feat(tui): change markdown table format to simple ASCII style

- Add render_table_simple() function for minimal ASCII table rendering
- Tables now render without outer box borders
- Uses simple format: 'Header | Header' with '---+---' separator
- More readable and clean table display in conversations
- Keep original render_table() for backwards compatibility

Author: factorydroid

cortex-core/src/markdown/renderer.rs

@@ -39,7 +39,7 @@ use unicode_width::UnicodeWidthStr;
 use crate::markdown::code_block::CodeBlockRenderer;
 use crate::markdown::inline::{render_blockquote_prefix, render_hr};
 use crate::markdown::list::ListContext;
-use crate::markdown::table::{TableBuilder, render_table};
+use crate::markdown::table::{TableBuilder, render_table_simple};
 use crate::markdown::theme::MarkdownTheme;
 
 // ============================================================
@@ -593,10 +593,9 @@ impl<'a> RenderState<'a> {
             let mut table = builder.build();
             table.calculate_column_widths(self.renderer.width);
 
-            let table_lines = render_table(
+            // Use simple ASCII table format without outer borders
+            let table_lines = render_table_simple(
                 &table,
-                self.renderer.theme.table_border,
-                self.renderer.theme.table_header_text,
                 self.renderer.theme.table_cell_text,
                 self.renderer.width,
             );
@@ -863,10 +862,9 @@ impl<'a> RenderState<'a> {
             let mut table = builder.build();
             table.calculate_column_widths(self.renderer.width);
 
-            let table_lines = render_table(
+            // Use simple ASCII table format without outer borders
+            let table_lines = render_table_simple(
                 &table,
-                self.renderer.theme.table_border,
-                self.renderer.theme.table_header_text,
                 self.renderer.theme.table_cell_text,
                 self.renderer.width,
             );

