fix: Improve consistency and add rollback support

1. haproxy_add_servers - disk-first pattern
   - Save ALL servers to config FIRST
   - Then update HAProxy
   - Rollback all on unexpected error
   - Rollback failed slots individually

2. remove_domain_from_config - file locking
   - Add fcntl.LOCK_EX for consistency with other config ops
   - Prevents race conditions during concurrent access

3. haproxy_add_domain - rollback on HAProxy failure
   - Wrap HAProxy map update in try/except
   - Rollback map file if HAProxy command fails
   - Rollback server config if server setup fails

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

mcp/server.py

@@ -561,15 +561,21 @@ def remove_server_from_config(domain: str, slot: int) -> None:
 
 
 def remove_domain_from_config(domain: str) -> None:
-    """Remove all server configurations for a domain.
+    """Remove domain from persistent config with file locking.
 
     Args:
         domain: Domain name to remove
     """
+    lock_path = f"{SERVERS_FILE}.lock"
+    with open(lock_path, 'w') as lock_file:
+        fcntl.flock(lock_file.fileno(), fcntl.LOCK_EX)
+        try:
             config = load_servers_config()
             if domain in config:
                 del config[domain]
                 save_servers_config(config)
+        finally:
+            fcntl.flock(lock_file.fileno(), fcntl.LOCK_UN)
 
 
 def get_server_suffixes(http_port: int) -> List[Tuple[str, int]]:
@@ -788,28 +794,43 @@ def haproxy_add_domain(domain: str, ip: str = "", http_port: int = 80) -> str:
         entries = get_map_contents()
         entries.append((domain, pool))
         entries.append((f".{domain}", pool))
+        try:
             save_map_file(entries)
+        except IOError as e:
+            return f"Error: Failed to save map file: {e}"
 
-        # Update HAProxy map via Runtime API (immediate effect)
+        # Then update HAProxy map via Runtime API
+        try:
             haproxy_cmd(f"add map {MAP_FILE_CONTAINER} {domain} {pool}")
             haproxy_cmd(f"add map {MAP_FILE_CONTAINER} .{domain} {pool}")
+        except HaproxyError as e:
+            # Rollback: remove the domain we just added from entries and re-save
+            rollback_entries = [(d, b) for d, b in entries if d != domain and d != f".{domain}"]
+            try:
+                save_map_file(rollback_entries)
+            except IOError:
+                logger.error("Failed to rollback map file after HAProxy error")
+            return f"Error: Failed to update HAProxy map: {e}"
 
         # If IP provided, add server to slot 1
         if ip:
             # Save server config to disk first
             add_server_to_config(domain, 1, ip, http_port)
 
+            try:
                 for suffix, port in get_server_suffixes(http_port):
                     server = f"{pool}{suffix}_1"
                     haproxy_cmd(f"set server {pool}/{server} addr {ip} port {port}")
                     haproxy_cmd(f"set server {pool}/{server} state ready")
+            except HaproxyError as e:
+                # Rollback server config on failure
+                remove_server_from_config(domain, 1)
+                return f"Domain {domain} added to {pool} but server config failed: {e}"
 
             return f"Domain {domain} added to {pool} with server {ip}:{http_port}"
 
         return f"Domain {domain} added to {pool} (no servers configured)"
 
-    except IOError as e:
-        return f"Error: Failed to update map file: {e}"
     except HaproxyError as e:
         return f"Error: {e}"
 
@@ -1072,22 +1093,38 @@ def haproxy_add_servers(domain: str, servers: str) -> str:
     except ValueError as e:
         return f"Error: {e}"
 
-    # Add all servers
+    # Save ALL servers to config FIRST (disk-first pattern)
+    for server_config in validated_servers:
+        slot = server_config["slot"]
+        ip = server_config["ip"]
+        http_port = server_config["http_port"]
+        add_server_to_config(domain, slot, ip, http_port)
+
+    # Then update HAProxy
     added = []
     errors = []
-
+    failed_slots = []
-    for srv in validated_servers:
-        slot = srv["slot"]
-        ip = srv["ip"]
-        http_port = srv["http_port"]
 
     try:
-            server = configure_server_slot(backend, server_prefix, slot, ip, http_port)
+        for server_config in validated_servers:
-            # Save to persistent config
+            slot = server_config["slot"]
-            add_server_to_config(domain, slot, ip, http_port)
+            ip = server_config["ip"]
+            http_port = server_config["http_port"]
+            try:
+                configure_server_slot(backend, server_prefix, slot, ip, http_port)
                 added.append(f"slot {slot}: {ip}:{http_port}")
-        except (HaproxyError, IOError) as e:
+            except HaproxyError as e:
+                failed_slots.append(slot)
                 errors.append(f"slot {slot}: {e}")
+    except Exception as e:
+        # Rollback all saved configs on unexpected error
+        for server_config in validated_servers:
+            remove_server_from_config(domain, server_config["slot"])
+        return f"Error: {e}"
+
+    # Rollback failed slots from config
+    for slot in failed_slots:
+        remove_server_from_config(domain, slot)
 
     # Build result message
     result_parts = []