Function handle_reorder_tabs_bulk 

pub(super) fn handle_reorder_tabs_bulk(
    state: &mut State,
    workspace_id: String,
    tab_ids: Vec<String>,
) -> Vec<Event>

Phase E.5.3 — replace a workspace’s tab_ids with the given list. Validates the workspace exists and the new list is a permutation of the current set (same elements, possibly different order). No-op if identical.