feat: gate a run of blocks to chosen output formats

text/src/layout.rs

@@ -122,6 +122,9 @@ impl<'a> Layout<'a> {
                 prefix,
                 Placement { align: Some(*align), inset: margin.unwrap_or(0) as usize },
             ),
+            // Gates are filtered out before rendering; keeping the content is
+            // the harmless reading if one ever arrives here.
+            Block::Gated { block, .. } => self.block(block, prefix, place),
             // Nothing paginates here, so a divider has nothing to divide.
             Block::CardBreak { .. } => {}
             Block::Html(_) => {}