Implementing basic markdown previewer

Cargo.lock

@@ -515,6 +515,7 @@ dependencies = [
  "ignore",
  "lime-core",
  "lime-syntax",
+ "pulldown-cmark",
  "ratatui",
  "serde",
  "toml",
@@ -631,6 +632,17 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "pulldown-cmark"
+version = "0.13.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e9f068eba8e7071c5f9511831b44f32c740d5adf574e990f946ddb53db2f314e"
+dependencies = [
+ "bitflags",
+ "memchr",
+ "unicase",
+]
+
 [[package]]
 name = "quote"
 version = "1.0.45"
@@ -1061,6 +1073,12 @@ dependencies = [
  "tree-sitter-language",
 ]
 
+[[package]]
+name = "unicase"
+version = "2.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dbc4bc3a9f746d862c45cb89d705aa10f187bb96c76001afab07a0d35ce60142"
+
 [[package]]
 name = "unicode-ident"
 version = "1.0.24"

Cargo.toml

@@ -32,3 +32,4 @@ serde = { version = "1", features = ["derive"] }
 toml = "0.8"
 dirs = "5"
 tempfile = "3"
+pulldown-cmark = { version = "0.13", default-features = false }

LICENSE

@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2026 Owen
+Copyright (c) 2026 Owen Qwen
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

README.md

@@ -1,16 +1,10 @@
-<p align="center"><strong>Codex CLI</strong> is a clean, modern terminal text editor written in Rust.</p>
+# Lime
 
-<p align="center">
+Lime is a clean, modern terminal text editor written in Rust.
-  <img
-    src=".github/assets/preview.gif"
-    alt="Lime editor preview"
-    width="80%"
-  />
-</p>
 
-<p>It aims to be approachable like Nano, efficient and clean like Vim, and easy to use like VS Code, while keeping a standard non-modal editing model.</p>
+It aims to be approachable like Nano, efficient and clean like Vim, and easy to use like VS Code, while keeping a standard non-modal editing model.
 
----
+This is a test edit.
 
 ## Status
 
@@ -53,6 +47,7 @@ lime --force huge.log
 | `Ctrl-F` | Open file picker |
 | `Ctrl-R` | Search current file |
 | `Ctrl-G` | Go to line |
+| `Ctrl-P` | Toggle markdown preview |
 | `Ctrl-Z` | Undo |
 | `Ctrl-Y` | Redo |
 | `Ctrl-A` | Start of line |

crates/lime-ui/Cargo.toml

@@ -15,3 +15,4 @@ dirs.workspace = true
 unicode-width.workspace = true
 lime-core = { path = "../lime-core" }
 lime-syntax = { path = "../lime-syntax" }
+pulldown-cmark.workspace = true

crates/lime-ui/src/app.rs

@@ -18,7 +18,8 @@ use crate::config::Config;
 use crate::editor_view::{gutter_width, render_editor, Viewport};
 use crate::file_picker::FilePickerState;
 use crate::input::{map_editing_key, AppAction};
-use crate::layout::{app_layout, centered_rect};
+use crate::layout::{app_layout, centered_rect, with_preview};
+use crate::markdown_preview::render_preview;
 use crate::prompt::{ConfirmKind, ConfirmState, PromptKind, PromptState};
 use crate::status_bar::{render_status_bar, StatusInfo};
 use crate::terminal::TerminalSession;
@@ -65,6 +66,9 @@ pub struct App {
     highlights: Vec<HighlightSpan>,
     highlighted_revision: Option<u64>,
     highlighted_language: Language,
+    preview_open: bool,
+    preview_top_line: usize,
+    preview_revision: Option<u64>,
 }
 
 impl App {
@@ -90,6 +94,9 @@ impl App {
             highlights: Vec::new(),
             highlighted_revision: None,
             highlighted_language: Language::PlainText,
+            preview_open: false,
+            preview_top_line: 0,
+            preview_revision: None,
         };
 
         if let Some(path) = options.path {
@@ -181,7 +188,13 @@ impl App {
 
     fn draw(&mut self, frame: &mut Frame<'_>) {
         let area = frame.area();
-        let layout = app_layout(area);
+        let base_layout = app_layout(area);
+        let show_preview = self.preview_open && self.language == Language::Markdown;
+        let layout = if show_preview {
+            with_preview(base_layout, 55)
+        } else {
+            base_layout
+        };
         let total_lines = self.editor.line_count();
         let gutter = gutter_width(total_lines, self.config.show_line_numbers);
         let text_width = layout.editor.width.saturating_sub(gutter) as usize;
@@ -202,6 +215,24 @@ impl App {
             &self.highlights,
         );
 
