Function setup_torn_off_block_layout 

fn setup_torn_off_block_layout(
    store: &WaveStore,
    new_tab_id: &str,
    block_id: &str,
) -> Result<(), Box<dyn Error>>

Phase E.5.5 — set up the layout tree for a tab that just received its first block via the TearOffBlock saga. Called from the TearOffBlock RPC handler after the saga’s reducer-state portion (CreateTab + MoveBlock) completes. Mirrors the layout-rootnode

• leaforder construction that wcore::tear_off_block previously embedded in its single function.

Layout state migration is E.4 — until then layout writes are wcore-direct and not reducer-routed. Best-effort: a failure here leaves the new tab with the moved block but a malformed layout; the user-visible symptom is an empty render in the new window.