sure! Let’s do it"},
+                "contentBlockIndex": 1,
+            }
+        },
+        {"contentBlockStop": {"contentBlockIndex": 1}},
+        {"messageStop": {"stopReason": "end_turn"}},
+        {
+            "metadata": {
+                "usage": {"inputTokens": 112, "outputTokens": 764, "totalTokens": 876},
+                "metrics": {"latencyMs": 2970},
+            }
+        },
+    ]
+
+    stream = strands.event_loop.streaming.process_stream(agenerator(response))
+
+    last_event = cast(ModelStopReason, (await alist(stream))[-1])
+
+    message = _get_message_from_event(last_event)
+
+    assert "signature" not in message["content"][0]["reasoningContent"]["reasoningText"]
+    assert message["content"][1]["text"] == "Sure! Let’s do it"
+
+
+@pytest.mark.asyncio
+async def test_process_stream_with_signature(agenerator, alist):
+    response = [
+        {"messageStart": {"role": "assistant"}},
+        {
+            "contentBlockDelta": {
+                "delta": {"reasoningContent": {"text": 'User asks: "Reason about 2+2" so I will do that'}},
+                "contentBlockIndex": 0,
+            }
+        },
+        {"contentBlockDelta": {"delta": {"reasoningContent": {"text": "."}}, "contentBlockIndex": 0}},
+        {"contentBlockDelta": {"delta": {"reasoningContent": {"signature": "test-"}}, "contentBlockIndex": 0}},
+        {"contentBlockDelta": {"delta": {"reasoningContent": {"signature": "signature"}}, "contentBlockIndex": 0}},
+        {"contentBlockStop": {"contentBlockIndex": 0}},
+        {
+            "contentBlockDelta": {
+                "delta": {"text": "Sure! Let’s do it"},
+                "contentBlockIndex": 1,
+            }
+        },
+        {"contentBlockStop": {"contentBlockIndex": 1}},
+        {"messageStop": {"stopReason": "end_turn"}},
+        {
+            "metadata": {
+                "usage": {"inputTokens": 112, "outputTokens": 764, "totalTokens": 876},
+                "metrics": {"latencyMs": 2970},
+            }
+        },
+    ]
+
+    stream = strands.event_loop.streaming.process_stream(agenerator(response))
+
+    last_event = cast(ModelStopReason, (await alist(stream))[-1])
+
+    message = _get_message_from_event(last_event)
+
+    assert message["content"][0]["reasoningContent"]["reasoningText"]["signature"] == "test-signature"
+    assert message["content"][1]["text"] == "Sure! Let’s do it"
+
+
 @pytest.mark.asyncio
 async def test_stream_messages(agenerator, alist):
     mock_model = unittest.mock.MagicMock()