+        if let Some(preview_area) = layout.preview {
+            let revision = self.editor.revision();
+            if self.preview_revision != Some(revision) {
+                self.preview_revision = Some(revision);
+            }
+            let preview_text = self.editor.text();
+            let preview_lines = crate::markdown_preview::render_lines(&preview_text, &self.theme);
+            let height = preview_area.height.saturating_sub(2) as usize;
+            self.ensure_preview_visible(preview_lines.len(), height);
+            render_preview(
+                frame,
+                preview_area,
+                &preview_text,
+                self.preview_top_line,
+                &self.theme,
+            );
+        }
+
         let file_name = self.file_label();
         render_status_bar(
             frame,
@@ -256,6 +287,10 @@ impl App {
                 self.mode = Mode::Prompt(PromptState::new(PromptKind::Search, "Search"));
                 Ok(())
             }
+            AppAction::ToggleMarkdownPreview => {
+                self.toggle_preview();
+                Ok(())
+            }
             AppAction::ClosePopup | AppAction::Cancel => {
                 self.mode = Mode::Editing;
                 Ok(())
@@ -589,6 +624,9 @@ impl App {
             self.language = language;
             self.highlighted_revision = None;
             self.highlighter.clear();
+            if language != Language::Markdown {
+                self.preview_open = false;
+            }
         }
     }
 
@@ -605,6 +643,37 @@ impl App {
         self.highlighted_language = self.language;
     }
 
+    fn toggle_preview(&mut self) {
+        if self.language != Language::Markdown {
+            self.set_status("Preview available for markdown only");
+            return;
+        }
+        self.preview_open = !self.preview_open;
+        if self.preview_open {
+            self.preview_top_line = 0;
+            self.preview_revision = None;
+            self.set_status("Preview opened");
+        } else {
+            self.set_status("Preview closed");
+        }
+    }
+
+    fn ensure_preview_visible(&mut self, total_preview_lines: usize, viewport_height: usize) {
+        if viewport_height == 0 {
+            return;
+        }
+        let cursor_line = self.editor.cursor().position.line;
+        let margin = 2usize.min(viewport_height / 3);
+        if cursor_line < self.preview_top_line + margin {
+            self.preview_top_line = cursor_line.saturating_sub(margin);
+        } else if cursor_line >= self.preview_top_line + viewport_height.saturating_sub(margin) {
+            self.preview_top_line =
+                cursor_line.saturating_sub(viewport_height.saturating_sub(margin + 1));
+        }
+        let max_top = total_preview_lines.saturating_sub(viewport_height);
+        self.preview_top_line = self.preview_top_line.min(max_top);
+    }
+
     fn file_label(&self) -> String {
         self.editor
             .buffer()

crates/lime-ui/src/command_bar.rs

@@ -32,6 +32,14 @@ pub fn render_help_bar(frame: &mut Frame<'_>, area: Rect, theme: &UiTheme) {
             "Go line ",
             theme.normal().fg(theme.help_fg).bg(theme.help_bg),
         ),
+        Span::styled(
+            " Ctrl-P ",
+            theme.normal().fg(theme.heading).bg(theme.help_bg),
+        ),
+        Span::styled(
+            "Preview ",
+            theme.normal().fg(theme.help_fg).bg(theme.help_bg),
+        ),
         Span::styled(
             " Ctrl-Q ",
             theme.normal().fg(theme.heading).bg(theme.help_bg),

crates/lime-ui/src/input.rs

@@ -9,6 +9,7 @@ pub enum AppAction {
     OpenFilePicker,
     OpenGoToLine,
     OpenSearch,
+    ToggleMarkdownPreview,
     ClosePopup,
     Confirm,
     Cancel,
@@ -26,6 +27,7 @@ pub fn map_editing_key(key: KeyEvent) -> AppAction {
             KeyCode::Char('f') | KeyCode::Char('F') => AppAction::OpenFilePicker,
             KeyCode::Char('g') | KeyCode::Char('G') => AppAction::OpenGoToLine,
             KeyCode::Char('r') | KeyCode::Char('R') => AppAction::OpenSearch,
+            KeyCode::Char('p') | KeyCode::Char('P') => AppAction::ToggleMarkdownPreview,
             KeyCode::Char('z') | KeyCode::Char('Z') => AppAction::Editor(EditorCommand::Undo),
             KeyCode::Char('y') | KeyCode::Char('Y') => AppAction::Editor(EditorCommand::Redo),
             KeyCode::Char('a') | KeyCode::Char('A') => {
@@ -77,4 +79,10 @@ mod tests {
         let action = map_editing_key(KeyEvent::new(KeyCode::Char('x'), KeyModifiers::NONE));
         assert_eq!(action, AppAction::Editor(EditorCommand::InsertChar('x')));
     }
+
+    #[test]
+    fn maps_preview_toggle_shortcut() {
+        let action = map_editing_key(KeyEvent::new(KeyCode::Char('p'), KeyModifiers::CONTROL));
+        assert_eq!(action, AppAction::ToggleMarkdownPreview);
+    }
 }

crates/lime-ui/src/layout.rs

@@ -3,10 +3,13 @@ use ratatui::layout::{Constraint, Direction, Layout, Rect};
 #[derive(Debug, Clone, Copy)]
 pub struct AppLayout {
     pub editor: Rect,
+    pub preview: Option<Rect>,
     pub status: Rect,
     pub help: Rect,
 }
 
