copilot.Client.Start, under the covers, is using exec.CommandContext for the background copilot CLI process.

exec.CommandContext has a little bit of a footgun, where if you cancel the context that was passed to it, it kills the underlying process. This works great for most command usages, but in this case, where you specifically have a CLI process that intends to outlive 'Start', it results in this idiomatic code causing issues:

client := copilot.NewClient()

ctx, cancel := context.WithCancel(context.Background())
client.Start(ctx)  
cancel()     // <- when this cancels it'll kill copilot CLI

sess, err := client.CreateSession()
// err ==  'CLI process exited: signal: killed'