Function channel_endpoint 

pub fn channel_endpoint(channel: UpdateChannel) -> &'static str

The manifest URL a channel reads from.

This is the entire mechanism separating the two lines. The version comparator cannot assist: semver ranks a prerelease above the stable release it precedes (0.1.1-beta.1 > 0.1.0), so a beta manifest reaching a stable install would be offered and installed. Keeping betas out of releases/latest — by marking those releases prerelease in release.yml — is therefore load-bearing, not cosmetic.