diff --git a/routes/history_routes.py b/routes/history_routes.py
index 9efaa94..bcadeee 100644
--- a/routes/history_routes.py
+++ b/routes/history_routes.py
@@ -15,6 +15,26 @@ from routes.session_routes import _verify_session_owner
 logger = logging.getLogger(__name__)
 
 
+def _merge_continue_rows_to_delete(db_messages, db1, db2):
+    """DB rows to delete when merging the last two assistant messages.
+
+    Always the second assistant message (db2), plus ONLY the single
+    intervening "continue" user message (the one carrying "previous response
+    was interrupted") — matching the in-memory merge. The previous code
+    deleted the whole index range between the two assistant rows, destroying
+    any tool/system/user messages in between and desyncing the DB from the
+    in-memory history.
+    """
+    to_delete = [db2]
+    i1 = next((i for i, m in enumerate(db_messages) if m is db1), None)
+    i2 = next((i for i, m in enumerate(db_messages) if m is db2), None)
+    if i1 is not None and i2 is not None and i2 - 1 > i1:
+        between = db_messages[i2 - 1]
+        if getattr(between, "role", "") == "user" and            "previous response was interrupted" in (getattr(between, "content", "") or ""):
+            to_delete.append(between)
+    return to_delete
+
+
 def setup_history_routes(session_manager) -> APIRouter:
     router = APIRouter(tags=["history"])
 
@@ -418,11 +438,13 @@ def setup_history_routes(session_manager) -> APIRouter:
                     db1.content = merged_content
                     db1.meta_data = _json.dumps(merged_meta)
 
-                    # Remove the continue user message if between them
-                    db_idx2 = db_messages.index(db2)
-                    db_idx1 = db_messages.index(db1)
-                    for di in range(db_idx2, db_idx1, -1):
-                        db.delete(db_messages[di])
+                    # Mirror the in-memory deletion: remove the second assistant
+                    # message and ONLY the "continue" user message between them
+                    # (not arbitrary tool/system/user rows). The old
+                    # range-delete destroyed every row between the two assistant
+                    # messages, desyncing the DB from the in-memory history.
+                    for _row in _merge_continue_rows_to_delete(db_messages, db1, db2):
+                        db.delete(_row)
 
                     db.commit()
             finally:
diff --git a/tests/test_merge_last_assistant_rows.py b/tests/test_merge_last_assistant_rows.py
new file mode 100644
index 0000000..31a99e7
--- /dev/null
+++ b/tests/test_merge_last_assistant_rows.py
@@ -0,0 +1,41 @@
+"""merge-last-assistant must not delete tool/system rows between the messages.
+
+The in-memory merge removes the second assistant message plus only the
+"continue" user message between the last two assistant replies. The DB path
+deleted the ENTIRE index range between them, destroying any tool/system/user
+rows in between — so on reload the DB lost messages the in-memory history
+kept (data loss + count desync). _merge_continue_rows_to_delete makes the DB
+deletion mirror the in-memory rule.
+"""
+from types import SimpleNamespace
+
+from routes.history_routes import _merge_continue_rows_to_delete
+
+
+def _m(role, content=""):
+    return SimpleNamespace(role=role, content=content)
+
+
+def test_tool_message_between_is_not_deleted():
+    u, a1, tool, a2 = _m("user", "q"), _m("assistant", "a1"), _m("tool", "RESULT"), _m("assistant", "a2")
+    rows = _merge_continue_rows_to_delete([u, a1, tool, a2], a1, a2)
+    assert rows == [a2]            # only the 2nd assistant
+    assert tool not in rows        # the tool result survives
+
+
+def test_continue_user_message_is_deleted():
+    u, a1, cont, a2 = (_m("user", "q"), _m("assistant", "a1"),
+                       _m("user", "(the previous response was interrupted)"), _m("assistant", "a2"))
+    rows = _merge_continue_rows_to_delete([u, a1, cont, a2], a1, a2)
+    assert a2 in rows and cont in rows and len(rows) == 2
+
+
+def test_adjacent_assistants_delete_only_second():
+    a1, a2 = _m("assistant", "a1"), _m("assistant", "a2")
+    assert _merge_continue_rows_to_delete([a1, a2], a1, a2) == [a2]
+
+
+def test_plain_user_between_not_deleted():
+    a1, usr, a2 = _m("assistant", "a1"), _m("user", "a real follow-up question"), _m("assistant", "a2")
+    rows = _merge_continue_rows_to_delete([a1, usr, a2], a1, a2)
+    assert rows == [a2] and usr not in rows