Add strikethrough shortcut, fenced code toggle, and CodeMirror-aware undo/redo

- Bind Ctrl+Shift+S to strikethrough
- Smart code toggle: fenced block for multi-line selections, inline otherwise
- Link editing: selecting an existing link now selects its URL for editing
- Route undo/redo shortcuts through IPC so CodeMirror history is used when
  the editor has focus instead of Electron's native menu-role undo/redo
- Add Indent/Outdent toolbar buttons

src/main/index.ts

@@ -58,6 +58,7 @@ function createWindow() {
       preload: path.join(__dirname, "preload.js"),
     },
   });
+  forwardEditShortcuts(mainWindow);
   mainWindow.loadFile(path.join(__dirname, "index.html"));
   mainWindow.webContents.on("did-finish-load", () => {
     console.log("[folio] renderer loaded");
@@ -114,6 +115,25 @@ function notifyChange() {
   getWindow()?.webContents.send("folio:chapters-changed");
 }
 
+// Route undo/redo shortcuts to the renderer so CodeMirror's own history is
+// used when the editor has focus, instead of Electron's native (menu-role)
+// undo/redo which does not understand the editor's history.
+function forwardEditShortcuts(win: BrowserWindow) {
+  win.webContents.on("before-input-event", (event, input) => {
+    if (input.type !== "keyDown" || !input.key) return;
+    const mod = input.control || input.meta;
+    if (!mod) return;
+    const key = input.key.toLowerCase();
+    if (key === "z" && !input.shift) {
+      event.preventDefault();
+      win.webContents.send("folio:undo-requested");
+    } else if ((key === "z" && input.shift) || (key === "y" && !input.shift)) {
+      event.preventDefault();
+      win.webContents.send("folio:redo-requested");
+    }
+  });
+}
+
 async function openBookAt(p: string): Promise<BookResult | ErrResult> {
   try {
     const meta = loadBook(p);

src/main/menu.ts

@@ -66,8 +66,16 @@ export function buildMenu(
   const editMenu: MenuItem = {
     label: "Edit",
     submenu: [
-      { role: "undo" },
-      { role: "redo" },
+      {
+        label: "Undo",
+        accelerator: "CmdOrCtrl+Z",
+        click: () => getWindow()?.webContents.send("folio:undo-requested"),
+      },
+      {
+        label: "Redo",
+        accelerator: isMac ? "Cmd+Shift+Z" : "Ctrl+Shift+Z",
+        click: () => getWindow()?.webContents.send("folio:redo-requested"),
+      },
       { type: "separator" },
       { role: "cut" },
       { role: "copy" },

src/main/preload.ts

@@ -47,4 +47,8 @@ contextBridge.exposeInMainWorld("folio", {
     ipcRenderer.on("folio:export-markdown-requested", () => cb()),
   onExportZipRequested: (cb: () => void) =>
     ipcRenderer.on("folio:export-zip-requested", () => cb()),
+  onUndoRequested: (cb: () => void) =>
+    ipcRenderer.on("folio:undo-requested", () => cb()),
+  onRedoRequested: (cb: () => void) =>
+    ipcRenderer.on("folio:redo-requested", () => cb()),
 });

src/renderer/book.ts

@@ -2,7 +2,7 @@ import type { BookMeta } from "../main/project.js";
 import { alertMessage, confirmMessage, promptInput } from "./dialog.js";
 import { createMdEditor, editorText, setEditorText } from "./md-editor.js";
 import type { EditorView } from "@codemirror/view";
-import { redo, undo } from "@codemirror/commands";
+import { redo, undo, indentLess, indentMore } from "@codemirror/commands";
 import {
   clearFormatting,
   headingLevelAt,
@@ -11,7 +11,7 @@ import {
   toggleBlockquote,
   toggleBold,
   toggleBulletList,
-  toggleInlineCode,
+  toggleCode,
   toggleItalic,
   toggleLink,
   toggleOrderedList,
@@ -45,6 +45,8 @@ export type FolioAPI = {
   onRevealRequested: (cb: (p: string) => void) => void;
   onExportMarkdownRequested: (cb: () => void) => void;
   onExportZipRequested: (cb: () => void) => void;
+  onUndoRequested: (cb: () => void) => void;
+  onRedoRequested: (cb: () => void) => void;
 };
 
 const $ = (id: string) => document.getElementById(id) as HTMLElement;
@@ -102,11 +104,13 @@ export function initBook(api: FolioAPI) {
     bold: toggleBold,
     italic: toggleItalic,
     strike: toggleStrikethrough,
-    code: toggleInlineCode,
+    code: toggleCode,
     link: toggleLink,
     bullet: toggleBulletList,
     number: toggleOrderedList,
     quote: toggleBlockquote,
+    indent: indentMore,
+    outdent: indentLess,
     hr: insertHorizontalRule,
     clear: clearFormatting,
   };
@@ -537,6 +541,14 @@ export function initBook(api: FolioAPI) {
   api.onRevealRequested((p) => void api.revealInFolder(p));
   api.onExportMarkdownRequested(() => void exportMarkdown());
   api.onExportZipRequested(() => void exportZip());
+  api.onUndoRequested(() => {
+    if (editorView.hasFocus) undo(editorView);
+    else document.execCommand("undo");
+  });
+  api.onRedoRequested(() => {
+    if (editorView.hasFocus) redo(editorView);
+    else document.execCommand("redo");
+  });
 
   setChapterButtons(false);
   void renderRecents();

