Fix plugin server start: use existing server instead of killing it

Plugin now checks if port 8000 is already in use and skips starting
its own server. This fixes CI where an external server is pre-started,
and avoids killing unrelated servers (like godot-mcp-studio).

The plugin still manages its own server lifecycle via _server_pid —
_stop_server kills only the process the plugin started, not foreign
ones.

Verified locally: macOS headless Godot + external server = 35/35 tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: dsarno

plugin/addons/godot_ai/plugin.gd

@@ -65,9 +65,11 @@ func _exit_tree() -> void:
 
 
 func _start_server() -> void:
-	## Kill any stale listener on our HTTP port (leftover from crash,
-	## old install, or a different server like godot-mcp-studio).
-	_kill_listener_on_port(McpClientConfigurator.SERVER_HTTP_PORT)
+	## If a server is already listening on our HTTP port, use it.
+	## This covers: CI (external server), another Godot instance, or manual start.
+	if _is_port_in_use(McpClientConfigurator.SERVER_HTTP_PORT):
+		print("MCP | server already running on port %d, using existing" % McpClientConfigurator.SERVER_HTTP_PORT)
+		return
 
 	var server_cmd := McpClientConfigurator.get_server_command()
 	if server_cmd.is_empty():
@@ -86,20 +88,16 @@ func _start_server() -> void:
 		push_warning("MCP | failed to start server")
 
 
-func _kill_listener_on_port(port: int) -> void:
+func _is_port_in_use(port: int) -> bool:
 	var output: Array = []
-	## -sTCP:LISTEN finds only the server process, not clients connected to it
-	var exit_code := OS.execute("lsof", ["-ti:%d" % port, "-sTCP:LISTEN"], output, true)
-	if exit_code != 0 or output.is_empty():
-		return
-	var pids_str: String = output[0].strip_edges()
-	if pids_str.is_empty():
-		return
-	for pid_str in pids_str.split("\n"):
-		var pid := pid_str.strip_edges().to_int()
-		if pid > 0:
-			OS.kill(pid)
-			print("MCP | killed stale process on port %d (PID %d)" % [port, pid])
+	if OS.get_name() == "Windows":
+		var exit_code := OS.execute("netstat", ["-ano"], output, true)
+		if exit_code == 0 and output.size() > 0:
+			return output[0].find(":%d " % port) >= 0 and output[0].find("LISTENING") >= 0
+	else:
+		var exit_code := OS.execute("lsof", ["-ti:%d" % port, "-sTCP:LISTEN"], output, true)
+		return exit_code == 0 and output.size() > 0 and not output[0].strip_edges().is_empty()
+	return false
 
 
 func _stop_server() -> void: