diff --git a/packages/runtime/src/__tests__/fake-backend.test.ts b/packages/runtime/src/__tests__/fake-backend.test.ts
new file mode 100644
index 00000000000..fc628537a3b
--- /dev/null
+++ b/packages/runtime/src/__tests__/fake-backend.test.ts
@@ -0,0 +1,28 @@
+import assert from 'node:assert/strict';
+import { test } from 'node:test';
+import type { SessionHeader } from '@maka/core';
+import { FakeBackend } from '../fake-backend.js';
+import type { SessionStore } from '../session-manager.js';
+
+test('text deltas preserve the exact completed response, including Markdown line breaks', async () => {
+  const backend = new FakeBackend({
+    sessionId: 'session-1',
+    header: { model: 'fake-model' } as SessionHeader,
+    store: {} as SessionStore,
+    appendMessage: async () => {},
+  });
+  const deltas: string[] = [];
+  let completedText = '';
+
+  for await (const event of backend.send({
+    turnId: 'turn-1',
+    text: '结论先行。\n\n| 名称 | 状态 |\n| --- | --- |\n| A | 完成 |',
+    context: [],
+  })) {
+    if (event.type === 'text_delta') deltas.push(event.text);
+    if (event.type === 'text_complete') completedText = event.text;
+  }
+
+  assert.equal(deltas.join(''), completedText);
+  assert.match(completedText, /\n\n\| 名称 \| 状态 \|/);
+});
diff --git a/packages/runtime/src/fake-backend.ts b/packages/runtime/src/fake-backend.ts
index fcb4bfaa321..b7a07e3c208 100644
--- a/packages/runtime/src/fake-backend.ts
+++ b/packages/runtime/src/fake-backend.ts
@@ -26,7 +26,9 @@ export class FakeBackend implements AgentBackend {
     const attNames = (input.attachments ?? []).map((a) => a.name);
     const attLine = attNames.length > 0 ? `\nAttachments received: ${attNames.join(', ')}` : '';
     const text = `Fake backend received: ${input.text}${attLine}\n\nThis proves the session stream, JSONL storage, and renderer loop are connected.`;
-    const chunks = text.match(/.{1,9}/g) ?? [text];
+    // Every delta must concatenate to text_complete; `.` would silently drop
+    // line terminators and make structured Markdown reflow only at completion.
+    const chunks = text.match(/[\s\S]{1,9}/g) ?? [text];
 
     for (const chunk of chunks) {
       if (this.stopped) {