JSON_OBJECT_FILTER_KEYS does not evaluate array_keys per row

Description

When the `array_keys` argument of `JSON_OBJECT_FILTER_KEYS(obj, array_keys)` comes from a table column, the function returns NULL for every row instead of evaluating that argument per row. A literal key array works correctly.

The source path reviewed for the lightweight report evaluates `args[1]` while fixing result metadata and only reevaluates `args[0]` during row execution. The relevant locations are `sql/item_jsonfunc.cc:6227-6270` and `sql/item_jsonfunc.cc:6274-6318`. This implementation observation is supplemental; the externally observed behavior is the reporting basis.

How to Repeat

CREATE TABLE json_filter_test (

  obj LONGTEXT CHECK (JSON_VALID(obj)),

  keys_json LONGTEXT CHECK (JSON_VALID(keys_json))

);

INSERT INTO json_filter_test VALUES

  ('{"a":1,"b":2,"c":3}', '["b"]'),

  ('{"a":10,"b":20,"c":30}', '["a","c"]');

-- Negative control.

SELECT JSON_OBJECT_FILTER_KEYS('{"a":1,"b":2}', '["b"]');

-- Positive case.

SELECT JSON_OBJECT_FILTER_KEYS(obj, keys_json)

FROM json_filter_test

ORDER BY obj;

CREATE VIEW json_filter_view AS

SELECT JSON_OBJECT_FILTER_KEYS(obj, keys_json) AS filtered

FROM json_filter_test;

SHOW COLUMNS FROM json_filter_view;

Actual Result

The literal call returns `

`. Both table-column calls return NULL, and the view column is described as `binary(0)`.

Expected Result

The function should evaluate `array_keys` for each input row. The result should be equivalent to:

{"b": 2}

{"a": 10, "c": 30}

The view metadata should describe a normal JSON/string result width rather than `binary(0)`.