diff --git a/desktop/src/lib/selectionComposer.test.ts b/desktop/src/lib/selectionComposer.test.ts
new file mode 100644
index 00000000..6b6d8262
--- /dev/null
+++ b/desktop/src/lib/selectionComposer.test.ts
@@ -0,0 +1,15 @@
+import { expect, it } from 'vitest'
+import { buildSelectionComposerText } from './selectionComposer'
+
+it('renders a readable block with locator + change + source', () => {
+  const text = buildSelectionComposerText({
+    pageUrl: 'http://127.0.0.1:4321/preview-fs/s1/index.html',
+    sourceHint: 'index.html',
+    element: { selector: '#title', tag: 'h1', text: '模型还没用熟', classes: [] } as never,
+    change: { text: { from: '模型还没用熟', to: '模型用熟了' }, description: '标题改积极一点' } as never,
+  })
+  expect(text).toContain('#title')
+  expect(text).toContain('index.html')
+  expect(text).toContain('模型用熟了')
+  expect(text).toContain('标题改积极一点')
+})
diff --git a/desktop/src/lib/selectionComposer.ts b/desktop/src/lib/selectionComposer.ts
new file mode 100644
index 00000000..68d87722
--- /dev/null
+++ b/desktop/src/lib/selectionComposer.ts
@@ -0,0 +1,24 @@
+import type { ElementMetadata } from '../preview-agent/metadata'
+import type { EditDiff } from '../preview-agent/popover'
+
+export type SelectionPayload = {
+  pageUrl: string; sourceHint?: string
+  element: ElementMetadata
+  change?: EditDiff & { description?: string }
+}
+
+export function buildSelectionComposerText(p: SelectionPayload): string {
+  const lines: string[] = []
+  lines.push(`针对页面元素 \`${p.element.selector}\`（${p.element.tag}${p.element.text ? `，文本「${p.element.text}」` : ''}）：`)
+  if (p.sourceHint) lines.push(`- 来源：${p.sourceHint}`)
+  lines.push(`- 页面：${p.pageUrl}`)
+  const c = p.change
+  if (c?.text) lines.push(`- 文本：「${c.text.from}」→「${c.text.to}」`)
+  if (c?.color) lines.push(`- 文字颜色：${c.color.from} → ${c.color.to}`)
+  if (c?.background) lines.push(`- 背景：${c.background.from} → ${c.background.to}`)
+  if (c?.opacity) lines.push(`- 不透明度：${c.opacity.from} → ${c.opacity.to}`)
+  if (c?.fontFamily) lines.push(`- 字体：${c.fontFamily.from} → ${c.fontFamily.to}`)
+  if (c?.description) lines.push(`- 说明：${c.description}`)
+  lines.push('请在源码中落地以上修改。')
+  return lines.join('\n')
+}