Function delete_block 

pub fn delete_block(
    store: &Store,
    tab_id: &str,
    block_id: &str,
) -> Result<(), StoreError>

Delete a block’s rows: remove it from its parent tab’s blockids and delete the Block row.

SPEC_864 site #6 — the layout-tree prune that used to live here (wcore-direct LayoutState write, the last Path-B writer on the block-delete path) moved to the reducer: the delete_block saga dispatches LayoutDeleteNodeByBlock as its Step 2, and the persist subscriber writes the reducer’s resulting tree from the LayoutNodeDeleted{new_tree, tree_cleared} event. This fn is row-ops only, keeping db_layout single-writer. SPEC_864 Phase 5 deleted the prune_block_from_layout/heal_layout backstop that used to live below — no Path-B writer remains to produce the orphans it swept.