cortex-core/src/markdown/table.rs

@@ -493,6 +493,115 @@ pub fn render_table(
     lines
 }
 
+/// Renders a table as a simple ASCII code block without outer borders.
+///
+/// This produces a cleaner, minimal table format suitable for code blocks:
+/// ```text
+/// Header 1 | Header 2  | Header 3
+/// ---------+-----------+---------
+/// Cell 1   | Cell 2    | Cell 3
+/// Cell 4   | Cell 5    | Cell 6
+/// ```
+///
+/// # Arguments
+/// * `table` - The table to render
+/// * `style` - Style for all text (headers and cells use the same style)
+/// * `max_width` - Maximum total width for the table
+///
+/// # Returns
+/// A vector of `Line`s ready for display in ratatui.
+pub fn render_table_simple(table: &Table, style: Style, max_width: u16) -> Vec<Line<'static>> {
+    // Handle empty table
+    if table.is_empty() {
+        return Vec::new();
+    }
+
+    // Clone and calculate widths if not already done
+    let mut table = table.clone();
+    if table.column_widths.iter().all(|&w| w == 0) {
+        table.calculate_column_widths(max_width);
+    }
+
+    // Handle case where we still have no columns
+    if table.num_columns() == 0 {
+        return Vec::new();
+    }
+
+    let widths = &table.column_widths;
+    let alignments = &table.alignments;
+
+    let mut lines = Vec::new();
+
+    // Header row (if present)
+    if !table.headers.is_empty() {
+        lines.push(render_simple_row(&table.headers, widths, alignments, style));
+
+        // Header separator line: ---+---+---
+        lines.push(render_simple_separator(widths, style));
+    }
+
+    // Data rows
+    for row in &table.rows {
+        lines.push(render_simple_row(row, widths, alignments, style));
+    }
+
+    lines
+}
+
+/// Renders a simple row without outer borders.
+///
+/// Format: `content | content | content`
+fn render_simple_row(
+    cells: &[TableCell],
+    widths: &[usize],
+    alignments: &[Alignment],
+    style: Style,
+) -> Line<'static> {
+    let mut spans = Vec::new();
+
+    for (i, width) in widths.iter().enumerate() {
+        // Get cell content or empty string if missing
+        let cell = cells.get(i);
+        let content = cell.map(|c| c.content.as_str()).unwrap_or("");
+        let alignment = alignments.get(i).copied().unwrap_or_default();
+
+        // Truncate and align
+        let truncated = truncate_with_ellipsis(content, *width);
+        let aligned = align_text(&truncated, *width, alignment);
+
+        // Add cell content with padding
+        spans.push(Span::styled(format!(" {} ", aligned), style));
+
+        // Add separator between columns (not after last)
+        if i < widths.len() - 1 {
+            spans.push(Span::styled("|", style));
+        }
+    }
+
+    Line::from(spans)
+}
+
+/// Renders a simple separator line for the header.
+///
+/// Format: `---+---+---`
+fn render_simple_separator(widths: &[usize], style: Style) -> Line<'static> {
+    let mut spans = Vec::new();
+
+    for (i, &width) in widths.iter().enumerate() {
+        // Each column segment: padding + content + padding (same as cell)
+        let segment_width = width + 2; // +2 for the spaces on each side
+        let segment: String = std::iter::repeat('-').take(segment_width).collect();
+        spans.push(Span::styled(segment, style));
+
+        // Add separator between columns (not after last)
+        if i < widths.len() - 1 {
+            spans.push(Span::styled("+", style));
+        }
+    }
+
+    Line::from(spans)
+}
+
 /// Renders a horizontal border line.
 ///
 /// # Arguments
@@ -996,4 +1105,115 @@ mod tests {
         assert_eq!(cell.content, "");
         assert_eq!(cell.width(), 0);
     }
+
+    // ============================================================
+    // Simple Table Tests
+    // ============================================================
+
+    #[test]
+    fn test_simple_table_empty() {
+        let table = Table::default();
+        let lines = render_table_simple(&table, Style::default(), 80);
+        assert!(lines.is_empty());
+    }
+
+    #[test]
+    fn test_simple_table_basic() {
+        let mut builder = TableBuilder::new();
+        builder.start_header();
+        builder.add_cell("Header".to_string());
+        builder.end_header();
+
+        builder.start_row();
+        builder.add_cell("Value".to_string());
+        builder.end_row();
+
+        let table = builder.build();
+        let lines = render_table_simple(&table, Style::default(), 80);
+
+        // Should have: header, separator, data row = 3 lines (no outer borders)
+        assert_eq!(lines.len(), 3);
+    }
+
+    #[test]
+    fn test_simple_table_multiple_columns() {
+        let mut builder = TableBuilder::new();
+        builder.start_header();
+        builder.add_cell("A".to_string());
+        builder.add_cell("B".to_string());
+        builder.add_cell("C".to_string());
+        builder.end_header();
+
+        builder.start_row();
+        builder.add_cell("1".to_string());
+        builder.add_cell("2".to_string());
+        builder.add_cell("3".to_string());
+        builder.end_row();
+
+        let table = builder.build();
+        let lines = render_table_simple(&table, Style::default(), 80);
+
+        // Check that separator line contains + characters
+        let separator_content: String = lines[1].spans.iter().map(|s| &*s.content).collect();
+        assert!(
+            separator_content.contains('+'),
+            "Separator should contain + for column separation"
+        );
+        assert!(
+            separator_content.contains('-'),
+            "Separator should contain - for dashes"
+        );
+    }
+
+    #[test]
+    fn test_simple_table_without_headers() {
+        let mut builder = TableBuilder::new();
+
+        builder.start_row();
+        builder.add_cell("A".to_string());
+        builder.add_cell("B".to_string());
+        builder.end_row();
+
+        builder.start_row();
+        builder.add_cell("C".to_string());
+        builder.add_cell("D".to_string());
+        builder.end_row();
+
+        let table = builder.build();
+        let lines = render_table_simple(&table, Style::default(), 80);
+
+        // Should have: 2 data rows only (no header, no separator)
+        assert_eq!(lines.len(), 2);
+    }
+
+    #[test]
+    fn test_simple_table_format() {
+        let mut builder = TableBuilder::new();
+        builder.start_header();
+        builder.add_cell("Name".to_string());
+        builder.add_cell("Value".to_string());
+        builder.end_header();
+
+        builder.start_row();
+        builder.add_cell("foo".to_string());
+        builder.add_cell("bar".to_string());
+        builder.end_row();
+
+        let table = builder.build();
+        let lines = render_table_simple(&table, Style::default(), 80);
+
+        // First line should be header with | separator
+        let header_content: String = lines[0].spans.iter().map(|s| &*s.content).collect();
+        assert!(
+            header_content.contains('|'),
+            "Header should have | separator between columns"
+        );
+
+        // Second line should be separator with -+-
+        let separator_content: String = lines[1].spans.iter().map(|s| &*s.content).collect();
+        assert!(
+            separator_content.contains('+'),
+            "Separator should have + at column intersections"
+        );
+    }
 }