fix(mcp): make list-item truncation cap configurable in get_dashboard_info (#41698)

(cherry picked from commit 62ccdfacc2)

tests/unit_tests/mcp_service/utils/test_token_utils.py

@@ -677,3 +677,75 @@ class TestTruncateOversizedResponse:
         assert isinstance(result, dict)
         assert result["id"] == 1  # Scalar fields preserved
         assert len(notes) > 0
+
+    @staticmethod
+    def _build_large_dashboard_response() -> dict[str, Any]:
+        """A dashboard with 463 charts and 48 native_filters, shared by the
+        default- and custom-max_list_items regression tests below."""
+        return {
+            "id": 1,
+            "dashboard_title": "x" * 2000,  # forces Phase 2 to trigger
+            "charts": [{"id": i, "slice_name": f"chart_{i}"} for i in range(463)],
+            "native_filters": [{"id": i, "name": f"filter_{i}"} for i in range(48)],
+        }
+
+    def test_large_dashboard_respects_default_max_list_items(self) -> None:
+        """Regression test for the Medialab large-dashboard report.
+
+        A dashboard with 463 charts and 48 native_filters should have
+        native_filters (48 items) left untouched under the new default cap
+        of 100, while charts (463 items) is truncated to 100 — a clear
+        improvement over the old flat 30-item cap, which truncated both.
+        """
+        response: dict[str, Any] = self._build_large_dashboard_response()
+        result: Any
+        was_truncated: bool
+        notes: list[str]
+        result, was_truncated, notes = truncate_oversized_response(response, 3000)
+        assert was_truncated is True
+        assert isinstance(result, dict)
+        assert len(result["charts"]) == 100
+        assert len(result["native_filters"]) == 48
+        assert any("charts" in n and "463" in n for n in notes)
+        assert not any("native_filters" in n for n in notes)
+
+    def test_large_dashboard_respects_custom_max_list_items(self) -> None:
+        """A custom max_list_items below both list sizes should truncate both fields."""
+        response: dict[str, Any] = self._build_large_dashboard_response()
+        result: Any
+        was_truncated: bool
+        notes: list[str]
+        result, was_truncated, notes = truncate_oversized_response(
+            response, 3000, max_list_items=30
+        )
+        assert was_truncated is True
+        assert isinstance(result, dict)
+        assert len(result["charts"]) == 30
+        assert len(result["native_filters"]) == 30
+        assert any("charts" in n and "30" in n for n in notes)
+        assert any("native_filters" in n and "30" in n for n in notes)
+
+    def test_custom_max_list_items_below_phase_four_survives_phase_four(self) -> None:
+        """A max_list_items below Phase 4's hardcoded 10 should not be widened.
+
+        Phase 2 truncates ``charts`` to 5 first; the response is still over
+        budget because of the oversized ``form_data`` dict, so truncation
+        proceeds to Phase 4, whose ``_truncate_lists(..., max_items=10)``
+        call only shrinks lists larger than 10 — it must leave the
+        already-smaller 5-item list untouched rather than re-expanding it.
+        """
+        response: dict[str, Any] = {
+            "id": 1,
+            "charts": [{"id": i, "slice_name": f"chart_{i}"} for i in range(300)],
+            "form_data": {f"key_{i}": f"val_{i}" for i in range(50)},
+        }
+        result: Any
+        was_truncated: bool
+        notes: list[str]
+        result, was_truncated, notes = truncate_oversized_response(
+            response, 200, max_list_items=5
+        )
+        assert was_truncated is True
+        assert isinstance(result, dict)
+        assert len(result["charts"]) == 5
+        assert any("form_data" in n for n in notes)