fix(chat): keep live reasoning on one renderer path

Clean rebase of rodboev's #5773 (rebase-first).

Co-authored-by: rodboev <rodboev@users.noreply.github.com>

static/messages.js

@@ -5024,8 +5024,10 @@ function attachLiveStream(activeSid, streamId, uploaded=[], options={}){
       if(d.text&&S.session&&S.session.session_id===activeSid) _completeAutomaticCompressionOnLiveProgress(activeSid);
       syncInflightAssistantMessage();
       if(text&&S.session&&S.session.session_id===activeSid){
-        _upsertAnchorReasoning(_liveThinkingText());
-        _updateLiveThinkingCard(_liveThinkingText());
+        const liveThinkingText=_liveThinkingText();
+        if(!_upsertAnchorReasoning(liveThinkingText)){
+          _updateLiveThinkingCard(liveThinkingText);
+        }
       }
     });
 

tests/test_regressions.py

@@ -931,8 +931,12 @@ def test_messages_js_supports_live_reasoning_and_tool_completion(cleanup_test_se
         "messages.js must listen for live reasoning SSE events"
     assert "liveReasoningText += text" in src, \
         "live reasoning SSE events must update the active Worklog Thinking Card text"
-    assert "_updateLiveThinkingCard(_liveThinkingText())" in src, \
-        "live reasoning SSE events must refresh the current segment's Worklog Thinking Card"
+    assert "const liveThinkingText=_liveThinkingText();" in src, \
+        "live reasoning SSE events must compute the current segment's Worklog Thinking Card text once"
+    assert "if(!_upsertAnchorReasoning(liveThinkingText))" in src, \
+        "live reasoning SSE events must prefer the anchor renderer before falling back"
+    assert "_updateLiveThinkingCard(liveThinkingText)" in src, \
+        "live reasoning SSE events must keep the current segment's Worklog Thinking Card as fallback"
     assert "source.addEventListener('tool_complete'" in src or 'source.addEventListener("tool_complete"' in src, \
         "messages.js must listen for live tool completion SSE events"
     assert "function _parseStreamState()" in src, \

tests/test_stable_assistant_turn_anchor_registry.py

@@ -1306,7 +1306,9 @@ def test_slice6_live_shadow_feed_wires_anchor_scene_for_visible_order_handoff():
     assert "_upsertAnchorProcessProse(displayText" in src
     reasoning_body = _event_listener_body(src, "reasoning")
     assert "_applyToAnchor" not in reasoning_body
-    assert "_upsertAnchorReasoning(_liveThinkingText())" in reasoning_body
+    assert "const liveThinkingText=_liveThinkingText();" in reasoning_body
+    assert "if(!_upsertAnchorReasoning(liveThinkingText))" in reasoning_body
+    assert "_updateLiveThinkingCard(liveThinkingText)" in reasoning_body
     assert "function _flushReasoningToAnchor()" in src
     assert "_upsertAnchorReasoning(reasoningText" in src
     assert "`live-reasoning:${streamId}:final`" in src

tests/test_ui_tool_call_cleanup.py

@@ -670,6 +670,40 @@ class TestToolCallGroupingStatic:
             "Tool starts must not split consecutive tools into one-tool Activity rows."
         )
 
+    def test_reasoning_stream_uses_one_live_renderer_path(self):
+        reasoning_match = re.search(
+            r"source\.addEventListener\('reasoning',e=>\{(.*?)\n\s*\}\);",
+            MESSAGES_JS,
+            re.S,
+        )
+        assert reasoning_match, "reasoning listener not found"
+        reasoning_fn = reasoning_match.group(1)
+        render_live_thinking_fn = _function_body(MESSAGES_JS, "_renderLiveThinking")
+
+        assert reasoning_fn.count("_liveThinkingText()") == 1, (
+            "_liveThinkingText() should be computed once inside the active-session branch."
+        )
+        assert "const liveThinkingText=_liveThinkingText();" in reasoning_fn, (
+            "Reasoning SSE updates should cache the live thinking text before routing."
+        )
+        assert "_upsertAnchorReasoning(liveThinkingText)" in reasoning_fn, (
+            "Anchor reasoning must remain the primary renderer path."
+        )
+        assert reasoning_fn.index("_upsertAnchorReasoning(liveThinkingText)") < reasoning_fn.index(
+            "_updateLiveThinkingCard(liveThinkingText)"
+        ), (
+            "The legacy thinking card should only run after anchor upsert fails."
+        )
+        assert "if(!_upsertAnchorReasoning(liveThinkingText)){" in reasoning_fn, (
+            "The legacy thinking card should be a falsy-anchor fallback."
+        )
+        assert reasoning_fn.count("_updateLiveThinkingCard(liveThinkingText)") == 1, (
+            "Reasoning SSE updates should call the live thinking card only in fallback."
+        )
+        assert "_updateLiveThinkingCard(" in render_live_thinking_fn, (
+            "Inline parsed thinking still needs the live thinking card renderer."
+        )
+
     def test_live_thinking_card_is_segment_scoped_not_global_singleton(self):
         live_thinking_fn = _function_body(UI_JS, "appendThinking")
         placement_fn = _function_body(MESSAGES_JS, "_liveThinkingPlacement")