Launcher NUL refusal reports ParamName 'start' instead of the public 'options' #401

What. The public OpenCodeServer.StartAsync(OpenCodeServerOptions? options, …) refuses a NUL in a command entry with ArgumentException("OpenCodeServerOptions.Command entries cannot contain NUL.", nameof(start)). ParamName is therefore "start", the name of an internal parameter that callers cannot see. It should name the public parameter, options, as the door's other option refusals do.

Where. src/OpenCode.Sdk/Hosting/Launcher/Internal/WindowsServerChild.cs (the NulText.Occurs refusal) and src/OpenCode.Sdk/Hosting/Launcher/Internal/PosixServerChild.cs (same refusal).

Fix. The NUL refusal moves to the door's option validation (or ChildCommand, RT-E6 step 2), with ParamName == "options" pinned by a test. Found during the RT-E6 characterization inventory (internal faz4/RT-E6/characterization-inventory.md §5.3).