fix(middleware): normalize tool result adjacency before model calls (#2939)

* normalizing tool-call transcripts before invocation

* test(middleware): cover tool result regrouping edge cases

backend/tests/test_dangling_tool_call_middleware.py

@@ -158,6 +158,88 @@ class TestBuildPatchedMessagesPatching:
         assert patched[1].name == "bash"
         assert patched[1].status == "error"
 
+    def test_non_adjacent_tool_result_is_moved_next_to_tool_call(self):
+        middleware = DanglingToolCallMiddleware()
+        msgs = [
+            _ai_with_tool_calls([_tc("bash", "call_1")]),
+            HumanMessage(content="interruption"),
+            _tool_msg("call_1", "bash"),
+        ]
+        patched = middleware._build_patched_messages(msgs)
+        assert patched is not None
+        assert isinstance(patched[0], AIMessage)
+        assert isinstance(patched[1], ToolMessage)
+        assert patched[1].tool_call_id == "call_1"
+        assert isinstance(patched[2], HumanMessage)
+
+    def test_multiple_tool_results_stay_grouped_after_ai_tool_call(self):
+        mw = DanglingToolCallMiddleware()
+        msgs = [
+            _ai_with_tool_calls([_tc("bash", "call_1"), _tc("read", "call_2")]),
+            HumanMessage(content="interruption"),
+            _tool_msg("call_2", "read"),
+            _tool_msg("call_1", "bash"),
+        ]
+
+        patched = mw._build_patched_messages(msgs)
+
+        assert patched is not None
+        assert isinstance(patched[0], AIMessage)
+        assert isinstance(patched[1], ToolMessage)
+        assert isinstance(patched[2], ToolMessage)
+        assert [patched[1].tool_call_id, patched[2].tool_call_id] == ["call_1", "call_2"]
+        assert isinstance(patched[3], HumanMessage)
+
+    def test_valid_adjacent_tool_results_are_unchanged(self):
+        mw = DanglingToolCallMiddleware()
+        msgs = [
+            _ai_with_tool_calls([_tc("bash", "call_1")]),
+            _tool_msg("call_1", "bash"),
+            HumanMessage(content="next"),
+        ]
+
+        assert mw._build_patched_messages(msgs) is None
+
+    def test_tool_results_are_grouped_with_their_own_ai_turn_across_multiple_ai_messages(self):
+        mw = DanglingToolCallMiddleware()
+        msgs = [
+            _ai_with_tool_calls([_tc("bash", "call_1")]),
+            HumanMessage(content="interruption"),
+            _ai_with_tool_calls([_tc("read", "call_2")]),
+            _tool_msg("call_1", "bash"),
+            _tool_msg("call_2", "read"),
+        ]
+
+        patched = mw._build_patched_messages(msgs)
+
+        assert patched is not None
+        assert isinstance(patched[0], AIMessage)
+        assert isinstance(patched[1], ToolMessage)
+        assert patched[1].tool_call_id == "call_1"
+        assert isinstance(patched[2], HumanMessage)
+        assert isinstance(patched[3], AIMessage)
+        assert isinstance(patched[4], ToolMessage)
+        assert patched[4].tool_call_id == "call_2"
+
+    def test_orphan_tool_message_is_preserved_during_grouping(self):
+        mw = DanglingToolCallMiddleware()
+        orphan = _tool_msg("orphan_call", "orphan")
+        msgs = [
+            _ai_with_tool_calls([_tc("bash", "call_1")]),
+            orphan,
+            HumanMessage(content="interruption"),
+            _tool_msg("call_1", "bash"),
+        ]
+
+        patched = mw._build_patched_messages(msgs)
+
+        assert patched is not None
+        assert isinstance(patched[0], AIMessage)
+        assert isinstance(patched[1], ToolMessage)
+        assert patched[1].tool_call_id == "call_1"
+        assert orphan in patched
+        assert patched.count(orphan) == 1
+
     def test_invalid_tool_call_is_patched(self):
         mw = DanglingToolCallMiddleware()
         msgs = [_ai_with_invalid_tool_calls([_invalid_tc()])]