fix(jinja): reuse get_request_json_body in get_dataset_id_from_context (SC-118456)

get_dataset_id_from_context (used by the metric() Jinja macro) read the
ambient Flask request via a raw request.get_json() call guarded only by
request.is_json, which checks the Content-Type header but not whether the
body actually parses as JSON. When the metric() macro is evaluated from
the MCP get_chart_data tool, the ambient request is the raw MCP transport
request -- Content-Type: application/json, but not a chart-data JSON
payload -- so request.get_json() raised an unhandled Werkzeug BadRequest.

get_form_data() had the identical pattern and was already fixed for this
in #42196, which added views/utils.get_request_json_body() to coerce a
non-JSON body to {} instead of raising. get_dataset_id_from_context() has
its own separate copy of the old pattern and was missed by that fix.

Switches to the existing helper instead of duplicating the guard.

Fixes SUPERSET-PYTHON-1516

superset/jinja_context.py

@@ -1293,7 +1293,7 @@ def get_dataset_id_from_context(metric_key: str) -> int:
     """
     # pylint: disable=import-outside-toplevel
     from superset.daos.chart import ChartDAO
-    from superset.views.utils import loads_request_json
+    from superset.views.utils import get_request_json_body, loads_request_json
 
     form_data: dict[str, Any] = {}
     exc_message = _(
@@ -1302,7 +1302,7 @@ def get_dataset_id_from_context(metric_key: str) -> int:
     )
 
     if has_request_context():
-        if payload := request.get_json(cache=True) if request.is_json else None:
+        if payload := get_request_json_body():
             if dataset_id := payload.get("datasource", {}).get("id"):
                 return dataset_id
             form_data.update(payload.get("form_data", {}))

tests/unit_tests/jinja_context_test.py

@@ -1441,6 +1441,31 @@ def test_metric_macro_no_dataset_id_no_context(mocker: MockerFixture) -> None:
         DatasetDAO.find_by_id.assert_not_called()
 
 
+def test_metric_macro_no_dataset_id_non_json_body_with_json_content_type(
+    mocker: MockerFixture,
+) -> None:
+    """
+    Test the ``metric_macro`` when the request context's Content-Type claims
+    JSON but the body isn't parseable JSON -- the shape of the request an MCP
+    tool call runs in. Previously ``request.get_json()`` let a raw Werkzeug
+    ``BadRequest`` escape here instead of falling through to the
+    dataset-not-specified path.
+    """
+    DatasetDAO = mocker.patch("superset.daos.dataset.DatasetDAO")  # noqa: N806
+    mock_g = mocker.patch("superset.jinja_context.g")
+    mock_g.form_data = {}
+    env = SandboxedEnvironment(undefined=DebugUndefined)
+    with current_app.test_request_context(
+        data="not-json-at-all", content_type="application/json"
+    ):
+        with pytest.raises(SupersetTemplateException) as excinfo:
+            metric_macro(env, {}, "macro_key")
+        assert str(excinfo.value) == (
+            "Please specify the Dataset ID for the ``macro_key`` metric in the Jinja macro."  # noqa: E501
+        )
+        DatasetDAO.find_by_id.assert_not_called()
+
+
 def test_metric_macro_no_dataset_id_with_context_missing_info(
     mocker: MockerFixture,
 ) -> None: