fix: strip partial think tags in streaming output

nanobot/utils/helpers.py

@@ -32,6 +32,8 @@ def strip_think(text: str) -> str:
          explanatory prose that mentions these tokens.
       5. Orphan closing tags `</think>` / `</thought>` **at the very start
          or end of the text** only, for the same reason.
+      6. Trailing partial control tags split across stream chunks, such as
+         `<thi`, `<thin`, or `<tho`.
 
     Since this is also applied before persisting to history (memory.py),
     the edge-only stripping of (4) and (5) is deliberate: stripping those
@@ -58,6 +60,14 @@ def strip_think(text: str) -> str:
     text = re.sub(r"\s*</thought>\s*$", "", text)
     # Edge-only channel markers (harmony / Gemma 4 variant leaks).
     text = re.sub(r"^\s*<\|?channel\|?>\s*", "", text)
+    # Stream chunks may end in the middle of a control tag. Strip only known
+    # control-token prefixes at the very end.
+    partial_control_tag = (
+        r"</?(?:t|th|thi|thin|think|tho|thou|thoug|though|thought)"
+        r"|<\|?(?:c|ch|cha|chan|chann|channe|channel|channel\|?)"
+    )
+    text = re.sub(rf"(?:{partial_control_tag})$", "", text)
+    text = re.sub(r"^\s*<\|?$", "", text)
     return text.strip()
 
 

tests/agent/test_runner.py

@@ -972,6 +972,27 @@ async def test_loop_stream_filter_handles_think_only_prefix_without_crashing(tmp
     assert endings == [False]
 
 
+@pytest.mark.asyncio
+async def test_loop_stream_filter_hides_partial_trailing_think_prefix(tmp_path):
+    loop = _make_loop(tmp_path)
+    deltas: list[str] = []
+
+    async def chat_stream_with_retry(*, on_content_delta, **kwargs):
+        await on_content_delta("Hello <thin")
+        await on_content_delta("k>hidden</think>World")
+        return LLMResponse(content="Hello <think>hidden</think>World", tool_calls=[], usage={})
+
+    loop.provider.chat_stream_with_retry = chat_stream_with_retry
+
+    async def on_stream(delta: str) -> None:
+        deltas.append(delta)
+
+    final_content, _, _, _, _ = await loop._run_agent_loop([], on_stream=on_stream)
+
+    assert final_content == "Hello World"
+    assert deltas == ["Hello", " World"]
+
+
 @pytest.mark.asyncio
 async def test_loop_retries_think_only_final_response(tmp_path):
     loop = _make_loop(tmp_path)

tests/utils/test_strip_think.py

@@ -102,6 +102,14 @@ class TestStripThinkMalformedLeaks:
         assert strip_think("<channel|>喷泉策略：09:00 开启") == ("喷泉策略：09:00 开启")
         assert strip_think("<|channel|>answer") == "answer"
 
+    def test_partial_trailing_think_tag_after_visible_text(self):
+        assert strip_think("喷泉策略说明 <thin") == "喷泉策略说明"
+        assert strip_think("answer <thought") == "answer"
+
+    def test_partial_trailing_channel_marker_after_visible_text(self):
+        assert strip_think("喷泉策略说明 <|chan") == "喷泉策略说明"
+        assert strip_think("answer <channel") == "answer"
+
 
 class TestStripThinkConservativePreserve:
     """Regression: the malformed-tag / orphan cleanup must NOT touch