fix(agent-loop): release buffered prose when '<' is not a tool tag (#6757) (#6758)

src/agent_loop.py

@@ -27833,16 +27833,25 @@ async def stream_agent_loop(
                                 if _streamed_tool_markup or _streamed_tool_markup_starts(_delta_text):
                                     _streamed_tool_markup += _delta_text
                                     if not _streamed_tool_markup_complete(_streamed_tool_markup):
-                                        continue
-                                    _visible_markup_tail = strip_tool_blocks(
-                                        _streamed_tool_markup,
-                                        skip_fenced=True,
-                                    ).strip()
-                                    _streamed_tool_markup = ""
-                                    if not _visible_markup_tail:
-                                        continue
-                                    _delta_text = _visible_markup_tail
-                                    data["delta"] = _delta_text
+                                        if _streamed_tool_markup_starts(_streamed_tool_markup):
+                                            continue
+                                        # False alarm: a bare "<" (e.g. ``x < 2``) looked like
+                                        # a tag prefix, but the buffer can no longer become a
+                                        # tool tag. Release it as prose instead of holding the
+                                        # rest of the answer forever.
+                                        _delta_text = _streamed_tool_markup
+                                        _streamed_tool_markup = ""
+                                        data["delta"] = _delta_text
+                                    else:
+                                        _visible_markup_tail = strip_tool_blocks(
+                                            _streamed_tool_markup,
+                                            skip_fenced=True,
+                                        ).strip()
+                                        _streamed_tool_markup = ""
+                                        if not _visible_markup_tail:
+                                            continue
+                                        _delta_text = _visible_markup_tail
+                                        data["delta"] = _delta_text
                             full_response += _delta_text
                         if not _suppress_unavailable_web_delta:
                             _qwen_buffered_route = bool(

tests/test_streamed_tool_markup.py

@@ -27,3 +27,102 @@ def test_dsml_tool_markup_strips_to_empty_visible_text():
 def test_chunk_split_tool_call_prefix_is_buffered_and_not_persisted():
     assert _streamed_tool_markup_starts('I will search<tool_cal')
     assert _strip_incomplete_tool_markup_tail('I will search<tool_cal') == 'I will search'
+
+
+def test_bare_less_than_and_comparison_operators_false_alarm_recognition():
+    # A bare "<" starts buffering because it could be a tool-call tag prefix like "<tool_call>"
+    assert _streamed_tool_markup_starts(' <')
+    assert _streamed_tool_markup_starts('x <')
+    assert _streamed_tool_markup_starts('<tool_call')
+    assert _streamed_tool_markup_starts('<invoke')
+
+    # Once subsequent characters arrive and cannot become a tool-call tag, false alarm is detected
+    assert not _streamed_tool_markup_starts(' < 2')
+    assert not _streamed_tool_markup_starts('x < 2')
+    assert not _streamed_tool_markup_starts('len(items) < 2')
+    assert not _streamed_tool_markup_starts(' < 2:')
+    assert not _streamed_tool_markup_starts('x <= y')
+    assert not _streamed_tool_markup_starts('a < b')
+
+
+async def test_stream_agent_loop_does_not_truncate_at_less_than_operator(monkeypatch):
+    import json
+    import src.agent_loop as al
+
+    async def fake_stream(*args, **kwargs):
+        for d in ["def is_short(items):\n", "    return len(items)", " <", " 2\n"]:
+            yield "data: " + json.dumps({"delta": d}) + "\n\n"
+        yield "data: [DONE]\n\n"
+
+    monkeypatch.setattr(al, "get_setting", lambda k, d=None: d, raising=False)
+    monkeypatch.setattr(al, "get_mcp_manager", lambda: None, raising=False)
+    monkeypatch.setattr(al, "estimate_tokens", lambda *a, **k: 10, raising=False)
+    monkeypatch.setattr(al, "stream_llm_with_fallback", fake_stream, raising=False)
+
+    deltas = []
+    async for chunk in al.stream_agent_loop(
+        "http://local.test/v1",
+        "qwen3.6-35b-a3b-heretic",
+        [{"role": "user", "content": "Write python function"}],
+        max_rounds=1,
+        owner="test_user",
+    ):
+        for line in chunk.split("\n"):
+            line = line.strip()
+            if line.startswith("data: ") and line[6:] != "[DONE]":
+                try:
+                    payload = json.loads(line[6:])
+                    if "delta" in payload:
+                        deltas.append(payload["delta"])
+                except Exception:
+                    pass
+
+    full_text = "".join(deltas)
+    assert full_text == "def is_short(items):\n    return len(items) < 2\n"
+
+
+async def test_stream_agent_loop_still_hides_real_tool_markup(monkeypatch):
+    import json
+    import src.agent_loop as al
+
+    async def fake_stream(*args, **kwargs):
+        chunks = [
+            "Sure.",
+            " <",
+            "tool",
+            "_call",
+            '>{"name":"host_shell","arguments":{"command":"pwd"}}',
+            "</",
+            "tool",
+            "_call",
+            ">",
+            " done",
+        ]
+        for c in chunks:
+            yield "data: " + json.dumps({"delta": c}) + "\n\n"
+        yield "data: [DONE]\n\n"
+
+    monkeypatch.setattr(al, "get_setting", lambda k, d=None: d, raising=False)
+    monkeypatch.setattr(al, "get_mcp_manager", lambda: None, raising=False)
+    monkeypatch.setattr(al, "estimate_tokens", lambda *a, **k: 10, raising=False)
+    monkeypatch.setattr(al, "stream_llm_with_fallback", fake_stream, raising=False)
+
+    deltas = []
+    async for chunk in al.stream_agent_loop(
+        "http://local.test/v1",
+        "qwen3.6-35b-a3b-heretic",
+        [{"role": "user", "content": "run command"}],
+        max_rounds=1,
+        owner="test_user",
+    ):
+        for line in chunk.split("\n"):
+            line = line.strip()
+            if line.startswith("data: ") and line[6:] != "[DONE]":
+                try:
+                    payload = json.loads(line[6:])
+                    if "delta" in payload:
+                        deltas.append(payload["delta"])
+                except Exception:
+                    pass
+
+    assert "".join(deltas) == "Sure. done"