+/// Split `area` into the editor viewport, an optional markdown preview pane
+/// on the right, the status bar, and the help bar.
 pub fn app_layout(area: Rect) -> AppLayout {
     let chunks = Layout::default()
         .direction(Direction::Vertical)
@@ -19,11 +22,36 @@ pub fn app_layout(area: Rect) -> AppLayout {
 
     AppLayout {
         editor: chunks[0],
+        preview: None,
         status: chunks[1],
         help: chunks[2],
     }
 }
 
+/// Split the editor region horizontally to make room for a preview pane on
+/// the right. `editor_pct` is the width percentage (0-100) allocated to the
+/// editor; the remainder goes to the preview, with a one-column divider.
+pub fn with_preview(layout: AppLayout, editor_pct: u16) -> AppLayout {
+    let editor_pct = editor_pct.clamp(20, 94);
+    let div = if layout.editor.width > 30 { 1 } else { 0 };
+    let constraints = [
+        Constraint::Percentage(editor_pct),
+        Constraint::Length(div),
+        Constraint::Percentage(100u16.saturating_sub(editor_pct)),
+    ];
+    let split = Layout::default()
+        .direction(Direction::Horizontal)
+        .constraints(constraints)
+        .split(layout.editor);
+
+    AppLayout {
+        editor: split[0],
+        preview: Some(split[2]),
+        status: layout.status,
+        help: layout.help,
+    }
+}
+
 pub fn centered_rect(percent_x: u16, percent_y: u16, area: Rect) -> Rect {
     let popup_layout = Layout::default()
         .direction(Direction::Vertical)
@@ -43,3 +71,25 @@ pub fn centered_rect(percent_x: u16, percent_y: u16, area: Rect) -> Rect {
         ])
         .split(popup_layout[1])[1]
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn preview_split_gives_two_panes() {
+        let area = Rect::new(0, 0, 100, 24);
+        let base = app_layout(area);
+        let split = with_preview(base, 55);
+        assert!(split.preview.is_some());
+        assert!(split.editor.width < base.editor.width);
+        assert!(split.preview.unwrap().width > 0);
+    }
+
+    #[test]
+    fn preview_disabled_has_no_pane() {
+        let area = Rect::new(0, 0, 80, 24);
+        let layout = app_layout(area);
+        assert!(layout.preview.is_none());
+    }
+}

crates/lime-ui/src/lib.rs

@@ -5,6 +5,7 @@ pub mod editor_view;
 pub mod file_picker;
 pub mod input;
 pub mod layout;
+pub mod markdown_preview;
 pub mod prompt;
 pub mod status_bar;
 pub mod terminal;

