feat(04-02): wire virtual directory listing page with history and Tab-cycling

- navigate_to_directory() builds tree view via list_vault_files() + build_directory_lines()
- follow_selected_link() routes __directory__ sentinel to navigate_to_directory()
- navigate_back/forward regenerate directory listing fresh when target_path == __directory__
- handle_resize() skips re-render for directory pages (fixed-width text, no markdown)
- build_directory_lines() emits yellow-bold dirs and cyan bracketed file links with LinkRecord

src/app.rs

@@ -313,6 +313,11 @@ impl App {
     /// We re-render so horizontal rules, code block borders, and table widths adapt.
     /// On index.md, splash lines are re-prepended after the re-render.
     fn handle_resize(&mut self, new_width: u16) {
+        // Directory listing is fixed-width text — no width-based re-render needed
+        if self.current_path == "__directory__" {
+            return;
+        }
+
         if let Some(ref content) = self.raw_content.clone() {
             let vault_path = self.config.vault_path.clone();
             let (mut lines, mut link_records) = crate::renderer::render_markdown(
@@ -524,6 +529,46 @@ impl App {
         }
     }
 
+    /// Navigate to the virtual directory listing page.
+    ///
+    /// Generates a tree view of all vault files as styled lines with link records.
+    /// Saves current scroll/link state to history and pushes a new history entry.
+    fn navigate_to_directory(&mut self) {
+        let vault_path = self.config.vault_path.clone();
+
+        // Save current state to history
+        if let Some(entry) = self.history.get_mut(self.history_index) {
+            entry.scroll_offset = self.scroll_offset;
+            entry.selected_link = self.selected_link;
+        }
+        // Truncate forward history
+        self.history.truncate(self.history_index + 1);
+
+        // Build directory listing
+        let dir_entries = crate::vault::list_vault_files(&vault_path);
+        let (lines, link_records) = build_directory_lines(&dir_entries);
+
+        self.document = DocumentState::Loaded {
+            filename: "[Directory]".to_string(),
+            lines,
+        };
+        self.raw_content = None; // No raw markdown for virtual pages
+        self.link_records = link_records;
+        self.selected_link = None;
+        self.scroll_offset = 0;
+        self.current_path = "__directory__".to_string();
+        self.filename = "[Directory]".to_string();
+        self.page_meta = None; // No file metadata for virtual pages
+
+        // Push history entry
+        self.history.push(HistoryEntry {
+            path: "__directory__".to_string(),
+            scroll_offset: 0,
+            selected_link: None,
+        });
+        self.history_index = self.history.len() - 1;
+    }
+
     /// Navigate back one step in the history stack, restoring scroll and link selection.
     fn navigate_back(&mut self) {
         if self.history_index == 0 {
@@ -543,7 +588,23 @@ impl App {
 
         // Re-load and re-render the document (per research: don't cache rendered output)
         let vault_path = self.config.vault_path.clone();
-        if let crate::vault::VaultDocument::Loaded { path, content } =
+
+        if target_path == "__directory__" {
+            // Regenerate directory listing (always fresh, never cached)
+            let dir_entries = crate::vault::list_vault_files(&vault_path);
+            let (lines, link_records) = build_directory_lines(&dir_entries);
+            self.document = DocumentState::Loaded {
+                filename: "[Directory]".to_string(),
+                lines,
+            };
+            self.raw_content = None;
+            self.link_records = link_records;
+            self.selected_link = target_link;
+            self.scroll_offset = target_scroll;
+            self.current_path = "__directory__".to_string();
+            self.filename = "[Directory]".to_string();
+            self.page_meta = None;
+        } else if let crate::vault::VaultDocument::Loaded { path, content } =
             crate::vault::load_document(&vault_path, &target_path)
         {
             let filename = path
@@ -605,7 +666,23 @@ impl App {
         let target_link = self.history[self.history_index].selected_link;
 
