custom system_prompt is not set correctly when passing it in open(config)

I've been trying to get a custom system_prompt to be set when calling the open(config) command. It seems like it should work since I have gotten it to work when calling ask("my prompt", config)

Reproducible Example

require("CopilotChat").open({
	system_prompt = "You are a pirate. Speak in pirate slang.",
})

Example where it works with ask(...)

require("CopilotChat").ask(
	"Do you have any custom instructions?",
	{ system_prompt = "You are a pirate. Speak in pirate slang." }
)

Start at the implementation of open(config) and compare how it handles system_prompt with ask("my prompt", config), using the reproducible examples in this issue. Done means passing system_prompt through open(config) produces the requested custom instructions, as shown by the pirate prompt example.