fix(core): robust scroll sync — proportional ratio + bidirectional

Replace heading-based _syncScrollByHeading with solid proportional sync:
- _syncScroll(): uses scrollTop/scrollHeight ratio for both gutter and preview
- Prevents sync loops with _syncing flag and rAF debounce
- Bidirectional: preview scroll also syncs back to source textarea
- Ratio-based approach handles height mismatches (e.g. word-wrap in textarea)
- Remove fragile heading detection and scrollIntoView calls

Also fix setValue and _applyHistory to reset scroll positions consistently

src/core.js

@@ -113,6 +113,7 @@ class MarkdownEditor {
     this._outlineTimer = null;     // 大纲防抖计时器
     this._zenMode = false;         // v0.1.12: Zen 模式
     this._wordWrap = true;         // v0.1.12: 自动换行
+    this._syncing = false;         // 滚动同步锁
 
     // 渲染函数：自定义覆盖内置解析器
     this._renderFn = (typeof this.config.render === 'function') ? this.config.render : parseMarkdown;
@@ -357,14 +358,28 @@ class MarkdownEditor {
     ta.addEventListener('keyup', onCursorActivity);
 
     const onScroll = () => {
-      if (this.gutter) this.gutter.scrollTop = ta.scrollTop;
-      // v0.1.12: 标题感知同步
-      if (this.config.syncScroll && this._mode === 'split') {
-        this._syncScrollByHeading();
-      }
+      this._syncScroll();
     };
     ta.addEventListener('scroll', onScroll);
 
+    // v0.1.12: 预览区滚轮反向同步到源码
+    const onPreviewScroll = () => {
+      if (!this.config.syncScroll || this._mode !== 'split') return;
+      if (this._syncing) return; // 防止循环触发
+      this._syncing = true;
+      const pmax = this.previewPane.scrollHeight - this.previewPane.clientHeight;
+      if (pmax <= 0) { this._syncing = false; return; }
+      const ratio = this.previewPane.scrollTop / pmax;
+      const tmax = ta.scrollHeight - ta.clientHeight;
+      ta.scrollTop = ratio * tmax;
+      if (this.gutter) {
+        const gmax = this.gutter.scrollHeight - this.gutter.clientHeight;
+        this.gutter.scrollTop = gmax > 0 ? ratio * gmax : ratio * tmax;
+      }
+      requestAnimationFrame(() => { this._syncing = false; });
+    };
+    this.previewPane.addEventListener('scroll', onPreviewScroll);
+
     const onFocus = () => {
       this._emit('focus');
       if (typeof this.config.onFocus === 'function') {
@@ -406,6 +421,7 @@ class MarkdownEditor {
       ta.removeEventListener('keydown', onKeydown);
       ta.removeEventListener('keypress', onKeypress);
       ta.removeEventListener('scroll', onScroll);
+      this.previewPane.removeEventListener('scroll', onPreviewScroll);
       ta.removeEventListener('click', onCursorActivity);
       ta.removeEventListener('keyup', onCursorActivity);
       ta.removeEventListener('focus', onFocus);
@@ -874,8 +890,9 @@ class MarkdownEditor {
     this._render();
     this._renderGutter();
     this._updateWordCount();
-    // 同步行号滚动位置
+    // 重置滚动
     if (this.gutter) this.gutter.scrollTop = this.textarea.scrollTop;
+    if (this.previewPane && this.config.syncScroll) this.previewPane.scrollTop = 0;
     this._emit('change', this._value);
     if (typeof this.config.onChange === 'function') {
       try { this.config.onChange(this._value, this); } catch (e) { console.error(e); }
@@ -1236,46 +1253,35 @@ class MarkdownEditor {
     }
   }
 
-  // ============ 滚动同步 v2 — 标题感知（v0.1.12） ============
+  // ============ 滚动同步（v0.1.12 重写 — 比例同步 + 双向联动） ============
 
-  _syncScrollByHeading() {
-    if (!this.config.syncScroll || this._mode !== 'split') return;
+  /**
+   * 源码滚动 → 同步行号 + 预览
+   * 使用比例而非直接 scrollTop，兼容不同内容高度
+   */
+  _syncScroll() {
+    if (this._syncing) return;
+    this._syncing = true;
     const ta = this.textarea;
-    if (!ta) return;
+    if (!ta) { this._syncing = false; return; }
 
-    // 1. 先做比例同步（基础行为，保证平滑）
-    const max = ta.scrollHeight - ta.clientHeight;
-    if (max <= 0) return;
-    const ratio = ta.scrollTop / max;
-    const pmax = this.previewPane.scrollHeight - this.previewPane.clientHeight;
-    this.previewPane.scrollTop = ratio * pmax;
+    const tmax = ta.scrollHeight - ta.clientHeight;
+    if (tmax <= 0) { this._syncing = false; return; }
+    const ratio = ta.scrollTop / tmax;
 
-    // 2. 如果有标题，微调到最近的标题位置
-    const val = this._value;
-    if (!val) return;
-
-    // 估计 textarea 视口顶部的行号
-    const lineHeight = 13.5 * 1.7; // font-size * line-height
-    const scrollLines = Math.floor(ta.scrollTop / lineHeight);
-    const beforeLines = val.split('\n').slice(0, Math.max(0, scrollLines));
-    const visibleText = beforeLines.join('\n');
-
-    // 找到视口顶部之前最近的标题
-    const headings = [...visibleText.matchAll(/^(#{1,6})\s+(.+)$/gm)];
-    if (!headings.length) return;
-
-    const lastH = headings[headings.length - 1];
-    const headingText = lastH[2].trim();
-
-    // 在预览区查找对应标题
-    const previewEls = this.previewEl.querySelectorAll('h1, h2, h3, h4, h5, h6');
-    let found;
-    for (const el of previewEls) {
-      if (el.textContent.trim() === headingText) { found = el; break; }
+    // 同步行号（比例方式，不受内容高度差异影响）
+    if (this.gutter) {
+      const gmax = this.gutter.scrollHeight - this.gutter.clientHeight;
+      this.gutter.scrollTop = gmax > 0 ? ratio * gmax : ta.scrollTop;
     }
-    if (found) {
-      found.scrollIntoView({ block: 'start', behavior: 'instant' });
+
+    // 同步预览（比例方式）
+    if (this.config.syncScroll && this._mode === 'split' && this.previewPane) {
+      const pmax = this.previewPane.scrollHeight - this.previewPane.clientHeight;
+      if (pmax > 0) this.previewPane.scrollTop = ratio * pmax;
     }
+
+    requestAnimationFrame(() => { this._syncing = false; });
   }
 
   _updateWordCount() {
@@ -1325,8 +1331,9 @@ class MarkdownEditor {
     this._renderGutter();
     this._updateWordCount();
     this._updateOutline();
-    // 同步行号滚动
+    // 重置滚动位置到顶部
     if (this.gutter) this.gutter.scrollTop = 0;
+    this.textarea.scrollTop = 0;
     if (!opts.silent) {
       this._emit('change', this._value);
       if (typeof this.config.onChange === 'function') {