Mixed case GITHUB_HOST is classified as GitHub Enterprise Server #3524

What happens

--gh-host / GITHUB_HOST values are classified with an exact, case sensitive comparison against github.com and ghe.com. A host that differs only in letter case is treated as a GitHub Enterprise Server instance, so the server builds GHES style URLs for it.

For example:

The GraphQL, upload, raw and authorization server URLs are derived the same way, so every API call fails. Classification as GHES also triggers the subdomain isolation probe against raw.<host>/_ping, and ParseHostType reports HostTypeGHES, which changes which host specific capabilities are enabled.

A data residency tenant whose subdomain is written with a capital letter, as company names often are (https://Contoso.ghe.com), is enough to hit this.

What should happen

Host names are case insensitive (RFC 4343), so https://GitHub.com should behave like https://github.com, and https://Contoso.GHE.com like https://contoso.ghe.com. isLoopbackHost in the same file already lowercases the host before comparing.

Repro

host, _ := utils.NewAPIHost("https://GitHub.com")
u, _ := host.BaseRESTURL(context.Background())
fmt.Println(u) // https://GitHub.com/api/v3/

Root cause

classifyHost in pkg/utils/api.go compares u.Hostname() directly. net/url lowercases the scheme but keeps the host as written, so the github.com and ghe.com checks never match a mixed case host.