增强转图浏览器启动健壮性并修正日志来源标识

变更项：1) html_to_image 改为候选浏览器逐个尝试启动，避免单一路径失败导致整体异常。2) Linux 增加系统浏览器路径探测（google-chrome/chromium）并保留 Playwright 缓存路径作为候选。3) 修正启动日志来源标识，区分 system 与 playwright-cache，避免误判。4) 所有候选失败时自动回退到 bundled 浏览器，提高转图成功率。

utils/markdown_to_image.py

@@ -1,6 +1,7 @@
 import subprocess
 import time
 from pathlib import Path
+import shutil
 
 import psutil
 from playwright.async_api import async_playwright
@@ -478,8 +479,9 @@ def check_chromium_installed(path):
 
 async def html_to_image(html_content, output_image):
     async with async_playwright() as p:
-        browser_path = None
+        browser_candidates = []
         if os.name == 'nt':
+            # Windows 优先尝试常见系统安装路径。
             possible_chrome_paths = [
                 r"C:\Users\Liu_WIN10\AppData\Local\Google\Chrome\Application\chrome.exe",
                 r"C:\Users\Liu-OPEN\AppData\Local\Google\Chrome\Application\chrome.exe",
@@ -488,24 +490,41 @@ async def html_to_image(html_content, output_image):
             ]
             for path in possible_chrome_paths:
                 if check_chromium_installed(path):
-                    browser_path = path
-                    break
+                    browser_candidates.append(("system", path))
         else:
             import glob
+            # Linux 先尝试系统可执行文件，再尝试 Playwright 缓存浏览器。
+            for bin_name in ("google-chrome", "google-chrome-stable", "chromium", "chromium-browser"):
+                bin_path = shutil.which(bin_name)
+                if bin_path and check_chromium_installed(bin_path):
+                    browser_candidates.append(("system", bin_path))
             user_home = os.path.expanduser("~")
             glob_pattern = os.path.join(user_home, ".cache", "ms-playwright", "chromium-*", "chrome-linux", "chrome")
             chrome_paths = glob.glob(glob_pattern)
             for path in sorted(chrome_paths, reverse=True):
                 if check_chromium_installed(path):
-                    browser_path = path
-                    break
+                    browser_candidates.append(("playwright-cache", path))
 
         launch_args = ["--no-sandbox", "--disable-setuid-sandbox", "--disable-dev-shm-usage", "--disable-gpu"]
+        browser = None
+        launch_errors = []
 
-        if browser_path:
-            logger.debug(f"Launch chromium with system chrome: {browser_path}")
-            browser = await p.chromium.launch(executable_path=browser_path, args=launch_args)
-        else:
+        # 优先按候选路径逐个尝试，失败自动降级，不让单一路径问题导致整体失败。
+        for source, browser_path in browser_candidates:
+            try:
+                logger.debug(f"Launch chromium with {source}: {browser_path}")
+                browser = await p.chromium.launch(
+                    executable_path=browser_path,
+                    args=launch_args,
+                    timeout=20000,
+                )
+                break
+            except Exception as e:
+                launch_errors.append(f"{source}:{browser_path} -> {e}")
+                logger.warning(f"Launch chromium failed with {source}: {browser_path}, error={e}")
+
+        # 如果候选都失败，回退到 Playwright bundled 浏览器。
+        if not browser:
             logger.debug("Launch chromium with bundled browser")
             browser = await p.chromium.launch(args=launch_args)