feat: add step-by-step connectivity diagnostics to health_check

Break connectivity check into three stages — DNS resolution, TCP connect,
and API auth — each reported separately so failures pinpoint the exact layer.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

outline_sync.py

@@ -16,11 +16,13 @@ import os
 import sys
 import re
 import json
+import socket
 import subprocess
 import time
 import logging
 import argparse
 from pathlib import Path
+from urllib.parse import urlparse
 from typing import Dict, List, Optional, Tuple
 
 import requests
@@ -177,13 +179,38 @@ class OutlineSync:
             return None
 
     def health_check(self) -> bool:
-        print("Checking API connectivity...", end=" ", flush=True)
+        parsed = urlparse(self.base_url)
+        host = parsed.hostname or "outline"
+        port = parsed.port or (443 if parsed.scheme == "https" else 80)
+
+        print(f"Checking API connectivity to {self.base_url} ...")
+
+        # 1. DNS resolution
+        print(f"  DNS resolve {host!r} ... ", end="", flush=True)
+        try:
+            ip = socket.gethostbyname(host)
+            print(f"✓  ({ip})")
+        except socket.gaierror as exc:
+            print(f"✗  DNS failed: {exc}")
+            return False
+
+        # 2. TCP reachability
+        print(f"  TCP connect {ip}:{port} ... ", end="", flush=True)
+        try:
+            with socket.create_connection((host, port), timeout=5):
+                print("✓")
+        except (socket.timeout, ConnectionRefusedError, OSError) as exc:
+            print(f"✗  {exc}")
+            return False
+
+        # 3. API authentication
+        print(f"  API auth ... ", end="", flush=True)
         result = self._api("/api/auth.info")
         if result and "data" in result:
             user = result["data"].get("user", {})
-            print(f"✓  ({user.get('name', 'unknown')})")
+            print(f"✓  (user: {user.get('name', 'unknown')})")
             return True
-        print("✗")
+        print("✗  bad response")
         return False
 
     def get_collections(self) -> List[Dict]: