I've been wondering what it would take to create a decent Linux REPL on a webpage, backed by ephemeral "free" CI.
The page would need start with doing something that CI can react to. Could be OAth to comment on a GitHub issue, which count as CI events these days. The build would start by "finding" the waiting user, eg edit the comment, which the web page would poll, and then establish a web socket for the rest.
You'd want an asymmetric key so that only the initiator can talk to that build.