Codex gate finding on #5031: when _mountSearchableModelSelect is absent the
fallback returns the old plain <select>, but the post-render rehydration
(modelSel.value = ONBOARDING.form.model) was removed — so a saved/default model
that isn't the first option would be silently replaced by option[0] on render.
Restore the rehydration in an else branch + add a regression test.
Co-authored-by: rodboev <rodboev@users.noreply.github.com>