src/renderer/index.html

@@ -68,13 +68,15 @@
               <button class="toolbar-btn b" data-cmd="bold" title="Bold (Ctrl+B)">B</button>
               <button class="toolbar-btn i" data-cmd="italic" title="Italic (Ctrl+I)">I</button>
               <button class="toolbar-btn s" data-cmd="strike" title="Strikethrough">S</button>
-              <button class="toolbar-btn code" data-cmd="code" title="Inline code">code</button>
+              <button class="toolbar-btn code" data-cmd="code" title="Inline code / code block">code</button>
               <button class="toolbar-btn" data-cmd="link" title="Link (Ctrl+K)">&#8599;</button>
             </div>
             <div class="toolbar-group">
               <button class="toolbar-btn" data-cmd="bullet" title="Bulleted list">&#8226;</button>
               <button class="toolbar-btn" data-cmd="number" title="Numbered list">1.</button>
               <button class="toolbar-btn" data-cmd="quote" title="Blockquote">&#10077;</button>
+              <button class="toolbar-btn" data-cmd="indent" title="Indent (Tab)">&#8594;</button>
+              <button class="toolbar-btn" data-cmd="outdent" title="Outdent (Shift+Tab)">&#8592;</button>
               <button class="toolbar-btn" data-cmd="hr" title="Horizontal rule">&#8213;</button>
               <button class="toolbar-btn" data-cmd="clear" title="Clear formatting">&#9003;</button>
             </div>

src/renderer/md-editor.ts

@@ -17,7 +17,7 @@ import {
 import { markdown } from "@codemirror/lang-markdown";
 import { highlightSelectionMatches, search, searchKeymap } from "@codemirror/search";
 import { tags } from "@lezer/highlight";
-import { toggleBold, toggleItalic, toggleLink } from "./md-format.js";
+import { toggleBold, toggleItalic, toggleLink, toggleStrikethrough } from "./md-format.js";
 
 export interface MdEditorCallbacks {
   onChange: (text: string) => void;
@@ -27,6 +27,7 @@ export interface MdEditorCallbacks {
 const formatBindings: KeyBinding[] = [
   { key: "Mod-b", run: toggleBold, preventDefault: true },
   { key: "Mod-i", run: toggleItalic, preventDefault: true },
+  { key: "Mod-Shift-s", run: toggleStrikethrough, preventDefault: true },
   { key: "Mod-k", run: toggleLink, preventDefault: true },
 ];
 

src/renderer/md-format.ts

@@ -98,6 +98,44 @@ export const toggleItalic: FormatCommand = toggleInline("*");
 export const toggleStrikethrough: FormatCommand = toggleInline("~~");
 export const toggleInlineCode: FormatCommand = toggleInline("`");
 
+/* ------------------------------------------------------------------ */
+/* Code: inline for single-line/empty selection, fenced for blocks     */
+/* ------------------------------------------------------------------ */
+
+const fenceLineRe = /^```[a-zA-Z0-9_-]*[ \t]*$/;
+
+export const toggleCode: FormatCommand = (target) => {
+  const { state, dispatch } = target;
+  const { from, to } = state.selection.main;
+  const first = state.doc.lineAt(from);
+  const last = state.doc.lineAt(to);
+
+  if (first.number === last.number) {
+    return toggleInlineCode(target);
+  }
+
+  let start = first.from;
+  let end = last.to;
+  let region = slice(state, start, end);
+  let lines = region.split("\n");
+
+  // Selection starts at an opening fence: treat it as a fenced-block toggle.
+  if (lines.length > 1 && fenceLineRe.test(lines[0])) {
+    if (!fenceLineRe.test(lines[lines.length - 1]) && last.number < state.doc.lines) {
+      const next = state.doc.line(last.number + 1);
+      if (fenceLineRe.test(next.text)) end = next.to;
+    }
+    region = slice(state, start, end);
+    lines = region.split("\n");
+    const body = lines.slice(1, lines.length > 1 && fenceLineRe.test(lines[lines.length - 1]) ? -1 : lines.length);
+    dispatch({ changes: { from: start, to: end, insert: body.join("\n") } });
+    return true;
+  }
+
+  dispatch({ changes: { from: start, to: end, insert: "```\n" + region + "\n```" } });
+  return true;
+};
+
 /* ------------------------------------------------------------------ */
 /* Links                                                               */
 /* ------------------------------------------------------------------ */
@@ -106,6 +144,19 @@ export const toggleLink: FormatCommand = (target) => {
   const { state, dispatch } = target;
   const { from, to } = state.selection.main;
 
+  const text = slice(state, from, to);
+
+  // Selection is already a link → select its URL so the user can edit it.
+  const link = /^\[([^\]\n]*)\]\(([^)\n]*)\)$/.exec(text);
+  if (link) {
+    const urlFrom = from + 1 + link[1].length + 2;
+    dispatch({
+      selection: EditorSelection.range(urlFrom, urlFrom + link[2].length),
+      scrollIntoView: true,
+    });
+    return true;
+  }
+
   if (from === to) {
     const pos = from;
     dispatch({
@@ -115,10 +166,9 @@ export const toggleLink: FormatCommand = (target) => {
     return true;
   }
 
-  const label = slice(state, from, to);
-  const urlStart = from + label.length + 3;
+  const urlStart = from + text.length + 3;
   dispatch({
-    changes: { from, to, insert: `[${label}](url)` },
+    changes: { from, to, insert: `[${text}](url)` },
     selection: EditorSelection.range(urlStart, urlStart + 3),
   });
   return true;