crates/lime-ui/src/markdown_preview.rs

@@ -0,0 +1,767 @@
+//! Render markdown source into styled ratatui lines for the preview pane.
+//!
+//! This is a pure converter: feed it the buffer text and a theme, get back a
+//! `Vec<Line>` that the caller can slice to the visible viewport. Parsing uses
+//! `pulldown-cmark` so we get correct CommonMark handling for free.
+
+use pulldown_cmark::{CodeBlockKind, Event, HeadingLevel, Options, Parser, Tag, TagEnd};
+use ratatui::style::{Modifier, Style};
+use ratatui::text::{Line, Span};
+use ratatui::widgets::{Block, Borders, Paragraph, Wrap};
+use ratatui::{layout::Rect, Frame};
+
+use crate::theme::UiTheme;
+
+/// Render the full markdown document into styled lines.
+pub fn render_lines(text: &str, theme: &UiTheme) -> Vec<Line<'static>> {
+    let opts = Options::ENABLE_TABLES
+        | Options::ENABLE_STRIKETHROUGH
+        | Options::ENABLE_TASKLISTS
+        | Options::ENABLE_GFM;
+    let parser = Parser::new_ext(text, opts);
+    let mut renderer = Renderer::new(theme);
+    for event in parser {
+        renderer.handle(event);
+    }
+    renderer.finish();
+    renderer.lines
+}
+
+/// Draw a slice of the rendered markdown into the given area, scrolling by
+/// `top_line` lines from the top of the document.
+pub fn render_preview(
+    frame: &mut Frame<'_>,
+    area: Rect,
+    text: &str,
+    top_line: usize,
+    theme: &UiTheme,
+) {
+    let block = Block::default()
+        .title(" Preview ")
+        .borders(Borders::ALL)
+        .border_style(Style::default().fg(theme.popup_border))
+        .style(theme.normal().bg(theme.background));
+    let inner = block.inner(area);
+    frame.render_widget(block, area);
+
+    let all_lines = render_lines(text, theme);
+    let height = inner.height as usize;
+    let start = top_line.min(all_lines.len());
+    let end = (start + height).min(all_lines.len());
+    let visible: Vec<Line<'_>> = all_lines
+        .iter()
+        .skip(start)
+        .take(end.saturating_sub(start))
+        .cloned()
+        .collect();
+
+    frame.render_widget(
+        Paragraph::new(visible)
+            .style(theme.normal().bg(theme.background))
+            .wrap(Wrap { trim: false }),
+        inner,
+    );
+}
+
+struct Renderer<'a> {
+    theme: &'a UiTheme,
+    lines: Vec<Line<'static>>,
+    /// Spans accumulated for the line currently being built.
+    line_spans: Vec<Span<'static>>,
+    /// Pending text run waiting to be flushed into a span.
+    run: String,
+    /// Style applied to the current text run.
+    run_style: Style,
+    /// Base style for the current block (heading, code, paragraph, ...).
+    base_style: Style,
+    /// Saved `run_style` values for nested inline tags (bold/italic/...).
+    inline_saves: Vec<Style>,
+    /// Prefix strings contributed by enclosing blocks (blockquote bar, list
+    /// indent, ...). Concatenated to form the left margin of each line.
+    indent_parts: Vec<&'static str>,
+    /// One entry per open list. `Some(n)` is an ordered list whose next item
+    /// marker is `n.`; `None` is an unordered list using `-`.
+    list_stack: Vec<Option<u64>>,
+    /// Marker to emit at the start of the current list item's first line.
+    item_marker: Option<String>,
+    /// Whether the next inline content should begin a fresh line.
+    at_line_start: bool,
+    /// Whether a blank separator line should be inserted before the next line.
+    pending_blank: bool,
+    /// Block-level state for fenced/indented code blocks.
+    in_code_block: bool,
+    /// Buffered lines for the current code block, emitted as a full box at
+    /// `TagEnd::CodeBlock` once the width and line count are known.
+    code_block_lines: Vec<String>,
+    /// Partial line being accumulated for the current code block.
+    code_block_current: String,
+    /// Language label for the current fenced code block, if any.
+    code_block_lang: Option<String>,
+    /// Block-level state for blockquotes (affects prefix only).
+    quote_depth: usize,
+    /// Pending link destination URLs, one per nested `Link`/`Image` tag.
+    link_urls: Vec<String>,
+    /// Minimal table support: track current row cell separator state.
+    table_cell_index: usize,
+    in_table_row: bool,
+}
+
+impl<'a> Renderer<'a> {
+    fn new(theme: &'a UiTheme) -> Self {
+        Self {
+            theme,
+            lines: Vec::new(),
+            line_spans: Vec::new(),
+            run: String::new(),
+            run_style: theme.normal(),
+            base_style: theme.normal(),
+            inline_saves: Vec::new(),
+            indent_parts: Vec::new(),
+            list_stack: Vec::new(),
+            item_marker: None,
+            at_line_start: true,
+            pending_blank: false,
+            in_code_block: false,
+            code_block_lines: Vec::new(),
+            code_block_current: String::new(),
+            code_block_lang: None,
+            quote_depth: 0,
+            link_urls: Vec::new(),
+            table_cell_index: 0,
+            in_table_row: false,
+        }
+    }
+
+    fn handle(&mut self, event: Event<'_>) {
+        match event {
+            Event::Start(tag) => self.start_tag(tag),
+            Event::End(end) => self.end_tag(end),
+            Event::Text(text) => self.text(&text),
+            Event::Code(code) => self.inline_code(&code),
