The step_tree_json_valid BDD step was asserting a raw list from
format_output, but the function wraps all machine-readable output in
a spec-required envelope dict ({"data": [...]}). This PR fixes the
step to correctly validate the envelope structure (dict with data key)
and removes @tdd_expected_fail from the @tdd_issue_4254 scenario so
it runs as a permanent regression guard.
The code producing decision_id in tree nodes was already correct; only
the test assertion needed fixing.
ISSUES CLOSED: #9096
controller-ci-rerun
HAL9000