feat(kebab-tui): p9-fb-24 task 5 — Library column header row

Wire `format_doc_header` into `render_doc_list`: render the block
independently, split block_inner into a 1-row header + list via
vertical Layout, and drop the `.block(block)` from the List widget.
Remove `#[allow(dead_code)]` from `format_doc_header` now that it
is consumed. Add `library_renders_column_header_row` integration test.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/kebab-tui/src/library.rs

@@ -199,13 +199,29 @@ fn render_doc_list(f: &mut Frame, area: Rect, state: &App) {
         "Library"
     };
     let block = Block::default().title(header_text).borders(Borders::ALL);
+    let block_inner = block.inner(area);
+    f.render_widget(block, area);
 
     if inner.docs.is_empty() {
-        f.render_widget(block, area);
         return;
     }
 
-    let title_w = (area.width as usize).saturating_sub(40).max(20);
+    // p9-fb-24: split the inner area into a 1-row column header on top
+    // and the doc list below. Header reuses the same width math as
+    // `format_doc_row` so labels line up with their data columns.
+    let layout = Layout::default()
+        .direction(Direction::Vertical)
+        .constraints([Constraint::Length(1), Constraint::Min(0)])
+        .split(block_inner);
+    let header_area = layout[0];
+    let list_area = layout[1];
+
+    let title_w = (list_area.width as usize).saturating_sub(40).max(20);
+
+    let header_para = Paragraph::new(format_doc_header(title_w))
+        .style(state.theme.style(crate::theme::Role::Heading));
+    f.render_widget(header_para, header_area);
+
     let items: Vec<ListItem> = inner
         .docs
         .iter()
@@ -213,12 +229,11 @@ fn render_doc_list(f: &mut Frame, area: Rect, state: &App) {
         .collect();
 
     let list = List::new(items)
-        .block(block)
         .highlight_style(state.theme.style(crate::theme::Role::Selected))
         .highlight_symbol("> ");
 
     let mut list_state = inner.list_state.clone();
-    f.render_stateful_widget(list, area, &mut list_state);
+    f.render_stateful_widget(list, list_area, &mut list_state);
 }
 
 /// p9-fb-24: render the column-label row that sits directly above
@@ -229,9 +244,6 @@ fn render_doc_list(f: &mut Frame, area: Rect, state: &App) {
 /// Layout: `TITLE<title_pad>  TAGS<tags_pad>  UPDATED  CHUNKS`.
 /// The title column width matches `area.width.saturating_sub(40).max(20)`
 /// — the same calculation `render_doc_list` uses for `title_w`.
-///
-/// Task 5 wires it into render_doc_list.
-#[allow(dead_code)]
 pub(crate) fn format_doc_header(title_w: usize) -> Line<'static> {
     let title_label = "TITLE";
     let tags_label = "TAGS";

crates/kebab-tui/tests/library.rs

@@ -286,6 +286,52 @@ fn filter_overlay_render_places_cursor_on_focused_field() {
     );
 }
 
+/// p9-fb-24: rendered Library pane shows the column header row above
+/// the data rows. Header is in `Role::Heading` style; data rows in
+/// the `Role::Body` / `Role::Selected` defaults.
+#[test]
+fn library_renders_column_header_row() {
+    let docs = vec![
+        make_doc("notes/alpha.md", "doc-alpha", vec!["rust"]),
+        make_doc("notes/beta.md", "doc-beta", vec!["docs"]),
+        make_doc("notes/gamma.md", "doc-gamma", vec![]),
+    ];
+    let app = app_with_docs(docs);
+    let backend = TestBackend::new(80, 20);
+    let mut terminal = Terminal::new(backend).unwrap();
+    terminal
+        .draw(|f| {
+            let area = Rect::new(0, 0, 80, 20);
+            render_library(f, area, &app);
+        })
+        .unwrap();
+    let buffer = terminal.backend().buffer().clone();
+    let rendered: String = (0..buffer.area.height)
+        .map(|y| {
+            (0..buffer.area.width)
+                .map(|x| buffer[(x, y)].symbol())
+                .collect::<String>()
+        })
+        .collect::<Vec<_>>()
+        .join("\n");
+    assert!(
+        rendered.contains("TITLE")
+            && rendered.contains("TAGS")
+            && rendered.contains("UPDATED")
+            && rendered.contains("CHUNKS"),
+        "header row labels not visible in:\n{rendered}"
+    );
+    let title_line_idx = rendered
+        .lines()
+        .position(|line| line.contains("TITLE"))
+        .expect("TITLE header should be present");
+    let lines_after = rendered.lines().skip(title_line_idx + 1).collect::<Vec<_>>();
+    assert!(
+        lines_after.iter().any(|line| line.contains("doc-")),
+        "no data rows after header:\n{rendered}"
+    );
+}
+
 /// p9-fb-10: Library renders Hangul / CJK titles without overflowing
 /// the title column. Smoke pin — render with a mixed Korean fixture
 /// and confirm no panic + the truncated width fits the column.