+            Event::Html(html) | Event::InlineHtml(html) => self.text(&html),
+            Event::SoftBreak => self.soft_break(),
+            Event::HardBreak => self.hard_break(),
+            Event::Rule => self.rule(),
+            Event::TaskListMarker(checked) => self.task_marker(checked),
+            Event::InlineMath(math) | Event::DisplayMath(math) => self.inline_code(&math),
+            Event::FootnoteReference(label) => {
+                let s = format!("[^{label}]");
+                self.text(&s);
+            }
+        }
+    }
+
+    fn start_tag(&mut self, tag: Tag<'_>) {
+        match tag {
+            Tag::Paragraph => {
+                self.end_line();
+                self.reset_block_style();
+            }
+            Tag::Heading { level, .. } => {
+                self.end_line();
+                self.request_blank();
+                self.base_style = self.heading_style(level);
+                self.run_style = self.base_style;
+                let hashes = "#".repeat(level as usize);
+                self.line_spans
+                    .push(Span::styled(format!("{hashes} "), self.base_style));
+                self.at_line_start = false;
+            }
+            Tag::CodeBlock(kind) => {
+                self.end_line();
+                self.request_blank();
+                self.in_code_block = true;
+                self.base_style = self.code_style();
+                self.run_style = self.base_style;
+                self.code_block_lines.clear();
+                self.code_block_current.clear();
+                self.code_block_lang = match kind {
+                    CodeBlockKind::Fenced(lang) if !lang.is_empty() => Some(lang.into_string()),
+                    _ => None,
+                };
+            }
+            Tag::BlockQuote(_) => {
+                self.end_line();
+                self.indent_parts.push("│ ");
+                self.quote_depth += 1;
+                self.reset_block_style();
+            }
+            Tag::List(start) => {
+                self.end_line();
+                if !self.list_stack.is_empty() {
+                    self.indent_parts.push("  ");
+                }
+                self.list_stack.push(start);
+                self.reset_block_style();
+            }
+            Tag::Item => {
+                self.end_line();
+                self.item_marker = Some(self.next_item_marker());
+                self.reset_block_style();
+            }
+            Tag::Emphasis => self.push_inline(self.italic_style()),
+            Tag::Strong => self.push_inline(self.bold_style()),
+            Tag::Strikethrough => self.push_inline(self.strike_style()),
+            Tag::Link { dest_url, .. } => {
+                self.link_urls.push(dest_url.into_string());
+                self.push_inline(self.link_style());
+            }
+            Tag::Image { dest_url, .. } => {
+                self.link_urls.push(dest_url.into_string());
+                self.line_spans
+                    .push(Span::styled("image: ", self.theme.dim()));
+                self.push_inline(self.link_style());
+            }
+            Tag::Table(_) => {
+                self.end_line();
+                self.request_blank();
+            }
+            Tag::TableHead | Tag::TableRow => {
+                self.end_line();
+                self.in_table_row = true;
+                self.table_cell_index = 0;
+                self.reset_block_style();
+            }
+            Tag::TableCell => {
+                if self.table_cell_index > 0 {
+                    self.line_spans.push(Span::styled(" │ ", self.theme.dim()));
+                }
+                self.table_cell_index += 1;
+                self.at_line_start = false;
+            }
+            Tag::HtmlBlock => {
+                self.end_line();
+                self.request_blank();
+                self.base_style = self.theme.dim();
+                self.run_style = self.base_style;
+            }
+            Tag::FootnoteDefinition(_)
+            | Tag::DefinitionList
+            | Tag::DefinitionListTitle
+            | Tag::DefinitionListDefinition
+            | Tag::MetadataBlock(_)
+            | Tag::Superscript
+            | Tag::Subscript => {
+                self.reset_block_style();
+            }
+        }
+    }
+
+    fn end_tag(&mut self, end: TagEnd) {
+        match end {
+            TagEnd::Paragraph => {
+                self.end_line();
+                self.request_blank();
+            }
+            TagEnd::Heading(_) => {
+                self.end_line();
+                self.request_blank();
+                self.reset_block_style();
+            }
+            TagEnd::CodeBlock => {
+                self.in_code_block = false;
+                if !self.code_block_current.is_empty() {
+                    self.code_block_lines
+                        .push(std::mem::take(&mut self.code_block_current));
+                }
+                self.render_code_box();
+                self.request_blank();
+                self.reset_block_style();
+            }
+            TagEnd::BlockQuote(_) => {
+                self.end_line();
+                if !self.indent_parts.is_empty() {
+                    self.indent_parts.pop();
+                }
+                self.quote_depth = self.quote_depth.saturating_sub(1);
+                self.request_blank();
