Function launch 

pub async fn launch(
    store: &TemplateStore,
    id: &str,
    target: VersionSelector,
    launched_by: Option<&str>,
) -> CliResult<LaunchOutcome>

Available on crate feature templates only.

Launch a version: make it stable, so unpinned callers start using it.

This is the one deliberate act that moves consumers. Registering a build never does — that is the whole point of the model, so a nightly can land without dragging anyone along.

Refuses to launch while the template is deprecated: reviving a retired template by moving its live pointer is almost certainly a mistake, and --undo makes the intent explicit.