diff --git a/app/startup/composition/system.py b/app/startup/composition/system.py
index 4bf277cbb..b8d3f4353 100644
--- a/app/startup/composition/system.py
+++ b/app/startup/composition/system.py
@@ -121,15 +121,27 @@ class _FileLogAdapter(SystemLogPort):
         async with aiofiles.open(path, mode="r", encoding="utf-8", errors="replace") as file:
             await file.seek(0, 2)
             previous_size = (await asyncio.to_thread(path.stat)).st_size
+            pending = ""
             while not runtime_stop_state.is_system_stopped:
                 if await disconnected():
                     break
                 current_size = (await asyncio.to_thread(path.stat)).st_size
+                if current_size < previous_size:
+                    await file.seek(0)
+                    previous_size = 0
+                    pending = ""
                 if current_size > previous_size:
-                    line = (await file.readline()).strip()
-                    if line:
-                        yield line
-                    previous_size = current_size
+                    pending += await file.read()
+                    previous_size = (await asyncio.to_thread(path.stat)).st_size
+                    fragments = pending.splitlines(keepends=True)
+                    if fragments and not fragments[-1].endswith(("\n", "\r")):
+                        pending = fragments.pop()
+                    else:
+                        pending = ""
+                    for fragment in fragments:
+                        line = fragment.strip()
+                        if line:
+                            yield line
                 else:
                     await asyncio.sleep(0.5)
 
diff --git a/tests/test_agent_realtime_log.py b/tests/test_agent_realtime_log.py
new file mode 100644
index 000000000..d6a830488
--- /dev/null
+++ b/tests/test_agent_realtime_log.py
@@ -0,0 +1,49 @@
+"""验证 Agent 多行日志在实时日志轮询中的传输完整性。"""
+
+import asyncio
+from pathlib import Path
+from types import SimpleNamespace
+
+import pytest
+
+from app.startup.composition.system import _FileLogAdapter
+
+
+@pytest.mark.asyncio
+async def test_file_log_follow_drains_all_lines_from_one_append(tmp_path: Path) -> None:
+    """一次写入包含多行时，实时跟随器应逐行转发全部新增内容。"""
+    log_path = tmp_path / "moviepilot.log"
+    log_path.touch()
+    adapter = _FileLogAdapter(SimpleNamespace(get=lambda key: tmp_path))
+
+    async def is_disconnected() -> bool:
+        """保持测试连接，直到断言收集到全部新增日志。"""
+        return False
+
+    stream = await adapter.follow("moviepilot.log", 50, is_disconnected)
+    collected: list[str] = []
+
+    async def collect_lines() -> None:
+        """收集同一次写入产生的三行日志。"""
+        async for line in stream:
+            collected.append(line)
+            if len(collected) == 3:
+                break
+
+    collector = asyncio.create_task(collect_lines())
+    await asyncio.sleep(0.05)
+    log_path.write_text(
+        "【INFO】 2026-09-11 11:39:36,300 callback - Agent消息: 首段\n"
+        "...\n"
+        "⚙️ => 读取技能说明：moviepilot-api\n",
+        encoding="utf-8",
+    )
+
+    await asyncio.wait_for(collector, timeout=2)
+    await stream.aclose()
+
+    assert collected == [
+        "【INFO】 2026-09-11 11:39:36,300 callback - Agent消息: 首段",
+        "...",
+        "⚙️ => 读取技能说明：moviepilot-api",
+    ]