+                self.reset_block_style();
+            }
+            TagEnd::List(_) => {
+                self.end_line();
+                let was_nested = !self.list_stack.is_empty();
+                self.list_stack.pop();
+                if was_nested {
+                    if !self.indent_parts.is_empty() {
+                        self.indent_parts.pop();
+                    }
+                } else {
+                    self.request_blank();
+                }
+                self.reset_block_style();
+            }
+            TagEnd::Item => {
+                self.end_line();
+                self.item_marker = None;
+                self.reset_block_style();
+            }
+            TagEnd::Emphasis | TagEnd::Strong | TagEnd::Strikethrough => self.pop_inline(),
+            TagEnd::Link | TagEnd::Image => {
+                self.pop_inline();
+                if let Some(url) = self.link_urls.pop() {
+                    if !url.is_empty() {
+                        self.ensure_line_started();
+                        self.flush_run();
+                        self.line_spans
+                            .push(Span::styled(format!(" ({url})"), self.theme.dim()));
+                    }
+                }
+            }
+            TagEnd::Table => {
+                self.end_line();
+                self.request_blank();
+            }
+            TagEnd::TableHead | TagEnd::TableRow => {
+                self.in_table_row = false;
+                self.table_cell_index = 0;
+            }
+            TagEnd::TableCell => {
+                // Cell content already emitted inline; nothing to do.
+            }
+            TagEnd::HtmlBlock => {
+                self.end_line();
+                self.request_blank();
+                self.reset_block_style();
+            }
+            _ => {}
+        }
+    }
+
+    fn text(&mut self, text: &str) {
+        if self.in_code_block {
+            self.code_block_text(text);
+            return;
+        }
+        self.ensure_line_started();
+        self.run.push_str(text);
+    }
+
+    fn code_block_text(&mut self, text: &str) {
+        for (i, part) in text.split('\n').enumerate() {
+            if i > 0 {
+                self.code_block_lines
+                    .push(std::mem::take(&mut self.code_block_current));
+            }
+            self.code_block_current.push_str(part);
+        }
+        self.at_line_start = false;
+    }
+
+    fn render_code_box(&mut self) {
+        let lines = std::mem::take(&mut self.code_block_lines);
+        if lines.is_empty() {
+            return;
+        }
+
+        let prefix = self.current_prefix();
+        let dim = self.theme.dim();
+        let code_style = self.code_style();
+        let line_num_width = lines.len().to_string().len();
+        let max_code_len = lines
+            .iter()
+            .map(|l| l.chars().count())
+            .max()
+            .unwrap_or(0)
+            .max(1);
+
+        // Layout per line: "│ " + {n:>w} + " │ " + {code:<pad} + " │"
+        let box_width = 2 + line_num_width + 3 + max_code_len + 2;
+
+        let push_prefix = |spans: &mut Vec<Span<'static>>, p: &str| {
+            if !p.is_empty() {
+                spans.push(Span::styled(p.to_string(), dim));
+            }
+        };
+
+        // Top border
+        let top = {
+            let header = match &self.code_block_lang {
+                Some(lang) => format!("┌─ {lang} "),
+                None => "┌".to_string(),
+            };
+            let header_len = header.chars().count();
+            let fill = box_width.saturating_sub(header_len + 1);
+            format!("{}{}┐", header, "─".repeat(fill))
+        };
+        let mut spans = Vec::new();
+        push_prefix(&mut spans, &prefix);
+        spans.push(Span::styled(top, dim));
+        self.lines.push(Line::from(spans));
+
+        // Code lines with line numbers
+        for (idx, code) in lines.iter().enumerate() {
+            let num = format!("{:>width$}", idx + 1, width = line_num_width);
+            let code_len = code.chars().count();
+
+            let mut spans = Vec::new();
+            push_prefix(&mut spans, &prefix);
+            spans.push(Span::styled("│ ", dim));
+            spans.push(Span::styled(num, dim));
+            spans.push(Span::styled(" │ ", dim));
+            spans.push(Span::styled(code.clone(), code_style));
+            let pad = max_code_len.saturating_sub(code_len);
+            if pad > 0 {
+                spans.push(Span::styled(" ".repeat(pad), code_style));
+            }
+            spans.push(Span::styled(" │", dim));
+            self.lines.push(Line::from(spans));
+        }
+
+        // Bottom border
+        let bottom = format!("└{}┘", "─".repeat(box_width.saturating_sub(2)));
+        let mut spans = Vec::new();
+        push_prefix(&mut spans, &prefix);
+        spans.push(Span::styled(bottom, dim));
+        self.lines.push(Line::from(spans));
+    }
+
+    fn inline_code(&mut self, code: &str) {
+        self.ensure_line_started();
+        self.flush_run();
+        let style = self.code_style();
+        self.line_spans.push(Span::styled(code.to_string(), style));
+    }
+
+    fn soft_break(&mut self) {
+        if self.in_code_block {
+            return;
+        }
+        self.end_line();
+        self.at_line_start = true;
