fix(ccb): make toolbar undo/redo work when an external surface owns focus in design mode

In design mode the active document can sit behind a surface that owns
DOM focus instead of a CodeMirror editor — e.g. the markdown viewer's
iframe when it's in edit mode. EditorManager.getFocusedEditor() returns
null in that case, so the CCB undo/redo buttons (and anything else
routing through EDIT_UNDO / EDIT_REDO) silently no-op'd even though the
underlying Phoenix document had perfectly good history.

When design mode is active and no editor is focused, fall back to
EditorManager.getCurrentFullEditor() so toolbar undo/redo drives the
active document. External surfaces that sync their edits back to that
document (like the md viewer) will re-render to reflect the rolled-back
text. Outside design mode the pre-existing no-op behavior is preserved.

Author: abose

src/editor/EditorCommandHandlers.js

@@ -33,6 +33,7 @@ define(function (require, exports, module) {
         Editor = require("editor/Editor").Editor,
         CommandManager = require("command/CommandManager"),
         EditorManager = require("editor/EditorManager"),
+        WorkspaceManager = require("view/WorkspaceManager"),
         StringUtils = require("utils/StringUtils"),
         TokenUtils = require("utils/TokenUtils"),
         CodeMirror = require("thirdparty/CodeMirror/lib/codemirror"),
@@ -1185,6 +1186,16 @@ define(function (require, exports, module) {
         var editor = EditorManager.getFocusedEditor();
         var result = new $.Deferred();
 
+        // In design mode the active document often lives behind an external
+        // surface that owns DOM focus (e.g. the markdown viewer iframe in
+        // edit mode), so getFocusedEditor() returns null even though there
+        // is an underlying Phoenix editor whose doc captures the changes.
+        // Fall back to the active-pane full editor so toolbar undo/redo
+        // still drives the document's history in that state.
+        if (!editor && WorkspaceManager.isInDesignMode()) {
+            editor = EditorManager.getCurrentFullEditor();
+        }
+
         if (editor) {
             editor[operation]();
             result.resolve();