Function find_tab_for_layout 

fn find_tab_for_layout(store: &WaveStore, layout_oid: &str) -> Option<String>

Phase E.4 (Option A) — reverse lookup: given a LayoutState.oid, find the Tab.oid that owns it (i.e., the tab whose layoutstate field matches). Returns None when the layout is unowned (legacy or partially-migrated row) or the wstore read fails — caller treats either as “skip the reducer dispatch and fall through to the wcore write.” Linear scan over all tabs; acceptable here because the layout-update path is low-frequency relative to drag-resize and the reducer mutex itself is held for sub-millisecond intervals.