+        // Continuation of the same block: reuse the current prefix/marker flow
+        // but do not re-emit the item marker (it was consumed on the first
+        // line of the item).
+    }
+
+    fn hard_break(&mut self) {
+        if self.in_code_block {
+            return;
+        }
+        self.end_line();
+        self.end_line();
+    }
+
+    fn rule(&mut self) {
+        self.end_line();
+        self.request_blank();
+        let prefix = self.current_prefix();
+        if !prefix.is_empty() {
+            self.line_spans.push(Span::styled(prefix, self.theme.dim()));
+        }
+        let width = 40usize;
+        let rule = "─".repeat(width);
+        self.line_spans.push(Span::styled(rule, self.theme.dim()));
+        self.flush_line();
+        self.request_blank();
+    }
+
+    fn task_marker(&mut self, checked: bool) {
+        // Task list markers replace the bullet marker.
+        self.item_marker = None;
+        self.ensure_line_started();
+        self.flush_run();
+        let glyph = if checked { "[x] " } else { "[ ] " };
+        self.line_spans.push(Span::styled(glyph, self.theme.dim()));
+    }
+
+    fn ensure_line_started(&mut self) {
+        if self.at_line_start {
+            self.begin_line();
+            self.at_line_start = false;
+        }
+    }
+
+    fn begin_line(&mut self) {
+        if self.pending_blank {
+            self.pending_blank = false;
+            self.lines.push(Line::default());
+        }
+        let prefix = self.current_prefix();
+        if !prefix.is_empty() {
+            self.line_spans.push(Span::styled(prefix, self.theme.dim()));
+        }
+        if let Some(marker) = self.item_marker.take() {
+            self.line_spans
+                .push(Span::styled(marker, self.theme.normal()));
+        }
+    }
+
+    fn end_line(&mut self) {
+        self.flush_run();
+        if !self.line_spans.is_empty() || self.in_code_block {
+            self.lines
+                .push(Line::from(std::mem::take(&mut self.line_spans)));
+        }
+        self.at_line_start = true;
+    }
+
+    fn flush_line(&mut self) {
+        self.flush_run();
+        self.lines
+            .push(Line::from(std::mem::take(&mut self.line_spans)));
+        self.at_line_start = true;
+    }
+
+    fn flush_run(&mut self) {
+        if !self.run.is_empty() {
+            let span = Span::styled(self.run.clone(), self.run_style);
+            self.line_spans.push(span);
+            self.run.clear();
+        }
+    }
+
+    fn request_blank(&mut self) {
+        if !self.lines.is_empty() {
+            self.pending_blank = true;
+        }
+    }
+
+    fn current_prefix(&self) -> String {
+        let mut s = String::new();
+        for part in &self.indent_parts {
+            s.push_str(part);
+        }
+        s
+    }
+
+    fn next_item_marker(&mut self) -> String {
+        match self.list_stack.last_mut() {
+            Some(Some(n)) => {
+                let marker = format!("{}. ", n);
+                *n += 1;
+                marker
+            }
+            _ => "- ".to_string(),
+        }
+    }
+
+    fn push_inline(&mut self, style: Style) {
+        self.ensure_line_started();
+        self.flush_run();
+        self.inline_saves.push(self.run_style);
+        self.run_style = style;
+    }
+
+    fn pop_inline(&mut self) {
+        self.flush_run();
+        if let Some(saved) = self.inline_saves.pop() {
+            self.run_style = saved;
+        }
+    }
+
+    fn reset_block_style(&mut self) {
+        self.base_style = self.theme.normal();
+        self.run_style = self.base_style;
+    }
+
+    fn finish(&mut self) {
+        self.end_line();
+        // Trim trailing blank lines.
+        while self.lines.last().is_some_and(|line| line.spans.is_empty()) {
+            self.lines.pop();
+        }
+    }
+
+    fn heading_style(&self, level: HeadingLevel) -> Style {
+        let color = match level {
+            HeadingLevel::H1 | HeadingLevel::H2 => self.theme.heading,
+            HeadingLevel::H3 | HeadingLevel::H4 => self.theme.function,
+            HeadingLevel::H5 | HeadingLevel::H6 => self.theme.type_name,
+        };
+        let mut style = Style::default().fg(color).bg(self.theme.background);
+        if matches!(level, HeadingLevel::H1 | HeadingLevel::H2) {
+            style = style.add_modifier(Modifier::BOLD);
+        }
+        style
+    }
+
+    fn code_style(&self) -> Style {
+        Style::default()
+            .fg(self.theme.string)
+            .bg(self.theme.selection_bg)
+    }
+
+    fn bold_style(&self) -> Style {
+        self.run_style.add_modifier(Modifier::BOLD)
+    }
+
+    fn italic_style(&self) -> Style {
+        self.run_style.add_modifier(Modifier::ITALIC)
+    }
+
+    fn strike_style(&self) -> Style {
+        self.run_style.add_modifier(Modifier::CROSSED_OUT)
+    }
+
+    fn link_style(&self) -> Style {
+        Style::default()
+            .fg(self.theme.keyword)
+            .bg(self.theme.background)
+            .add_modifier(Modifier::UNDERLINED)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn line_text(line: &Line<'_>) -> String {
+        line.spans
+            .iter()
+            .map(|span| span.content.as_ref())
+            .collect::<Vec<_>>()
+            .join("")
+    }
+
+    #[test]
+    fn renders_heading_with_hashes() {
