Fix tool-call tail ordering in session merge

api/models.py

@@ -5822,7 +5822,17 @@ def merge_session_messages_append_only(
                 if _tc:
                     _ck = _session_message_content_key(msg)
                     if _ck in seen_content_keys and dedup_key not in seen_dedup_keys:
-                        pass  # different tool_calls from sidecar — preserve
+                        # Different tool_calls from sidecar — preserve, but keep
+                        # the row in timestamp order. Falling through to the
+                        # generic append path would move older tool-call-only
+                        # assistant rows after the settled final answer.
+                        if _insert_state_message_chronologically(merged_messages, msg):
+                            seen_message_keys.add(key)
+                            seen_dedup_keys.add(dedup_key)
+                            seen_content_keys.add(_session_message_content_key(msg))
+                            seen_visible_keys.add(visible_key)
+                            _remember_merged_message(msg)
+                        continue
                     else:
                         _merge_session_display_metadata(merged_by_message_key.get(key), msg)
                         continue

tests/test_merge_key_tool_calls.py

@@ -126,6 +126,34 @@ class TestMergeToolCallsEndToEnd:
         }
         assert tc_ids == {"call_1", "call_2"}
 
+    def test_older_state_tool_call_assistant_stays_before_final_answer(self):
+        """Older tool-call-only state.db rows must not become the final tail.
+
+        The WebUI sidecar can already contain a settled final answer while
+        state.db still has empty-content assistant rows that carry distinct
+        tool_calls from earlier in the turn. Those rows are real activity and
+        should be preserved, but appending them after the final answer makes the
+        renderer treat the final answer as a non-final assistant segment.
+        """
+        sidecar_tool = _assistant_tc("call_1", "read_file", timestamp=1000.0)
+        final_answer = {
+            "role": "assistant",
+            "content": "Final answer is complete.",
+            "timestamp": 1001.0,
+        }
+        state_tool = _assistant_tc("call_2", "terminal", timestamp=1000.5)
+
+        result = merge_session_messages_append_only(
+            [sidecar_tool, final_answer],
+            [state_tool],
+        )
+
+        assert result[-1] == final_answer
+        assert [m.get("tool_calls", [{}])[0].get("id") for m in result if m.get("tool_calls")] == [
+            "call_1",
+            "call_2",
+        ]
+
     def test_no_tool_calls_still_deduped(self):
         """Messages without tool_calls are deduplicated by legacy key as before."""
         msg = {"role": "assistant", "content": "hello", "timestamp": 1000}