启用md2img强保活模式：移除浏览器主动关闭逻辑

1. safe_close_browser 改为保活模式下直接返回，不执行 browser.close\n2. 去除 safe_close_browser 中的 terminate/kill 进程树逻辑\n3. 保留函数签名与调用链，确保现有流程兼容\n4. 增加中文注释说明长期常驻场景下的设计意图

utils/markdown_to_image.py

@@ -120,59 +120,17 @@ def _simple_markdown_to_html(md_content: str) -> str:
 
 
 async def safe_close_browser(browser, timeout: float = 4.0) -> None:
+    """保活优先：不执行浏览器关闭。
+
+    设计说明：
+    1. 当前业务要求浏览器进程长期常驻，因此这里显式禁用“主动关闭进程”；
+    2. 即使上层调用了 safe_close_browser，也只记录日志并直接返回；
+    3. 保留函数签名是为了兼容现有调用点，避免大范围改动影响稳定性。
+    """
     if not browser:
         return
-
-    for context in browser.contexts[:]:
-        for page in context.pages[:]:
-            try:
-                await asyncio.wait_for(page.close(), timeout=1.5)
-            except Exception:
-                pass
-        try:
-            await asyncio.wait_for(context.close(), timeout=timeout)
-        except Exception:
-            pass
-
-    try:
-        await asyncio.wait_for(browser.close(), timeout=timeout)
-        logger.debug("browser closed gracefully")
-        return
-    except (asyncio.TimeoutError, Exception) as e:
-        logger.warning(f"browser.close failed: {e}")
-
-    if browser.process and browser.process.pid:
-        try:
-            parent = psutil.Process(browser.process.pid)
-            children = parent.children(recursive=True)
-            for proc in children:
-                try:
-                    proc.terminate()
-                except (psutil.NoSuchProcess, psutil.AccessDenied, psutil.ZombieProcess):
-                    pass
-            try:
-                parent.terminate()
-            except (psutil.NoSuchProcess, psutil.AccessDenied, psutil.ZombieProcess):
-                pass
-            try:
-                gone, alive = psutil.wait_procs([parent] + children, timeout=2)
-            except Exception:
-                gone, alive = [], [parent] + children
-            for proc in alive:
-                try:
-                    proc.kill()
-                except (psutil.NoSuchProcess, psutil.AccessDenied, psutil.ZombieProcess):
-                    pass
-            try:
-                gone, alive = psutil.wait_procs([parent] + children, timeout=3)
-            except Exception:
-                alive = []
-            if alive:
-                logger.warning(f"process still alive after kill: {[p.pid for p in alive]}")
-            else:
-                logger.debug("process tree terminated")
-        except (psutil.NoSuchProcess, Exception) as e:
-            logger.warning(f"force kill failed: {e}")
+    logger.info("[md2img] 保活模式：跳过 safe_close_browser，不主动关闭浏览器进程")
+    return
 
 
 def _clean_text(html: str) -> str: