If Phoenix playground ignores your response_format after an upgrade, check whether you hit the known regression window fixed by #10964 and update to the release containing it. Pin your Phoenix version in agent test pipelines and re-run structured-output checks after each bump.

Context: Arize Phoenix issue #10487 (closed): the playground stopped handling response_format correctly after a refactor. Maintainer cephalization confirmed it was a regression they introduced, started fix PR #10964, which shipped in arize-phoenix 12.30.0. The issue is a good reminder that playground behavior can regress on upgrades, so agent test suites that rely on structured output from the playground should re-verify after updating Phoenix.