+        let theme = UiTheme::default();
+        let lines = render_lines("# Title\n\nBody", &theme);
+        assert!(line_text(&lines[0]).starts_with("# Title"));
+        assert!(line_text(&lines[1]).is_empty());
+        assert_eq!(line_text(&lines[2]), "Body");
+    }
+
+    #[test]
+    fn renders_unordered_list() {
+        let theme = UiTheme::default();
+        let lines = render_lines("- one\n- two\n- three", &theme);
+        assert_eq!(line_text(&lines[0]), "- one");
+        assert_eq!(line_text(&lines[1]), "- two");
+        assert_eq!(line_text(&lines[2]), "- three");
+    }
+
+    #[test]
+    fn renders_ordered_list_with_increasing_numbers() {
+        let theme = UiTheme::default();
+        let lines = render_lines("1. first\n2. second\n3. third", &theme);
+        assert_eq!(line_text(&lines[0]), "1. first");
+        assert_eq!(line_text(&lines[1]), "2. second");
+        assert_eq!(line_text(&lines[2]), "3. third");
+    }
+
+    #[test]
+    fn renders_nested_list_with_indent() {
+        let theme = UiTheme::default();
+        let lines = render_lines("- top\n  - nested\n- back", &theme);
+        assert_eq!(line_text(&lines[0]), "- top");
+        assert_eq!(line_text(&lines[1]), "  - nested");
+        assert_eq!(line_text(&lines[2]), "- back");
+    }
+
+    #[test]
+    fn renders_blockquote_with_bar_prefix() {
+        let theme = UiTheme::default();
+        let lines = render_lines("> quoted text", &theme);
+        assert_eq!(line_text(&lines[0]), "│ quoted text");
+    }
+
+    #[test]
+    fn renders_fenced_code_block_with_box_and_line_numbers() {
+        let theme = UiTheme::default();
+        let md = "```rust\nfn main() {}\n```\n";
+        let lines = render_lines(md, &theme);
+        let combined: Vec<String> = lines.iter().map(|l| line_text(l)).collect();
+
+        // Top border with language label
+        assert!(
+            combined.iter().any(|s| s.starts_with("┌─ rust ")),
+            "missing top border: {combined:?}"
+        );
+        // Code line with line number and side borders
+        assert!(
+            combined
+                .iter()
+                .any(|s| s.contains("│ 1 │") && s.contains("fn main()")),
+            "missing numbered code line: {combined:?}"
+        );
+        // Bottom border
+        assert!(
+            combined.iter().any(|s| s.starts_with('└')),
+            "missing bottom border: {combined:?}"
+        );
+    }
+
+    #[test]
+    fn renders_code_block_line_number_padding() {
+        let theme = UiTheme::default();
+        let md = "```\na\nb\nc\nd\ne\nf\ng\nh\ni\nj\n```\n";
+        let lines = render_lines(md, &theme);
+        let combined: Vec<String> = lines.iter().map(|l| line_text(l)).collect();
+        // Single-digit line numbers should be right-aligned to width 2
+        assert!(
+            combined.iter().any(|s| s.contains("│  1 │")),
+            "line 1 not padded: {combined:?}"
+        );
+        // Double-digit line numbers should have no extra padding
+        assert!(
+            combined.iter().any(|s| s.contains("│ 10 │")),
+            "line 10 not correct: {combined:?}"
+        );
+    }
+
+    #[test]
+    fn renders_code_block_without_language() {
+        let theme = UiTheme::default();
+        let md = "```\nhello\n```\n";
+        let lines = render_lines(md, &theme);
+        let combined: Vec<String> = lines.iter().map(|l| line_text(l)).collect();
+        assert!(
+            combined
+                .iter()
+                .any(|s| s.starts_with('┌') && !s.contains("┌─ ")),
+            "plain code block should have bare top border: {combined:?}"
+        );
+        assert!(
+            combined.iter().any(|s| s.contains("hello")),
+            "missing code content: {combined:?}"
+        );
+    }
+
+    #[test]
+    fn renders_horizontal_rule() {
+        let theme = UiTheme::default();
+        let lines = render_lines("above\n\n---\n\nbelow", &theme);
+        let combined: String = lines
+            .iter()
+            .map(|l| line_text(l))
+            .collect::<Vec<_>>()
+            .join("\n");
+        assert!(combined.contains("───"), "{combined}");
+        assert!(combined.contains("above"));
+        assert!(combined.contains("below"));
+    }
+
+    #[test]
+    fn renders_link_with_url() {
+        let theme = UiTheme::default();
+        let lines = render_lines("[Lime](https://example.com)", &theme);
+        let text = line_text(&lines[0]);
+        assert!(text.contains("Lime"), "{text}");
+        assert!(text.contains("(https://example.com)"), "{text}");
+    }
+
+    #[test]
+    fn renders_task_list_markers() {
+        let theme = UiTheme::default();
+        let lines = render_lines("- [ ] todo\n- [x] done", &theme);
+        assert_eq!(line_text(&lines[0]), "[ ] todo");
+        assert_eq!(line_text(&lines[1]), "[x] done");
+    }
+
+    #[test]
+    fn renders_bold_and_italic_text() {
+        let theme = UiTheme::default();
+        let lines = render_lines("**bold** and _italic_", &theme);
+        let text = line_text(&lines[0]);
+        assert!(text.contains("bold"), "{text}");
+        assert!(text.contains("italic"), "{text}");
+    }
+
+    #[test]
+    fn empty_input_yields_no_lines() {
+        let theme = UiTheme::default();
+        let lines = render_lines("", &theme);
+        assert!(lines.is_empty());
+    }
+}