fix(mdviewer): use single undo stack via CM with cursor preservation

Route all undo/redo through CM (single source of truth). Save/restore
cursor offset around innerHTML re-render only when md editor has focus,
preventing CM cursor interference. Fix Ctrl+Shift+Z redo detection.

Author: abose

src-mdviewer/src/bridge.js

@@ -8,6 +8,7 @@ import { getState, setState } from "./core/state.js";
 import { setLocale } from "./core/i18n.js";
 import { marked } from "marked";
 import * as docCache from "./core/doc-cache.js";
+import { getCursorOffset, restoreCursor } from "./components/editor.js";
 
 let _syncId = 0;
 let _lastReceivedSyncId = -1;
@@ -152,7 +153,7 @@ export function initBridge() {
     // Undo/redo is routed through CM5's undo stack so both editors stay in sync.
     // Unhandled modifier shortcuts are forwarded to Phoenix's keybinding manager.
     const _mdEditorHandledKeys = new Set(["b", "i", "k", "u", "z", "y", "a", "c", "v", "x"]); // Ctrl/Cmd + key
-    const _mdEditorHandledShiftKeys = new Set(["x", "X", "z"]); // Ctrl/Cmd + Shift + key
+    const _mdEditorHandledShiftKeys = new Set(["x", "X", "z", "Z"]); // Ctrl/Cmd + Shift + key
 
     document.addEventListener("keydown", (e) => {
         if (e.key === "Escape") {
@@ -196,14 +197,14 @@ export function initBridge() {
         const isMod = _isMac ? e.metaKey : e.ctrlKey;
         if (!isMod) return;
 
-        if (e.key === "z" && !e.shiftKey) {
+        if ((e.key === "z" || e.key === "Z") && !e.shiftKey) {
             e.preventDefault();
             e.stopImmediatePropagation();
             sendToParent("mdviewrUndo", {});
             return;
         }
 
-        if ((e.key === "z" && e.shiftKey) || e.key === "y") {
+        if (((e.key === "z" || e.key === "Z") && e.shiftKey) || e.key === "y") {
             e.preventDefault();
             e.stopImmediatePropagation();
             sendToParent("mdviewrRedo", {});
@@ -378,17 +379,27 @@ function handleUpdateContent(data) {
         if (entry) {
             entry.mdSrc = markdown;
             entry.parseResult = parseResult;
-            // Don't replace innerHTML — let file:rendered handle it
-            // since the editor may be active
         }
     }
 
     setState({
         currentContent: markdown,
         parseResult: parseResult
     });
+
+    // In edit mode, save/restore cursor around re-render
+    const content = document.getElementById("viewer-content");
+    let savedCursorOffset = null;
+    if (getState().editMode && content && document.activeElement === content) {
+        savedCursorOffset = getCursorOffset(content);
+    }
+
     emit("file:rendered", parseResult);
 
+    if (savedCursorOffset !== null && content) {
+        restoreCursor(content, savedCursorOffset);
+    }
+
     _suppressContentChange = false;
 }
 

src-mdviewer/src/components/editor.js

@@ -42,7 +42,7 @@ let lastChangeType = "";
 let currentInputType = "";
 let isPerformingUndoRedo = false;
 
-function getCursorOffset(el) {
+export function getCursorOffset(el) {
     const sel = window.getSelection();
     if (!sel || !sel.rangeCount) return 0;
     const range = sel.getRangeAt(0);
@@ -52,7 +52,7 @@ function getCursorOffset(el) {
     return pre.toString().length;
 }
 
-function restoreCursor(el, offset) {
+export function restoreCursor(el, offset) {
     const walker = document.createTreeWalker(el, NodeFilter.SHOW_TEXT);
     let remaining = offset;
     let node;
@@ -1308,7 +1308,7 @@ function enterEditMode(content) {
             setState({ isDirty: undoStack.length > 0 });
             return;
         }
-        if (mod && ((e.key === "z" && e.shiftKey) || e.key === "y")) {
+        if (mod && (((e.key === "z" || e.key === "Z") && e.shiftKey) || e.key === "y")) {
             e.preventDefault();
             performRedo(content);
             setState({ isDirty: true });