fix: skip proxy server startup when port 8081 is already in use

When Claude Desktop and Claude Code both load the MCP, the second
instance crashed because uvicorn couldn't bind port 8081. Now checks
port availability first and skips startup gracefully, leaving all
MCP tools fully operational against the already-running proxy.

Author: john-walkoe

src/fpd_mcp/main.py

@@ -1716,12 +1716,24 @@ async def run_hybrid_server(enable_always_on: bool = True, proxy_port: int = 808
 
         # Start proxy server immediately if always-on mode is enabled
         if enable_always_on:
-            logger.info(f"Always-on mode: Starting HTTP proxy server immediately on port {proxy_port}")
-            _proxy_server_task = asyncio.create_task(_run_proxy_server(proxy_port))
-            _proxy_server_running = True
-            # Brief wait to ensure server starts cleanly
-            await asyncio.sleep(0.5)
-            logger.info(f"Proxy server started successfully on port {proxy_port}")
+            import socket
+            with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
+                port_free = s.connect_ex(("127.0.0.1", proxy_port)) != 0
+
+            if not port_free:
+                logger.info(
+                    "Port %d already in use — skipping proxy server startup "
+                    "(another instance is running; MCP tools are still fully available)",
+                    proxy_port,
+                )
+                _proxy_server_running = True  # treat as running so tools work
+            else:
+                logger.info(f"Always-on mode: Starting HTTP proxy server immediately on port {proxy_port}")
+                _proxy_server_task = asyncio.create_task(_run_proxy_server(proxy_port))
+                _proxy_server_running = True
+                # Brief wait to ensure server starts cleanly
+                await asyncio.sleep(0.5)
+                logger.info(f"Proxy server started successfully on port {proxy_port}")
         else:
             # Legacy on-demand mode: proxy starts on first download request
             logger.info(f"On-demand mode: Proxy will start on first document request (port {proxy_port})")