         let vault_path = self.config.vault_path.clone();
-        if let crate::vault::VaultDocument::Loaded { path, content } =
+
+        if target_path == "__directory__" {
+            // Regenerate directory listing (always fresh, never cached)
+            let dir_entries = crate::vault::list_vault_files(&vault_path);
+            let (lines, link_records) = build_directory_lines(&dir_entries);
+            self.document = DocumentState::Loaded {
+                filename: "[Directory]".to_string(),
+                lines,
+            };
+            self.raw_content = None;
+            self.link_records = link_records;
+            self.selected_link = target_link;
+            self.scroll_offset = target_scroll;
+            self.current_path = "__directory__".to_string();
+            self.filename = "[Directory]".to_string();
+            self.page_meta = None;
+        } else if let crate::vault::VaultDocument::Loaded { path, content } =
             crate::vault::load_document(&vault_path, &target_path)
         {
             let filename = path
@@ -664,9 +741,13 @@ impl App {
             // Resolve wiki-link to vault-relative path
             match crate::vault::resolve_wiki_link(&vault_path, &dest) {
                 Some(resolved) => {
+                    if resolved == Path::new("__directory__") {
+                        self.navigate_to_directory();
+                    } else {
                         let rel = resolved.to_string_lossy().to_string();
                         self.navigate_to(&rel);
                     }
+                }
                 None => {
                     // Broken wiki-link — already shown as red/strikethrough in render.
                     // Do nothing on Enter for broken links.
@@ -674,6 +755,9 @@ impl App {
             }
         } else {
             // Standard markdown link — resolve relative to current document's directory
+            if dest == "__directory__" {
+                self.navigate_to_directory();
+            } else {
                 match crate::vault::resolve_standard_link(&vault_path, &self.current_path, &dest) {
                     Some(resolved) => {
                         let rel = resolved.to_string_lossy().to_string();
@@ -689,6 +773,7 @@ impl App {
                 }
             }
         }
+    }
 
     // ── Link cycling helpers ───────────────────────────────────────────────────
 
@@ -1053,6 +1138,67 @@ impl App {
     }
 }
 
+// ── Directory listing builder ─────────────────────────────────────────────────
+
+/// Build styled lines and link records from vault directory entries.
+fn build_directory_lines(
+    entries: &[crate::vault::DirEntry],
+) -> (Vec<Line<'static>>, Vec<crate::renderer::LinkRecord>) {
+    let mut lines: Vec<Line<'static>> = Vec::new();
+    let mut link_records: Vec<crate::renderer::LinkRecord> = Vec::new();
+
+    // Title header
+    lines.push(Line::from(Span::styled(
+        " VAULT DIRECTORY".to_string(),
+        Style::default().fg(Color::LightCyan).add_modifier(Modifier::BOLD),
+    )));
+    lines.push(Line::from(Span::styled(
+        "=".repeat(40),
+        Style::default().fg(Color::LightCyan),
+    )));
+    lines.push(Line::default()); // blank separator
+
+    for entry in entries {
+        let indent = "  ".repeat(entry.depth.saturating_sub(1));
+        let indent_chars = indent.chars().count();
+
+        if entry.is_dir {
+            // Directory: yellow bold, not a link
+            lines.push(Line::from(vec![
+                Span::raw(indent),
+                Span::styled(
+                    format!("{}/", entry.name),
+                    Style::default().fg(Color::Yellow).add_modifier(Modifier::BOLD),
+                ),
+            ]));
+        } else if let Some(ref vault_rel) = entry.vault_path {
+            // File: cyan link — navigable via Tab-cycling
+            let display = format!("[{}]", entry.name);
+            let col_offset = indent_chars;
+            let span_len = display.chars().count();
+            let line_index = lines.len(); // This line's index in the lines vec
+
+            lines.push(Line::from(vec![
+                Span::raw(indent),
+                Span::styled(
+                    display,
+                    Style::default().fg(Color::LightCyan),
+                ),
+            ]));
+
+            link_records.push(crate::renderer::LinkRecord {
+                line_index,
+                col_offset,
+                span_len,
+                dest: vault_rel.clone(),
+                is_wiki: false, // Direct vault-relative path, not a wiki-link
+            });
+        }
+    }
+
+    (lines, link_records)
+}
+
 // ── Breadcrumb helper ─────────────────────────────────────────────────────────
 
 /// Build a breadcrumb trail from a vault-relative path.