fix: YouTube JS runtime check, Douyin health check, cli bare except, config permission race (#104)

- YouTube: warn when only Node.js is installed but yt-dlp config file
  is missing (previously returned "ok" incorrectly)
- Douyin: use `mcporter list` instead of calling with a hardcoded
  invalid share URL that always fails
- cli: replace bare `except:` with `except Exception:` in
  `_detect_environment` to avoid catching KeyboardInterrupt/SystemExit
- cli: fix unclosed file handle for cloud VM detection
- config: use `os.open()` with 0o600 mode to eliminate permission
  race window when saving credentials

tests/test_channel_contracts.py

@@ -29,6 +29,82 @@ def test_channel_check_contract_with_minimal_runtime(monkeypatch, tmp_path):
         assert isinstance(message, str) and message.strip()
 
 
+def test_youtube_warns_when_node_only_and_no_config(monkeypatch, tmp_path):
+    """YouTube should warn when only Node.js is installed but no yt-dlp config exists."""
+    from agent_reach.channels.youtube import YouTubeChannel
+
+    def fake_which(cmd):
+        if cmd == "yt-dlp":
+            return "/usr/bin/yt-dlp"
+        if cmd == "node":
+            return "/usr/bin/node"
+        return None  # deno not installed
+
+    monkeypatch.setattr("shutil.which", fake_which)
+    # Point to a non-existent config file
+    monkeypatch.setattr("os.path.expanduser", lambda p: str(tmp_path / ".config/yt-dlp/config"))
+
+    ch = YouTubeChannel()
+    status, message = ch.check()
+    assert status == "warn"
+    assert "--js-runtimes" in message
+
+
+def test_youtube_ok_when_deno_installed(monkeypatch):
+    """YouTube should return ok when Deno is installed (no config needed)."""
+    from agent_reach.channels.youtube import YouTubeChannel
+
+    def fake_which(cmd):
+        if cmd == "yt-dlp":
+            return "/usr/bin/yt-dlp"
+        if cmd == "deno":
+            return "/usr/bin/deno"
+        return None
+
+    monkeypatch.setattr("shutil.which", fake_which)
+
+    ch = YouTubeChannel()
+    status, _msg = ch.check()
+    assert status == "ok"
+
+
+def test_douyin_check_does_not_call_with_invalid_url(monkeypatch, tmp_path):
+    """Douyin check should use 'mcporter list' instead of calling with a hardcoded URL."""
+    import subprocess
+
+    from agent_reach.channels.douyin import DouyinChannel
+
+    calls = []
+    original_run = subprocess.run
+
+    def tracking_run(cmd, **kwargs):
+        calls.append(cmd)
+        # Simulate mcporter config list returning douyin
+        if "config" in cmd and "list" in cmd:
+            class R:
+                stdout = "douyin  http://localhost:18070/mcp"
+                returncode = 0
+            return R()
+        # Simulate mcporter list douyin returning tools
+        if "list" in cmd and "douyin" in cmd:
+            class R:
+                stdout = "parse_douyin_video_info"
+                returncode = 0
+            return R()
+        return original_run(cmd, **kwargs)
+
+    monkeypatch.setattr("shutil.which", lambda cmd: "/usr/bin/mcporter" if cmd == "mcporter" else None)
+    monkeypatch.setattr("subprocess.run", tracking_run)
+
+    ch = DouyinChannel()
+    status, _msg = ch.check()
+
+    # Should NOT contain any hardcoded douyin.com URL in subprocess calls
+    for call in calls:
+        call_str = " ".join(call) if isinstance(call, list) else str(call)
+        assert "https://www.douyin.com" not in call_str
+
+
 def test_channel_can_handle_contract():
     url_samples = {
         "github": "https://github.com/panniantong/agent-reach",